z,go-w-98-O02 LOANCOPY ONLY Recent ResearchIn Coastal Louisiana: Natural System Functionand Respo Human Influenc A Symposium 1998
Thissymposium was funded by generousgrants and support from the Louisiana UniversitiesMarine Consortium LUMCON!, Louisiana Sea Grant Program, Coastal Ecology instituteof LouisianaState University, Louisiana Environmental Research Center of McNeese StateUniversity, U.S. Environmental Protection Agency, U.S, Geological Survey in Baton Rouge,NOAA Coastal Services Center, Louisiana Department of Natural Resources, LUMCON Foundation,inc., T. BakerSmith and Sons,inc., andthe Coalition to RestoreCoastal Louisiana. Themeeting was planned and organized byDenise Reed, Nancy Rabalais, John Day, Andy Nyman,Ed ProAitt, Lawrence Rozas, Gary Shaffer, and Gene Turner. We thank the presentcrs andattendees forsharing their research, staying onschedule, andallowing stimulating discussion.Thefollowing persons assisted tremendously inthe preparation ofthis volume by reviewingthe manuscripb presented here: Clark Alexander, Jim Allen, Mahalingarn Baskaran, AaronBass, Thomas Bianchi, Donald Boesch, Kirk Bundy, Donald Cahoon, Dan Childers, RobertChristen, Robert Costanza, Sherri Cooper, John Dingier, Quay Dortch, Mike Durako, KeithEdwards, Steve Farber, Miriam Fearn, Mark Ford, Jon French, Gary Gaston, Robert Grambling,Courtney Hackjney, KenHeck, Fred Hitzhusen, ClintJeske, Barb Kleiss, Dwight LeBlanc,Paul Leberg, Terry Logan, Lynn Leonard, Karen Manel, Brent McKee, Thomas Minello,Cynthia Moncrief, Hillory Neckles, William Nuttle, Chris Onuf, Jonathan Pennock, GaryRay, Harry Roberts, Rickey Ruebsarnen, GaryShaffer, Charles Simenstad, Fred Sklar, DonnySmoak, Thomas Soniat, Marilyn Spalding, Karen Steidinger, Judy Stout, Eric Swenson, RobertTWilley, ivan Valie!a, Milan Vavrek, Shio Wang, James Webb, and Erik Zobrist. We greatlyappreciate theefforts ofBonnie Ducote with the Louisiana SeaGrant CoBege Program forher work on the production of this volume.
LOUlSlANA Publishedbythe Louisiana SeaGrant College Program, apart of the National SeaGrant College Programmaintained bythe National Oceanic andAtrnosphenc Administration ofthe U.S. Department of Commerce. 1999.
Louisiana Sea Grant CommunicationsOffice LouisianaState University BatonRouge, LA 70803-1507 225-388-6449 FAX 225-388-tt331 Website: httpJ/www.laseagrant.org PREFACE
Thecoa»tal barriers, bays, mar»hes, and swamps of Louisianacompose one of thelargest deltaicsystems of the world. In contrasttomany other deltas on Earth, where wetland» have beendrained and barrier islands built upon, the MississippiDelta Plain i». still a highly productiveecosystem. It i»,however, a systetn that had been dramatical]y altered from it» natural stateand a placewhere the challenges of managing and sustaining ecosystem function are faced everyday. The research community in Louisiana hasfor many years been at the forefront in dealingwith management issue» and ensuring that decisions are made on the basi» of thehe»t availablescience, ln thelast decade with the advent of a large-scalewetland restoration program underthe Coastal Wetlands Planning Protection and Restoration Act, with increasedawareness ofthe potential consequences ofriver diversions, andwith a renewedeffort to exploit subsurface mineralresources in the coastalzone, it hasbecome essential that the research conununity be proactiveindisseminating themost current scientific understanding tocoastal managers and decision makers.
Withthis in mind,we convened a broad-basedcommittee from amongst the research communityworking incoastal Louisiana todesign a coastal research meeting. The goal was to provideanopportunity fordissemination anddiscussion ofresearch findings among scientists, managers,andpolicy makers. The result was the conference 'Recent Research in Coastal Louisiana:Natural System Function and Response toHuman Influences'. Theconference was heldin February]998 in Lafayette,Louisiana. Over three days, 48 oral and 20 poster presentationsweremade toan audience ofover 150 people. Plenary presentations byCharles Simenstadon wetland restoration in thePacific Northwest and Ron Jones on thechallenges of ecosystemmanagement inthe Florida Everglades provided a context forus to consider the problemswe facein coastalLouisiana, Theconference wasa great success, andthe papers in this volume represent apartial recordof thediscussions that occurred Scientific advances will continueand our understanding ofsystem function will only increase. Inthat sense, theinformation presented hereis a snapshot of thestate of coastal science knowledge in the late 1990'». There are few venues where managersandresearchers canopenly discuss their observations, findings, anddoubts. Perhap» moreenduring, therefore, isthe recognition thatwe all share a commongoal of a sustainable. productivecoastal Louisiana and that the best efforts of all are needed toget there.
This publicationshould be citedas: Rozas,L.P, J.A, Nyrnan, C.E. Proffitt, N.N. Rabalais, D.J. Reed, and R,E. Turner editors!.1999. Recent research incoastal Louisiana: Natural »ystetn function andresponse tohuman influences. louisiana Sea Grant College Program, Baton Rouge, LA. TABLE OF CONTENTS
PAGE
ACKNOWLEDGMENTS .
PREFACE .....
HYDRODYNAMICS AND SEDIMENTARY PROCESSES
Hale, L, M.G, Watdon,C,F. Bryan, and PA. Richards Historicpatterns of sedimentationin Grand Lake, Louisiana
Ketnp,G. P J. W. Day, Jr D.J, Reed, D,R. Cahoon, and Af. Wang Sedimentation.consolidation andsurface elevation change in twosalt marshes ofthe Mississippi River deltaic plain: Geotechnical aspects of wetland loss,
Pepper,D.A., G.W. Stone, and P. Wang A prelitninary asses sment of wave, current, and sediment interaction on the Louisianashoreface adjacent to the isles Dernieres
Meselhe,E.A.. A,A. Bradley, A. Kruger,and M. VL Muste ParticleImage Veloeimetry PIV! and numerical modeling for flow estimationand analysis, ...... ,...... ...... ,...... ,......
Mendelssohn.LA. and JV.l Kuhn Theeffects of sediment addition onsalt marsh vegetation and soil physi co-chemi stry ...55
WATERQUALITY AND ENVIRO%VIENTALCHEMISTRY
Parsons,hl,L, 0. Dnrtch,R.E Turner,and h/,A'.Rabalai s Theuse of di«tom remains asa proxyofhistorical salinity changes in AirplaneLake, Loui siana,
Waldon,M.G. andC,F. Bryan Annualsalinity and nutrient budget ofLake Pontchartrain andimpact of theproposed Bonnet C~ diversion...... ,.. .. ...... ,... ,...... 79 Day,J,W, Jr., R.R. Lane, R.F. ltfach, C.G. Brantley, and M,C. Daigle Waterchemistry dynamics inLake Pontchartrain, Louisiana, during the 1997opening of theBonnet Carre Spillway ...... ,...... -...,."--"-
Ri-~o,WM. and R.G. Boustany Sediment-watermaterial fluxes in benthic microalgal-dominat Boustarii; R,G, and W,M Ri=-o Wholesystem material fluxcs within meadows of Vai isnertaamericana from Lake Pontchartrain,LA: Effects of light and nutrient manipulations, Pr>irrier,Af.A., B. Afagiic. J.C, Francis,C.D. Fran e, and 8.-J, Cho Effectsof the1997 Bonnet CaW Spillwayopening on Lake Pontchartrain submersedaquatic vegetation Dortch, Q M.L Parse>nt,H.X. Rabaiais,and R.F. Turner What is thethreat of harmfulalgal blooms in Louisianacoastal water." Turner, R.E. Nitrogenlosses in waterflowing through Louisiana swamps ... Day.J. W, Jr J.M. Rybc-vk, L Cardoch,WH. Conner,P. Delgado-Sanche R.l. Pratt, and A. Westpha A reviewof recentstudies of theecological and economic aspects of the applicationof secondarily treated inunicipal effluent to wetlandsin southern Louisiana Gauthreaux,K, J, Sneddon,TAf. Falgoust, Af.J. Beck, and J.N. Beck Migrationof speciatedmetals in soils reclaimed from ship channel sediments,. . 167 COASTAL LAND LOSS AND WETLAND RESTORATION Turner, R.F.. Wetlandloss in theBarataria Estuary; Empirically-defined relationships and multiple workinghypotheses ...... ,. ,...,...... ...... , 183 Day,J.W. Jr., G.P. Shager, LD. Britsch,D.J. Reed, XR, Hau>es, and D. Cahoon Patternand process of land loss in the Louisiana coastal zone: An analysisof spatialand temporal patterns ofwetland habitat change .. , 193 Reyes,F., J,F, Afartin, ML White,J.W. Day Jr., and. G.P, Kemp Landscapemodeling mcoastal Louisiana: Regional mechanisms of '7P3 land loss Pmfgtt, C.E, andJ. Young Saltmarsh plant colonization, growth, and dominance onlarge mudAats createdusing dredged sediments . 21g Turner, R.E Low-costwetland restoration and creation projects for coastalLouisiana. PAGE WETLAND MANA GEMKNT Bote~eois, J.A. artdE.C Webb Effectsof weirs on the depth and duration of flooding in a Louisianamarsh ., ... 241 Hess,X J.J G.E.Melan on,B.C. Wilson, and C,M, Witsd!tarn Emectof 3-D seistnic vehicular traffic on marsh soil elevations in a SouthwestLouisiana coastal marsh ... 254 Wilson,8.C., T,J.Hess Jr., M. C, Wittdhatn, and 8.E. hfoser EfFectof 3-Dseismic on vegetation ofa SouthwestLouisiana coastal marsh . ... 262 Rnberts,K,J., PA. Coreil, and A,J, Ortega, Jr. Taxationofprivate marshland: Theuse of value method applied to Lou i siana's coast ... 270 COASTAL FLORA AND FAUNA Stickle, 8!8. Jr, Effectsofestuarine environmental factorgradients onthe tolerance and physiologyofthe southern oyster drill, Stramonita =Thais! !taemastotna: Anitnportant predator ofthe American oyster, Crassostrea virginica...... , 277 Fleun',B,E, T.WSlterry, and J.V. Htitter Agriculturalwetlands andthe conservation ofcolonial wading birds in Louisiana ... 287 Visser,J,M.. F. Frankeri,arid C.E, Sasser Effectsofgrazing onthe recovery ofoligohaline marshes impacted by HumcaneAndrew...... ,...... ,...... ...... ,.... ...... ,. .... ...... ,.... . .. HYDRODYNAMICS ArVD SEDIMENTARY PROCESSES 4. Hale et al Intrriduefion Unlikethe Missisiippi,thc AtchafalayaRiver emptiesinto the Gu!f of Mexicothrough passes into Today,the AtchafalayaRiver originates near a relativelyshallow bay. Thui. in contrastto thc the conflucncc of Old River and thc Red River. Miisiiiippi delta, thc AtchafalayaRiver Delta is Locationsalong thc channelare typically identified activelygrowing Adamsand Rauriutnn I 'WO;van as river miles downstream lnim this confluence Heerdene al. 1983k Thii accretingdelta will which ii I'ive river rnilei north tif Simmesport, provide benefits to [ ouiiiana'.i lishcriei and Louisiana, The prcient 219 l kmi 846 mi-'! protectionof existing land.i and property from AtchafalayaBaiin Floodwaythat lies betweenthe erosionand stormi. Althoughthi.i growing delta Eaitand West Florxf way I'nitcct ton Levers has been causei some manageableproblcrns f'or navigation termed"Americas Gleatcit River Swamp" United andpotentially impacts local flooding, its benefits States Fish and %'ifdlifc Service 1978!. The vastlyoutweigh these costi which ultimat.clyrrmy AtchafalayaBasin extend»nland 01 km 25 mi! hc unavoidable. andii roughly24 km I Smi t widc. The Atchafalaya River ii cffcctivcly r}arnrnctlacroii iti entireliiwcr The Flood Control Act of 1928 authorized the cndhynatural levcei of'l At the beginning of the nineteenthcentury the relationship of the Red River and thc Atchafalaya River to the Missiisippi River was different from the presentconfiguration Fisk 1952;Hebert 1967; Reuis 1991; Hale 1996: Reuss 199g!. At that time, the Rcd River wa» a tributary to the Mississippi River in a large meanderloop, and the Atchafalaya River was a very minor Misiiiiippi River distributary originating just downitreani of the confluenceof the Redand 1Vlississippi Ri veri. The Fig, 1 CirandIMe GL! and1 Mchauisc point tf I-pr head of the Atchafalaya River at this time was ihorelines as fnapped in 1'f1 ' Locaiioni of the ft blocked by a massivelog jam; so masiivc that cattle Rangelinei examined in th!»tudy aic shotsn 1 ff-A were driven across it and live willow trees werc 19-A. 20 A. 2 1-A. --A. -3-A. '4. and 5!. Grand Lake Sedimentation Patterns 5 «liscrvcil grovving !rum it IHehcri lufi7; Rcuss suspendedscdi»icnt concentration has decline<1 1998!. The rc latiunshipof thcscrivers v as«harigcd recently. !ikely causedbv the cuiilpleii 'ii'i if Rci draniatically in l 3! when aptain Henry Shrcvc River lock and dam priifects. This recentdecline in was uuth BasittProtection Levee, The rapid disappearance 1988 were availablefor this study Tablel. AverageGrand l.ake rangeline elevation in metersabove mean sea level AMBI.!. A1ain channeland main channelnatural or artificial leveesare excluded. Year 18-A 19-A 2 !-A 22- A 23- A 25 1916 -1.65 -1.86 1917 - 1,07 -1. 35 -1,44 -3,19 1934 -0,52 -0.91 -1.41 -1.68 1940 0.09 -0.28 -0.77 -1.62 - .09 1941 -1.34 -1,31 1950 0.47 0.13 -0,64 -0,9 l 1951 0.72 0.39 -0.50 -0,91 -1,71 -1.58 1953 0.35 -1.14 1956 - ! 74 1959 -0.18 -1,19 1963 0.71 0,76 -0. 13 -0.70 -0.411 1964 0.07 -1,02 - .51 -0 78 1967 -0.16 1968 0.78 0.77 0.33 -0.54 i 972 0.04 -0.27 -0.22 -0.05 1974 0.98 0.34 0.51 1975 0,39 0.56 1976 0.47 0.01 0.16 0.14 1978 0.93 0.03 -0.34 1980 0.07 0,22 1987 1.18 0.40 1988 -0. 17 0.10 0.00 ktn 100 tao 200 2.5 2.0 E 1.5 8 CO 1.0 0.5 60 70 80 90 100 110 120 1 30 River M tie Ftg.2, Model eqtti!ibrium clevations heavp bne}, and f owlines ofwater surface elevation at3000, 4000. and 6000 m's' dischargederived from l974t'SACE stage data. L. Ha o et at Elevationsat ButteLa Rose,Six Mile Lake, and For Grand Lake these parameters were MorganCity were determined forthree Atchafalaya estimated through a visual calibration to the River dischargesmeasured at Simmesport. observedvalues. An optimal value of theexponent Flowlinesfor 3000,4000,and 6000 m' s' 06, 14!, "a" wasf'ound to bc nearunity, and a valueof I was 2 thousand cfs! were determined. These acceptedasthe calibrated value. The parameter r, dischargesrepresent approximate! y the 25, 40, and was dcterrninedto be !,803 s m- yr' through 60 % flowduration i.e. percentof daysthat the calibration.For theseparameter selections, the f!ow is not exceeded!since the OtdRiver Control averagevalue of r over thc periodfrom 1934to Structurebegan operation We! Is and Demas, !977!. 1990is 9.95 cm yr' Theparameter K wasfound, throughca!ibration, to bc 0.4 m at all range!ines. ModelDevelopment Themaximum accretion elevation, E . was found to dependon the range!inc location, and generally Observationslist.ed in Table ! are difficult to decreastx!from upstreamto downstreamlocations. analyzebecause of the large number of missing For the range!ines18-A, 19-A,2O-A, 2 I-A, 22-A, valuesforany speciftc year, Additionally, variability 23-A,24, and 25, the value of E, wasestimated to in individualobservations obscures more general be 0.9, 0,8, 0,5, 0.4, 0.35, 0.2, 0.!, and 0,1 m, trends.ln orderto overcomethese d!ffrculties, a respectively Table 2; Fig. 2!. simple empirical model of annualaccretion was developedand compared to thevalues in Tablel. Becausethe spatial pattern of flowsthrough Sedimentationand accretionmodels a.re most theAtchafalaya Basin was radically changed in the commonlybased on an assumedparticle settling 1930's, the calibrated model was initiated in 1934 ve!ocitydetermined through calibration ar using Table2!, Initial valueswere input for !934, and Stoke'sLaw Cercoand Co!e !995; Dortch 1996!, subsequentyears werc then calculatedon an Excel Application ofthese mode Is requires ata mintmu rn, spreadsheetusing the parameters cited above Table a knowledgeof water velocities and depths; these 2!. Calcu!atedvalues were in close agrecmeot Fig. wereunavailable for GrandLake. ln consideration 3! with the observationslisted in Table l. of'this !imitation,the model deve!oped here is empiricaland is basedon observedtrends and Onegoal of thisstudy is to providea more asymptoticreasoning. Annual change in average generalizedmethod for projectingaccretion which elevation was modeledas: may be particularlyuseful in planningriver diversionsfor habitatrestoration. It is therefore E E r =l:-E further conjecnuredthat r can be related to annual K+E E average suspendedsediment concentration, c and o water application rate discharge per unit area inundated!,q, by: ! C r =r~q wherer tsthe annual accretion rate over year I ltllI ! m yr'k E, isaverage range!inc elevation AMSL where ml at the endof year t, E is theequilibrium maximum! r' isa dimension!essconstant which may be accret>onc!evatron fm j, expressedas a percentage, r is themaximum accretion rate rn yr '!, y is surficia! sedimentbulk density,the dry Q isriver annual calendar-year average weight of bottomsediments per unit accreted volume 'kg I '!, volumetricdischarge m's '!, K isthe distance m! belovs E at which accretionrate is reducedto ha! f r, and Q r, anda areconstants. Grand Lake Sed!menta ion Patterns 9 Table 2. Model calculatedaverage Grand l.ake rangelirieelevation in m abovemeara sea level AMSL!. Model parameters«re displayednear the top of the table. Range!ineJRlverMl!e Range!inc 18-A I '9-A 20 A l! A Il River Mile 85 90 9H 10! 103 105 [; m! 09 G.H 0.4 !.35 0.2 Ol 0.1 K m! 0.4 04 0.4 0,4 0.4 0,4 0.4 r,, crncms 'yr '! 1.803 1.803 1.803 1.803 1.803 !.803 I .803 1.803 1.000 1. XX! I, XX! 1. XX! ! . 0 1.000 1.0 X'I 1. XX! YEAR ! 916 ¹N/A ¹N/A ¹N/A ¹N/A ¹N/A ¹N/A ¹N/A ¹N/A 1917 ¹'N/A ¹N/A ¹N/A ¹N/A ¹N/A ¹N/A ¹N/A ¹N/A 1934 -0.30 -0.70 -l, -1.8 ! -! .90 -3.00 i 60 -3. 10 I 1940 O. X! -O.3H -0.82 -1.45 -1.55 -2.63 73 1941 0.04 -0.33 -0.78 -1,40 -1.50 -2.58 i !9 -'.6H !950 0.59 0,29 -0. 13 -0.68 -0.77 -1 79 -1.43 I. 89 195! 0.64 0.36 -0.05 -0.58 -0.68 -1.68 -!,32 -I 78 1953 0.71 0.45 0.05 -0.46 -0 55 - I,s4 -1.19 -1.64 I '956 0.77 0.53 0.15 -0,34 -0.42 -1.39 -1.05 - !.49 1959 O.S3 0.65 0.29 -O. I 3 -0.22 -1.13 -0.81 23 1963 0.87 0.73 0.40 0.07 -0.01 -0.84 -O.56 - !.94 1964 0.88 0.74 0.4 ! 0.09 0.01 -0.81 -0.52 -0.9! 1967 0.89 0.77 0.45 0.19 0.12 -0.63 -0.38 -0 73 1968 0.89 0,78 0.46 023 0.16 -0.56 -0.32 -0.66 1972 0.90 0.79 0.49 0.34 0.28 -0.28 -0. I! -0 38 1974 0.90 0.80 0.50 0.38 0,32 -0,10 0. IX! -0.20 1975 0.90 0.80 0,50 0.38 033 -0.03 0. 03 -0 13 1976 0.90 0.80 0.50 0. 39 0.34 0.00 0.04 -0.10 !977 0.90 0.80 0.50 0.39 0.34 0.03 0.05 -0.07 1978 0.90 0.80 0.50 0.39 0.34 0.06 0.06 -0.04 1980 0.90 0.80 0.50 0,4O 0.35 0.12 0.08 0,02 1987 0.90 0.80 0.50 0,40 0,35 0.19 0.10 0.09 1988 0.90 0.80 0,50 0.40 0.35 0.19 0.10 l!.O9 The valueof q is commensurablewith precipitation Using parameter values available from the rate and other area-specific intensive parameter~, literature, the value of r can be roughly estimated. and may be most convenientlyreported as m yr '. Over the period 1964 through 1974, Atchafalaya River suspendedsediment concentration averaged The parameterr' can be interpretedas the 4GO mg 1' Wells and Demas 19771. Although fraction of the suspended sediment which is su spended sediment conCentrations in the removed from the water column in thc processof Mississippi River have declined .sincethe middle accretion and is related to trapping efficiency of this century Dardeau and Causey 19901. a def!ned in other sedimentation studies Strand and constant value is used here for analysis in order to Pembcrton 1982; Salasand Shin !999!. Solving simplify computation,and because very roughly half F~uations 2 and 3 give~: of the suspendedsedirncnt of the AtchafalayaRiver is supplied by the Red River Mossa 1990! which is not kr!own to have declined in suspended scdirnenl r =r AUc o a concentration prior to the relatively recent 10 L. Wry et al, Hoch- QsaervedKhvaOon {m! 0.0 -1.0 -2,0 4.0 40 -235 -2.G -1.5 -1.0 4.5 0 0 0.5 Observed J 1' z 19A ~ 2i a 25 a 2DA v 2M ~ 22M ~ 2~ P:f Pig.1. Comparison ofmodel and observed average rangeline elevations. Solidline is line of perfect fit :1 slope!. 170 1.0 0$ 0.0 4.5 -1.0 -3.0 95 too Rior N 11e Fig.4.Average elevanooalong Grand Lakerangelines. Points per s incis equilibriumines.elevation. Points from 1916-1917 arcobserved Grand Lake Sedimentation Patterns 11 navigation improvements, Bottom surficial rcport that net scour of the Basin was observed sedirncntdensities have been cornpilcd for a large during the floods of 1973. 1974,and 1975. number of lsorth American lakes hy Dcndy and Champion 969!. A typicalvalue of 1.12kg 1' 0 Discussion and Conclusions lh ft-'! is used herc. Combining these values with the original areaof Grand Lake providesan estimate Accretion in GrandLake peaked around 1950, of 49% for r'. and hasgenerally diminished since that time Fig 5!. Sedimentationand successionof GrandLake will This estimate tnay bc further cotnpared to the continue in isolated areas,but at a greatly reduced peakpercent of load removalprojected in the model. rate. ln the future, sedimentation wifl likely focus Wells and Demas 977! report that the average on theremaining low-lying areasof the former lake suspendedsedirncnt load passing Simrnesport is 86 asupper range! ines equilibrate at a meanelevation x 10' tyr ' 60,000 td '!. The peakmodeled annual of <1 rn, During the disappearanceof' deep open accretionrate 'ig. 5! is 38 x 10' m', which, using water, the river channel extended itself through its 1.] 2t m -',converts to 43 x 10' t yr ', or 50% of the growingfloodplain. Developmentof a morc averagesuspended sediment load. Averageannual efficient channel must, to some degree,reduce the accretionprojected by thc modelfrom 1965through scditnentload flowing over the elevated floodpl ain. 1971 is 11.8 x 10'm' yr . This would correspond andaffect final equilibriumelevations. Succession to an annual removal of' 13.2 x 10' t. Wells and is approachinga final equilibrium condition with a Dernas 977! rcport that although dataare limited, typical channel,natural levee, and flood plain it is estimatedthat over this periodapproximately morphology. Today, the rate of sedimenttrapping 755cof the suspendedsediment load at Simmesport in the former Grand Lake has greatly slowed or wastransported through the two outlets. They also stopped, and Grand Lake is approaching an equilibrium surfaceelevation. Grand Lake Volume and Aeeiretfon 35 30 E 25 t 0 20 E 15 10 C 5 0 0 1920 193Q 1940 1950 1960 1970 1950 1990 2000 Year Voltrne n -Acoetion Fig.5, Modelprojected Grand Lake volurnc below equilibrium elevation! and annual accretion rate. g2 L Hale ei al. Duringthe decades ofthe 1930's and 1940's a A betterunderstanding is needed of thefactors significantfraction, perhaps 20-40%, of the sus- thatdetermine the equilibrium surface elevation. It pendedsediment load entering the Atchafalaya ely that thiselevation is relatedto some statistic Basin remainedin the Basinand was unavailable e.g.mean annual low water!of local water-surface for deltaaccretion in AtchafalayaBay, Fisk 952! elevation. Mechanismswhich reduce observed projectedthat the Atchafalaya Basin would be filled accretionas thc equilibriuin elevation is approached withsediment by theearly 1970's, and a newmatine includeloss of sedimentsource, increase scourand dehawould then build in AtchafalayaBay Tyeand erosion,and enhanced consolidation of higher Coleman 1989b!. Since the rnid 1970's, Grand Lake elevation surfaces. has bccn effectivel filled. Today,thc sediinent trappingefficiency at the lake has declined to near Preferentialaccretion in deepwater may be zero,and nearly all suspendedsediment entering one mechanismcontributing to indirect land loss GrandLake is delivered to Atchafalaya Bay. Siinilar ftxim excavationof canalsin wetlands, In situations successionalpatterns have been observed in man- where suspendedsediment supply is limited, inadcreservoirs Lajczak 1996; Kern and Westrich sedimentsmay preferentially settle in deepcanals I IPJ7! and thereforeare unavailableto maintain surface elevationsof surroundingwetlands, patternsaf sedimentationhave been identified in LITERATURE CITED sedimentation in a forested wetland, Black Swamp.Arkansas. Wetland» 10:107-124. Atrxsts, R. D. Arnr R. H. BAuvin~x. 1980. Land Hoer, C, R M. D, Wooixsuot:. hist>T. M. Y,xiosxv. building in coastal I.ouisiana: Emergenceof 1993. Sediment and trace element trapping in thc Atchafalaya Bay Delta. No. LSU T-80-0, a fore sted wet land, C hi c kaho min > R i vc r, Center for Wetland Resources. Sea Grant Virginia. Wetlands 13:95-104. publication,Louisiana State University, Baton Knows, M, P E, A, Dwrtot:*u, Ai t> E. M. CAusav. Rouge. Louisiana. 1986, Historic trends in the scdirnent flow Cattco, C. F. Atst!T. M. C nu-. 199>.User's guide to regime of the Mississippi River. Water Re- the CE-QUAL-ICM three-dimensional sources Research 22:S55-564. eutrophication rnodcl. release vcrston 1.0. KEttn',U. Avo B. Wt.sxtttcH.1997. Sediment budget Technical Report EL-95- 15. U.S. Army analysis for river reservoirs. Waterarrd Soil Engineer Waterways Expcrimcnt Station, Pollution 99:105- l 1 2. Vicksburg, Mississippi. I-AJcxAK,A. 1996. Modeling the long-term course CHANsoN,H. ANtrP. JAvlt;s.1998. Rapid Reset'vou of non-flushed reservoir sedimentation and Sedimentation of Four Historic Thin Arch estimating the life of dams. Earth Surface Dams in Australia. Jrrurna r>f Perfrrrmance of Processes and Landfurrns 21: 1091-1107. Constructed Far iliti es. A SCE 12:85-92. McPHEE,J, 1989. The Control of Nature, Noonday DARDEAu,E, A, AwrrE. M. Cusn. 1990. Downward Press, New York. trend in Mississippi River sediment loads. MossA, J. 1990. Discharge-SuspendedSediment PotamologyProgram P-1 ! Rcport5, Environ- Relationshipsin the Mississippi-Atchafalaya rnental Laboratory, U.S. Army Engineer River System, Louisiana. Dissertation, WaterwaysExperiment Station, Vicksburg, LouisianaState University, Baton Rouge. Mississippi. MossA, J. 1993. Hydrodynamics and suspended Dt:.~uv,F. E. xNr>W. A. CH dominated!acustrine de!tas; Mississippi delta plain. Journal of Sediinentary Petrology 59:973-996. TvE, R. S. AttDJ. M. CoLt:MitN,1989b, Evo!ution of Atchafalaya lacustrine de!tas, south-central Louisiana.Sedimentary Geoiogy 65:95-! ! 2. Unix> SrwrEsFtstt zn'n WttLtLtrsSEav G. PAULKEIIP', JOHNW. DAY,JR.', DENISEJ. REED-'. DONALDR. CAHOON',MENGLOU WANG-' 'naturalSystems hfodeling Group, Cerrter for Coastal,Energy and Environmental Resources,Louisiana State University.Boron Rouge,LA 70803 TEL: 225-388-6358,FAX: 225-388-6326;email: ockemp@unixl,sncc.lsu,edu 'Dept.of Oceanographyand Coastal Sciences and CoastalEcology Institute, Louisiana State University,Baton Rouge,LA 70803. TEL: 225-388-6508,FAX: 225-388-6326;email; ceidayC~unix1.sncc.lsu.edu 'Departmentof Geologyand Geophvsics, University of A'ewOrleans, Hew Orleans, LA 70148,TEL: 504-280-7395,FAX: 504-280-7396; email. dj reed0uno.edu 'National WetlandsResearch Cenrer, U.S. Geological Survey, 700 Caj undorne Blvd., Lafayette,LA 70506,TEL: 225-767-9131,FAX: 225-767-9108; 'Louisiana TransportationResearch Center, 4101 Gourier Ave., Baron Rouge,LA 70808 ABSTRACT:A geotechnicalprocess acting to reducethe strengthof themarsh soil substratum is proposedto explainobserved patterns of saltmarsh loss in theMissitnippi River deltaic plain. Factorsaffecting marsh surface elevation, including sedimentation, accretion and consoihfation,were investigated at twosites about 60 km apart, one adjacent to, and onedistant fromdirect fluvialinfluence. The sites are end memberson b sustainabihtyscale. Theisolated marshat Bayou Chitigue BC! is rapidly submerging and converting to openwater. The Old OysterBayou OB! marshhas remained stable as it basbeen increasingly affected by the AtchafalayaRiver, a MississippiRiver dislxibutary now carrying about 30 percentof total floe. Elevationat BC, 10cmlower on averagethan at OB, did notincrease at a sufficientrate tooffset any relative sea level rise RSLR! greater than sera, much less the 1 cxn-y'estimated for thissite, even though it is nxeivingsediment at morethan tvrice the rate at OB. Shallow subsidence D4 m!was estimated at 3.6 and 1.6 cxn y' atBC and OB, respectively, or more than three titnesRSLR estimatedFor these sites. A detaoedanalysis of marsh surface soil < 25 nn! propertiesdisclosed only subtle differences between the two sites,suggesting that the marsh capitself remains relatively unchanged as it declinestoward tbe lower bound of marshplant viabihty.Shallow subsidence is taking place in themarsh substratum beneath the marsh cap. Sedbnentavailability is enhanced atBC as a consequenceofthe higher frequency and duration of flooding,but does not resultin a proportionalincrease m accretionor marsh aggradation. TheBC marshcaptures less than half of theavailable sedunent as this material apparently retnainsin lux under the prolongedflooding characteristic of thissite. Marsh vegetation persistsat doseto the lowerelevation limit and breaksup as mdiv&ualplants die. TheOB marsh,in contrast,captures virtually ail of the smallerinput of sedimentavailable and is aggradingat a ratethat appears to approximatelocal RSLR c cany'}. A theoretical geotechnicalanalysis of the load imposed by tbe marsh cap under normal drainage conditions Fromthe SyrnposirrmRecent Research in CoastalLouisiana: Xanrral SystemFuncrton and Itesponsero HurnonInttvence. Rozas,L.P., J.A. Nyman,C.E. Proffia,N.N. Rabalais,DJ. Reed,aod R.E. Turner edirrrrs!. 999. Publishedby Louisrasra SeaGrant College Program. 15 G. P. Kemp et al. isusual toshow that shat!otv subsidence should,like sedimentation, bea function ofposition vvithtnthetidal frame. Adecrease inloading ofthe marsh substratum drivesa reduction in strengthinthis section, leading toan increased potential forsudden settlement that can precipitatemarshloss. Soil stxength profHing issuggested nsa basis forpredicting the restorabilityandresponse oftklnl ntarshes toriver diversions andother restoration projects. INTRODUCTION accumulationof organic matter rather than mineral sedimentisbetter correlated with vertical accretion Dunbaret al. 992! cstirnatedthat 400,000 Hattonct al. 1983.Brickcr-Urso et al. 1989,Craft ha of estuarinewetlands associated with the etal. 1993,Nyman e al, 1993,Callaway 1994!. MississippiRiver delra in Louisianahave submergedand converted t«open water since the A collapsiblesoil matrixresults when much 193 ls.Much evidence points to waterlogging asa of thcsoil volume is contributed byplant material primarymechanism forthis marsh die-off Naidoo andvoid space, both high Iy compressibleelements et a!. 1992,Emst 1990, Pczeshki et al. 1991, McCai'freyand Thomson 1980, Hackney and Pejvshkirtal. 1988, Mcnde I sohri~ and McKee 1988, Cleary1987, Krone 1987, Oenema and Delaunc Monis andDacey 1984!. Rates ofrclative sea level 1988,Cahoon et al. 1995a!.Salt marsh soils of the rise RSLR! for thisarea range from 0.5 to more than2,0 cm y ' Penlandand Ramsey 19901. For MississippiRiver deltaic plain are not as organic as coastalmarshes tosurvi vc. the rate of aggradation, someat higherlatitudes on the U, S. eastcoast orabsolute surface elevation gain, must equal or Bertncss1988, Turner 1976!, But void space and cxcecdRSLR Baurnann c al. 1984,Reed and organicrnatter together take up 95 percentof the Cahoon1992, Reed 1995a!. volumeoftypical Louisiana salt marsh soils Nyrnan et al. 1990,Delaune et al. 1983!, lncontrast to the general pattern oi loss,salt marshescontinue to flourish adjacentto the Cahoonetal. 995a! compared precise, direct measurementsof marsh surface elevation change unleveedmouth of thc Atchafalaya River, a distri- butaryofthe Mississippi thatcarries approximately usinga sedimenterosion table SET! Boumans and 30percent of thetotal flow tFig. 1!. The exact Day 19931with standardmeasures of vertical mcchanisrnsthrough which thc salt marsh is affecte accretion. Theyfound that accretionwas not a byriver discharge, however, remain priorly under- reliablepredictor of aggradationin somesalt storrd Turner 1997!. Such detailed information is rnarshes,particularly those expcricncing high rates requiredto optimize design and operation of the of RSLR.Despite high rates of accretionin these riverdiversion structures and channels that are marshes,the elevationof themarsh surface cithcr proposedasthe primary means for restoring the didnot change or decreased. Cahoon etal. 995a! wetlandsofthc Mississippi Riverdeltaic plain Reed attributedthis to the offsettingeffect of 1995b,Boesch et al. 1994!. autocompactionor shallow subsidence occurring betweenthe marsh surface and the baseof theSFT Aggradationhasbeen shown to track scdirnent supportpipe, generally 3 to5 rn deep.They accreuonforsalt rnarshes with mineral soils Pethick distinguishedthissettlement from deeper subsidencc 198l,Sturnpf 1983, Stoddart etal 1989,French causedby consolidationand tectonic movement l99'3,Allen 19941. Stevenson etal. 11986! below the baseof the SET. examinedaccretion inmarshes froma varietyof Terzaghi 936! proposedthat most changes tidalranges and concluded thatmineral sedimem insoil consolidation, bearing strength and shearing inputwas critical even inrelatively peaty sah tnarsh resistancecanbe attributed tochanges inthe loading settings.Others have found, however, that forceor effectivestress imposed on that soil. Geotechnicai Aspects of Wetland Loss t 7 NISSISSIPPI RIVER DELTAIC PX,AIN Mn ths o -he At thaf a ay~ Rive= littM Figure1, Locationsof Bayou Chitigue {BC! and Old Oyster Bayou OB! salt marsh sites. Consolidation,from this perspective,is definedby instrength with depth Kosters 1987. Kuecher 1994, therate at which thesoil losesvoid space in response Kayeand Barghoorn 1964!. The loading resulting to an increase in effective stress. Soils will be from sedimentationand drainageare affected both affectedby all additionsto the loadthat must be byproximity to a sedimentsource Leonard 1997, supported.A lower soil voidvolume is generally Allen 1994, Reed 1988, Stumpf 1983! and by associatedwith greater soil strength and the ability positionwithin the tidal frame French 1993, Reed tosupport added loads without settlement Dunn et and Cahoon 1992, Krone 1987, Pcthick 1981, al. 1980!.Such loads are applied in a naturalwetland Pestrong1969!. settingthrough the addition of sedimentat the surface,or as a consequenceof drainage,The We extend the analysis of Cahoon et al. cxpectcdresult is a "normal"consolidation profile 995a! to quantifyprocesses that aff'ectsurface that exhibits a reductionin void volume and increase elevationat two MississippiRiver deltaic plain sites 08 6 P. Keinp et at. proximalto and distantfrom riverineinfluence. ! 994! described a 10 to ! 5 cm loss ol elevation Thefirst was rapidly submerging and converting to associatedwith vegetationdeath in humrnocksnear openwater, while the latter has remained stable for BC. Theydetermined that thiselevation change at!east 30 years f Dayet al. 1994!. Wehypothesi zed was causedby an in-place col!apse of the marsh thatdivergence of thcelevation trajectories of thc soil matrix, rather than hy mcchanica!rcrnoval or two sites, and their marsh!oss histories,could be erosion. re!atedto differences in ! sedimentsupply. ! in theability of nearsurface marsh soi!s to support Relativesurveys of the inursh surface at thc addedsedirncnt, or ! to s-ubsidenceoriginating at two sitesshowed a pronouncednatural levee ridge greaterdepths. adjacentto thebayou at BC thatwas not as apparent at OB Wang 1994!. Marsh elevation at BC SITE DESCRIPTION exhibited20 cm of relief,cresting ! 5 m fromthe bayou,but then decreasing as abruptly on r.he inland The studysites werc ac!ectedabout 60 km side, anddeclining moregradually to the pond apart Fig. 1!. Bothmarshes arc of similarage and margin.Elevation at ORwas more uniform, except origin,derived fnim the Lafourc he deltaic coinp lcx for a 5 crn drop within l ! m of' thc pond margin thatwas acti ve between 3, X and5 X!RP. though Wang ! 994! the thickness and sediment characteristics of thc underlyingHo!ocenc f'ill sequencesare quite Thc hydrology of these sites has been different Frazicr 1967, Penland e al, 1987!. describedby othersfmm concurrentgaging data obtainedin 1993 Wanget al. 1993, 1994;Wang ThcOld Oyster Bayou OB! inarsh is adjacent 1994,Wang 1997!. Both sitesexperience thc 20 to a baythat receivesinputs of sedimentsfrom the cmannual excursion in sealevel that istypical of Atchafa!ayaRiver. The bay system that provides thispart of the northernGulf of Mexico Marmer reworkedsediinents tothc Bayou Chitigue BC! site, 1954,Reed 1995b!. Sea !eve! is highestduring the in contrast,is currentlyisolated from directriver late sprinjand early fall and is lowest in thc winter. inflowsI Huhand Rouse 1994!. Representative salt Whenthe marsh was f!tx>ded by m»rethan 10 cm marshesdominated by Spuro'ncsulrerni fl<>ru were at the mid-transectgage, Aow at both siteswas from chosenfor bothsitcv, each 1 C 0 0 oCL cfI C LLI ma! qidaG Pools Asl~W 20 G P. Kempet et. Data collection was initiated at thc BC site in at both sites through December1993. One SET' September 1990. and continued at both sites stationwas located at the midpoint iit eachtransect, bctwccn October 1991 and December 1993. andthe secondwa.s ptaced just inlandof' the pond Hurricane Andrew, with sustained winds of about margin Fig. l!. 200 km h ', made landfall between the two sites on August2S. 1992, An analysisof the hurricane EachSET station provide» 36 individual impactat thescsitcsis given in Cahoon et al. measuringpoints grouped in quadrantsradiating 995h!. from a commonsupport pipe that servesils a benchmark Bournans and Day 1993!. Thc SET lVlATERIALS AND METHODS supportpipe was vibrated into the soil to a depthof approximately4 rn to proviclea stablebenchmark, SedimentDeposition, Accretion aad Elevation sothat measured changes in soil surfaceelevatioa Change integrateallprocesses thatresult in aggradationor degradationwithin thi» zone Cahoon et al, 1995al. Petri-dish sedimenttraps consisting of The SET collar elevationfrom the interior station precornhustcd,prewcighcd glass fiber fitters fixed at eachsite was later tied into thc regional to the marsh surface were used to mcasurc short- differentia!GPS survey to obtain thc absolute tcrmsediment depositiiin Dl.p! Reed,1989, 1992; differences in marsh surfaceelevation discussed Leonard19971. At eachsite, traps were arrayed at above Alawady and El Tahat 99S!.A pairedt-test 1ft locat.ion.sbetween thc bayou and pond. They was usedto assessthe significance of differences weredcploycd in groupsof threethat were collected betweenthe sites SAS Institute Inc. 1991!. Shallow biweeklyover 4 !intervals from l.cbruary 1992 to subsidence S!was calculated following Cahoon et Scptemhcr1993. No data was collected at BC over al. 995a! as the difference between ACC and E,Fr, one4 weekinterval including Hurricane Andrew August19 to September 28, 1992!. Thc filters were Soll Measurements washedwith dciunizcdwater to rcrnovcsalts and weighedafter drying in thcoven at 60"C, Cores,10,2 cm in diameterand 25 cm long, werecollected at eachsite from thc marshbetween Liingcr-tcrmrates of sedimentaccretion thebayou and the pond along tran sects that included ACC!werc dcterrnincd with feldspar ntarkcr the marker horizr!ns and SET stations. Two horizonsusing thc techniques of Cahoon and Turner preliminarycores acquired in March1993 at 60 and 989k Triplicatehorizons were established at nine g0 m frotnthe bayouat BC, and at 20 and45 rn into sitesatBC in September 199 and at OB in August thcmarsh at OB, havebeen described by Breuil 1991.1:ach rnarkcr was cored in the spring and fall 994!.A moreextensive coring program followed until Octoberl992 using thc cryogenicmethod laterthat year in Novemberthat produced the data Knausand Cahoon 199 !!. Abouthalf' of the analyzedhere. Fourcores werc collected from the horizonscould not be f'iiund after thc storm when BCsite at 10.20, 60 and g0 m fromthc bayou, and mostlocation indicators were stripped from thc sites. five coreswere extracted at OB at distancesof 5, Cahoonct al t 995h!werc more successful, 10, 20, 40 and45 m Wang1994!. Thin-walled however,in trrcat!ng similar layers at these sites after aluminumtubes were slowly pushed into the soil thcstorm, and concluded that surface erosion was by hand.while roots were cut along the outside to minor. limit compaction.The top and bottom were capped prior to withdrawal.Cores were frozenand later Changesinthe elevation of thcmarsh surface cut into5 crnsections that were dried at 80"C. Core E ,! at thetransect midpoints were deterrruned sectionswere weighed to yie!d bulk density and then usingthe SET method Bournans and Day ]993, were combustedat 5SO"C and reweighed to Cahoonet al. 1995a!.T»'o SET stations were determinepercent organic matter %OM!. A paired installedinthe marsh atBC in September 1990 and t-test was usedto comparemeasurements from the atOB in August 1991, and measurements continued two sites SAS In.stituteinc. 1991!. Geotechoica Aspects of Wetland Loss 21 Void Ratio and Moisture Content V i» thc that portion of'the void volume occupied hy water Dunnet ai 198 !'l.ln real marsh soils, full Consolidationis dctcrmined asa reduction in saturation is never reached. as roots introduce and the diincnsionless void ratio, e, defined as: trap gaSesinxide living niemhranCsthat are not displacedhv water Naidoo ct al. 1992!. Vv e= V RFSI JLTS AND DISCUSSION where V is thc volume of the voids and V is thc volumeof' thc solids Dunn ct al. 1980!. The void Sediinentationand organic soil development ratio is derived from laboratory analysisof thc soil: can leadto aggradation Vyman ct al. 199 f}. Converselv,loading of thc surfaceand consolidatiiin of underlyingsoil layerscontributes to settlenicnt ! Kayeand Barghoorn 1964!. lf relativeposition within the tidal fratnc is onc of the primary factor» whereG, is thc dimensionlessspecific gravity of affectingsalt marsh survival, then it is iinportanttii thc soil solid~,g i»thc unit weightof water g relateobserved changes in surfaceelevation to short crn-'or9,81 kN rn'!, andg, is thedry unit weightor and long-termprocesses that operate ! at thc bulk densityof thc soil Dunnet al. 1980,Bowles surface, 1 within thc root zone. ! in that portioii 1992!. of the shallow subsurfacemonitored by the SET, and, fmally, ! in the deepersubsurface. 6, was not determineddirectly but was estiinatedfrom g, and%OM based upon laboratory Cahoon et al. 995a! have shown how SET measurements made by Breui 1 9941 on and accretion data can be combined to estimate representativesoils from the two sites. These results shallow subsidence. Here, we examined void ratios wereconsistent with specificgravities of 2.61 and to estirnatc compaction or expansion within the 1.14 for tnineral and organic soil constituents, upper25 cm where wetting and drying, as well as respcctivcly,that werepreviously determined by root growthand decomposition might be expected Delauncet al. 983!, and havebeen used by others to cause deviation from a normal consolidation to characterize Louisiana salt marsh soils Nyman profile.It wasthen possible to estimatehow much et al. 1990,Callaway 1994!. consolidation must take place in the substratum betweenthe marshcap and the baseof thc SET Because the marsh soil volume is largely supportpipe rn!. voids,water that entersand is trappedin thesevoids can result in a moist unit weight that is far greater Finally,we calculatedthe effects of elevation thanthe dry unit weight. If thetide level is at or and normal drainageon loading of the marsh abovethe marshsurface so that the soil is saturated. subslratum. This provided thc basis for a thenthe weight of thewater and a portionof thatof geotechnicalmodel proposed to explainobserved the soil solidsis hydrostaticallysupported. Only differencesin marsh elevationdynamics at the two the uncotnpensated buoyant! weight of thc solids sites. loadsthe underlying soil Dunnet al, 1980!, When the water level decreases below the marsh surface Sedimentation,Aggradation and Accretion andsome drainage occurs, the soil moisturecontent dropsbelow saturation.The weightof the water Short-term sedimentation on thc marsh that doesnot drain, but remains strandedabove the surfaces DEP! did notvary significantly within sites watertable, must thenalso be supportedby the soi! with distancefrotn the bayouor pond, hut was four matrix andso contributesto the loading. The degree timesgreater at BCthan atOB Table1>. Fstimated of saturationcan bc expressedas: daily ratesspanned two order~of magnitude Fig. 3!. HighDEP at bothsites was associated v ith V ! HurricaneAndrew in August1992, but elevated V 22 G. P. Kemp et al. N IO CD O C4 O O Q O O O O Q O O Q D Q Q Q QO L-~ap i.w~ 5! Uogisoda0guawipag GeotechnicalAspects of Wetland Loss 23 Table l. Marsh elevationat corelocations h;!,short-term sedltnentation DEpi, elevation change at SETstation F-, !, markerlaver accretion ACC] and shallow subsidence S!from October l991 to Octoher 1993; mean + S.E.. * indicatessignificant difference between sites p 0.01]. ratesof deposition persistedat both sitesfor at least margi~ SET station. This resu!ted in an 8 cm iwo months following the storm{Cahoon et al. decreasein elevation in one quadrant during the 995b!. Increaseddeposition alsooccurred at OB winter of ]991-92 {Day et al. ]994!. This during the period of high river dischargein April degradationcoincided with vegetation death at this andMay, 1993,and s]ightly laterat BC in May and location and is simi!ar to the soil collapse Juneof the satneyear. Despite its proximity to the phenomenondescribed by Nyinan ct al, ]993! and unlevecd mouth of the Atchafa!aya River, De! aune et al. ]994!, Data from the interior marsh sedimentation at OB was limited by the 10 cm SET stations arc compared here, to focus on the difference in tnarsh elevation and lower flooding more gradua! elevation change that takes place prior frequency Fig. 2!. to vegetationdeath. The mean rate of sediment accumulation Elevation measuredby SET rises through the ACC! measuredby marker layeraccretion was 40 suinmer and fall and decreases in the winter Fig. percent greater at BC than that at OB, but this 4! This cyclic behavior may track the annual Gulf differencewas not statistica]lysignificant, primarily ascii!ation in sea level Marmer 1954. Reed 1995b!. becauseso many stationscould not berelocated after The annualelevation rangefor the longer record at the hurricane Table !!. Thc 08 value is almost BC was 1.7 cm y '. Siinilar seasonalvariations in twice that reportedby Cahoonet al. {1995a!, but is marsh elevation have been reported hy others only 28 percenthigher at BC. Bournans and Day 1994, Childers et al. ]993!. The pond shoreline at OB was stab]c but F levationtrajectories at thc two sitesdiverged retreated at BC into the area monitored by the pond in the interval that included Hurricane Andrew, Thc 2I G. P Kemp et al, GeotechnicaiAspects of Wetland Lass 25 OS marsh expcricnced riiorc than 2 cm uf significantly p = 0.0!tr!. Void ratio increasedfrom aggradation. while the BC surf'acc decreased 0.3 cm the surface to about cm at OB in the zone of over the same interva!, F!cvation dynamics at thc active rrrotgrowth, andthen dropped off, while the RC marsh werc !itt!c affcctcd by thc storm and BC rorcs showed less variation with depth, Thc continued ro l'luctuaicwithin the range previouslv rilffcrence ln void i'atlo ili!tcd between tllc sites a't established,whi!e the marsh at OB shifted upward the surfacedisappears with depth Table 2!. into a ncw c!cvation range I ig, 4!. This analysis l'ocuscs on diffcrcnces betwccn Nct elevation changes at the two sites differed thc two sites. Rut these are relatively subtle signii'icantlytTab!c !!. E!evation at OH moved considering that these two salt rnarshes exist at upward at 0.5 cm y ', while the net changeat BC oppositeends of a sustainahilityscale. Thc summary was not significant!y different from zero. These data ma.sksdifferences a!ong each of thetransccts, va!ucscompare with annualrates at OB andBC of which bath showed a decline in the rnineralsediment 0.65 and 0.15 cm- y ', respectively, measured content of thc upper 25 cm of the marsh with independently at nearby stations between 1992 and distancefrom the bayou, This trend was not present 1994 by Cahoon et al. !995a!. in thc organic matter content, which was uniform along both transects and between sites. as has been Shallow Subsidence attd Soils of the Root Zone noted more generally for the Mississippi deltaic plain by Chasse!inket a!. 984!. With these cavcats, Shallow subsidence at BC was more than twice the resultssuggest that thc vegetationdominated that at OR Tab!e 1!, Cahoonet al. !995a! reported soils of the marshcap remain re!atively unchanged S for the 1992-94 interval that was somewhat lower, as long as the surface is above that threshold in the 2.45 and 0,40 cm y ' at BC and OB, respective!y, tidal frame at which waterloggedp!ants die. but the 2 cm y ' difference hetweenthe siteswas common to both studies. Void ratios determined for the 0-5 cm surface !ayersshould be representativeof newly deposited The soil core analysesprovides more infor- sediments, given the measuredaccretion rates Tab!e rnation on processesoccurring in the upper 25 crn ! !. If thetype of sedimentdeposited does not change Tab!e2!, Mean bu!k density, g, wassignificantly greatly from year to year. the variation in mean void higher for thc whole25 cm at OB than at BC p = ratio withdepth below the surface ! ayerat the two 0,0002!, but only the upper 5 crn differed sites should indicate whether significam consoli- significantly p = 0.003!when individual layerswere dation isoccurring in this zone.Void ratiosgeneral! y compared between sites. %0M was significantly increasewith depthat both sites, suggestingthat lower for the wholecore at OB than at BC p = thc surfaceis overconsolidated,but end up at the 0.026!, and was also .significantly lower for the samevalue for the 20- 25 cm layer Tab!e 1!. This upper 5 em p = 0.0! 1!. The upper5 emaf. OB was suggeststhat most consolidation associated with this higher in bulk density and lower in organic matter layeris contemporaneous with depositionand takes than samplesfroin greaterdepths at both sites, placeat the surface,presumably as a consequence of desiccationrather than loading. Below the The calculated void ratios indicate that voids surface.void spaceis beingintroduced, possibly as occupy between8 and l0 times more soil volu~e a resultof root growthand infauna activity 1 Frey thanthe soil solidsin the sample.sfrom the two sites. and Basan 1978!, Shallow subsidence, then, as On averageat BC and OB, 90 and 88 percenr, monitoredby the SET,must take placeprimarily respectively,of the upper 25 cm of soil consistsof below the upper 5 cm for which soil data are void space Tab!c2l. The mean void ratio for the avai! able. entire 25 crn was significantly lower at GB than at BC p = 0,001!, The meanvoid ratio for the upper Breuii !994! determined void ratios on a 5 cm at BC wasnearly twice that at OB, but again smallernumber of samplesfrom coresacquired this wa.sthe only layer in which the sites differed earlier at the two sitesin spring, ! 993. At that time 26 G. P, Kernp et aj, 'I'bl '» Bulk d tv v! percentorganic ~eoM! specific gravityofsoil sohds G! and void ratio e!fmm salt marsh coresoB samples; meanvalues and1 S.K.Significant differences between sitesindicated by ** p <0.N! or * p< 0,95!. BayouChitkgnc n=4 0.23 l 0.02 0 38+ 0.24 ~ 0.03 0,25 -i; 0.20 + 0.03 0.22 + 0.21 + 0.03 0.27+: 0.23:~ 0.02 023 m 0.22+ 0.01 0.27 + 18.15 ~ 1,00 13,68 + 21,40+ 2.29 24.70 ~ 23.83 2 2.83 18 40+ 23.03 ~ 2.63 :19,62 2 22.03+ 2.36 21.42+ 21.69+ 1.02 19.56+ 2.34+ 0.01 2.30+ 0.03 2.26 ~ 0.04 2.27 4 0.04 2.29+ 0.03 2.29 =~0.01 5,64 k 8,08 10,34 7.75+ 9.43 8 25+ theSET measurements shov that the 08 marshwas althe highest elcvat»ol» recorded during the studv Fig,4!, less than half a yearafter IIumcanc Andrev . CQHlparlngmeasured accretion, ACC, w»th Meanvoid. ratios at that time from the upper 30 ctn thatpredicted from DEP can provide additional werc30 to 40 percentlower than for the cares insightinto factors that influence theaccunnllation descTlocdherc, which werc obtained eight »nonths of sedimentsat tbctao sites.A vcr icalaccretion later Table 2!. Differcnocsin technique cannot be ratecan be predicted fronl annual DFP using the ruledout, but these results suggest that seasonal bulk densityof theupper 5 cm as changes»nvo»dratio Tnay be Qccurr»ng with»n thc upper25 crn as a. consequence ofdcwatering, Toot growthlntauna o~decornposlt»on thatmay explain son»coi thc short-termvar!ar»ons ln clcvat»QB, GeafechnIca! Aspects Qt lVetIRAd Loss 27 may affect sails below the marsh cap in a similar H DF.PwRS 6.4. CIBy at BC, twice fhc observed accretion Rt this site Table 1!, and 2.5 times that wayprior to vcgetatiandeath. %hilc anincrease in measuredby Cahaon et al. 995R!. H, af 08 the lead Rpphcdto the marshsubstratum below 25 was 1,0 cn1y, half QfACC 1Bth1s study Table 1!, cIB fnay ca.uscsettlement, lt can also IncreasetlM but comparable to that reported for thissite by capacify of thesesai/s fo withstand greater loads. Cahocn et Rl. 995a!, To fest this kjjpafhcsis, wc calflbincd information RboUf.the hydfology, c/cvatian Rnd1nafsh soil ThC ScdImcntffap Inethad provides R good compositionta calculatethe theoreticalloading that standardized measurefof coAIpartng scdtmcnfatfon would bc apphedta the substratumat the twa sites patcnftal at d1ffcfenfsltcs Buf 1t 'ls sf11lposslblc during normal tidal drainage Dunn ct Rll.1980!. that the capturecftIciency of the trapsmay be mare or less than that of the fnafsh surface Itself. At BC, Sediments accumulate and add mass at tbc it appearsthat more than half of the sedimentmass surf Rcc. Th1s cRA affect surface clcvRtlon relative tlfat is trapped on the artificial surface is not to .meansea level MSL!, as apparentlyoccurred incorporated 1n the Rccfctlng surface lRyc1, after the hmTicaneRt 08 Fig. 4!, As has been Rcsulspcns1ondurfng fhc lQBgper lao rcquu'edtQ1' discussed, however, much af fhe effective stress consoltdatIQBQf thc dcpasl1'ffon3 a fhndmud R'tfhts fcsul'tsfrom drainagedurmg k'Avtides thRtcxpascs morc cofttfnuausly Hooncd sttc IT1aylcdUcc 'thc the marsh substratum.to the full weight of the effcctIVCaccfcflon rate fra11 11c UatcnulBl prcd.'lcted drained surface layer. The load that must be by the trapdata. Accretion predicted fram BEPis calculate then, is a function of the flnckncss and : incloser agrcemcntwith observedaccretion at the effective weight of thc soil. column from which infrequently flooded 08 site. supparfIBgwatcf Is w1thdfRwn. For 8x1ysoil coklnrn, fhCCfrCCfive StrCSS 1S givCB by Thcsc fcsults sug~csfthat whllc an clcvatcd posttIQBwlthln fhc I tda]ff arnercduccs thc potcntIR. for sedimentation it appearsto positively affectthe captureand UIcorpofat3on af availablesediment 1nta where c' 1$ thc tafal Born1al stfcss, Rnd '0 Is that the deposit. It is probablethat becauseaf' its portion supportedby water Dunn et al. 1980!. H proximitytc the river, the 08 marshwould have is the thicknessof the soil layer abavethe depthfor fnore sediment available to it than the IBR1sh Rf BC whtch the efTecttve stress Is to be determmed, 0.25 :lf ItLwefcRt R coInpafable lower pos1BQDwnth1B l81c m in this case.If drainageoccurs, H is divided into fidali frame Hulh and Rouse 1994!, But the. Rnuppcf dIR1ncd portIQB, H, anda lower,UndralIMd differencein aggradationobserved Rt the two sites ar saturatedsecf1on, H~. Tile total BofntalstI'css is 18:I1otslLlnply cxplatncd 1B Lcrn1s of scduncnfslLlIpplv. glvcn by F'Urthef, th1s difference cannot bc attflbutcd to co11$oilldattonw1thln thc Upper 25 cIB. Thc 2 cn1y 0 =--y~H " + y~HgS,V, 1+e ' difference in shallow subsidence must then be [email protected] scttlenMntOccurring within tlM remainder where thc rcsul't Is 1Bunffs of prcssure kPR! l3UAB of tlM 4 IA zone matutafcd by thc SET. cf al. 1980!.The first term insidethe bracketsis the wcfghtof thc sotl solidsand thc second1S that of Effective Stressand Soll Strength the water that remains within the soil matrix follawtng draInagc, Buoyantsuppoff. prov tdcd No sc.il data is available belaw 25 crn where within thc saturated sect ton 1s CLOASOLNRfIQBB1usf be taking place. Collapse and thc root material that provides IIIue::h»:ofthe soil sfr'Uctut'c cRB caUsc marsh :-dcgfadatianwitltauf any Increasem loadu1g Nyfnan The effecuvc stress, thus, increases with the et:::RI';::':1993,Belaune et al. 1994!, If is also possible spcclflcgfavtty af tlMsa11 soitds, depth of dra1nagc, divergencein theloading history and the moisnrfe content of the drained layer. Q, p, Kempetal. The effectivestress applied to the marsh estimatedat0,5 cm y' L.D, Britsch, U.S. Army substratumat the two siteswas computed for tide Co» of Engineers,New OrleansDistrict, pers levels from 25 cm above incan sea level to 25 crn corn.],lf thisdifference is correct.the BCmarsh below Fig. 5]. Layer-specificvalues of G, ande has alwayshad a greatersubmergence potentia! wereused direct!y Tab!e2! for mars.hsurface relativeto OB. Aggradationat BC wouldhave to elevationsat BC and OB of 5 and 15 cm, MSL, betwice that at QB to maintaina sustainab]e position respectively Table ]!. The drainedsoils were within the tidal frame. Bui an apparentloca] uniform]yassumed to beat 80 percentof saturation geoJogicpredisposition to submergenceis not S,=0,gh requiredto cause the observed di vergenccin marsh elevationtrajectories. A similaroutcome could a]so For tide levels greaterthan the marshsurface, resultfrom shifts in theseditnentation regiine that only the buoyantweight < 0.4 kPa!contributes to area norma]part of de!taic evolution Frazier ] 967!, theload. The buoyant weight differs by on!y 0.08 kPa betweenthe sites Fig, 5!. As the tide level TheOB and BC rnarshesexist at theupper dmpshe!ow the surface at OB, however, the loadat andlower bounds of the tidal fraine, Elevationat thissite increases dramatica]! y,when the full weight BC is 10ctn lower on average than at OB andis not ofthe drained soil and retained water begins toapply. increasingata sufficientrate to offsetany RSLR At incansca level. when 15cm of thesoil co]umn greaterthan zero, tnuch Jess the 1 cmy' estimated isexposed atOB, thc effective stress at25 cm be!ow for this site. Whi]eaccretion is greaterat BC, thesurface is anorder ot magnitudegreater than sha!lowsubsidence issimilarJy higher, resulting in whenthe marsh isHooded, For this tide level only noaggradation. Asmean sea level rises with respect 5 cmhc!ow the BC marsh surface, loadings due to tothe marsh surface, the depth of normaldrainage thcmarsh cap at BC and OB were estimated at 1.16 decreases,andthe load imposed onsoils underlying and2,92 kpa, respectively. Of this difference, 95 theroot zone is reducedproportionaJ!y. As the percenti sattributable tothe greater thi ckness of thc drainedlayer at OB, a functionofits higher position marshdeposit continues todevelop under a reduced within the tidal frame. loadingregime. soils be!ow the marsh cap wiJl experienceJess consolidation and develop less Thetheoretical difference in! oading resu!ting bearingstrength. fromnormal drainage should be reflected in the hearingstrengths ofthc marsh substrata atthe two A ~mousequi]ibrium develops atthe lower sites.Civcn that sha]low subsidence atBC is twice endof thetida! frame, The BC marsh csscntia!ly thatat OB Tab]c I!,it isapparent thatany added 'goats"over a weaksoil substratum untila drainage !oadingaiOB is not resu!ting inproportional ordcpositioneventirreversibly depresses thema h sett!cmcni,buiis, instead, contributing tosoil surfacebelow the point of noreturn. Con so! idan cia strengthin the marsh substratum. Jfincreased of thesubstratum is deferred, and then occurs drainageoccurred during a storm, it islikely thai suddenlyasa precursortothe collapse phenomenon settlementat8C could be far greater than that describedbyNyman et a!. 993! and Delaune et associatedwithnormal tides,and would eventua!l y al. ] 9941. forcethemarsh surface below thecritical threshold formarsh p!ant survival. At theupper end of thetidal frame, sed"n- tationis]inuted byinarsh e]evation asexisting ma " A GEOTECHNICALMODEL trajectorymodels predict AJJen!994,French ]9 ~ FORSALT MARSH LOSS Krone!9gj]. The OB tnarsh captures virtually a 1 ofthe srna!!er amount ofsediment available toit as Recentregional mapping ofthe depths of newlydeposit d mimcnts rapid}y undergo desic- radiocarbondatedpeats indicates thatRSLR atthe cationand consolidation. Thissyndepositi» BayouChitigue BCJsite isapproximately ] consolidation addsstrength tothe surface !ay " crny -',while that atOld Oyster Bayou OB!is withoutincreasing sha]low subsidence»d contributesto0.5 cm y 'of aggradation, arate th< Geotecnnioal Aspects of Wetland Loss IorJ V CP CJ cC 'V 'D 0Ft 'D a Ch C C Ol C> el cd 4l I 4. Cl CJ 2CCJ e UJ rv' ~ ~+I O lO ~V, c QSPg 'WO! UOI!BA8 Q aP~g 30 G. P. Kemp et at equalsRSLR for this area,A highere!evation at In contrast,the BC marshhas cxpcricnced a OB generatesgreater loadingof the marsh withdrawalof itsfluvial sediment source as nearby substratum, but this does not increasesettlement Mississippi River distributary channels werc TableI I. Marshelevation may not increase atany abandoned Fenland et al. !987!. This rcductiort rategreater than RSLR, but continuedsedimentation causedthe marsh to begin a declinethrough the tidaj anddrainage during storms Fig. 4! actover tirnc to frame. As marshelevation at BC decreasedtoward consolidatethcsubstratum and increase itsstrength MSL, shallow subsidenceol the marsh substratum Stutnpf !983!. The substratum becomes became a morc significant contributor to ovcrconsolidatcdwith respcci to the effectivestress degradation.It is likely thatthe decline at BC has appliedduring normal tides, Minor depression of accelerated, until now the marsh tccters at the theOB marsh surface during prolonged drainage thresho!dfor survival, waiting for a final doesnot imperil thc viability of theplant», as they precipitatingevent to pushit belowthe thresho!d startoff sohigh within thetidal frame,and e!evation for plantviability and into soil collapse. is quicklyrestored by increasedsedimentation. Analysisofthe end members of a sustainability Accretionand aggradation is limited at thc gradient unfortunately provides litt!c direct lowerbtrund of thetidal frarnc by a lowsedirncnt indication of the amount of river influence that is captureefficiency. This f'actorhas not been requiredto re ven'e degradation for marshesthat are parametcnrMin existing marsh trajectory models current!y at intermediatepoints in the decline AI!enl994, French l993. Krone !987!. Deposit throughthe tidal frame. Further,the soils of the formationappear» torequire a consolidation step marshcap change only subtly through the decline followingsedimentation. Without some leadingto co!lapseand, ultimately, submergence. consolidation.newly deposited sediments may be For moredirect evidence, we will needin future to repeatedlyrcsuspended if f!ooding is prolonged. lookat additional sites between Old Oyster Bayou Thisresuspcnsion differs from erosion in thatit and Bayou Chitiguc, and obtain direct occursabove the surface monitored bythc SET or measurementsof in situ soil strength and bystandard accretion techniques. Sediment supply consolidationextending into the marshsubstratum. atBC appears tohe enhanced a»a consequenceof thehigher frequency and duration of flooding,but Thcresults nf thiswork can, however, provide may bc ACKNOWLEDGMENTS BrIWLt:s.J.E. 1992.Engineering Properties of Soil» and TheirMcasurcrncnt, 4th ed. McGraw-Hill. This work was supportedby a gruntf'rom thc New 'fork, U. S. GccilogicafSurvey USGSGrant No. 14-08- BREIu., S. A. 1994.Wave damping over cohesive XXJ1-23411! of thc I.J.S. Dcpurtmcnt of Interior. sediment»in wetlands. MS Thesis, Louisiana Wc gratetully acknowledgethe rcI!csof S. J. StateUniversity, Baton Rouge, Louisiana. Williams a»thc USGSgrant manager.and H. H. BRIcvI:R-URsru S., S. W. NIXOh,J. K. COCIIRAN,D. Roberts as study coordinator at Louisrana State J. HIRSCIIBERG.Ahv C. Hum, 1989. Accretion Univetsity.It is a synthesisof thc c 'fort»of many rates and sediment accumulation in Rhode researchers in addition to the authors. R. J. M, Island salt marshes. Estuaries 12:300-317. Boumansand N. Latif contributed the SET and ACC CAII ION,D. R, AhI'DR. E. TVRNER1989. Accretion data, respectively. J. N. Suhaydawas an important and canal impactsIn a rapidly subsiding sourcefor thc geotechnicalconcepts. The paper wetland, ll. Feldsparmarker horizon benefitedgreatly from reviews by D, Johnsonat the technique.Estuaries 12:260-268. USGS National Wetlands Research Center and B. CAIRIoh',D., D. J. Retro,ANn J. W, DAY. JR, 1995a. Lock, Chair of the Departmentof Geology at the Estimatingshallow subsidence in microtidal University of' SouthwesternLouisiana, and for the salt marshesof the southeastern United States: constructiveefforts of three anonymousreviewers Kaye and Barghoorn revisited. Marine coordinatedby J, A, Nyrnanat the Universityof Cieology128: ] -9. Southwestern Louisiana, CAIIoou, D., D. J, REED,J, W. DAY.JR.. G. D. StEYER, R. BouMAhs,J. LYNctt, D. McNALLY. ANnN. LITERATURE CITED LArIE. 1995b, The influence of hurricane Andrew on sediment distribution in Louisiana ALAWADI AND EL TAHA. 1995. Elevational Data coastal marshes Journal of Coastal Research, Gathering.Barataria-Terrebonne National SpecialIssue 21:280-294. EstuaryProgram Published Report No. 25. CAI.IAwAY, J. C. 1994. SedimCntationprOceSses in ALLLN, J. R. L, 1994. A continuity based selected coastal wetlands from the Gulf of sedimentological model for temperate-zone Mexico and northern Europe. Ph.D. tidal salt rnarshes.Journal of the Geological Dissertation,Louisiana StateUniven,ity, Baton Socrety,London, 151:41-49. Rouge, Loutstana. BAtlMANN, R., J, DAY, AhltsC, MILlER. 1984. cHILDERs,D. L., F. H. SKLAR,B. DRAicF, AND T. Mississippi deltaic wetland survival: sedi- JoRDAN. 1993, Seasonal meaaurements of mentationvs, coastal submergence.Science sediment elevation in three Mid-Atlantic 224:1093, estuaries.Journal of CoastalResearch 9:986- BrRrNrss, M. D, 1988. Peat accumulation and the 1003. successof marshplants. Ecology 69:703-713, CRAFr, C. B., E. D. sENEcA, AND s. w. BRooME. Borsclr, D. E M, N. JossELYN,A, J. MEmA, J. T. 1993. Vertical accretion in microtidal MORRls,W, K. NL~, C. A. SIMENsrAD,D. J. regularly and irregularly flooded estuarine P. Sv rtn. 1994. Scientific assessrncnt of coastal rnarshes, Estuarine, Coastal and Shelf Science wel.land loss, restoration and management in 37: 371-386. Louisiana.Journal of CoastalResearch, Spec. DAY, J. w., JR-, D. J, REED, J. N, SVHAYDA, G. P. Issue20. 103 pp, KEMp, D, CAHooN, R. M. BVLMANs, N, LArIF. Bot MANs,R. M. ANDJ. W. DAY, JR. 1993. High 1994. Physical processes of marsh precisionmeasurements of sediment elevation deterioration,p. 5.1-5.40. In H. H. Roberts in shallowcoastal areas using a sedirnentation- ed.k Critical Physical Processesof Wetland eroston table. Estuaries 16;37S-380. Loss,1988 - 1994.Open-file report to the U. BOUMANs,R. M, ANDJ. w. DAv, JR. 1994. Effects S. Geological Survey. Reston, Virginia. of two Louisianamarsh management plans on LouisianaState University. Baton Rouge, water and materials flux and short-term Louisiana. sedimentation. Wetlands 14: 247-261, 32 G. P. Kemp et al. DELAI!NF.,R. D R, H. BhuMANN,AND J. G. Processesof Wetland Loss, 1988 1994 0 GosSEI.IsIK.1983. Relationshipsainong file reportto the LI. S. GeologicalSurvey verticalaccretion, coastal submergence, and Reston,Virginia. Louisiana State L1niversit erosionin a LouisianaGulf' coast.marsh. BatonRouge, Louisiana. Jottrnalof SedimentaryPetrology 53: 147- KAVE,C. A., ANDE, S. BARGHOOR.sI 157. tluaternarysea-level change and crustaluse DFLAuhT:,R. D J. A, NvstAIs,ANu W, 1L PATRICK, at Boston, Massachusetts, with notes on d 1994,Peat collapse, pondtng and wetland loss autocotnpactionof peat. Bulletin of the ina rapidlysubmerging coastal marsh. Jourrial GeologicalSocieties of Amerir a. 75-63 go of CoastalResean h 10:1021-1030. &'At'S R M t ANnD. R. CAItOOIY.1'990. ImprOVed Dui'aAR, J. B., L. D. BRrrSCnAsIO E, B, KEMP.1992. cryogeniccoring devicefor measuringsoil LandLoss Rates: Report 3, LouisianaCoastal accretionand bulk density. Journal of Plain.Technical Report GL-90-2, U. S. Army SedimentaryPetrology 60;622-623. Corpsof Engineers.Waterways Experiincnt KOsTERs, E. C. 19&7.ParameterS Of peat forrnatiOn Station.Vicksburg, Mississippi. in the Mississippidelta. Ph.D. Dissertation, Dt Iss'.1. S., L. R, Asntatsov,ARu F. W. KIEFER.1980. LouisianaState University, Baton Rouge, Fundamentalsof GeotechnicalAnalysis. J. Louisiana, Wiley & Sons, New York. KRosiE,R. B, 1987.A methodfor simulatinghistoric ERnsr,W. H. O. 1990.Ecophysiology of plants in marshelevations, p. 316-323. In N. C. Kraus waterloggedand Hooded environtnents. ed.!, Coastal Sediments '87. American AquaticBotany 38:73-90. Societyof Civil Engineers,New York. FRAr»;R,D. E. 1967.Recent deltaic deposits of the KIIECHER,G, J. 1994. GeologiCframewOrk and MississippiRiver, Transactions of the Gulf consolidationsettlement poteritial of thc CoastAssoct'ation of Geological Societies Lafourchedelta, topstraturnvalley fill 17:287-315. sequence: implications for wetland loss in FREecn,J. R. 1993. Numericalsimulation of Terrebonneand Lafourche Parishes, vertical marshgrowth and adjustmentto Louisiana.Ph,D, Dissertation, Louisiana State acceleratedsea icvel risc, northNorfolk, University,Baton Rouge, Louisiana. UnitedKingdom Earth Surface Processes k LFaNARD,1 .A, 1997. COntrols ofSediment transpOrt 4edforrns 18:63-8L anddeposition in an incisedmain]and marsh FRIY, R. W. 1978.Coastal salt marshes, p. 101- basin,southeastern North Carolina. Wetlands 169.In R. A, Davis ed. k CoastalSedimentary ] 7:263-274, 1".nvironrnents,Springer-Verlag, NewYork. MARSHIER,H. A. 1954. TideSand sea 1Cvel in the GossELIRK,J,G., R. HhrroÃ,AsID C. S. HDPKlissoN. Gulfof Mexico. US. Fish and Wildlife Service 1984,Relationship of organiccarbon and FisheryBulletin 89:101-118. mineralconteni to bulkdensity in Louisiana MCCAFFRFY,R.J., Avo J, THOKssoz. 1980, A record marshsoils. Soi!Science 137;177-180. HACKREY,c T.Asi> W, J. CLEARY. 1987, Saltmarsh of the accumulationof sedimentand trace lossin southeastern NorthCarolina lagoons: metalsin a Connecticutsalt marsh.Advances importanceofsea level rise and inlet dred ging. in Geophysics22;165-236. Journalof CrtastalResearch 3:93-97. MEs:OEISsoHis,J. A., As;oK. L. McKEE. 1988, HATTos,R.S.. R. D. Du.huuE, AvoW. H. PATRicK, Spartinaalternifiora dieback in Louisiana: JR.1983. Sedimentation, accretion and time courseinvestigation of soil and subsidencein inarshes of Barataria Basin waterloggingeffects. Journalof Fcology Louisiana.limnology & Oceanograph 7' 76;509-521. 28:494-502. y MOtutts, J. T., NAIO DAV[D A. PEPPER' Departmentof Oeeanri graphy and Coastal Stiettt e», Louisiana State Unit ersiti; BatonRotrge, LA 70803.TFL: 225-388-4728,'FAX: 225-388-2520; email: dpepper@tiger. Isu.edu GRECORV W. S~ nit[.. CoastalStudies Institute and Departmentrrf Oceattographyand Coastal Sci enr es. Louisiana State University! Baton Rouge, LA 70803, TFL: 225-388-6I88; FAX: 225-388-2520; email: gagregN!unixl.snce,lsu.edu P[N j WAvG CoastalStudies Institute, Lriui siana State Uni ver»it@, Baton Rouge, LA 70803, TFI.:225-388-5330; FAX: 225-388-2520; email: ptvang2@" unril.»neo!su.edu 'Corrcspondi[tg author ABSTRACT:The Louisiana coast is generally characterized asa lowwa ve~aergy environment wheresediment transport is doxninatedbythe influence oftbe Mississippi and Atchafalaya Rivers.Winter cold fronts, however, generate waves and currents that have s significantimpact ona varietyof Louisiana's coastal environments, although field data regarding their influence on theinner shelf are extremely sparse. During a 12-dperiod that included the passage of two coldfronts, waves and near-bed currents were ineasured on the Louisiana inner-shelf depth- 8 m!using a sophisticatedbottom-mounted instrumentation system. Bottoxn boundary layer paraineterswere then caictdated using wave-current interaction models, and sediment transport waspredicted byassuming steady state turbulent diffusion within and above the wave boundary layer, Resultsindicate that the second front Front2! wasthe more energetic of thetwo. A maximum significantwave height of 1&3 rn and inaximuxn current speed of 0.21xn s' occurredduring thisevent. Additionally, mean current-induced shear velocity .95 cms'! andwave-current shearvelocity .99 cms'! werehighest during this event's frontxd and pxefrontai stages, respectively.During the postfrontal stage, curxents were strong and well organized, although combinedshear velocities were low as a resultof reducedwave heighL Predicted sediment transportvaried considerably in direction and magnitude throughout the deployment, but was highest 2.7-16.2 mg cm' s' toward the southeast! during the prefrontal andfrontal stages of Front2. Fair weather transport was low and to thewest. Thus, winter cold fronts are likely sn ixnportantmechanism for sediment movement on theLouisiana inner shelf, although the associatedtransport direction and magnitude require further quantiflcation. From heSympostum Recent Resean h inCoastal Louisiana: tttaruratSystem Function and Response to Human tn/luence. Rozas.L.R, J.A. Nymao,C.E. Proffitt. h!.N. Raba[ats. D.J. Reed,and R.E. Turner editors!.1999. Puh[ohed by Louisiana SeaGrant Co[[ege Protoam. 35 lntroductiosr Our ob]ective is to discussthc resultsof a 12- Thc Mississippi and Atchafa!ayaRivers d instrumentedfield deploymentthat included two introducevast amounts of sedimentinto the wet!and, coldfront passages andtwo intervening low-energy estuarine.shorefacc, and shelf systems along the periods.Waves, near-bottom currents. and bottom northernGulf of Mexico,particularly a!ong the boundarylayer parameters are quantified and used Louisianacoast Crout and Harniter 1979!. Although to predict sediment transport magnitude and muchof this materialis depositedlocally, a direction.The results arc significant in a practical considerableamount of finematerial is transported sense,given that the inner she!fi» an important withprevailing cunents as suspendedsediment componentof thc sedimentarysystem that includes plumesand deposited offshore. Not surprisingly, south-centra! Louisiana's barrier islands and coastal therefore,these f!uvia!!y-derived sedirnenLsserve wetlands, which are currently experiencing asimportant sources of depositionalmaterial on the extremelyhigh rates of erosion. shoreface and continental shelf Croutand Hamitcr 1979;Adams etal. 1987;Roberts etal. ! 987;Wright Materials and Methods ct al. 1997!. Water level, wave, current, and seabed !n contrast,the importanceof entrainmentand elevation data werc collected from November 20 to transportol' inner-shelf bottom sediment by waves Deccrnber1, !997, at an8-m deep, sandy-bono med, andcuncnts along the Louisiana coast is poorly siteon thcLouisiana shorcface Fig. 1! usi.nga docurncntcdand quantified. Entrainmentof bottom-mounted! nstrumentat ion systcrnnamed scdirnentfrom the bed requires the combined action WADMAS Fig. 2!. The system inc!uded a of wavesand currents to generate a shear velocity F!uxgate"compass, a Paroscientific'~pressure u.! that exceeds a critical threshold determined transducer,a Digisonicsr"sonar altimeter, «nd a predominantly by sediment diameter. Since the verticalarray of thrccbi-axial Marsh-McBirney~ northernGulf of Mexicois generallyconsidered a elcctrornagneticcurrent meters at cle vations of 20. low-energyenvironrncnt, scdirncnt transport on thc tr7, and 120 crn above the bcd!. Sensorswere Louisianainner shelf during fair weatherislike!y programmedforburst-mode sampling; specifically, minimal Wright and Nittroucr!995; Jaffcct al. thc pressuresensor and curn nt meterssampled for 1997;Wright el a.l. 1997!. g,2minh - ata frequency of 4 Hz,while the compass andaltirnetcr recorded onc measurementevery 30 Thc passageof cold fronts, however,is a min.Samplesof bottom sediment were obtained notableexception to theselow-energy, fair-weather usinga grab-sampler,and later were dry-sieved to conditions.Occurring with a frequencyof roughly determinemean grain size, Additionally, hourly 30times yr ', chieflybetween November and April rnctcorological data front C-MAN Station GDIL! Robertset al. 19g7!,the passageof coldfronts GrandIs!cl anddaily weathermaps from the generatesimportant hydrodynamic andsedimentary SouthernRegional Climate Center in BatonRouge, responses in various coasta! environments in Louisianawere acquired. Louisiana,including dehaic wetlands Murray et al. 1993!,the chenicr plain Robertset al. 1987!,and Meteorologicalevents were ana!yzcd using a barrierislands Ding!cr and Reiss 1990; Stone and qualitative approach in which each event was Wang!999!. Data on inner-she!f' bonom boundary subdividedinto four stageson the basis of changes layerand seabed responses to frontal passages in in wind velocity. Stagesincluded fair weather,and thisregion, however. are sparse. With thc exception threefrontal stages: pre-frontal, frontal, andpost- of Jaffe ct al. 997!, who mode!ed sediment fronta!.The threshold established for windspeed transportusing representativevalues of wave and associatedwith pre- and post-frontalconditions was current parameters rather than direct fie!d the meanvalue for the study periodp!us one measurements, no published data for south-central standarddeviation. The beginning of the pre-frontal Louisiana arc availab!e. A PreliminaryAssessment of Wave,Current 37 Fig, l. Thc StudyArea. Instrumentwas located at 28'50.68'N,91'07.52'W. Depth contours arc in mctcrs. Fig.2. Schematicdiagram ofthe WADMAS instrumentation system. D,A. Pepperet al. phaseof thestorm was identified as the hour when boundarylayer wbI! of thickness ~ ! develops the«ind exceededthis threshold and blew fromthe duringwave activity, and the velocity profile is south i.e, between 90' and 270", measured definedseparately within and above this layer as: clockwise!.The frontal phase encompassed the periodwhen winds were variable in directionand lessthan the threshold speed. The post-fmntaI phase In: z<5 wasdefined as the interval during which the wind W blewfrom a directioribetween 270' and90' at a u speedexceeding the threshoM.All otherwind tr ! conditionswete considered Fair weather. u = " In ' z>6 K z Or Significantwave height I !,peak wave period T !,and mean wave direction 8 ! werecalculated whereu, andu, arethe currentand cotnbined fromthe pressure andcurrent-meter datausing wave-current-inducedshearvelocities, respectively, cross-spectralana!ysis, with horizontal-,and z isthe height above the bouom, z,is the roughness pressure-attenuationcorrection factors applied to producedbythe sand grains =D/30, where D isthe compensateforsignal decay with depth Earle et meangrain diameter!, andz is the apparent bottoin al.I 995!.Current- velocity profiles were generated roughnessexperienced hy thecurrent above the usingthe log-profile method, which involves log- waveboundary layer, z was usedbecause the linearregression ofthe burst-averaged currentmeter currentexperiences drag due to the cormbined velocities Drake and Cacchione I992!. Two influencesofphysical elements grain roughness conditionswereassumed necessary fora profile to andbed forms! as well as non-linear interaction with beconsidered logarithmic in a statisticallythewave boundary and mobile bedload layers significantsense:first, a correlationcoefficient r ! Grosset al. 1992!. > 0.994 Drake and Cacchione f992!; and second, a meandirectional variation between cunellt meters Theassumptions were made that the currettt- 30", Hourlymeasurements thatwere not inducedshear velocity, u., actsin thcsame direction logarithmicwereexcluded rom the analysis. asthe mean current, and that the direction of u. Current-inducedshearvelocity u,! andapparent oscillatesduring the course of thewave cycle. As bottom-roughnesslengthfora! I logarithmic profiles such,when the wave orbital velocity isat a minimum werecalculated using the von ICartnan-Prandtl nearzero!, the direction of u. is thesame as that equation: of thecurrent; when it is at its maxitnum,its direction q! ! is betweenthe wave and current directions,given by [modifiedfrom Cacchione et u z!=u /tc tn z/z ! al. I 994!I: whereu z! is the horizontal velocity atheigh z abovethebed. and tcis von Karman's constant ,4!. Oncethc sediment concentration inthe water sing columnhad been predicted discussed laterin this Q section!,theshear velocity calculations were cos tti+ -=- iterativelymodified toaccount forthe possible tz effectsofsuspended sediment induced stratification. Sedimenttransport was estimated based on the Todo so, the buoyancy parameter Z/LIemployed assumptionof steady-state,upward, turbulent inthe tnodel introduced byGlenn and Grant 987!I diffusionof sedirncntthrough the watercolutmn. was used. First,an entrainment function was defined, based onthe Yalin paraimeter :-!: TheGrant-kladsen l979, !9g6! model was usedtoaccount forthe combined influence ofwaves andcurrents. According tothe tnodel, a wave A PreliminaryAssessment ot Wave,Current 39 where r and r are thc respective densities of wherer! is thesea surface elevation, and u is the sediment ,65 8 cm'i!and»cawater .025 g cm-'!, current velocity. D i»the grain diatneter, and v is thekinematic fluid viscosity .013 cm-'s '!. Thc critical Shield's Results and Discussion criterion ! !, and shear stress t werc then calculated using: MeteorologicalConditions log8 = 0.041 log! 0.35 ilog 0,977 Meteorologicaldata indicated that the study dnr periodcould be»ubdi vided into two intervals offair ! weatherand two co!d fronts hereafter,Front 1 and cur CPV I ! Front2!. The fair weatherphases lasted from ! 9;00 UTM on November18 prior to the dep!oyment!to Normalized excess shear sire»s S'! was then defined 18 00 UTM on November 2!, and froin03:00 UTM as: on November 25 until 18:00 UTM on November 28. The fair weatherphases were characterized by tight !.3-6.6 rn s'! southerlyor easterlywinds; ! whereasboth frontal passageswerc characterized by a sequenceof strongsoutherly winds, followed varil by light and variablewinds, and finally by strong where t is the observed shear sire»».This was then northerly winds Table 1 and Fig.3!. Front.al used to define the "near-bcd" sediment concen- passagesdiffered froin each other in several tration C z !!: respects,Strongest winds during thc pre- and post- frontalphases were from the southand northeast yS respectively!in thecase of Front1 andfrom the c z !=c southeast and northwest during Front 2. Most d brd1+'!r $ 8! {i notably,however, these fronts differed inarkedly in intensity.Front 2, whichhad inaxirnum pre-fronta! where C is the sedimentconcentration in the bed «ndpost-fronta! wind velocities of 11.3and 13.7 in .65! andy~ is anempirica! constant with a value s 'was much more powerful than Front 1. Thus, the of 0,002.Suspended sediment concentrations were discussionwill focusprimarily on hydrodynatnic assumedto take the forin of Rouseprofi! es, defined andsedimentary responses associated with Front 2, by: Hydrodynamic Responses c ->= c ~ ! " , where a = The influence of the frontal passages, par- ticularlyyFront 2, onthe wave field isshown in Tab!e y isthe ratio of the eddydiffusivity of sedimentto 2 and Fig, 4. During fair weatherand during the that of momentum -1!, and w i» the particle fall first fron4d passage,significant wave height was ve!ocity. generallybe!ow 0.6 m. In contrast,during the pre- frontalstage of theFront 2, a maximumsignificant Fina!!y,burst-averaged sediment transport Q! waveheight of 1.34m wasmeasured. The trend in wascalculated by integratingthe velocityand waveheight was, not surprisingly, accompanied by sedimentconcentration profiles within, and above, a very similar trendin near-bedorbita! velocity, thewave boundarylayer suchthat: which reached a maximum of 55 cm s ' during the l pre-frontalstage of Front2, Patternsin wave period {!= f !'uCddt for z! 6 accompanyingthe frontal passages were lessclear, s althoughthe pre-frontaland fronta!phases of Front 0! 2 were notablefor the presenceof comparatively long period waves, and peak period was observed for z<6 Q= J I «Cdzdh W TaMek. Front Phase Amval Time Mean U Rangeof U Dominant m/d/h! m s'! rn s'! Direction Fair 11/1 8/19:00 ' 4.2 2.7 6.2 South 11/21/1 8:00 5.6 4.3 6,9 South 11/22/4:00 3.1 1.5 4,3 Variable Post 1 1/22/21:00 6.7 2.9 9.0 Northeast Fair 1 1/25/3:00 4.1 1 3 6.6 est 11/28/18:00 7.0 3.6 1 1.3 Southeast Front 11/29/16:00 2.1 0.3 3.4 Variable 1 1/30/6:00 8.7 5.4 13,7 Norlhwcst 5.3 0.3 13.7 todecline with theonset of the frontal episode. These 16 patternsin wave heightand periodwere likely causedby strongsoutheasterly winds blowing over 12 a longfetch priorto the secondfrontal passage, allowinghigh swell waves ta develop,Following v 4 thefrontal passage, hawever, strong northerly winds E likelygenerated choppy seas dominated by short, 0 steepwaves, whoseperiod gradually increased -4 throughnon-linear energy transfer as the post-frontal -e phaseprogressed, -12 Waterlevel alsoappears tohave responded to -t6 thewind shif % d~occu~during thedeployment D 50 'iDD 150 200 250 300 hamfram t 600 trrM Navambar20 althoughwith perhapsunexpectedly long lag times Fig. 5!. During bothfrontal passages, strong Fig. 3. Hourly wind velocityvectors in s '!, Arrows southerlywinds causeda peakin waterlevel, indicatethe direction in whichthe wind was blowing apparently4iue to set-upagainSt the adjacent coast. Table2, Wave characteristics during the deployment. Key: Hs = sigaiflcarttwave height; Tp = peak wave period. Front Phase Hs Tp Orbitalvelocity DominantDirection m'1 s! crn s '! of Propagation Fair 0.36 6.3 15.4 Northeast 0.43 5.5 15.9 Northeast Front 0.5 ] 5.7 18,4 Northeast Post 0,38 5.1 15.8 East Fair 0.54 6.5 21.5 Northeast 1.07 7.2 38.2 Northeast Front 0.67 7.6 29.5 Northeast Post 0.53 5.3 19.9 North ALL 0.52 6.1 21.5 significantamount of time and thus rotated the majority of the post-frontalstage before clockwise from northward-to southward-flowing eventuallyrotating toward the south.Also of note aseach front passed. The data suggest that currents duringthis deploymentwere the strong, steady, weredriven both by directwind stressand by southwardcurrents that dotninatedthe secondfair "inertial"forces resulting from relaxationof sea weatherphase, levelset-up as discussed byDaddio 977!. Currents werestrongest during the post-frontal phases ofboth BottomBottndarty Layer Parameters passageswhen maximum mean current velocity at 120 cm above the bed reached22 and 21 ctn s', Current-inducedshear velocity was strong, and respectively.This standsin contrastto orbital logarithmiccurrent profiles werc well developed velocity,which was at itstnaximutn during pre- duringpost-frontal stages Table 4!, which is frontalstages. The current direction during each of intuitivelyconsistent with the presence of strong, thepre-frontal periods differed between the two frontalpassages. lnthe case of Front1, post-frontal currentswere predominantly southward; whereas duringFront 2, currentsremained northeasterly for so .' Front 1 Front 2 South -40 0 sO 'i00 1 50 200 25G ~~ tram1880 tlTM November 2G Fig,5. Hourly water level and water level smoothed Fig.6. Mean hourly current velocity vector lcm s '1at usinga 24-h moving-averagewindow. 120 cm abave the bed. 42 D.A. Pepperet ul, TaMe3. Currentspeed s! und direction at 26 bot!,67 mid!,120 top!cm above the bed. Fmnt Phase s mid! s bot! DoininantDirection cm s'! crn s'! of flow Fair 6.1 5.4 3.2 Variable 6.2 5.3 3.4 North 6.9 5.5 2,3 South Post 14.0 1 2,0 7.3 South Fair 7.5 6.2 3.0 South 5.9 5,2 2.6 Variable Front 7.2 3,7 Northeast Post 13.4 1 1.4 6,6 Northeast AI L 9.2 7.8 4.2 Table4.Bottom botsudary layerparameters calculated forull hourly bursts with logarithmic proliles.Key: x =roughness length;u = current shear velocity; u = wave~urrentshear velocity. C 'er Front Phase z u u % Logarithxnic Gc C lcm! crn s'! cm s'! Profiles 5.0 1.41 2.05 29 1,6 0.69 2.23 18 Front 9,2 1.08 1,87 69 Post 3.5 1.59 1.94 67 8,2 1,25 2.18 7,1 0,97 3.08 Front 8,9 1.90 3.08 23 Post 7,0 1.75 2.10 47 6.1 1,44 2,12 40 steadycurrents atthese times. It ismore difficult to byhigh waves. Shear velocity was low duringthe makegeneral izations regarding thecombined wave- post-frontalstage, despite the presence of stm-ng currentshear velocity, because throughout all stages currents.This alone has unclear implications for the of From1, its valueremained fairly constant, and net movement of bed sediment within the water low, relativeto Front 2. Front2, in contrast, column,which requires a combinationof entraining illustratestheimportance ofhigh waves, rather than forces shear velocity! and transporting forces strongcurrents, in generating high combined wave- currentflaw!. The sedimenttransport model currentshear velocities atthe study site. Specifically, accountsfor this, however,and the resultsderived thehighest shear velocities occurred during the pre- fromthis model are discussed in the foilowirtg fmntaland frontal stages, which were characterized section. A PreliminaryAssessment of Wave, Current 43 Table5. Predictedsediment transport. Key: Q = predictedtransport; z Phase Q z wb]! Direc'tion Q z>wb]! Direction Q f total! D2rect ion 1. Fair 7.26 122 1,48 175 8.25 270 1,23 313 0.21 324 ].43 Front 0.27 148 0.086 0.39 357 Post 5.17 126 1.65 175 6.39 269 2. Fair 2.23 119 0,19 150 2,40 276 11.90 120 1.11 168 12.67 Front 14,67 1]0 1.88 69 16.15 146 Post 7,4 357 2.57 49 9. 20 Average 3.29 104 0.73 140 3.91 Sethnertt Tratrsport teristics of the front and the associated current direction,which serve to shifttransport toward one Fronts1 and2 differedconsiderably in terms componentof the waveorbital flow. Furthermore, of bothsediment transport magnitude and direction themajority of predictedtransport occurred within Table5!, Perhapsthe most notable aspect of these thewave boundary layer during all stages,reflecting resu]tsis thehigh transport rate associated with t.hc both the importanceof wavesin mobilizing pre-frontaland frontal stages of Front2. Although sedimentin thislow-energy environment and the thetransport direction during these time periods is fact thatsediment does not likely diffuse very high towardthc southeast essentially offshore!, it is into the water column. Finally, our predictions interestingto notethat the transportduring the indicatethat fair weatherperiods are characterized prefrontaland frontal stages of Front] is roughly by low ratesof westwardsediment transport. in theopposite direction. Since wave stresses are essentiallybi-directional, it is possiblethat sediment Results from the sonar altimeter Fig. 7! transportdirection during cold front passages isvery indicateappreciable movement of bedmaterial sensitiveto the specific meteorologicalcharac- throughoutthe study,including bed height fluctuationsof up to 20 cm. These changes occurred overtime-scales of hoursand includedalternating 02- episodesof erosion and deposition, with the result Fnmt2 thatno net change occurred during the study period. 51 Themost logical interpretation for these f]uctuations E 005 C 0 is that bed forms, such as sand ripples, were y 4% migratingbeneath the altimeter throughout most of Ol o <5 the dcployrnent.Thc time seriessuggests no W2 particularperiodicity to thesemigrations, which %25 shouldbe expected,given the changingwave and i currentconditions that occurred,There is also no indication that rates of changewere higher during Fig.7. Bed elevauon fm! during the study. The mean bedelevation for thestudy period has been assigned a frontalpassages than during low energy conditions. valueof zero,negative values indicate bed erosion. and Thereare severalpossible explanations for this. positivevalues indicate hed accretion. First,the 30-rtunutcsampling frequency of the O.A.Pepper et al altimelerwOuld not have permitted bed forin their significan contributions o the design migrationrates greater than one wavelength h-i as cOnstruction, and deployment of mayhave occurred during high-energy conditions! instrumentation.This work was fundedby the tobe resolved. Second, rapid changes in thedirec- MineralsManagement Service under contractlf lionof waveand current stresses that accompanied 3066/ff19911. lhcfrontal passages may not have facilitated uni- directionalbed fOrm migration, even Overa very LITERATURE CITED shorttime scale. Finally, thc increasedimportance of sedimententrainment and transport high in the ADAMs,C, E JZ., D. I .P.SWm. ANDJ. M. COmvi Botton>. Journal of Geophystcal Research 84:1797-1807. GRANT, W. D, wist>O. S. M>I»st w. 1986, The continental-shelf bottom boundary layer. Attnual Reeie>v nf Fluid Met harit'cs 18 265- 305. GRoss,T. I'., A. E. IsLI:v, its» C. R. SIInawooo. 1992. Estimation of stressand bcd roughnessduring storms on the northern California Shelf. Continental Shelf Resealsh 12:389-413. JAFR=.,B. E, J. H. LlsT At.nA. H. sALLE>;GER,JR, 1997. Massive seditnent bypassingon the lower shorefacc offshore of a wide tidal inlet- Cat Island Pass. Iwuisiana. Marine Geology 136:131-149. MtRR~y, S. P,, N. D. W>II.KRR,xNI>C. E,AowMS, JR. 1993. Impactsof' winter stormson sediment transportwtthin the TerrebonneBay Marsh Complex. Coasth'nesof the Gulf of Merit o: Proceedings of the ASCE Svtnposiunt on Coastaland OceanManagetnent 8;56-70. ROBERTS,H, H., O. K. Hmt, S. A, HSG,L J. Rousr:, JR., AN»D. RtcKMAN,1987. Impact of cold- front passageson geornorphicevolution and sedimentdynamics of thc complex Louisiana coast. Coastal Sediments '87: 1950-1963, STohE,G. W. A~I>P. Wmo. 1999.The importance of cyclogcnesison the short term evolution of Gu}f coast barriers. Transactions-Gulf Coast Assoctation of Geological Societies.49:478- 486, WIBERG,P. L., D. E. DRAKEAND D. A. CAccHIONI', 1994, Sedimentresuspension and bed armor- ing during high bottomstress events on the northern California inner continental shelf: Measurement~and predictions.Continental Shelf Research14: 1191-1219. WRIGHT,L. D. A>st>C. A. NrITROGI.R.1995. Dispersal of river sediments in coastal seas: Six con- trastingcases. Estuaries 18:494-508, WRIGHT,L. D., C. R. SHBRwoODAYD R. W. STER~BI:.RG.1997. Field measurementsof fair- weatherbottom boundary layer processesand sedimentsuspension on the Louisianainner continentalshelf, Maritte Geology 140;329- 345. 47 E.A. Meselhe et a! inforniation in the study of the ! 993floods on thc determinedusing a statisticalapproach. Thc key UpperMississippi and MissouriRivers, For thc «dvantagcof P!V is that. whcrea»methods such as Amazon River, Mertes ! 994} combined estimates Laser-Doppler Ve!ocirnetry quantifyaeration processes downstream of a PIVField 1VIeasurenten Sys cm spillway.These exainples show that PIV techniques haveapplications beyond fundamental fluids A schetnaticdiagram of thc large-scalePIV eaearch,and that P1V has enormous potential for mcasurernentsystein is depictedin Fig. 1. It should measurementof fIows in thc naturalenvironment, benotedthatancarby bridge, building, lifting truck, PIVHeld Measurement Tadsnlqttes or anyother lifting mcchanisrn that the video camera canbe mounted on can bc usedto lift the camera highenough torecord images. The PIV components Thcrequirements forPIV measurement arca includea highquality video carncra, a computer- suitablescrics of' images, flow tracers, a rncthodof controllablevideo recorder, flow tracers, and PIV digitizingthcimages,a computer, andPIV sohware, Theimage~ may be comprised ofradar images, a softwareto obtainthc velocity fieldfrom the seriesof photographs. ordirect vi feoimages. ln recordedimages. The flow tracers must be large thelatter case. thc irnagcs may be digitized with a enoughso that they map to at leastone pixel, but personalcomputer cquippcd with a frame-grabber. theymus be small and light enough toaccurately Thcimages mus then be pr x:essedusing amotion tracethe free surface movements. In orderto obtain estimationtechnique. Animportant component for accuratevelocity vectors, a largenumber of tracers fieldmeasuremcnt isthc regis rationof image arc required.ln addition,the traces must form coordinatesinphysical space for lowoblique camera sufficientcontrast with thewater surface, ln a viewingangles. The details of thc proposed PIV laboratoryexperiment, onecan control most nf these fieldmcasureimcnl system are discussed inthe factors,but in a fieldexperiment, hismay present followingsubsections. a chall engc. Mdao Carrsoro NdO-anglelens 'i iv i I I i 1 i Confioi Vie so Monitor Pcrn. 4 Fig,.l. ProposedfieldPanicle ]mage Velocimc setup. ry 49 E.A. Meseihe el al. While PIV is conceptually simple, theri: arc differential techniques, and b! corrcspondcnce many small detailsthat must be resolvedin order to techniques, In ditfercntial nicthods, thc image gct reliable velocity rneasurernents.Thc irnage- scqucncc is modeled with a three-dimensional prOCessingsOftWarC was dCVelOpCd OVer nlany years function ' x, y. t!. This enables derivation of a sei hy a PIV expert, Dr, lchiro Fujita from Gifu of linear relationships for thc spatio-temporal University in Japan.and modi tcd ior large-scale dcrivativcs of thc image. In correspnndcncc applicationsat IowaInstitute of'Hydraulic Research methods,onc searchesfor a directcorrespondencc IIHR!, The code is solid and very well-testedin correlation! belwccn a group oi' piscis between severalprior applications Ettcnia ct al. 1997;Fuji a rames.There are manys ariants of c Second image of river overlaid with an imaginary grid n,-l First image of river overlaid with an imaginary grid Search area around corresponding grid point in second image . interrogation spot at center of grid point in first image Fig. 2, Two consecutiveflow fields overlaid with an imaginary gnd. PIV 5 NumericalMotteling for FIOwEStimation 50 the flow facility. Then performa 2-dimensional aroundthe centerof a grid point in the first field, bilinear! interpolationto estimate the location of Next,the most I ikelylocation of this group of pixels the pixel in physicalspace. In thc laboratory,this in the secorid field is identified as follows An importantstep is straightforwardbecause one can enclosing search area is selected around the normallyensure that grid point»corrcspond exactly correspondinggrid pointin the secondfield, The or very closelyto integerpixel locations e.g. by interrogationspot is placed in theupper left-hand changingthe grid size, zooming, etc!. Also,if higher comerof the search area. and the linear correl ation accuracyis required,higher-order interpolation coefficientR betweenthe two setsof pixel» is functions can bc used,or the grid size can be computed.The interrogationspot is then moved decreased.Furthermore, since thc cxperirnentsare rightone position and R iscomputed again. This almostalways set up»o that the camerais per- procedurei» repeated for all thepossible locations pendicularto the imagedarea, the analysis is of the interrogationspot in the searcharea. The inherentlytwo-dimensional. The experiments locationwhere the correlation coefficient takeson typicallyrequire a small field of view,typically less itshighest value is taken as thc most likely location thanfive to seven degrees such that the camera lens ofthc pixels from the interrogation spotin thcsearch introduceslittle spatialdistortion. Oftentimes, so- area. With thc displacementand time difference called~~optic lenses,which preserve spatial betweenfields now known, one can compute an relationships,arcused. In thesystcrn used herein, cstimatcdvelocity ar the specificgrid point. The imagingis performedat a low obliqueangle. wholeprocess isrepeated at everygrid point and Consequently,the field of view is muchlarger so theresult is a fieldof velocityvectors, To analyze thatlens distortion may not be negligible. The basic 300images on a 133MHz PentiumPC requires approachof overlayingthe imaged area with a grid about24 hours. With proper seeding, fewer images of known dimensionsis no longer feasible,and arerequired, and a fastercomputer should drop thc practicaJlyonly few selecttxl poinns on the perimeter processingtime to a few hours. of theimaged area are available Ic.g., trees, power line poles,building corner», etc. for rectification Thesize of rhcgrid determines thc pitch of purpo»e»!.Thc location of these~otr i~linis w iI I thcvelocity field a» well as the overall computation oftenbe dictated by what is available out in thefield. time. It i» not obvious what thc best size for the A generalapproach for image registration is thc usc inlerrogarioltspot ol the Seareliarea Is. If the of a three-dimcn»ional conformal coordinate intcrrogatiiinspot i» roo small, many sets of pixels transformation Wolf 1983!. Fujita et al. 997! used inthc search area may give high correlation, leading a sirnplcr,more direct approach, based on an eight- ro crroneou» vccton'. Thc»arne is true if the search pararneterprojective transformation to estimate the areai» too large On the other hand,if the inter- physicallocation of pointsfrom the image.This rogationspot is too large,the differencesbetween fractionallinear transformation can empirically thecomputed correlation coct5cients become small, modelthe distortion cffccts for obliqueimage» alsoresulting in emineou»vectors. I Mikhail and Ackerman I 976!. However, the approacha»surne» a horizontal water surface, and I mageRegistration requirescontrol points on the horizonralsurfacefor parameter estimation. lnorder to estimate velocities from an image sequence,pixel displaccments/locationsmust be Flow Estimation relatedto physicaldi»placemcnts/locations. In traditionalPIV-based mcasurernenrs, a grid of PIV measurementsmay be usedto estimate knowndimension» is placed in thefl rr> 150 IP ~ 200 ~250 350 400 300400500 600 x Pixels! I'>g.tIn>ag» ola »eel>nn tm 'lear .'reek over!,d>d >x'>thexhmatcx t>f'i:ree xt>rface vclt>oitiex. Vectvr~xht>v' the a>»rag» p>x»Ithxp!a»cn>ent » p>x»!dx!.n I'hc average >xhaxed on > >>nag»a ! takenatI xe»ond>nterva!s. ' In '. I >' ~ .I5thv>nelrx datator tht i»reeved rea»hvn C!ear Creek 6 A Mesr,lhe er al Depth-AveragedVeloctt~. 0.24 0.2 tri 0,16 E 0.12 0.08 0.04 0 8 12 x feet! I ig.S. Depth-averaged velocity estimates based uncurrent meter measurements points! and thc kinematic i! Discussion To avoid introducingany environmentally harmfulmaterial, flo~ seedingcan he achieved w ith Thisease study demonstrates the effectiveness biodeg The rncthiid i» suitable for wide bodies of 1.H'ERATO RE CITEB v'atcr,as it captureslarger areas per frame compared to point measuremcnts,which would be both ABlrit,M,A. x<;t R. C. C . face . l BaA tulsa tnoa,G. R., J. C. K~ox,E. D. PAvLOtfI, , patternsof flood Aow,p, S7 81, In J. E.Costa, Aw'DF. J. M> 56 I.A. Mttndelaaohn a N.L. Kuhn accumu!ation and sediment addition interact to dredgedfrom thc Gulf of Mexico to fi!! a pipeline preventsalt marsh submcrgcnce. Reduced sediment cana!.Much of thisfill materia!accidentally inputscause a dec!incin thcaccumulation of rnincral overf!owedinto an adjacent deteriorating salttnarsh matterand thc supp]yof plantnutrienhs, which in located13 km southwestof thecity of Venice, turnreduces the rate of salt marsh accretion through Louisiana,near the mouth of theMississippi River. dosed plantgrowth. organic matter production, A gradientin.sediment depth was created with levels «ndsediment trapping viathc network of plant roots rangingfrom trace amounts to asmuch a» 60cm of OcLaunccta!, 1990;Wi!sey er al. l992!. With sediinenrabove the natural tnarsh surface over a 43 reducedrates of saltmarch vcrticat accretion, the ha area.Thc creationof this sedimentaddition saltmarsh surface issubmerged morcfret!uent!y and gradientprovided a unique opportunity tostudy the fora longerperiod of time Baurnann and DeLaune effectsofdifferent lcve!s of sediment deposition on 19gI!. !nnea~ suhmergcnccinthc salt marsh ran vegetativccondition and soil physico-chemistry in create,stressfulconditions which kill or reducethe gniwthofresident plants through processes suchas a deterioratingsatt inarsh. Although some research reducedsubstrate aeration N!endc! ssohn etal. 19f ! hasbeen done on spreading dredged material in the Sulfide concentrationsin the Reference and SAR-I siteswere atleast 15X higher than those for SAR-II androughly two ordersof rnagnitLidehigher than thosein the SAR-III and -IV areas.Average sulfide concentrationsfor the Reference and SAR-I were notto levelsknown to belethal to saltmarsh plartts t0 >2,0 mM!,but wereapproaching concentratiotts Ist highenough to impair plant growth >1.0 mM!. Ext ractab le ammon i um- N concentrations decreasedasadded sediment depth increased, but Ilf F SAIH SAIHI Sallies SAtHY thedifferences were not significant p=0,4! ExtractableNH,-N concentrations in the SAR-III, and-IV siteswerc as much as 2,5X lowerthan those inthe Reference and SAR-I and -Il areas.However, ex~le NO,-Nconcentrations were significantly higher p&.0075! in SAR-IV. In addition,ex- tractablephosphorus concentrations significantly rose p=0,04! from the Reference to SAR-IV sites Table 1!. Interstitialsoil salinity was higher with more addedsediment p .0001!. Individual corrt- parisonsindicate that areas receiving the most sediment SAR-III and SAR-IV! had significantly SAR-II aafHI SA«t-W higher p&.0003! salinioes than those receiving the least Referenceand SAR-I!, but in t.ertnsof actual Fig.1 .The effects in 1993of sediment«ddiiion on a,!iel«tive etevatinn and h.! percent vegetative cover differencesin concentration, thegreatest of these inthe five tre«tmeni «remi. All elevationmeasurements wasonly about 4 g1 ' e,g 7.~5 g l' vs.4.2M. I arerel«tive toa referencemarsh with an elevation equal g I ' forSAR-IV and Reference areas, respectively! iozero. Data are means «nd standard errors n=5!. The one lettersindicate no st«tisi.ical difference between Discussion treatinentmeans Fishers, LSD pc0.05!. Bothvegetative and physical parameters Bulkdensity showed a steady and pronounced respondedtosediment additions. Plant height and increasefrom the Reference to the SAR-IV sites coverwere greater with increasing sediment deposi- pcs.0001!, SAR-IV hulk densities were roughly tion. Thechange in tnarshelevation associated with fourtimes higher tlute in the Reference and SAR-i sedimentaddition may help explain this pattertt. areas Reference; 0,25M.03; SAR-I; 0.26M.04; Marshsurface elevation substantially rose as more SAR-II;0.4~.08; SAR-III:0 61&.06.and SAR- sedimentwas added, and this increasein elevation IV:0.97M. I 5 g cc'!.Only the Reference and S AR- positivelyinfluenced a number of factors affecting I sitesappeared to havesimilar bulk densities. plantgrowth. Extractableiron and manganese concentrations sigmficantlyincreased p=0.0012 and p<0.0001, Floodingdepth was reduced and soi]aeration respectively!with increased sediment deposition wasimproved with increasing sediment additions. Table I !. Redoxpotential increased with sediment addition indicatingthat soils were more oxidized inthe higher Interstitialsulfide concentrations fellsharply elevationsites than in areaswhich received less withinixed sedimentaddition p=0.004! Table 1!, sediment.With a reductioninflooding, the water Effects of Sediment Addition. to a Sati Marsh 59 TableI. Extractahleelement concentrations mtuol cc'! for the five sediment affected areas for 1993. Interstitialsulfide concentrations mM! weremeasured in1994. Data are means with standard errors in parentheses.' Treatment NH,-N NO,-N Sulfide Reference 0,26' .05! 0.002' .0003! ! 69' 4! 3' ! 0.561' .184! SAR - I 0 17' ,04! 0,002' .0006! 47' l l ! l08" 5! 8 ! 0.384~ .162! SAR II 0 17> .Q7! 0.00' ,000~! 79" 3! 357" 71 3 y' ! 0.0 6' .0 0! SAR III 0.12' .08! 0.003' .0002! 55' 9! 287" 8! 28' ! 0.003' .001! SAR IV 0.10' .04! 0 005' .0010! 102' 7! 286" 83! 32'" ! 0.005~' .002> ' Thcsame letters within a columnindicate no statistical difference between means Fishers Protected LSD pc0.05!, table would moreoften fall belowthe soil surface that donot produce sulfide during respiration are allowingfor soil drainage and direct exchange of usuallymost active. Results show that sulfide lcvc! s gasesbetween the air andthe soil deep into the soil inthe highest elevation sites SAR-lll and -IV! were profile.Also, reduced flooding, helped aerate the farbelow those that negatively affect plants, but in rhizospheresince more aboveground parts of the the lowest elevation sites Reference and SAR-11 plantthat contain aerenchyina would be exposed to sulfideconcentrations did at leastapproach those theair fora longerperiod of time. Plantgrowth whichreduce the growth of S.aherniflora -1 mM! canbe reducedin hypoxicsoils because of an Kochand Mendelssohn 1989!. In addition,since oxygendeficiency in the rooting zone which forces sulfidealso inhibits plan uptake of' nitrogen NH, p!antsto rely more heavily on anaerobic rnetaboli sin N! [kochet al. 1990!,which is theprimary liiniting for theirenergy production Mendelssohn et al, nutrientto saltmarsh plant productivity Valiela and 1981!.However, since soils were less flooded and Teal 1974!, productionmay have been f'uriher moreaerated at thehigher elevation sites, the roots reduced in the lowest sites by its presence. ofplants in these areas could respire aerobically and reducetheir reliance on alcoholic fermentation Physicalcharacteristics of the sediment may Mendelssohnet al. 1981; Mendelssohn and Mc Kee alsohelp explain the increase in productionas the 1988!resulting in moregrowth. amount of added sedimentrose, Bulk densitics indicate that mineral matter content was much In addition,thc improvementin soil aeration higherin areasreceiving the mostsediment. also reduced the concentrationof phytotoxins Wetlandsoils with a higherinineral content havea commonlyfound in morereduced salt marsh soils. greaterability to takeup andsequester nutrients Freesulfide is the majorplant toxin typically Mitschand Gosselink1993!, and they also have preducedin reduced salt marsh soils Mendelssohn beenshown to providemore nutrientson a per andMcKee 1988!. In highlyreduced salt marsh volumebasis when compared to organicsalt inarsh soils suchas thosein Referenceand SAR-I sites, soils Delwuneet al. 1979!.Sites receiving the inost obligateanaerobic bacteria use sulfate from sea sedimentaddition also had greater extractable Fe wateras their tertnina!electron acceptor during and Mn concentrations. These elements are respirationand convert it to sulfide.However, in iinportantin theirability to precipitatesulfides and soils like SAR-III and -IV which were more therebyreduce toxic so!uble sulfide concentrations oxidized,aerobic and facultative anaerobic bacteria Gambrelland Patrick 1978!, 00 t.h, Mendaiaaohrr K N,L. Kuhn The effect sedimentadditions had on soil CoastalErosion and Wetland Modification in nutrientpools may also helpexplain plant responses. Louisiana:Causes, Consequences, and AlthoughNO,-N concentration was lower with Options.United States Department of Interior, greatersediment addition, the high plant biomass UnitedStates Fish and Wildlife Service. atsites receiving the most sediment suggests that BOEscrI,D, F., J. W. Dav, JR., ANDR, E. TIIRNER. thelow interstitial N was a resuItof plantuptake. 1984. Deteriorationof coastal environments In fact,erttractable NO,-N in theoriginal dredge in theMississippi deltaic plain: Options for materialwas 40X higher than that for the soil Management,p. 447-466, In V. S. Kennedy materialcoBected within the study area in 1993 date ed,!,The Estuary as a Filter,Academic Press, notshown!. Thus, the sediment initially mtroduced Jnc.,New York, New York. intothis salt marsh was of highN fertility. Thisis BOFSCtr,D. F M. N. Josstz.vN,A. J. MRHt'a,J. T. likelythe key reason for the much higher cover and MORRIS,W, K. NtlrrLE,C, A, SIMENSYAD,ANcr plantheights seen in this area, since nitrogen isthe D.J. P, Swrvr, 1994. Scientificassessment of majornutrient limiting salt marsh plant growth coastal wetland loss, restoration and ValielaandTeal 1974!, In addition,the increase in managementin Louisiana.Journal of Coastal extractableP concentrations withsediment additions ResearcitSpecial Is.rue No. 20. upto SAR-IV also likely had a positiveeffect, BRADLEv,P M. ANDE. L. Duva. 1989. EffectSof sulfide on the growth of three salt marsh Condtssion halophytesof the southeasternUnited States. AmericanJourna of Botany76: 1707-1713. Se.dimentadditions appear to havesuc- BREMNFR,J. M, AND D, R. KIII-.NFv. 1966. cessfullyrehabilitated thisdeteriorating saltmarsh, Determinationand isotope-ratio analysis af Withsediment additions salt marsh plant growth differentforms of nitrogenio soils.3. Ex- improveddue to increased soilaeration, nutrient and changeableammonium, nitrate, and nitrite by mineralrnatter conte'.nt. Areas receiving inter- extraction-distillationmethods. Soil Science mediateand high amounts of sedimentshowed Sociervof AmericaProceedings 30: 577-582. increasedplant cover FurtherTnore, thehighest BYRNslor.',D. S, ANDlvl. B. SrtrRors.1958. Soil SAR'sare likely to be the most long-lived because phosphorousand its fractions as related to ofthe effects ofsubsidence andsea level rise. Thus, responseof sugarcane to fertilizer phos- sedimentadditions could play a positiverole in the phorous,Louisiana State University and Agri- managementof sediment starved rnarshes, although culturaland Mechanical College, Agriculture successfulenhancement maybe mediated by a ExperimentStation, Baton Rouge, Louisiana. numberof otherconsiderations, CAHOON,D. R. ANDJ, H. CowaN,JR. 198&. Environmentalimpacts and regulatory policy LITERATURE CITED implicationsof spraydisposal of dredged material in Louisiana wetlands, Coastal BAKER,D.E, Av» M, C. AIvracrew. 1982. Nickel, Atanagement 16: 341-362, copper,zinc, and cadmium, pp. 323-336. In DELat,Nr, R. D R. J. BcrtESrt,AND W. H. ParatcK, A. L Page,R.H Miller,and K. R.Keeney JR. 1979 Relationshipof soil properties to eds.!,Methods of SoilAnalysis. Part II. standingcrop biomass ofSparrina alterniflora Chemicaland Microbiological Properties, in a Louisianamar sh. Estuarineand Coastal AgronomyMonograph no, 9 nd edition!. Afarr'neSci ence 8: 477-487. AmericanSociety of Agronotny,lnc., Soil DELaUNE, R. D.,W. H. Parruca,JR., asm C. J. SstrrH. ScienceSociety of America,lnc., Madison, 1992, Marshaggradation and sediment distri- Wisconsin, butionalong rapidly submerging Louisiana BatrstavN,R H. ANDR. D. DELAUNE.1981. Gulf Coast,Environmental Geology and Sedrrnentationandapparent sea-level rise as Water Science 20; 57-64, factorsaffecting land loss in ~ Louisiana, DELatrNE, R. D.,S. R. PEzESHKI,J.H. PARDun, J.H. p,2-13. In Proceedingsof the Conference on WHrrcoMe,AND W. H. PATRrcK,JR. I990 Effects ctf Sedtrnerst Addlfton to a Saii Marsh 61 Sornc infittences of sedirncnt addition to a MITsctt,W. J. ANDJ. G. GossELINK.]993. wetlands dctcrioratingsalt marsh in the Mississippi nd Fruition'i.Van NostrandReinhold, Ncv Riverdeltaic plain: A pilot study.Journal of York, New York. Coastal Research 6: 181-188. NYMAN,J. A R. D. DFLAiNi-;. AND w, H. PATRtcs. DUNSAR,J. B., L. D. BRT'sett,AND E. B. Kt:Mpill. JR. 1990.Wetland soil forTnationin the rapidly 1992. Land loss rates.Report 3: Louisiana subsidingMississippi River deltaic plain: coastalplain. TechnicalReport GL-90-2, Mineral and organic matter relationships. United States Army Corps of Engineers Estuarine, Coastal artd Shelf S WATERQUALITY, EUTROPHICATION, AND SALINITY CHANGES The Use of Diatom Remains as a Proxy of Historical Salinity Changesin AirplaneLake, Louisiana MtCttAatL, PAttsoNSr QUAYDORTCH r R. EUC!Evt:.TttrtNrra'. NANCY N, RAttALAts' 'Lrruisianu Unit ersities Mari ne Consortium.8124 Hvty, 56, Charrvin,I> 70344; TEL: 504-85/-288!; FAX: 504-851-2874; email rnparsrrnsrisrlumcrrn,edu -louisiana Unit ersities Marine Consortium, 8124 Hu v, 56, Chauvin, IA 70344: TEL. 504-85/-2800: FAX: 504-85/- li'74i email: qdortchOlumcon,edu 'CoastalEcology lnstrture and Department r~fOceanography and Coastal Sciences. LouisianaStare University, Baton Rouge, LA 70803 TEL: 225-388-64542FAX: 225-3Hlf-6326; email: [email protected]'wrlsu.edu Louisiana Universt'ties hfarine Cr>nsortium, A 4 Ha y. 56, Chauvin,I A 70344;TEL: 504-851-2800; FAX: 504-851-2874; email; nrabutaisC lNTRODUCTlON t.hemovement and shifts of vegetativezones of marshplants over the pastseveral decades CoastalLouisiana is experiencinghigh rates Chabreckand Linscombe 1982; Fuller ct al. 19951 of landloss .86% per year between 1955 and 1978; and a northwardextension of oysterleases in Baumannand Turner 1990!, Wetlandloss has been BaratariaBay VanSickleet al. ]976!,Conversely, linkedhypothetically to increasing coastal salinity. studiesof long-termsalinity data demonstrate that Sahwater can stress and kill marshplants, especially salinities have increased in someareas but decreased freshwater plants, which in turncan result in land or remainedunchanged in others Wisernanet al. lossdue to thereduced ability of themarsh plants 1990a;Swenson and Swarzenski 1995!, Therets to hold organicmatter in place McKee and nostrong evidence for a coast-wideincrcasc in Mendelssohn 1989!. The primary evidence salinity. Rather,salinity increases appear to bc supportingacoast-wide increase in salinityincludes localizedevents probably due to the dredgingof navigationcanals Wisernan et al. 1990at.While Framthe Symposium Recent Researctr in Coastal Lorrtstonrr reportsof documentedsalinity changes exist, the IVartrratSystem Funcrion and Response roHuman /nfluence. availablesalinity data are too sparse temporally and Roza~,L.P., ],A. Nyman,C,E. Proton, h;,tv, Rabelais. 0 J. spatiallyto properlytest for coast-widesaiinity Reed,and R,E. Turner editors!. 1999. Published hy Louisiatta increases. SeaGrant College Program 65 M M. L. Parsons stal. Oneapproach that can provide historical laboratory.Cores were stored at 4 C,and the longest informationon changingmarsh salinity is the sedimentcore was split thc followingday on a analysisof diatomremains preserved in thesediment custom-madeprecision core extruder a threaded record.The morphologyof a diatomvalve is extruderallowing precise measurements for slicing!. species-specificandgenerally preserves well in the Visualinspections and length measurements of the sediment,Many diatom species have specific corewere recorded prior to andduring core extrts- sahnitypreferences, which can result in changesin sion. Wesplit the coreinto l -crriincrements which a diatomcommunity if and when salinity changes. were then hornogenizcdand subdividedfor Thus,diatom valves are useful indicators of past subsequentanalyses, salinity. Identificationand enumeration of diatom valvescoupled with information onoptimal salinity Coredating conditionsfor growthcan be used to "reconstruct" thewater conditions at the time the diatoms were Selectedcore increments were dated by '~Cs li v ing Battarbec 19$6!. This study introduces some Milanet al, 1995!and" Pb CutshaBetal. 1983! ofthe concepts and formulations asapplied to one usinga PrincetonGamma-Tech 60-mm diameter salinityreconstruction thatwas part of a largerstudy intrinsicgerrnaniurn "N" type coaxial detector 0% presentedin Parsonset al. 999!. efficiency! interfacedto an EG&G Ortec 92X spectrummaster integrated gamma-spectroscopy MATERlALS AND METHODS system.Samples for ""Pbwere held for two weeks beforeanalysis to allowfor rxluilibrium between Core collecOon atmospheric'-~Rn and '"Pb. Samplesfor "'Cs were countedfor at least4 hto yield a countingerror of Wecollected two sediment cores in August, 10% in the vicinity of the 1963/4 peak, 1993,from Airplane Lake, a 19 hectare water body correspondingto the peak '"Cs fallout for the westof ~a Bay Fig, 1! utilizing 3-in diameter, southeasternUnited States Pcnnington etal, 1973!. 1.3-rnlong plastic tubes. Because ofthe nature of Samplesfor '- 'Pb werc counted briefly with a source thecore collection process fusing -1-m tubesto of "'Pb to measurethc sample se!f-absorption collectcores underwarer ina -l -mdeep salt marsh potential.The samples were then recounted for 24 pond!,it was impossible toaccurately measure core h toobtain a significantamount of netcounts above compactionduring core collection. Wc measured background.Additional counts werc conducted for corecompaction during core extrusion in the "'Pb activityso thatsupported -""Pb could be l ie~xudc 'g-- m pofc4L'rlLo»sianashowing thelocationofArrplaneLakeandimportantgeographicfeaiu s. SalinityTrends in CoastalLouisiana: Diatoms 67 determined.Supported ""Pb was subtracted from Dtatotndata analysis the total to obtain excess '"Pb, from which sedimentationrates werc determined.Results for A diatom-based salinity index t Sl1 was ' "Cs and '-"'Pbare reported as pCi g ' dry weight formulated using a multiple-variable rcgrcssion sediment!. techniquecomparing diatom speciessalinit> groupingswi hthe available salinity data Parsons The '-"Cs-based scdin>entation rate was et al. 1999!,A similarapproach was taken by l'lower determinedby dividing the difference between the 986!, in his studyof pH changesin lakes. The datethe corewas collected and 1963/4,by thc depth salinity groupings were detcrmincd from the where the peak in "'Cs activity occurred, A literaturefor as manydiatotn spccics as possible sedimentation rate was determinedfrom the excess thatwere >L5% of the population,Broad salinity ""Pbutilizing the constant rate of supply CRS! classificationswere used to standardizethe disparate model.assuming that there is negligiblemigration salinitygroupings devised by these rel'erences, and of "Pb in the sedimentand that the supplyof excess to acknowledgethe dynamic environment typical "'Pb is constantover titne, The sedimentationrate, of the Louisiana coastal marshes. The salinity therefore,was determinedthrough the inverseof groupsused in thisstudy, based on Kolbe 927! theslope of theleast-squares regression line that and Round 981!, refer to salinityranges within wasfitted to the'"Pb profile.The '"Cs and"OPb which a particularspecies best thrives,or most estimatedsedimentation rates were averaged to give commonly occurs; ol igohalobc1 0-5 ppt!, an overallsedimentation rate that wouldapply for mesohalobe -20 ppt!,and polyhalobe 0+ ppti, thewhole length of the sedimentcore, Thepercentage of the diatom population classified in eachgroup was summed for each sample. Diatom analysis There were several casesin which a saliniiy Separateportions of selectedhomogenized classificationcould not be assignedto a diatom sampleswere prepared and analyzed for diatorns speciesbecause either the speciescould not be accordingto Parsons 998!. A 100 itl aliquot identified,or no salinity information wasfound in containinga known concentrationof glass the literature. This discrepancywas correctedby rnicrospheres 0 ltm diameter, Unisciencesa, Ltd,! dividingthc percentage ol'the diatom population wasadded to «n approximate0.5 cc portionof within eachsalinity group by thepercemage that sediment to estimatediatom absolute abundance; could be classified, thereby standardizingthe Battarbeeand Kneen 1982! in a 15 ml graduated classifications to one and allowing direct polypropylenecentrifuge tube and rinsed several comparisonsamong the samples. The SI was timeswith 2% sodiumpyrophosphate NaPP! to computedusing two ratios,the oligohalobe io removeclay particles Bates et al. 1978!.Samples rnesohalobecotnponent OM! andthe mesohalobe werecleaned to removeorganic matter! with 2 rnl to polyhalobecomponent MP! in thefollowing of concentratednitric acid which wasboiled for 30 manner;SI = 35.72 OM! 0.62 MP!+ 9,17, Our min in a water bath, followed by six rinseswith preliminarystudies have shown that the SI predicts distilled-deionizedwater DDW!. Rinsesinvolved salinitywith an R'E!,8309and a slopeof 0,83, centrifugingthe sample for 10min at 2100rpm, indicatingthat the Sl is a reasonableproxy for subsequentremoval ofthe supernatant, andaddition salinity Parsonset al. 1999!. of freshNaPP or DDW Microscopicslides were madeby placing one or two drops of cleaned sample Regressionanalysis now in solutionin 10 ml DDW! ontoa ¹1 25x25 mmcoverslip. The coverslip was dried and mounted Sedimentationrate estitnatesacquired through ona slidewith Hyrax", Slides were examined on a coredating allowed us to assignan approximate date Hiss universalmicroscope. At least250 diatotn toeach sample analyzed for diatoms. The Sl model valveswere counted per slide,which provides a wasthen appliedto the diatomdata to estimate goodestimate of the diatomspecies >L5% of the salinitytrends through the core, and therefore over population Parsons 1996!. thetime frame representedby the sedimentcore. 08 M. L Parsronset at. Salinitytrends were estimated using regression weresubjected to a regressionanalysis to determine analysisof theSI versusthe cote dates. Significant if trends were evident. regressionresults would indicate annual trends in theSI, andtherefore, salinity. Regression analyses Freshwaterinputs werecomputed using the PROC REG procedure of theSAS statisticalprogram SAS 198g!. An indexof freshwaterinputs was formulated fromavailable precipitation data and discharge data Salinitycbsta anal yshs for the Mississippi and Atchafalaya Rivers. Precipitationdata were obtained from the Louisiana Salinitydata were obtained for AirplaneLake State ClimatologyOffice Monitoring Station in from the LouisianaDepartment of Wildlife and Houina LA¹4407!. The data were summed into Fisheries.Salinity averaged 20,5 ppt overall with a annualprecipitation from 1930-1994in preparation rangeof 2-34ppt over the ~ourse of therecord. The for further analysis. River dischargedata were dataare typical of salinitydata gathered around the obtainedfrom the United StatesArmy Corpsof state,in thatthe dani were collected on a weekly Engineers courtesy of Dr. W, Wiscman,Coastal basisfrom 1972 to 199g. The datawere collected StudiesInstitute, Louisiana State University, Baton sporadically,however, resulting in actual rnea- Rouge,Louisiana! for TarbertLanding, Mississippi surernentsbeing collected only 42% of the time, MississippiRiver! and Simrnesport, Louisiana Weattempted to circumventpotential analytical AtchafalayaRiver!. Theriver data were converted problemsdue to the highly variablenature of the to average annual dischargefrom 1900-] 994. The dataand sporadicsampling by incorporatinga threesets of annualdata precipitationand the two seasonal-correctiononthe data. Salinity Auctuates riverdischarge! were standardized about their means seasonallyin coastalLouisiana in responseto by dividingeach annual value by theoverall mean varyingriver Aow andprecipitation Swenson and value.This was done so that these three principal Swarzenski1995!. Therefore., byreinoving this sourcesof freshwaterwould be weighed according cyclicvariability, we could reduce some variability to their Auctuations over time. Since it would be andcomet for sporadicsampling. For exainple, if impossibleto quantitative!ydetermine the past salinitywere measured solely during the spring proportionof freshwaterinputs riverine versus food ol' theMississippi River at a site influcnced precipitation,and Atchafalaya versus Mississippi byriver Aow!, salinity values would be lower than River !at varioussites, the three annual standardized if salinitywere measured in the winter whenriver values onlythe two riverinedata for pre-1930 Aowis low.Thc availabic salinity data i,e.,noi years!were averaged to formulatea relativemeasure onlythe dataused in, this study!contain data in of how totalfreshwater inputs in theregion have whichthi» very scenarioexists; the availabledata changedover ime. Themajor assumption of this fora givenyear might only exist for a.few spring standardizedtechnique is that the proportionof months e,g Airplane Lake!. Therefore.we useda freshwaterwithin each source precipitation or seasonal-correctionin an attemptto rectifysuch riverine!entering Louisiana coastal waters has not problemsthat can arise due to sporadic sampling, changedover time. The relative measurevalues weveplotted, and a regressionline wasfitted to the Theseasonal-correction wasaccomplished by 10-yearmoving average to test for changingtrends calculatingmonthly means for the. salinity data set, in freshwaterinputs over this century. subtractingthese values froin the specific measurementstaken during the resp':tive month, RESULTS thenadding this differenceback io the overall mean toreturn the data to the same range as the rawdata. Core dating and site descriptions Whilethis approach may be flawed i.e., the spring floodof the Mississippi River does not always occur Table1 presentsa general site description, field iil April!,we believedthai. little elsecould be done measurementsmade during the core ce lectiontrip, tocorrect for sporadicsampling, The salinity data andcore dating results. Airplane Lake is a 19 hectare SalinityTrends in Coastal Louisiana.Giatoms 89 Tablel. Descriptionaud core dating results for Airplane Lake. The area was estimated from scaled aerialmaps. Salinity ranges were computed from available salinity data froin Airplane Lake. Water depthswere recorded from field observations; major plant communities were identified inthe iield, Compactiondata include the core lengths prior to and after extrusion, from which % compaction valueswere computed. See text and refer to Figs. 2 and3 forcorv. dating results and discussion. surface water area hectares! 19 salinity ppt! waterdepth rn! majorplant community Spartirruatterniflora confirmedstability via maps! since 1955 date cores were collected 8/26/93 pre-extrusioncore length cm! i 10.4 post-extrusioncore length cm! 105.7 % compaction 4.3 ' "Cs peak cm! 9.5 "'Cs sedimentationrate crn yr '! 0.33 -'"Phslope ln i "Pb!pCi g'! -0.0997 -' Pb slopestandard error 0,011564 -"'Pbsedimentation rate cm yr '! 0,31 overall sedimentationrate cm yr'! 0.32 time frame representedby the core 1664-1993 waterbody surrounded by saltmarsh dominated by 100,and 106crn! in which 7762diatom valves Sparrinaalterrr i flor. Thepost-extrusion sediment representing165 species from 55 generawere corelength was 105.7 cm and compaction was4.3%, identifiedand enumerated, Diatom data from below 30 cm in the APL corewerc not usedin further Thepeak in '"Cs activityrepresents theyear s! analysesbecause of poordiatom preservation. 1963/4 Milan et al. 1995!, and occurredat a core Therefore,results are only presentedfor the top 30 depthof 9.5crn Fig. 2!. The""Pb regression line cm of the APL core, which was cstirnatedto Fig.3! indicatesthat both dating methods gave representfrom 1902 to 1992.Of the 165 specie~, similar estimates of sedimentation rates ,31 vs. 7Kwere .5% abundantin anyone sample in the 0.33cm yr'!. Weaveraged the two rate estimates upper30 cm of thecore!, and 31 of thesecould hc togive an overall sedimentation ra.te estimate of 0.32 classifiedin the halobiensystem Table2!. Thc cm yr ' onthc compacted sediment core-, The core proportionofvalves counted that could be c/assified containeda recordof 330 yearsaccording to these in thehalobien system ranged from a lowvalue of datingresults, although this estimate tnay be in error 54% and4 cin!to a highof 85% 0 cm!,overall, asthe -'"Pbresults areonly applicableto 150years 71%of' all valvescounted could be classified. HP at best. Statistical analyses Diatom analysis Regressionanalysis of the salinity index A totalof 27 sampleswere counted -10, ! 3, demonstratedthat there was an overallsignificant 17, 20-22,24, 26, 28, 30, 40, 50, 60, 70, g0, 90, increasein salinityof 0.13ppt yr ' overthe length VO M. L. Peraonttet el. 0.9 08 0,7 0.6 F05 ,' 0.4 02 IO 20 30 40 50 60 70 80 Fig.2."'CsversuscoredepthatAirplaneLake. depth cm!40 activity 10 20 50 70 depth ctn! Fig,3. Regression oftn "'Pb!activity versus core depth atAirplane IMe. Salinity Trends in COaStalLOuiSIane Diatome 71 Table2: A listof all diatomspecies counted that were>1.5'0 relative abundance in at leastone samplethat could be classified following the halobien system of Kolbe 927! and Round <1981! o=oligohalobe,m=mesohalobe, p=polyhalobe!. The references used to obtain these classifications areindicated by the superscript above each classiTication, which refer to the following works: 1 Foged1980; 2-Foged 1987; 3-Marshall and Alden 1993; 4-Prasad etal, 1990;5-Caljon 1983; 6-Vosand deWolf1993; 7-Foged 1986; 8-Hustedt 1955; 9-Hendey 1964. Species authority halobien classification Achnunthesbrevr'pes var, intermedia Kiitzing! Cleve 0' " m' Achnanthesdelicarula Kiitzing! Grunow P .6i Acti noptychus senari us Ehrenberg Amphoracopulata Giffen 0 0 I.n Aulacoseira granulata Ehrenberg! S irnonsen rn' Biremis ambr'guu Cleve! Mann Caloneis westir' W. Srrrith!Hendey 0I Cocconei s disculoi des Hustedt 01 57 Cocconeisplucenrula var. euglypta Ehrenberg Crati cula cuspidata Kiitzing! Mann 0" Cyclotella caspia Grunow Cvclorella chocrawhatcheeana Prasad 0' Cyclotellameneghini ana Kiitzing Diploneisdidymo Ehrenberg!Ehr. P rn-' Dirylumbrighttvellii West! Grunow Fallacia forci para Grevillc! Mann P' 0 I'I Fragrlariabrevistriata Grunow ol I Fragi laria pr'nnata Ehrenberg Gyrosigma peisonis Grunow!Hustedt P* hfelosira monili formis O.F. Muller!Agardh m' Melosi ra numnruloides Dill wyn!Agardh Navi cula abunda Hustedt Navicula pusilla W. Smith lVavicula salinarum var. minima Grunow! Colby lVavi cula yarrensis Grunow P rn' Ni tzschia compressa Bailey! Boyer Ni tzschia lane cola Grunow Nit~chia panduriformis Gregory P cs iV'rt schia scalaris Ehrenberg!W, Smith tn' Petroneis marina Ralfsin Pritchard!Mann Tryblioneilagranulata var, granulara Grunow!Mann 72 M. L Paiaona at al. 30 25 20 15 10 0900 ] 1910 1 9201930 1940 1950 1960 1970 1980 1990 2000 Fig.4,The diatom-based salinityindex Si!determined salinity!'C3fprofile forthe Airplane Lakesediment core. Statistically-significantoveralland recent trends inthe S1 are illustrated. 25 7Q o I vi1015 1970 1975 1980 1985 1990 1995 2000 Fig.5.Salinity datafrom Airplane Lake:1972-1998. A k9%ticall!-significant regressionlinevvas fit to the data f~m l98l-l998. »li>i' Trends iit Coastal Louisiana Diatoms 73 1.2 e 09 0.6 0.3 1960 1980 2001 1900 1920 1940 year Fig.6. Annually-averaged,standardized freshwater inputs to the region from 1900-1994, Moving 10-year averages plottedevery five years! are also plotted, and were used to generate thesignificant regression line pc0.01!. of the core p&.0008;Fig. 4!. Thetrend has two and1973; salinity levelsappear to decreasebetween components.The increase inainly occurs between 1973 and 1992,possibly reflecting increased 1902 and 1973 R'=0.4726; p=0.0134!. A freshwaterinputs Fig. 6!. This conclusionis significant,recent trend o< decreasing salinity is supportedby workpresented by Wisemanet al. evidentin the corebetween 1973-1992 -0.52 ppt 990a! andBratkovich et al. 994!, v ho yr', p=0.0088!.A significant pc0,0001! decreasing acknowledgedanincrease in riverdischarge since trendis alsoevident in theactual salinity data Fig, at leastthe 1950s.Wiseman et al. 990a! also 5! between1981-1998 -0.2 ppt yr'!. Freshwater demonstratedthat a negativerelationship exists inputshave increasedthis centuryat an averagerate betweeriMississippi River discharge and salinity at of 0.3%yr' Fig.6! basedon the significant trend stationsnear APL Grand Terre; Fig. I l. Wiseinan seen in the moving average. etal. 990b! indicatedthat this Mississippi River dischargeinfluences both lower and upper estuarine DISCUSSION salinitiesat proximaland distal locations, Salinitychanges at Airplane~e Other salinitystudies The SI reconstructionof salinity at Airplane TheSI resultsare corroborated by otherstudies Lake Fig.4! displayssignificant changes in salinity of coastalLouisiana salinity trends Wiscrnan ct al. andcan be summarizedas three characteristics;there 1990a;Swenson and Swarzenski 1995k prov iding is an overallincrease in salinity between1902 and further evidence that thc Sl reconstruction v as 1992;thc increaseis most prevalentbetween 1902 accurateand can be used as a proxyfor pastsalinity. 74 M. L. Parsons et al. WisernanetaL ] 990a!analyzed availablc salinity AirplaneLake -0.2 pptyr ' between]981-1998; recordsutilizing a seasonalKendall-Tau analysis, pcs.000];Fig. 5! just asthe SI corereconstructions whichis a non-parametric test for a monotonictrend predict.The trend in thesalinity data, however, was notnecessarily linear! that can handle the high lessthan the SI trend -0.52 ppt yr '!, eitherreflecting degreeof variabilitytypical of theseestuarine thesporadic nature of thesalinity data, or model sa]initymeasurements. Swenson and Swarzenski error diatom misclassification orcore dating error!. 995!rc-assessed sa]inity trends utilizing additional datacollected after the Wiseman etal. ] 990a!study Thesalinity data used in this studywerc wascompleted, by conductingvarious linear discretedata, and the spi>radic nature of thedata analyseson yeargroupings i,e., 1965-1969vs. collectionmay have resulted in a poorrepresentation 1969-1972!both of whichaccount for anddiscount of thesalinity regime. This is best exernpliflied by nalvariadon. These studies reveal that salinity the observationthat data were collected lessthan datafrom a differentmonitoring station near 50%of the time, and were often collected solely in Airp]aneLake Grand Terre, S3 l 5!displayed similar thespring e.g March through May be!ween 1992 trendsover the sametitne periods as theSl did. and1998!. Additionally, data were collected with Wisemanct al. l990a! showedthat there was an relativelylow frequency weekly!, which does not overallsignificant monotonic decrease insalinity reflecthe variability of salinity in coastalLouisiana atstation S315 over the time span analyzed 962 waters.The hydrologyof .ouisiana's coastal to1985!. S wensonandS warzenski 995! studied marshesisvery dynamic. Cyclic salinity variability theexpanded data from S315 in smallerincrements isinfluence by diurna] tides on daily scales!, river andfound that there was a significantincrease in flow,and precipitation seasonal to annua]sca]es: salinityfrom ]955-1969, followed bya significantSwensonand Swarzenski1995!. Sa]inity decreasefrom l969 to 1994.The APL SI showed measurementsshould take these cyclic variations similartrends Fig. 4!, intoaccount, which is generally not the case, Whilethe salinity increased overall from 1902 Diatomaand saiinity to 1992 mainlybetween 1902 and 1973!,it significantlydecreased between ]973 and 1992. Van Theresponses ofdiatorns to salinity can vary Sick]cet a]. 976! reporteda northward extension widelybetween species and within a species,There afoyster leases between l 947 and 1975, possibly is evidencetha a diatomspecies can display ducto increasing sa]inities innorthcm Barataria Bay, differentsalinity optima in different water bodies, whichis in agreementwith the APL SI results.It althoughtolerance ranges generally overlap wouldhe interesting tosee, however, if oyster leases Cumrningand Smol l993; Wilson et al. ]996!. haveretreated southward since 1975, since our Somediatom species may have very large tolerance resultsand S wensonandS warzenski 995! indicate ranges i.e., euryhaline!and thereforewi]I not be thatsalinitics appear tohave been decreasing inand usefulto reconstructestuarine salinities Juggins aroundBarataria Bay includingAPL! since the l992!. Wilderman 987! believedthat this was 1970s. especiallytrue at salirutiesbetween 8-16 ppt, in whichno reliable indicators may exist. Many Comparisonbetween the SJ specieswill exhibit a salinityoptima. Because these andacttsal salinity data responsesare no linear, linear niodels as was used forthis study! tnight not be the best analytical Thesalinity data from Airplane Lake were approach Juggins 1992!. Additional]y, a particu]ar successfullyutilized in thefortnulation of theS! diatomspecies response tosalinity changes may regressionmodel Parsons etal. 1999! itnplyiug that differbased on thcduration, frequency, and theSI was in agreement with the salinity data used magnitudeof change Carpe]an 1978; Admi raal and inthis study. This statement isstrengthened bytrend Peleticr1980!. It is itnportant.therefore, to know analysesofthe sa]inity data in whichrecent <20 howsalinity changes frequency, etc.! and how a years!decreasing, salimty trends were evident at specieswill reactto thesesa]inity changes. SalinityTrends in t oastaiLouisiana Oiatoms 75 Core dating Justification of the saliriitv index Sonicof the variabilityin theSI modelcould Wc believe that thc dittcrcnces that exist in beduc to coredating errors c.g.,counting '"Cs! themagnitude of thedccrcasc in thc salinity and gl andregression -'"Pb! errors! which could cause an trends for Arrplane Lake are priniarily duc to the inaccuratedate to beapplied to a core depth, thereby sporadicnature of thc salinity data and ihc alteringtrend analysis results. The ' "Cscounts were simplified,linear nature ol' thcmodel rather than designedto limitcounting error to 10'%near thc inherentmodel or coredating errors, Our results 1963/4peak Milan et al. 1995!, and the '-"Cs profile detnonstratc that thc SI can bc utilized successfully for thcAirplane Lake core was defined enough that asa proxyfor salinitychanges. This conclusion is thispeak is Hear Fig. 2!. The"'Pb profile Fig.3! supportedby thesimilarities presented between the wasclear after theanalysis of only four satnples, SI trendsand salinity datafr«m Airplane Lake i this andresulted in a highR' ,9738!. ThcAPL sedi- study!and GrandTcrrc Wiscmanet al. 1990a: mentationrate estimatesdetermined by '-"Csand Swenson and Swarzenski 1995!. This study ""Pbwere nearly identical .33 vs.0.31 crn yr ', demonstratesthat salinity signals arc evident in a Table2!, sowe areconfident that the core dates are coastalmarsh sediment record, regardless of thc high accuratefor the APL core. variabilitytypical of thisenvironment. Furthermore, a recent decreasing trend in salinity is evident. DeLaune et al. 978!, however,analyzed possiblyreflecting increased freshwater inputs into sedimentcores froin AirplaneLake for '"Csand the coastal waters of Louisiana. The decreasing estimatedsedimentation rates at 1,1 cm yr'. The trendexhibitedby thc Si indicatesthat salinity levels differencesbetween our estimatesand DeLauncet maybe dropping onthe order of 5 pptper decade at al. 978! are not surprising,as there were AirplaneLake. These results cast some doubt on differencesin sampleanalysis. DeLaune et al. how freshwater diversions which will lower 978!analyzed 3-cm sections, we analyzed I-crn salinitiesfurther! might affect marsh ecosystems if sectionsoffering better resolution, DeLaune et al. salinitiesare already decreasing at soinelocations. 978! useda lithium-driftedgermanium detector Forexample, the optimum salinity range for oyster to county particles,an instrumentthat is less growthand survival for Louisianahas been accuratethan the germaniuin"N" typecoaxial estimatedto be5-15 ppt Galtsoff1964; St. Arnant detectorwc usedsotne 15 yearslater. DeLauneet 1964!,If salinitiesare already decreasing in some al. 978! andMilan et al. 995!both reported a areas,and/or will be decreasingfurther with highdegree of core-to-corevariability both within freshwaterdiversions, oyster communities could be andaround Airplane Lake. DeLaune et al. 978! adverse I y impacted. H ypot bet i cal I y, other reportedthat onecore taken in AirplaneLake organismsdependent onbrackish water conditions displayeda prominent '"Cs peak while a second couldalso be impactedby decreasingsalinities coretaken 350 rn awaydid not. Milan etal. 995! includingbrown shriinp Barrenand Gillespie reportedthat - Cssedimentation rale estiinates 1973!,sponed seatrout Bourgeois etal, 1995!, and ditferedover 50% atdifferent locales, and over 30% saltmarsh plants e.g Spurriita ulterrriflara!. We withinreplicate cores at the same location. Lastly, argue,therefore, that available salinity data are our sedimentation rate is estimated for the inadequateto properly assess how salinityhas compactedsediment core, whereas the DeLaune et changedin coastal Louisiana over periods >30 al. 978! valueis foruncornpacted cores. We gave years!due to humanactivities. and that sahnity our valuesfor compactedcores because we were reconstructionsof datedsediment cores, utilizing notconfident in our estimates of compaction during ihemodel presented here or a future,more refined corecollection, and we were primarily interested in model,can provide a usefultool to makeaccurate datingthe core versusestimating actual sedi- assessments. mentationrates. Therefore,the differencesin sedimentationrates between our studyand others areexplainable and expected. 70 M. L Painona et al ACKIiilOWLEDC le ENTS riebulosus.Fishery Management Plan Series 3. LouisianaDepartment of Wildlife and Thisresearch was funded by LouisianaSea Grant Fisheries,Baton Rouge, Louisiana, 104 pp. CollegeProgram Grant RIM PE-59 awardedto R.E. C~or ',A,G. 1983,Brackish-water phytopmankton Turner.N,N. Rabalais,and Q. Dortch,a Stateof of theFlemish lowland, pp. 1-272.In H. J. LouisianaBoard of RegentsGraduate Fellowship Dumont ed.!, Developments inHydrobiology Program to M. L. P.l,and a LouisianaUni versities 18, Dr,W. Junk Publishers, The Hagttc. MarineConsortium Post-doctoral Fellowship toM. CAIIPELAR,I.. H, 1978.Evolutionary euryhalinity L. P. of diatOmsin Changing environmentS, IIIova Hedwigia 29:489-526. LlTKRATURE CITED CHAIIRECV R.H.attn G. LINscoMar. 1982. Changes in vegetationtypes in Louisianacoastal Arruiaaat,W. Ano H. Ptrct:rII;R,1980, Distribution rnarshesover a ten-yearperiod. Proceedings ofdiatom species on an estuarine mud flat and of rheLouisiana Academy ofSciences 45:98- experimentalanalysis of the selectiveeffect 102. of stress.Journal of Fxprranental Itrfarine CuarMIiIO,B.F, ANn J.P. SMoL. 1993. Development Birrl'ogyand F'roloogy 46:157-175. of diatom-basedsalinity models for paleo- BhRRI!IT,B.B. AND GILtj.SPIi., 1973. Primary factnrS climatic research from lakes in British whichinfluence commercial shrimp pro- Columbia Canada!. H ydrobiologia269/270: duction in coastaI Lou i siana. Loui si ana 179-196, Departmentof Wildlife and Fisheries CuTSHALL,N. H., I. L. LARSON,ANo C. R. OLSZ>'. TechnicalBulletin 9, Baton Rouge, Louisiana. 1983.Direct analysis of" Pb in sediment 28 pp. samples:self-absorption, Iti'uclear Instruments Batt:s,C. D., P. COKON. A%I>P. L, Graaatu!. 1978. A andMethods 206;309-312. newmethod for thc preparation of'clay-rich DtLauhIR,R. D., W. H. PATRrcic,JR., AIvD R. J, scditncntsamples for palynological Bt~aasH.1978. Sedimentationrates deter- investigation.IVewPh vrrilrigist 81:459-463. minedby '"Cs datingin a rapidlyaccreting BhtTaaar+,R.W. 1986.Diatom analysis, p.527- salt Inarsh.IIIature 275:532-533. 570.In B, E. Bcrglund cd.!. Handbook of F~waa.R, J. 1986.The relationship between HoloccncPalaeoccology andPalaeohy- surfacesediment diatom assemblages andpH drology.John Wiley &. Stins Ltd,. Chichester, II,K.. in33 Galloway lakes: some regression models Barraaau:..R.W. Atvu M. J. K~t.t-.s- 1982. Thc use forreconstructing pHand their application to ofelectronically counted microspheres in sedimentcores. Hydrobi'oiogia 143:93-103. absolutediatom analysts. I inrnology and Fooau,N. 1980. Diatomsin Oland,Sweden, Oceanography27:184- 188. Bibh'othecaPhycologia 49:1-193, 18plates. FooEo,N, I 986.Diatoms in Gambia. BibII'otheca Batttuastv,R.H. avn R, 1 Tt'Rat;R.. 1990, Direct Diatonrologica 12 a!:1-152, 25 plates. impactsofoutercontincntalshelfactivitieson Fooao.N. 1987.Diatoms from Vitu Levu, Fiji wetlandloss in thecentral Gulf of Mexico. Islands.Bihfiotheca Diatomologica 14:1-195, Fnyr'rr>nnrentalGeologyand Water ResaureeS 33 plates. 15:189-198. BRATxovtctr.A..S.P. Dts,S;Ig hitr D.A. GoOLSav. FULLY,D, A., J. G. GossaLn'x,J,BARRas, ~D C. 1994.Variability andprediction offreshwater E.Sasstx, 1995. Status and trends in vege- andnitrate fluxes for thc Louisiana-Texas tationand habitat tnodifications, pp.25-76. In shelf:Mississippi and Atchafalaya River D, J.Reed ed.!, Status and Historical Trends sourcefunctions, Fstuarr'es! 7:766-778, of HydrologicModification, Reduction in SedimentAvailability, and Habitat Loss/ BOI'RotOIS,M. J., Gt:ILtuav, V..ASO H. BLAslCHEr. Modifrcationinthe Barataria and Terrebonne 1996.A biologicaland ftshertes profile for EstuarineSystem, BTNEP Publication Louisianaspotted seatrout, Cynr>scion Number20, Barataria-TerrebonneNational EstuaryProgram, Thibodaux, Louisiana. SalinityTrende ln Cpastal Louiaiana:DietomS 77 GAI rsot-i-, P, S, 1964. The American oyster, PFKNINOTON,W,, R, S. AvlaRAV, ANt3E. H. FVSIIVR. Crassostrea virginia Gntclin!. Fisheries 1973 Observations on lake sediments using Bulletin 64, U.S, Departmentof the interior, fallout '-»C.s as a tracer. Suture 242;324-32tI. Fish and Wildlife Services, 480 pp. PRAsA», A. K, S, K., J. A. Nil Now, AN» R. J. HENDI.Y,N. l. 1964, An intrnduCtOryaCCOunt of LlviN< sToN. 1990. The genus Cvclotella thcsinaller algae of Britishcoastal waters; Part Baciflariophyta>in ChoctawhatcheeBay. V: Bacill ariophyceae Diatoms!, Ministry of Florida,with specialreference to C. striataand Agriculture,Fisheries, and Food, Fishery C. choctawhatcheeanasp, nov. Phycologia investigationsSeries lV. OttoKoeltz Science 29;418-436. Publishers,Koenigstein, West Germany, 317 RovNIi, 1, E. 1981. The Ecology of thc Algae. pp., 45 plates. Cambridge Uni versity Pres s, Cambridge, HvsTE»r, F. 1955. Marine littoral diatoms of England,653 pp. Beaufort,North Carolina. Duke University Sr. AMANr, L. 1964. Louisiana leads in oyster Press,Durham, North Carolina,67 pp. production.Louisiana Wild!ife and Fisheries JvoolNs,S. 1992. Diatotnsin thcThames Estuary, Commission,Wildlife Education Bulletin 84, England:Ecology, Paleoecology, and Salinity 11 pp. TransferFunction. BibliothecaDiatoniolngi ca SASe, 1988, SAS'~/STAR" User's Guide, Release 25:1-216. 6.03 Edition. SAS institute Inc,, Cary, North Kuv8E,R. W, 1927. Zur Okologie,Morphologic Carolina, 1028 pp. undSystematik der Brackwasser-Diatomeen. SWENSON,F.. M. AN»C. M. SWARZrtitSvt.1995. WatCr Pflanzenforschung7: 1-146, levelsand salinity in the Barataria-Terrcbonne MARsHALL,H. G, AN» R. w. AL»EN. 1993. A estuarinesystem, pp. 129-201.ln D, J. Reed comparisonofphytoplankton assemblages in ed.!, Status arid Historical Trends of the Chesapeakeand Delawareestuaries HydrologicModification, Reductionin USA!, withetnphasis on diatoms Hydro- SedimentAvailability, and Habitat Loss/ biologia2691270:251-26L Modification in the Barataria and Terrebonnc MCKEE,K, L. ANoI, A, MENnl.t.ssotts.1989. EstuarineSystem. BTNEP Publication Responseof a freshwaterplant community to Number 20, Barataria-Terrebonne National increasedsalinity and increasedwater level. EstuaryProgram, Thibodaux, Louisiana. AquaticBotany 34:301-316. YANS tcKvE,v. R., B, B. BARRErr,L, J. Gvi.lcK,AND Mite, C, S., E. M, SwENsoN,R. F.. TvRNER,AN» T. B. Foan. 1976. Barataria Basin: salinity J. M. LEE. 1995. Assessmentof the '"Cs changesand oyster distribution, Centerfor tnethodfor estimatingseditnent accumulation WetlandResources, Louisiana State Univer- rates: Louisiana salt marshes. Journal of sity,Baton Rouge, Sea GrantPublication Coastal Research 11:296-307, LSU-T-76-002, 22 pp, PARSoNs,M. L, 1996 PaleOindicatorsof changing VOs,P. C, ANOH. »EWOI F 1993. ReCO~struCtiOn water conditionsin Louisianaestuaries. Ph.D. of sedimentary environmentsin Holocene Dissertation,Department of Oceanography coastaldeposits of thesouthwest Netherlands; and Coastal Sciences, LouisianaState Univer- the Poortvlietboring. a casestudy of paleo- sity,Baton Rouge, 316 pp. environrnentaldiatom research. Hydro- PARsOrS, M. L. 1998. Salt marshSeditncntary biologia 270:297-306, record of the landfal I of Hurricane Andrew on WIL»ERMAN,C.C, 1987. PatternSofdistributionof the Louisianacoast: Diatorns and other paleo- diatom assemblagesalong environmental indicators. Journal of Coastal Research gradientsin thc SevernRiver Estuary, 14:939-950, ChesapeakeBay. Maryland. Journal of Phy- PARSONs,M.L., Q. DoRTcH,R. E,TV~R ANrN. N. cology 23:209-217, RAeALAtS,1999. Salinity historyof coastal wILsoN,S. E B. F, CvMMINc. ANn J, P. SvtoL. 1996. tnarshesreconstructed from diatom retnains. Assessingthe reliabilityof salinityinference Estuaries22: in press!. models from diatom asseinblages: An 78 M, L. Parsons et at examination of a 219-lake data set from western North America, Canadian Jour' of Fis!reriesand Aquatic Sciences53;1580- 1594. WtsEMm, W.J., JR., E. M. SwEnsov, ~ J. PowHt, 1990a.Salinity trendsin Louisianaestuaries. Esrrusri es 1 3:265-2'7 l, WtsEM~, W. J,, Ja., E.M. SwErrsov,~ F.J. Kit.r. 1990b. Control of estuarinesalinities by coastalocean salinity, pp. 84-193. ]n R, T. Cbeng ed.!, Coastal and Estuarine Studies vol. 38, ResidualCurrents and Long-term Trans- port, Springer-Verlag,inc., New York, Annual Salinity and Nutrient Budget of Lake Pontchartrain and Impact of the Proposed Bonnet Carre Diversion MICHAEL G. WALDON WPI, 20%! Rraft Drti e, Sttite /QXii, BlctcLsbttrg. VA 240rN, TEL: $40-5S7-6080; FAX .S40-.$57-608S: email: tvaldr>ttCctirnemhc rs,a.sc c~ .ttrtt C. FREDERtCI' BRYAN LouisianaC ctctperattreFish & WildlifeResearch Unit, /24 F ABSTRACT:A nutrientmass balance identifies the total massload of the nutriententering a waterbody,loss across the downstream boundary, and the rate at which the material is synthesized or Instwithin the waterbody.biutrient budgets for totalphosphnrus TP! and total nitrogen Tfctl weredeveloped, along with budgets for lake salinity and volumetric water llows. The analyses reported herewere initiated tosupport the evaluadon ofa proposaltodivert a smallfraction ofMississippi Riverdischarge through Lake Pontchartraln. These analyses determ/ne the sensitivity of Lake Pontchartrainto nutrient loading, and provkie a bash' for development ofmore complex hydrologic andwater quality models. Discharge and nutrient loading data have been analyzed using simplified formoins which predict annual average nutrient concentrations withinthe Lake. For other aquatic ecosystems,thissimpliiied analytical approach has often proven tobe a valuable management tool insupport ofenvironmental decision making. Total freshwater inflow, Q, is estimated tohe 13.2 km' yr', or'an annual average Inflow of 419 ms s ' 4~ cfs!.The proposed diversion would increase freshwaterinflow by 6.6 kms yr '. Averageresidence time is projectedtodrop from 102 d to76 d followingimplementation ofthe diversion. lnLake Pontchartraln, projected annual a verageTPand T'atconcentrations without the proposed river diversion project are 0 060mg-p I' and 065 mg-ht I '. Withthe proposed diversion these concentrations areprojected torise to 0.071 mg-P I' and 086 mg- N I t. determinationsfor controlof eutrophicationin lakes Itttrxtduction andimpoundments Mancini et al. 1983 i. ThisEVA There is a need for siinple quantitative guidancereviewed and was based on thc extensive assessmenttools for evaluatingthe impact of earlier work of Vollenweider l976! and others. nutrientadditions on lakesand estuaries. In theU.S., Here,as far aspossible, wc havefollowed thiv theClean Water Act requiresthe determination of guidance.This study provides a case study for thc thetotal maximum daily load TMDL!of nutrients applicationof these techniques to an estuary, and andother potential pollutants, and the ailocation of illustrateswhich factors must be included to extend theseloads among point and nonpoint sources within theprocedures of Mancini to coastalwaters. a watershed,To this end, EPA has developed A proposedMississippi River diversion a he wasteloadallocation guidance for TMDL siteof theexisting Bonnet Carrc Floodway led ici publicconcerns about the potential eutrophication Fromthe Sytnpostum Recent Rcseorrtc in Coccstat Lcp«ststnct' WatttrcstSystem t.tcnctietn ctndResponse tnHtcmctn tnft4«<'e of Lake Pontchartrain.This river dtversion was ROZaS.L,p,, S A. Nyman, C.E. prntfitt. N,V, Rabala», D.>. designedto reduce salinities in oyster beds near the Reect,anct R.E. Turner tedttorsI. I999 Published byLott»'an MississippiState border, beyond the downstrcain SeaGrant College Prograin. aO M.B, Waldon fL C.F, Bryan boundary of this study.Although alternative the MississippiSound through Chef' Menteur Pass diversiondischarge schedules have been considered «ndPass Rigolets. Circulation is drivenprimarily duringproject re-evaluation, only the monthly by wind, rather than by river discharge or tidal diversionsproposed in the generaldesign exchange Stone et al. f972; Gael 1980!.The long memorandum GDM! areanalyzed in thispaper retentiorttime of Lake Pontchartraincompared to UnitedStates Army Corps of Engineers1990!. other Gulf Coast estuaries Soils and PoweII 1999! MonthlyGDM diversiondischarges from January andlimited tidal exchange Swenson f980! reduce throughDecember are 0, 0, 306, 850,473, 413, 91, the spatialvariation of salinityand nutrients within 74,57, 156,QI,andOrn's', TheGDMdischarges Lake Pontchartrain. These characteristics make arehigher than those proposed inother plans which Lake Pontchartrainwell suitedfor the analytical havebeen considered since the publication of the methodologiesdeveloped for lakenutrient budget GDM. Thus,the GDM providesa maximum analysis.The Lake Pontchartrain watershed 4,490 diversion scenario, and diversions of smaller size km'!drains a largearea of southeasternLouisiana shouldhave proportionately smaller impacts. anda smallerarea of Mississippi.The poteruial sourcesof freshwaterinput, including drainage Ideally,a nutrientbudge analysis considers baSlns,open water areas, pumped stOrrnwater frOrn total nutrientconcentration, incorporating all theNew Orleans area, and the proposed diversion biologicallyavailable forms of the nutrients, werenumbered Figure I !. Sub-basindrainage areas includingnutrient which has been sequestered or werereported by Sloss 97 I ! and Earl 992!. incorporatedinto planktonicbiomass. Total phosphorus TP! analysis Atnerican Public Health Freshwater Inflows Association1992! providessuch an estimate,but may in some instancesalso includeP which is TheU.S.G.S. maintains continuous discharge unavailable.Total nitrogen TN! isnot directly records on the major streams in the Lake measured. and must be calculated as the suxn of PontchartrainBasin Arcernent etal. I 993!.Monthly measuredcomponents. Total Kjeldahlnitrogen meangaged discharges for theperiod-of-record were TKN! measuresthe concentration of organic usedas the basis for monthlydischarge estimates. nitrogenand ammonia nitrogen Metcaif and Eddy Theperiod-of-record for thesedischarge statistics inc. I 99I; AmericanPublic HealthAssociation endedwith water year I 992.Stream gaging station s 1992!, Therefore, TN is estimated as the sum of usedin thisstudy are locatedon the Arnite River TKN, and nitrate plus nitrite N, In rivers and nearDenham Springs, the Tickfaw River at Holden, estuarieswith shortdisplacernent time, both TP and theTangipahoa River at Robert,and the Pearl River TN may often be adequatelymodeled as nearBogalusa. Drainage areas associated with these conservative materials. In lakes and estuarieswith gagingsites are respectively 3,315 km', 640 km', longdisplacement time, it is unlikelythat such a l,673km' and 17,024 km'. Conventional discharge conservativemodel would be adequate because both gage sites must be located where a stable and TPand TN loss within the waterbody aresignificant sensitivestage-discharge relationship exists, often relativeto hydraulicdisplacernent, well upstreamof themouth. Additionally, small drainagesub-basins have no appropriate gaging site. Thus,gaged discharge from the Lake Pontchartrain Basin excluding the Pearl River Basin! represents Site Description only39% of thetotal Basin «rea Runoff,stream dischargeper unit of watersheddrainage area, is Lake Pontchartrainis located in southeastern commonlyused to extrapolate discharge toungaged Louisiana.Lake Maurepas, a smaller coastal lake, areas,Average monthly runoff calculated for each lies upstreamof Lake Pontchanrain.These lakes gagingstation provides a basis for estimating arehydrologically connected by a shortwaterway average monthly discharge frotn each Lake namedPass Manchac. At its downstreamboundary, Pontchartrainsub-basin by multiplying the most LakePontchartrain connects to LakeBorgne and appropriategaged runoff by the sub-basin drainage area. LakePontchartrain Selinity and Nutnent Budget St R>acrLock Figurel. Map ufLake Pontchartrain systemwith loading sources indicated bynumbers. Freshwaterinf!ow to LakePontchartrain must coefficientis theratio of runoff torainfal!, and can includenot only all tributaries,but also some provideanestimate ofrunoà in ungaged watersheds fractionof thePearl River flow Sikora and Kjerf ve Mancinietal. 1983!, Runoff coefficients typically 1985!,The mouth of the Pearl River is locatedjust varybetween 0.1 and 0,6, with increasing values outsideof LakePontchartrain atPass Rigolets, and beingassociated withincreased impervious ground thereforecontributes a part of itsflow to the Lake coverin the drainage basin Bowie et al. 1985!.Total duringeach tidal cycle. Assuming a symmetrical annualrunoff values indicate that considerably less tidecycle, this fraction must be less than half, and thanhalf of the averageannua! rainfall of 156cm for thepurposes of this analysis one third of the LouisianaOffice of StateClimatology! is dis- PearlRiver flow wasassumed to contributeto the chargedas runoff from the watershed. East Bank freshwaterinflow andnutrient loadingof Lake JeffersonParish storrnwatcrpumping stations recordsfor 1988indicate an annualrunoff Pontchartrain. coefficient of 0.5 Ear! 1992,Vo!umc 2, page5-22!. Dischargefrom leakage through the existing Totalaverage monthly discharge from the Yev BonnetCarre spillway structure was estimated to Orleansarea pump stations were therefore estimated be 15% of the flow and loadof the proposed as50% of the averagemonthly rainfall fa!!ing over diversion.Nutrient loadingfrom the proposed thepumped drainage areas F~! 1992,Volume 2, structurehas been adjusted to includethe anticipated pageA7!. Estimated drainage areas Jefferson Parish loadreduction that wil! resultfrom operation of the 131km'-, Orleans Parish 134 krni! andwater quality sedimentationbasin Benndorf and Klaus 1987; Putz of pumpedrunoff were also obtained from Earl andBenndorf 1998!. Based on an estimate that 30% 992, Tables5-6 and 5-7!. of the sedimentswi!! be reinoved within the sedimentationbasin, it isassumed here that this will Nutrient Cotacentrationand Loading resultin a 20%reduction in TP, anda 10%reduction inTN loading from the proposed Mississippi River The Office of Water Resources of the LouisianaDepartment of Environinental Quality diversion, LDEQ! maintainsa statewidewater quality An alternative method was used to estimate monitoringnetwork, This fixed station, !ong-term pumpedurban stormwater inflow. The runoff surfacewater quality monitoring network currentlv 02 M,B.Waldorr 4 C,F.8ryan providesdata from 186 rrronitoringsites. Sampling the averageof theproduct of two variablesdoes not and!aboratory procedures follow extensive quality equal theproduct of their averages.Consequently, assuranceplans available from LDEQ,Field mea- theptoduct of averageannual discharge and average suremcntsand samples are collectedat onemeter annual concentrationmay provide inaccurate or, in shallowstreams, at halfdepth. Laboratory estimatesof averageannual load, In order toreduce nutrient analysisis performed on whole water thisundesired effect, monthly average loads were satnplesand generally follows StandardMethods herecalculated and summedto developannual AmericanPublic Health AssociationI 992!. Data averageload estimates. frtrm 28 of thesesites werc usedin this assessment. Mostsites have more than IP yearsof data,and SimplifiedModel Analysis manyhave been monitored for morc than 20 years. Mostsites are monitoredon a monthlybasis, FollowingMancini ct al. 983! werepresent however some newer sites are monitored on a Lake Pontchartrainas a single well-mixed bimonthlybasis. The period-of-record utilized herc compartment,Assuming a first order loss term endsin Augustl 993. correspondingto net sedimentation: An environmentalorganization voiced a concernduring conunents on thc early plans for thc d ciVi!= W~ Qi+ K.Vi!ci rccvaluationof the Bonnet C~ diversionproject. dt It wassuggested that pollutant levels may have inc~ overpast decades, and load calculations wheret = timeand subscript t denotes time in this,study should be representativeof present dependentvariables; conditions.Bahr 983! also concludesthat P c = conrentrationwithin thc waterbody; loadinghas increased aver past decades. Therefore, V = volume; in this study.monthly mean concentrations, used W = sum of all massloads including all here in load calculations, werc calculatedfrom internalwaterbody sources; observationsmore recent than January, 1985, This Q = total of all volumetric flows into the shouldboth provide an adequate number of monthly watcrbody; observations,andalso educe thc influence of any and K = net sedimentationrate. long-termtrends in concentration which may exist bccauscof land usechanges or otherhistorical The long-termaverage value of the left handside factors. of Eq. I shouldapproach zero, This yieldsa result analogousto the steady-state solution of Eq. I: The termioad or loadingrate is therate at whichmass of substanceis entering a waterbody W W/V C throughpoint sources, rtonpoint sources, ortributary Q + K.V p+K, inflow.Regardless oftemporal, spatial, or dynatruc complexity, all modeI s of nutrients and eutrophicationrequire the developmentof nutrient wherep =Q/V. thc hydraulic displacernent rate; loadestimates. Thc load rrLass/time!ofa substance and all variablesin Eq 2 areaveraged over a period whichis longrelative to I/ p +K !. enteringa systemthrough water inflow is calculated fromconccntrauon ofthc substance mass/volume! multipliedby thestream discharge volume/time!. Thehydraulic displacement time, t = I/p, Loading Concentrationand volumetric inflowor stream rate comparisonsamong waterbodies is facilitated dischargefor each source of waterentering the by normalizingEq. 2 for watersurface area; waterbodyare necessarycomponents of a load estimate.1tmust also bc noted that average values w'/z c for concentrationand dischargemust be used with p+K, ! somecare in calculating loads because, in general, Lake PontchartrainSa!inity and NutrientBudget 83 where w' = load divided by surfacearea; constraint was 10.8 ppt, and average nutrient and z = mean waterbody depth. concentrationswere: TP&.082 mg-P! '. nitrateplus nitrite=0.037mg-N 1 '.and TKN=0.669 mg-N 1'. The occurrence of salinity within Lake Since!985, averagesalinity was3.6ppt at the Lake pontchartrain dcrnonstratcs that in addition to the Pontchartrain monitoring stations. freshwater inf!ows, there is a net sa!twater inflow, Q, enteringfrotn thc downstream seaward! Averageannual seawaterinf!ow, Q , is boundaries.The method applied here to estimate cstimatcdusing Eq. 4 tobe 6.44 km' yr ', or 33%of Q is a variation of the "fraction of freshwater tota! inflow. Annual averagetotal dischargeis method" reviewed in Bowie. et al. 985, page43- estimatedto be 19.65knt-' yr ' Table 2!. Tributaries 44! sndby So1 isand Po we!! 999!, andutilized by flowingfrom the watershed provide 36%, and thc Swenson 980! in estimatingLake Pontchartrain PearlRiver is estimatedto provide 20% of total retention time. Averagesalinity, S, representss inflow. The remaining !!% of flow» divided specia!case of Eqs.1-3, with K W, andthe salinity betweenurbanpumped stormwater discharge. direct load W= Q S, whereS is ihc boundarywater netprecipitation, and leakage from the Mississippi salinity.This assumesthat the salinityof the River.With these results, the averagesalinity in Lake freshwaterinflow is negligible,Average total inflow, Pontchartrainafter diversion can bc estimated by Q, equalsthe sum of theaverage total freshwater includingthe diversion discharge in a recalculation inflow,Q, andQ,. FromEq. 2, average salinity is; of Eq.4. Underthe GDM diversionscenario average LakePontchartrain salinity is projectedto decrease from 3.55 to 2.66 ppt. QeSa ! Qa+ Qr Annual Loading and Areal Loading Results Averageannual TP andTN !oadstotal 3,300 and35,700 metrictons yr, respective!y Tab!e 2!. For Lake Pontchartrain,area A! is 1637km' Loadingfrom the diversion is estimatedto add 1.050 Sloss1971!, incan depth z! is3,4 rn Stoneet al. and 17,030 metric tons yr' of TP and TN. The 1972!,resulting in volume V! of 5.56 km-'. TN:TP tnassratio of total nutrient source loadings Includinginflows as described earlier, Q=19.653 is thus estimated to be 10.8 without the diversion, km' yr' undercurrent conditions, and Q=26.252 and 12.1 following the proposeddiversion. A km-'yr ' afterthe proposed diversion. Thus. t= 0,28 characteristic inflow concentration may be yr 02 d! withoutthe proposeddiversion, and t= calcu!atedby dividing total!oad by totaldischarge. 0.21yr 6 d! afterthe pmposed diversion. ForTP andTN thisis 0. 168and 1.82mg 1' without diversion,and 0 6 and 2.01 with diversion,Areal Boundarysalinity and nutrient concentrations !oadingis loadingdivided by wate*ody surface can be estimatedfrom the highestsalinity values area.Area! loading of TP risesfrom 2,02to 2 66 g observedat the Lake Pontchartrain outlet monitoring m ' yr ' afterdiversion, and TN risesfrom 21,82ro sites,Chef Menteur Pass and Pass Rigolets, Over a 32.22g rn ' yr '. period-of-recordbeginning in 1978,maximum salinityobserved at thesesites was 12.9 ppt, and Annua! average LDEQ TP and TN obser- the95th percentile salinity was 9.8 ppt. It isassumed vations Table 1! in Lake Pontchartrainwere 0.060 that the characteristicsof the boundarywaters and0.65 mg 1', respectively.ATP netsedimentation enteringthe lake are similar to thosewhich are rate, K, of 6.4 yr ' was deterrnincd by mode! presentat theoutlet sites under these conditions of calibrationusing Eq. 2 andsubstituting va!ues of elevatedsalinity. An estimateof theboundary vo!urne, discharge, TP load, and average Lake salinityand concentrations was perfortned by Pontchartrain TP concentration, Equation - then averagingobservations where salinity met or projectsTP concentrationfollowing diversion exceeded9.8 ppt.Average salinity under this implementationto be 0.07! mg 1'. Simplified 04 HI,B.Waldon 8 C.F.Bryan Tablel. Averageparameters at DEQInonitoring sites 989-1993! by class L. PON,=Lake Poatchartraia,M. RIV.=MississippiRiver, OVTLET=Lake passes, TRIB.=tributaries!. Table2. Annualdischarge and nutrient loading values. Lake Pontchartra>n Salinity and Nutrient Budget BS modelingapproaches for TN havenot beenas appliedscaling factors rangingfrom !.06 to 2.4 to extensivelystudied and tested as those for TP. their tributary inflows. So!is and Powell 999l !vianciniet a!. 983! suggestthat an approach presentdisplacement titnes of Gulf CoastEstuaries siinilar to that usedhere for TP should also be in graphical format., with Lake Pontcharirain adequatefor other nutricnts. Ca!ibration of Eq. 2 residencetime near 140 d, Argyrou et a!. 997! for TN resultsin an estimateof K ='2.5 yr ',and a estimatehydraulic residencetime to be 537 d. This projectedaverage TN !akeconcentration of 0,972 anomalous!yhigh estimateresults primari!y fnm> mg1' afterdiversion. However, this calibration an underestimateof freshwaterinflow and also from ncg!ectsanestimate ofload froin N fixation as well failure to consider saltwater inflow or volume. asprecipitation load of TN to thelakes surfaces!. Calibration for TN is thereforedeemed to be Bianchiand Argyrou 997! estimatewater- inappropriatehere. Mancini et al. 983! notes that shednutrient loading of phosphate,aminonium, and bothTN andTP are removedfrom thc systemby nitrate plusnitrite, Bccausc those nutrients are permanentburial fo!lowing settling of particulate componentsof the TP andTN loads,wc anticipate organicmaterials, and conjecture that because this thattheir associated!oads shouldbe less than the inechanismof loss is the samefor TN andTP, it is totalnutrient loads estimated here. Although the total reasonableto assutuethat the K va!uefor TN i» tributaryinflow estimateof 142 m's' usedby equalto that for TP. Assuming K = 6.4yr ' forTN Bianchiand Argyrou is somewhatlower thanthe aswell as TP, a N fixationterm may be added to the valueused here, their publishedload estimatesare TN !oadsuch that Eq 2 is calibrat&,This gives a anoma!ous!yhigh and appear to bc in error.Loads N fixationload estimate of 14,100metric tons yr '. can be calculatedfrom nutrient concentrations Thisestiinated load is greater than any other sing te presentedbyBianchi and Argyrou, and these !oads loadsource listed in Table2, and65% of' the total areconsistent with loadscalculated here, loadfrom all otherexisting sources combined. Arealnutrient loading rate loadingper unit DisctIsaioa of !akesurface! in LakePontchartrain isestimated tobe 2.02 and 21.82 g m' yr ' forTP and TN. These lsphordinget al, !989!, andFlowers and valuesgenerally fall withinthe range of values lsphording 990! reportfreshwater discharge to whichhave been reported for lakes, Reckhow 1979; LakePontchartrain to be 6.8 km'yr ' 600 ft-'s '! Maneini et al. 1983!.Bahr 983! projecteda Pload andvolume of LakePontchartrain to be 5.77km' of 2 gm' yr' nearthe year 2000. .038 10"ft-'!. This compares favorably with the estimatespresented here .18 km-'yr' and5,49 Rydingand Rast !989! state that it israre that km'!.Argyrou et al 997! estimatea similar total availablenutrient sampling data will produce volume,6.58 km-',but estimate annualaverage nutrientload estitnates within M5%. In thecase of dischargeof riversinto theLake Pontchartrain LakePontchartrain, uncertainty invo! ving the Pear! Estuaryto be only4.48 km'yr ' 2 m's'!. River, N fixation, and the sa!twaterload Swenson 980! concludedthat gageddischarge contributionsadd uncertainty to thc load estimates. mustbe scaled by an average factor of 2.4 to provide However,for the purposesof this trophic anappropriate freshwater discharge, This compares comparisonandcomparison ofprojections with and closelywith thevalue of 2.6used herc. Swenson withoutthe implementationof the proposed alsoestimated a cotnparable displacernent timein diversion,these load estimates shou!d be adequate. Lake Pontchartrain, 105 d, using the "fractionof freshwatermethod" which reducesthe waterbody Calculationspresented here illustrate the volumeto theequivalent freshwater volurnc. The importanceof incorporating theseaward boundary displacernenttime of LakePontchartrain is contributionsinestuarine budgets, Even in thecase estimated here to be 102 d. Sikora and Kjerfve of LakePontchartrain, with a relativelylimited 985! alsorecognized the needto scalegaged seawardexchange, the magnitude of net sahwater dischargestoestimate total tributary discharge. They inflowand total nutrient loading was near!y as large 40 M,B. Waldon k C.F. Bryan asfreshwater runoff and nutrient !oading Tab!e 2!. the input Inay promote local algal blooms Failure to incorporatethis flow and loadsource can uncharacteristic of lake-wide events. Both of these resultin overestimation of estuarinedisplacement pOtentialconSequenCes illustrate ! IInitationSOf the time andsensitivity to loadingfor nutrientsand other average annual nutrient load and steady-state substances. modelingapproach presented here. More studyis neededto determinethe impact of these urban TheLake Pontchartrain seas ard boundary is sourcesand other sourcesnear their points of cotnplicatedby the locationof the PearlRiver at discharge.This should include application of oneseaward boundary channe!. For thepurposes of dynamicmode! ing with spatialresolution adequate thecomparison of diversion project ahematives, it to identifyloca! impacts. is notcritical to exactlyidentify the fractionof the Pearldischarge and load that should be incorporated The annua!steady-state nutrient modeling with othertributary inf!ow. However, this is one approachpresented here has clear valuein support sourceof urtcertainty,and determinationof the of environmenta!rnanagernent planning. This amountof thePearl River flow andload entering includesplans for evaluationof overall nutrient LakePontchartrain is worthy of furtherstudy. Both controlfrom point and nonpoint sources and TMDL thcPear! River contribution and the morc general determinations,and comparison of someimpacts seawardboundary exchange should be quantified of alternativedesigns. The approachalso provides in futurehydrodynamic computer mode!ing studies, a backgroundfor comparisonin studiesutilizing moretemporally or spatiallycomplex modeling. The In thismodel ~ over39% of presentN loading modelingapproach requires !irnited effort and resultsfrom fixation or otherunaccounted inputs computer resourcesre!ative to more complex suchas dry deposition or precipitation!,There is methodo!ogies,and provides simple straight- great uncertaintyin this estimate becausethis forwardpredictions which support comparison of loading was estimatedthrough an indirect a!ternatives It is essential, however, that the calculation.and is basedon Mancini'sconjecture projectionsof this simp!e approach not be applied that the sameK value is adequateto mode!net inappropriately.For example,thi» approach can not sedimentationloss af TP. TN, and othertotal nutrient predictimpacts resulting from changes in seasonal concentration~,such as total organic carbon TOC!. nutrientpatterns, or local impactsof discharges. Futureresearch in the Lake Pontchartrain Estuary, Appliedwith care,the approachis a valuabletool as well as other lakes and estuaries. should be for environmentalanalysis, management, and directedtoward obtaining a betterestimate of K decisionsupport. for total nutrientconcentrations, and testing Mancini's conjecture.For nutrientswith al!och- ACKNOWLEDGMENTS thonoussources and sinks, this will necessitatemore direct estimation. The NewOrleans District of the U.S.Army Corpsof Engineers,the LouisianaDistrict of the Althoughthe stormwaterdischarge and load U S.Geological Survey, the Louisiana Department estimatesare uncertain,they are small relative to of EnvironmentalQuality, and the LouisianaState the total estuarydischarge and load .5% of Office of Climatologyprovided data usedin this discharge,9% TP load,and 0.8% of TN !oad!.This research,Their assistanceis gratefully ack- suggeststhat the urban siormwater pumps have little nowledged.This research was funded in part by the impacton estuarytrophic state. This conclusionis New OrleansDistrict of theU.S. Army Corpsof like!y true,but it doesnot follow thatthese nutrient Engineers. sourcesare environmenta!!ybenign and neednot be consideredin a LakePontchartrain pollutant LITERATURE CITED managementplan. The pumpedstorrnwater load likely plays an importantro!e in the reductionof AMERlcAN PURL!CHEALTH ASSOCIATlors,1992. near-shorewater quality, and the pulsednature of Standard Methods for the Examination of Lake Pontchartrain Salinity and Nutnenf Budget 87 Water and Wastewater, American Public FLow Bus, G, C., ANI! W. C. I.iPIIDRDIMi, 1'990. Health Association, in cooperationwith the Environmental Sedimentology ot thc American Water Works Association, and thc Pontchartrairi Estuary. Trartsar"tirrns Ciulf- Water Fnvirontnent Fcdcration,Washington, Coast Assai'iatir>rt of Geolrrgir'al Srir.tetir'i 40: 237-250. D.C. ARci;MI:ter,G. J., L. J. Dhhirih. c. R GARRisoh,ANn Ghi L.B, T, 1980,Computation of Drift Patternsin W, M. Lr >vrxhcF.,1993. Water ResourcesData Lake Pontchartrain. Louisiana, 39-56. in J. H. Lou i sian a Water Year 1992. I; n ited States Stone. ed.l, Environmental Ana!ysis of Lake GeologicalSurvey Water-Data Report LA- 92- Pontchartrain, Louisiana: Its Surrounding !, preparCdin cooperatiOnwith the LOuiSiana Wetlands, and Sc!ected Land Uses. Center for Departmentof Transportationand Develop- Wetland Resources. Louisiana State Univer- rnent and with other State and Federa! sity,Ptepared for U,S. ArmyEngineer New Agencies,Baton Rouge, Louisiana. Orleans District, Baton Rouge. ARciYROU, M. E., T. S. BIARDIII.Asi! C. D. LAMaRRT. ]sPHDRInho,W. C., F. D, IMshho,hao G. C. FLowI=Rs. 1997,Transport and fate of dissolvedorganic 1989.Physical Charactenstics and Aging of carbon in the Lake Piin tahartrain estuary, Gulf Coast Estuaries.Transactions Gulf-Crurst Louisiana,U.S,A. B«rriror hemistry 38;207- Associationof GeologicalSocieties 39:387- 401. 226. BARR,L 1983, EcologicalCharacterization of the Mhhahit,J. L., G. c. Kht'IMAh,P. A. MANGARRLLA, MississippiDeltaic Plain Region: A Narrative AtrDE. D, DRiscoU . 1983. Technical Guidance with ManagementRccotntnendations. FWS/ Manual for PerformingWaste Load Al!o- OWS-82169,prepared I' or NationalCoastal cations,Book IV Lakesand Impoundment~, EcosystetnTeam, Div. of BiologicalSciences, Chapter2 Eutrophication Fina! Report!. Fish and WI!dlife Service, and Minerals ContractNo, 68-01-5918, U.S. Environmental ManagementService, Washington, DC. ProtectionAgency, Ofttce of WaterRegula- Baiv'vI>ORF,J., AIID P. KLAL'S.!987, COntrOlOf tions and Standards,Monitoring and Data Eutrophicationof Lakesand Reservoirs By SupportDivision. Meansof Pre-Dams- I. Mode of Operation MFrcht.F hwo EDDY !hie. 1991. WaStewater and Calculation of the Nutrient Flitnination Engineering:Treatment, Disposal, and Reuse, Capacity.Water Researr h 21:829-842, McGraw Hi]l, New York. BIAhcHI,T. S., hhn M. E. ARDYRou. 1997. Temporal PVrz, K., Ahn J. Bi=.vhiuoRF.1998. The imponanCe andSpatia! Dynamics of Particulate Organic of pre-reservoirsfor the control of Carbon in the Lake Pontchartrain Estuary, eutrophicationof reservoirs.Water Science Southeast Louisiana, U.S.A. Estuarine, and Technology37:317-324. Coastaland Shelf Science45:557-569. RzcKHow,K. H. 1979,Quantitative Techniques for BOwu,G. L., W. B. MILtS,C. B. PORC~A,C. L, the Assessmentof Lake Quality, EPA-440/5- 79-015, U.S, Environtnenta! Protection CAMPBELL,J. R. PhoahKDPF,G. L. RI.JPP,K. M, JOIINSOZ,P. W. H. CIIhh, ANnS. A. GHERih'I. Agency,Office of WaterPlanning and 1985. Rates, Constants, and Kinetic Standards,Washington, DC. Formulations in Water Qua!ity Modeling Rvnthro,S, O., A 9 t J.W. Day et al. sedimentsat the Caernarvon freshwaterdiversion the totalspillway area. A waterflow regulation site. Researchhas shown thatdiverting nutrient- structure,which has 350 flood gates each consisting rich waterthrough wetlands can lead to substantial of twenty20x30 cm wooden beams!, is locatedat nutrient removal arid to enhanced accretion thejuncture to the Mississippi River. The structure Richardsonk Nirho]s l9S5; Breauxand Day isopened and closed by reinoving or replacingthe 1994!. Wetherefore undertook an analysis of water beatnsone at a time. Thus, it can take several days chemistrydynamics during the 1997 opening of the to openor closethe structure. The spillwayis spill way. locatedwhere onc of themany crevasses breached thc MississippiRiver leveein thc 1800s and STVDV AaEA introducedup to 4,000 m-'s' of water into Lake Pontchartrain Davis 1993!. The presentspillway w The Bonnet C~ wasdesigned to divertup to 7,000m's ' from the Spillwaywas designed to carry floodwaters from riverduring floods, the Mississippi to Lake Pontchartrainwhen New Orleansis threatenedby high waterlevels, It was constructedin l93 l after the devastatingflood of large l 630km'! oligohaline take located north of 1927 Barry1997! and hasbeen opened eight times NewOrleans, Louisiana, with a meandepth of about duringhigh flow events Sikoraand Kjetfve 1985!, 3.7 m anda volumeof l.66 x ] 0' m' Fig. l !, Tides The BonnetC~ Spillway is located25 km upriver in thelake are diurnal with a meanrange of 12 c m. from NewOrleans, Louisiana Fig. l !. The 3,4 km Lake Pontchartrainis well mixedand is generally wide spillway is confined by two 8.6 krnlevees and not stratified. In the natural state, the lake was connects the Mississippi River to Lake surroundedby extensivewetlands, but large areas Pontchartrain. There are l 300 ha of forested have beenreclaimed or impoundedon the south wetlandsin the spillway, or approximately50% of shore due to growth in the New Orleans rnetro- Fig.l. Me of~e Pontch~n showing th l~~ions ofthe Bonnet C~ Spillwayand the s~phng st t ons. Bonnet Carrt5 '97 Freshwater Dwersion 91 politanarea. Thc lakereceives freshwater input were analyzedfor nitrite+nitrate NO,+NO,!, fromseveral rivers as well as periodic openings of ammonium NH,-N!,total Kjeldahl nitrogen TKN!. the BonnetCarrc Spillway. Withoutthe spil!way, Tota!Phosphorus TP, Wcrshaw et al. 1987!,tota! meanfreshwatci input to the lakeis about370 suspendedsolids TSS, Banse et al. 1963!.and m's', resultingin a replacementtime volumeof Salinity Greenburg ctal. 1985!.At least ! 0to 15'4 thelake divided by freshwaterinput! of about51 of all analyzedsamples were duplicates or spikes days.Three large inlets connect the lake to the larger toverify analytical performance. Tot« nitrogen TN! estuarinesystem. Two natural inlets, The Rigolcts was calculatedby adding NO.+NO, and TKN andChef MenteurPass, communicate with Lake values.Organic nitrogen ON! wascalculated by Borgneand Mississippi Sound; while a dredged subtractingNH, from TKN. Foreach station, the canal,the Inner Harbor Navigation Canal IMNC! measuredparameters werc plotted with respect to is connectedto BretonSound. The riverssupply time. 5% of the tidal prism in the lake, whereasthe remainderenters through the tidal passes Swenson 1981!, 45000 T'40000 The 1997 Opening r-:35000 C! v 30000 Duringthe Spillwayopening, Mississippi d 25000 Riverdischarge was 39,400 rn's ' .39x l y'cfs! on Z 20000 March17, 48,600 rn's' ,72x10" cfs! on March r> 25-26,and about 30,500 tn's ' .08x I0" cfs! on 4 15000 April20, The Bonnet Carry Spillway was opened onMarch 17 as a precautionagainst flooding. Water flowthrough the spillway gradually increased toa r r t r ~ r dl errr Cr d; rrl A rr maximumof about6800 m's' .40x10s cfs! on O rV N rd rd Ifl r CJI Al N rv rv cv g a d. March25-26, or about16.4% of the totalflow of rrr d rJ rr d a2k theMississippi River at the time Fig. 2!. Asriver Z stagedecreased, lessening thethreat of flooding, O«1r thestructure was gradually closed and flow through thespillway declined. The structure was fully closed onApril 17. Approximately 1.0 x 10"of riverwater wasdischarged from the Mississippi into Lake Pontchartrain,and the replacerncnt time of the lake .. 12 was reduced to five or six days. ~10 8 METHODS Individualwater samples were collected at approximatelyweekly intervals from March 17 to Scptetnber22 at sevenstations; the Mississippi r r r f dl Crrdr Ql errQr dr rrl Cfl River,5 stationsin LakePontchartrain, andone 0 vJ W id «0 a ri cu 4 rv 92Irv Q Q. stationin LakeBorgne near the outletof Chef a d a d ~ 4 MenteurPass. Water samples were collected 10-20 Z Z C C crnfrom thesurface in acidwashed glass or plastic containers with teflon coated lids. The water Fig.2. Top. Total flow of theMississippi River during sampleswere cooled to 4'C for preservation and theSpillway Opening shOwing the amount ot' v aier transportedtothe Corps of Engineers laboratory in whichwas diverted through the spillway BC, gray New Orleanswhere both filtered and unfiltered area!.Bonom. Percent of total flow of the Mississippi sampleswere frozen until analysis. The samples River diverted through the spillway. J !N Pay et ai. Statistics Spatialand Temporal Trends Statistic «1analyses were conducted to identify Theintroduction of river waterreduced changesover time and space. Temporal analysis salinityand increased nutrient levels in thelake wascarried out by comparingmean concentrations Figs.3-8!. Statistical analysis indicated that there fromApril 1 thoughMay 5 to concentrationsfrom werchigher NO.+NO,, TN, and Tp, as weH as lower July28 through September 22at each station; a total salinity at most stations during the periodthe of five sainpleswere usedfrom each of these spillwaywas open compared to laterin thesummer periods. Theseperiods were chosen to represent Table1!. This conditionwas most pronounced at conditions during and after the operdng of the stations2 and3 wherethe system went completely spillway,with a twoweek lag time in the first period freshwithin two wccksof the openingand nutrient to allow water to teach distant stations in thc lake. levelswere in thesame range as those in theriver Spatial analysis was carried out using the same Figs. 3 and4!. At thesetwo stations,high temporalgrouping five samlilesduring andafter concentrationsof NO,+NO, and TP persistedfor the .spillwayopening!, but compareddifferences abouta monthafter the closure of the structurebut betweenstations. Due to the small sample size, decreasedhy early to mid June. In contrastto the nonpararnctricanalyses using theWiicoxon Rank rapiddeclines in nutrientconcentratioit, salinity Sum test was usedto test for differencesbetween graduallyincreased through the study period. Total means Sall and Lehman 1996!. A probabilitylevel nitrogenincreased at all stations,except 6, during of <0.05was used to definea significantdifference. anddirectly after theopening of thespillway, and though not statistically significant, therewere RESULTS inrreased ON concentrationsat station~4-7 several monthsafter the spillway was closed. Concentrationsof the different parameters in MississippiRiver water varied during the diversion; At station4 in the midlake Fig.5!, YO,+NO, TKNranged fram 0.34-0.93 {ing 1 '!,TP 0.17-0.33 and TP concentration reached the levels in the river mg1'!. NH, 0.08-1.26 rng 1'!, NO,+VQ, 1.08- but a weekor two later thanat station2. Saliriity ! .26 mg 1 '!.and TSS 34-110 ing 1'!, Thesevalues declinedmore slowly and never reached completely aresomewhat low for averageMississippi River fresh coitditions. As with stations 2 and3, nutrient water,bui perhapsthe high watervoluine led to concentrationsreturned to preopening levels by rnid dilution of theseconstituents. Junewhile salinity did not returnto prcopening Table1.Results ofstatistical analysiscomparing meanconcentratiotts fromApril 1 throughMay5 to concentrationsfromJuly 2$ through September 22.Arrows denote ifconcentrations increased T1 « decreased l! during thespillway opening. NS-uosignificant ~~nce; * asap.05;++a<0.01; a<0.001;~~~~ acO.I}00L Station NQ +NO NH, TKN ON TN TP TSS Saliiuty NS NS + T >+T ~+T NS NS VS NS NS NS NS ,g J, NS NS NS NS NS NS NS NS NS NS NS NS Ns a~T +AT Bonnet Carre '97 Freshwater Diversion 93 200 200 0 0 l ali l00 50 50 r 0March A pa 0March Apn. Ma! !uhr !uir Aurar lo 10 e C 0 March'Aprr prri Mau !ahr !a 05 0.4 0.4 E 03 E 03 il.2 0.2 ! i 0! acpl 0 rr!arch pn! raay !uhc 0 March'App apu.*4 h 5 1.5 ls E E I l 0.5 0.5 i!M arch April May 0March Aprr !uur h!0, hoa h Imp;Ir cy - r!rr~ics man Nuu+Wr!VMlm!r/I, 0- OrrArrru!u levelsuntil September.Station 5, nearthe north NO,+NO,and TP concentrations aistation 6 were shore, was similar to station 4, but nutrient generally!ess than half of thatin the river, whi!e concentrations were lower and salinity was not concentrationsatstation 7 wereclose to river v'ater significantlychanged due to thediversion Figs. 5- formuch of April andearly May. NO.+NO,and 6, Table1!. 1VO,+NO,levels were significantly TPconcentrations returned to preopening!cvels by higher during the spillway opening, but never midJune at both stations. Salinity was near frehh at reachedthe concentrationsfound in the river while station7 for abouttwo weeksin mid April while TPdid soonly for a shortperiod in lateApril and salinitywas higher at station6 duringthe hainc eai!yMay. Sa!initywas near fresh for an extended period.Thc salinity and nutrient data suggest that periodfrom May to earlyJuly and had not returned riverwater moved preferentia!ly along thc south topreopening levels by late Septetnber, This is likely shoreof thelake and most of thetime flowed out of dueto dischargefrom north shorerivers. thelake through Chef Menteur Pass. ReSu!tsof the spatialstatist~ca! anal! hi» There was less influence of river water at station6 in thenortheastern portion of thelake Fig. indiCateSignifiCant differenCeS between statiOnh fOr 7!than at station7 inLake Borgne Fig. 8!. Station NO,+NO OV,TN and salinity during the spillway 6 appearedless affected by thespillway opening opening,but duringlate summer there werc no andthere was no sigmficanttemporal differences significantdifferences between station~, except lor betweennutrient, TSS or salinity concentrations. salinityfTahles 2 and3!. Duringthe spillwa! Si J.W. Day et el. opening,stations 5 and 6 hadlower YO,+NO, and severaltidal inlets. Mean riverine input to the I ake TN concentrations than all of the other stations Pontchartrainsystem is about370 m's ' I3ianch; Tables2a and 2c!. Organicnitrogen was higher at andArgyrou l 997!while the maximum transport at station2 thanstations 4, 5, and6, station3 hadhigher thetidal inlets is about6400 m's' Swensonan I ON thanstation 5, andstation 7 hadhigher ON than Chuang1983!, Peak spillway discharge was about station5 Table2b!. There were no significant 6800m's ', thusmaking it equivalentto max mum differences in salinity between stations, except tidaltransport in the inlets, Thus, while the spillway station6 hadhigher salinity than station2 fTable was open, freshwater input to the lake 2dl. ln thc late sutnmcrperiod, there were higher dominated by Mississippi River water salinitiesat station7 thanany other station Table approximately95%!. During the opening, 3 l. freshwaterflowed preferentiallyalong the south shore of the lake and out Chef Menteur Passa.s DISCUSSION suggestedby the higher salini ies at stations5 and 6. Transportthrough the three tidal inlets is npt Lake Circulation balanced.The Rigolets is thclargest inlet andcarries about 60% of the dischargeof the three inlets The circulationin the lake is affectedby compared to 30% for Chef Menteur Pass and I 0% freshwaterinput, winds, Coriolis force,and the for IHNC. Thc Rigoletsis Gooddominated with 2 H! I 5 l 150 I H! 1 no sn 5D ul> Augu! Sc!u ul! Auyu ln8 I> E V; 6 2 y Junc July Auu ! 4 !.5 E !I,I o4 n ~ 0.3 u. 0.2 ' iuu 25 2 E I 1.5 ! 5 0.5 uy Junc JUI! Autm o s mg/[, mg/!! ! 4! -v mun yuu!u! mt I> NOJy O!-8' my/I 4!. OcgmucS my I> NH444 my>I! 2' >m!'5fmm' Fi g . S.- W a'r qualityde alSM pn 4 donngand ~er theBonnet Carte Spigwa5 opening, Fig ty-Water quality data at Station 5 duringand after theBonnet Ca reSpillway opening. Bonnet Carry '97 Freshwater Diversion 95 floodtransport 27% greater than ehb transport, while kills attributedto the bloom were reportedduring theother two inletsare ebb dominated ebb transport Juneand July, during which time algalcell counts is 37%greater f'or Chef Menteur and 28% greater wereas high as 10'" cells per liter 1Poimcrand King for lHNC, Swensonand Chuang1983!. These 1998!. Thereis evidencethat the algaewere taking circulationcharacteristics help to explainthe water up ON earlyin the bloomand fixing nitrogenlater qualitypatterns in thelake. duringthe bloom Dortchet al. 1998!.There were increased ON levels in the central and northern Algal bloom portionsof the lake when the algal bloom wa» observed.Paerl et al. 998! found algal bkgomsin Followingthe closure of thespillway there was the Neuse River Estuary when high treshwater anextensive blue-green algal bloom, predominantly dischargeevents were followed by relativelylow AnabaenaCircinaliS and MicrOCVsnaaeriggincgsa, in dischargeperiods, presumably due to increased LakePontchartrain from lateMay whichpersisted retention time which allowed phytoplankton throughJuly Dortchet al. 1998;Poirrier and King biomassto accumulaterather than to be flushed out 1998!. Both of thesegenera are knownto be of the system, stimulatedby excessnutrients and are capable of positivebuoyancy, which allows them to avoid light The introduction of freshwater into estuaries limitationin turbidwaters Dortch et al, 1998!.Fish has broadaffects on phytoplanktonproductivity. 200 150 150 I IJP 100 5ii so 0 Marr.hApn prr! hiay 106 C 6 m m 4 V.' U; 0 MarchApni Ma! 0March' Apnl May 0.5 0.4 04 05 05 0 n 0 M ' *p 25 2 ]5 E E I I ti5 0.5 0vtarch ApnI 'May 0 Mam pni May Junc ~+40'l 4 Img/I I - 4! 0'.aanmI Img NOJ+I40vlitmg/! i -cy Orgmuc6 img4i IH44!mg'I> Q rural 4 img/I SHcggimg/Il g Tmci 4 .ng/I; »g 7.Water quality data at Station6 duringand after Fig.8, Water quality data at Station 7 duringand after the BonnetCarre Spillway opening. theBonnet Carre Spillway opening- 85 J.W, Oay et al. Table2. Post-ABC>VAresu}ts of statisticalanalysis comparing mean concentrations from April l throughMay 5 betweenstations. Greater than >! or lessthan Table 2A Table 2C Station 2 3 4 5 6 Station 2 3 4 5 6 NS NS NS NS NS C NS NS NS NS NS NS NS NS Table 28 Table 2D Station 2 3 4 5 6 Station 2 3 4 5 6 NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS Table 3. Post-A NOVA results of statistical attenuated rapidly in the water column and analysiscomparing mean salinity concentrations phytoplankton photosynthesis is confined to a from July 28 through September22 between shallowphotic zone. For this reason, phytoplankton stat}ons.Creater than >! orless than The results of this analysis showedthat the Highprimary productivity in estuariesreceiving lake was a sink for nitrate becausenitrate decreased freshwaterhas been related to the introductionof tnuch more rapidly than salinity increased. Various nutrients Nixon 1981!. but production is also studieshave reported similar reductjons in estuarine limitedby light avai labi}ity that is attenuated byhigh environmentswith a significantpart of the reduction. suspendedsedirnertt conccnttations usually due to denitrification Khalid and Patrick 19}}8; associatedwith freshwaterinputs Cole and Cloern Lindau and DeLaune1991; Nowicki et al. 1997!, 1984!. ln river-dominatedestuaries. environments 3enkinsand Kemp 984! reportedthat up to 50% with turbidityoften exceeding 50 rngI ', fight is of NO.+NO, introduced into the Patuxent River estuary underwent de nitrification. BonnetCarr4 '97 FreshwaterDiversion 97 Another traniformatio» of NO +NO ii rlircctlyafter ihc diversion.hut !eve!sdecreased aisimi!ation into particu!atc organic rnatter b> duringthe iummcr months, The high!y charged phytoplank ton. Both denitrification and phoiphatcanion PO ii rt.adi!viorbcd onto th< phytoplanktonuptake werc likely significant surfacciof «bargedclay land detritalorganic.! procesie» in thclake. Vascular p!ant uptake can also particlesat high concentrations, whi!e at lower rcmove NO,+NO, but thii wai probably not a conccntrationiPO, is relcascdinto the water, thus iignifi cant procc.isbecause thc vegetation:open inaintaininginoderate «rnbient concentrationi Jitti v,ater ratio of thi.i systemii low. NO, reductionto !959!.Cyclic aerobic and anaerobic conditions in NH,has a!io beenfound to occur Smithct al. 1982!, thesediinenti also effect the sorption and release of with as much as 50"i'r of NO, applied to marine phoiphate Patrick and Khalid !974!. Sharp et al. scdimenti being reducedto NH, Sorenson1978!. 982! foundthese sorption-desorption proccisei providea bufferingmechanism for phosphorusin Ammonium le vcl» increased in Lake thc Dc!awarecituary, and gladden ei al. 9881 Pontchartrain. Lane ct al, 999! reportedsimilar ihowedthai TP behavedsimilarly in Four!eaguc results for the Cacrnarvon freshwaterdiversion site Bay,Louisiana, with little change in concentration locatedfurther south on the Mississippi. This was throughoutthc year, The saincpmcessei, asv cli mostlikely causedby the regenerationot NH, by a»algal uptake, most likely affects TP concentrationi the decompositionof organicrnatter Kemp and in the lake. Boynton1984!, as well as reductionof NO,+NO, to NH, Sorenson1978!, Numerous studies have Suipendcdsediments were rapidly trapped in shownthc nct mobilization of NH, by benthic theestuary, This wai like!ydue to decreasing water seditnents Koike andHattori 1978;Ca!lender and velocitywhen entering thc estuary,allowing Hammond! 982; Tcague et al. ! 988!.The relatively suspendedsediment todrop out of the water column. shallowwater depths, rapid icttling rates and rapid Lanect al, !999! reported siinilar findingi I'or thc bacteria!utilization result in fairly shortresidence Caernarvondiversion and Villarrubia 998! times for organic material in estuarinewaieri reported164 ha of new marshhas formed in Breton Moranand Hodson 1989!. Therefore, much of the Soundestuary since the openingof the diversion. regenerationof nutricnts prohably takes place on prcsumab!yduc to sedimemaccumulation, or in the sediments, which is where NH, regenerationis highest Blackburn 1979!. Flint andRabalais 981! foundthe periodic additionsof freihwater into Corpus Cristi Bay had Totalnitrogen concentrations decreased inthc a beneficialaffect on ecosystem functioning. They lakeafter the spillway was closed, suggesting that suggestthat higher phytoplankton productivity LakePontchartrain acted a» a sink for inorganic associated with increased nutrient input ii nitrogen,TN is a combinationof all the forms of assimilated into benthic biomass Increased benthic nitrogendiscussed above, and its behavioris productionrepresents additional food supplyfor governedby processescontrolling those con- important fisheries such as shrimp. Increased stituents. Di!ution, however,could have been productionof oysters, finfishes andpenaid shrinip responsibleforsome TN reduction. Denitrification have been attributed to previous openings of the playsa majorrole in the loss of nitrate from estuarine Bonnet Carre Spillway Chew and Cali 1981! waters,but anotherpermanent loss of nitrogenii Caddy !993! proposed a model for the effect of throughburial of organicmaterial such as detritus increasingnutrient inputs on varioustrophic levels andsenescent phytoplankton cells. ON concentra- in large enclosed water bodies. Additions of tionsincreased in the lakeseveral weeks after the nutrientsiniiiallv increasesovera!! production for closureof the spillway,largely as a resultof the al! trophiclei'eli, with peak rate~occurring when alga!bloom, a portionofwhich undoubted!y settled thewater body ii slightly eutrophic.As the system to the bottom of the lake. becomei morc eutrophic the benthic community declineirapidly in responseto bottomwater anoxia. Theresults indicate that most stations in Lake Thistrend is followed by othertrophic levels and Pontchartrainhad increased levels of TPduring and leadsto eventual system collapse. Vihere I.ake J lsd,Day et al. Pontchaitrainis on this scale is uncertain, but future BARRY,J.M. ]997,Rising tide. the great MisSissippi studiesshould address this questionso the hea]th flood of 1927 and how it changed America. andtrophic functioning of the take can be properly Simon and Schuster, New York, New York managed. BiAvcHi,T, ARDM, ARc'Yaov,1997. Temporaland spatialdynamics of' particulate organicmatter CONCLUSIONS in the Lake Pontchartrain estuary, southeast Louisiana, U.S.A. Estuarine, Coasta and Thediversion of MississippiRiver water into Shelf Science45: 557-569. LakePontchartrain during the spring of l997had a BLACKBURN,T.H. 1979. Method for mcaSuringrateS profoundeffect on Lake pontchartrain water quality of NH turnover in anoxic marine sediments, during,and severalmonths after, thc diversion usinga "N-NH dilution technique.Applied ended, There were increasesin nitrogenand and Envirrmmental Mi crobio ogy 37: 760-765. phosphorusconcentrations in the ]akc associated BREAVX,A, M., ANDJ. W. DAY, JR. 1994. Policy with thc diversion, which triggereda blue/green considerations for wetland wastewater algal bloomthat persistedfor severalweeks, The treatmentin the coastal zone:a casestudy for lake systemdid, however,assimi]ate a significant Louisiana.Coastal Management 22:285-307. portion at the nutrient load either through algal CADDY,J. F. 1993.TOward a comparativeevaluation uptake,micmbial processes, or burial. Though the of human impacts on fishery ecosystemsof effects of the diversion on fisheries and wildlife enclosed and senu-enclosed seas. Reviews in popuI ationsin LakePontchartrain are not yet clear, Fisheries Science 1: 57-95. the resultsfrom this studyindicate only a short-term CALLr mnR, E. Atm D. E. HAviMO~~. 1982. Nutrient impacton waterquality in the lake.Although the exchangeacross the sediment-waterinterface !997 Spillway opening was for flood control in the Potomac River Estuary. Estitarine, purposes,the results of this studyhave implications Coastaland Shelf Science 15:395-413. for freshwaterdiversions. The lake rapidly CHFw,D. L. ANDF. J, CAi.i. 1981, Biological con- assimilatedmuch of the introducedsuspended siderations related to freshwater introduction sediments and nutrients, but there was an intense in coastal Louisiana, pp, 367-386. ln R. D. «tga]bloom. Results by Lane et al. ]999! and Crossand D. L. Williams eds!, Proceedings Vi]tarrubia !998! for the Caernaervondiversion of the National Symposiumon Freshwater indicatethat when the riveris divertedinto a marsh lnf]owto Estuaries.Slidell, Louisiana.Vo]. 1 dominatedestuary, there i» wetland enhancement out of 2. andrapid reduction in nutrientlevels without intense Ci.OFRi',J. E. 1987. Turbidityas a control on algal blooms. phytoplankton biomassand productivityin estuaries.Continental Shelf Research 7: 1367- AC KNOW LHlGMENTS 138]. COLi:.B- E. ANDJ. E, CLoERx.]984. Significance of Thisstudy was supported jointly by the biomassand light availability to phytop]ankton LouisianaSea Grant College Program and the U.S. productivityin San FranciscoBay. Ivlarine ArmyCorps of Engineers.Wethank Eric Swenson Fcotogy 17; 15-24. forhelp with data interpretation andanalysis. DAvis, D. W. ]993, Crevasses on thc lower course f theMississippi River, C 378. LITERATURE CITKD DORRACH,Q., T. PrmRspN,AND R.E. TtntNra A]galbloom resulting from the opening of the BA.'ssu,K.,C. P. FAi.Ls, Asn L. A, Hoasov.,1963. A BonnetCarre Spillway in 1997-In Bas' gravimetricmethod f'or determining suspended thcBasin Research Symposium. May 12-]3. matterin seawaterusing rnillipore filters. University of New Orleans,Louisiana DeepSea Research 10;634-642. Fim', R. W, ANDS. C. RAaALAis.] 981. Estuadne benthic community dynamics related « Bonnet Carrrl. '97 Freshwater Diversion 99 freshwaterinflow to thc CorpusChristi Bay 1991,FY 91, Section104 b! !. WaterQuality estuary,pp. 489-508. Irr R, D. Crossand D. ManagementDivision, Office of WaterRe- L, Williains eds!,Proceedings of the National sources. SyrnposiurnonFreshwater Inflow to Estuaries. MADDEs,C. J., J, w. DAYAND J. M, RAstiAra..!988. Slidell. Louisiana, Vol. 1 outof 2. pp. Freshwaterand marine coupling in estuaries GRI.ENBErtrj,A. E., R. R. TRUssELU,1.. S. CLESCt+>, ot the MississippiRiver deltaic plain. Lirri- M, A, H, FRA~soi, eds. 1985. Standard nologyand Oceanography33:982-1 K . Methodsfor the examinationof water and MottAi,M, A. AtvsaR. E. H<>usots.1989. Formation wastewater. American Public Health Asso- and bacterial utilization ot dissolved organic ciation. Washi~gto~D.C. carbon derived from detrital lignocellul WlLL1 ~M M, R17 RoxALD G. BGUsTANv UnitedStates Geological Survey/Biological Resources Division IVationalWetlands Research Center, 700 Caj undotne Blvd., Lafayette,IA 70506 etnaile ron houstanyC ABSTRACTBenthicmicroalgal communities, including those within beds of submersed vegetation, are importantcontributors toprimary production, waterquality, andoxygenat!on ofthe ~ster column, Theimpact ofeutrophication onthese communities hasreceived littlestudy. Weinvestigated tbe effectsoflight reduction andnutrient enrichment withammonium VII,!,phosphate Pf!,!,and nitrate+nitrite NO! on the exchanges ofoxygen DO!, dissoived inorganic carbon DIC!, NH,, POe andNO . Coreswere collected lnJuly, 1995 from Lake Pontchartrain, LA,from bare sediments withina bed ofVetNsneri««meric«n«. Afteracclhnation, oneset of cores wasused fordetermination ofinitial ambient fluxrates. The remaining cores» ereplaced ini 5cmWameter potsin greenhouse tanksandgrown under three light levels 00%, 60% and 40% ofambient! andtwo nutrient levels ainbient,Inpre-treatinent and enriched Julyatsamples, 3-6X ambient!. meannet production aadrespiration werehigh, $9and 71 mg 0, m'*h ',respectively. Ammoniuin wasreleased inthe light and dark but light fluxes were only 47% of darkrates, a significant difference 8and 146 Fmol m' b ',respectively!. Phosphate andNO were releasedfrom the sediments atlo» and variable rates under both light and dark conditioiLs, means < 40 InlsniolSeptember, m' h'. coresgrown under nutrient enriched conditions hsdsignificantly highernet production !.7-2.8x ambient! andchl. a concentrations x ambient! butwere unaffected by shading.Respiration wasalso significantly higher -3-1.4 x ambient!inenriched treatments, but wasalso higher inthe high light treatment. Nosignfflcant effectsof tres mentswerefound foranv othermaterial flux. Nutrient fluxes were extremely variable, withboth uptake and release occurring amongreplicate coreswithin each experhnentaI treatment.In general, sediments tookupNH, in the darkand released it inthe light, while PO, and DIC were taken up in the light and released inthe dark.Nitrate was taken up in enriched cores, snd in the dark, hut released under ambient nutrient levelsinthe light. Benthic autotrophy wasdearly stimulated bynutrient enrichment. withacoupled increaseinsediment oxygen consumption. Lighttreatment effects maybove been obscured through canopyformation byV«Nsneri«at theend of this experiment. Thelack of impact onnutrient fluxes indicatesthatexchanges ofthese constituents arenot as closely tiedto either photosvnthesis oraerobk respirationas in other systems. Fromthe Symposium kecent tteiearch tn Coastai letttisiana' A'araratSystem Function anti kesponse to HttntanInhuence. ROzxs,L.P., J,A. Nymnn, C.E. PrOtfin. hl.N. Rabalnts. D->- Reed,and R.E, Turner editors!. 1999. Published by Louisiana SeaClrant C.'allege Program. 102 Rizzoand Bouatany INTRODUCTION community.and to evaluatethe etfects on sed.iment- water nutrientexchange Benthicmicroalgae are significant sources of organicrnatter and ox,ygcn in estuarie~ Sundback MATERIALS AND METHODS etal. 1991;Rizzo et al. !992;!. Theycan a!sir reduce nutrientre!ease by sedimentsor rcmovenutrients Intactscdimcnt plug~. 15 cm in diameter;were fromthc water column Sundback and Ciraneli !988; taken from t.he north shore of Lake Pontchartrain Rizzo1990; Rizzo ct al. 1992,Rcay ct al 1995!. about5 km eas of the macrophyteco!lectiorn site, Most estuarieshave come under stressfrom eutro- on Ju!y ! I, !995. Cores weretaken frombare sedi- phicationwithin recent decades. Lutrophicat ion has mentsbetween clumps of submersedvegetation and hadwell docurnentcd effects iin thc autotrophic placedin f!ower pots for transportto thcgreenhouse communit.iesof phytoplanktonand submersed at.ambient temperature. At thc grccnhouse,the pots macrophytes{ Kc.mp ct al. 19g3,Lapointc and Clark were placedin thc samemesocosrn tanks containing !993;Va!ic!a et al. 1993;Ikiering ct al. 1995!.hut potswith submersedmacrophytcs, which had been therehave been fcw studies ot' the benthic microa! gal previously collected, The tanks were filled with a community.Infcrcnccs from thc t'cwexisting field micronutrient solution Smart and Barko 1985!. and microcosmstudies haveshown substantial and Water depth was adjusted to achieve light levels variableimpacts on. this c Wclschmcyer 994! andthe calibration procedures NH,,PO,. and NO, 'I respectively, inaddition toprc- of%ctzc! and Likens 9911. treatmentf!ux values. Results of the chl. a detemtinationsare shown io [email protected]. Theresults ol On july 25, we began thc experimental theanalyses of variance are presented in Table l. trcattnentsand continued them for 2 months.An Oxygenmetabolism increased significantlv as increasein nutrientloading was achieved by making resultof nutrient addition, while light reduction had 3-fold additionsof NH,andPO, anda 6-fold no effect. Net productivityin ambientnutrient additionof NO,above ambient concentrations. !n treatrrtents declined 1'rom prc-treatment values under thcabsence ofhistorical data for Lakepontchartrain, all lightlevels, while nutrient-enriched treatments webased the nutrientadditions on thc documented increasedatafl light levels, Oxygen uptake under level of nutrient enrichmentwhich occurredin enriched conditions was similar to pre-treatment Ga!vestonBay, where there have been extensive uptakerates, while rates under atrthient nutrient lossesof SAV Stan!ey 19921. Nutrient concen- trationswere determined prior to makingnutrient TableL Restt!ts F,> of two-wayanalysis of additions,and within 20 min fol!owingadditions. varianceon Aux rates attd chlorophylla. Addedinorganic nitrogen was removed between additionsexcept in thelowest light treatment, where Variable Incubation C.ondition NO concentrationsincreased during the experi- Ltgh t Dark rncnt,reaching concentrations near 40 p.M. Mean amhientconcentrations + standard deviation of Oxygen NH,,PO,, and NOx were 0.92 + 0.14!tM, 0,41 i Light 0.1692 0.0202 0.05pM, and 1.4! + 0,45!tM, respectively.Mean Nutrients 0.0002 0.0001 treatmentconcentrations were 3.97 4 1.52pM, !.50 Interaction 0.2338 0,5430 k 0.61!tM, and11.60 4 12, ItM, respectively. Thereforeenrichtnents averaged 4.3X for NH,, DIC 3.7Xfor PO,and 8,2X for NOx, Light 0.4152 0.5319 Nutrients 0.0529 0.1408 Thelight reduction treatments were based on 1 nteraction 0,3315 0.4338 Secchidisk monitoringdata Cormieret al. 1994!, which we usedto calculatethe degreeof light Ammonium reductionin areaswhere SAV wasformerly present Light 0 1222 0 7967 in LdcePontchartrain. These cakulations suggested Nutricnts 0.8994 0. 1566 thatimpacts would occur at reductionsof 40-60% 1 nteraction O. 385 3 0.5889 of ambient. Phosphate Final flux rate and chl. !t determinations were Light 0.2823 0.5253 donefrom September19-22, 1995. Incubation Nutrtents 0.8801 0.3773 procedureswere the sameas for the intial flux Interaction 0.2985 0.3780 measurementsexcept that dark incubationswere carriedout overnight, i.c, 16h. Finalsarnplc sizes Nitrate+nitrite were 9 cores for each treatment block. Two-way Light 0. 1099 0.7666 analysesof variancewere carried out on theflux Nutrients 0. ! 900 0.0655 andchl, a data, Effects wereconsidered significant Interact ton 0.4426 O. 896 at F, < 0.05. Chl. a RESULTS Light 0 2953 Nutrients 0.0102 Flux ratesas a functionof the experitnental Interaction O.6848 treatmentsare shown in Figs. 1-5 for oxygen,DIC, 10i Rizzoand Boun any Oxygen Flux utt tt Treaonent t Arnb eivtpAR! i xi> 4M i % say 4o'4 200 Q L GHT 8 100 I DARK II 0 8 F g JULY-L II JULY-D I i -100 0 0 0 0 0 0 JULY + + + + + + Nutrient Treatment Fig.! . Meanoxygen fluxcs mg0, in ' h '! " standarderror of sedimentsfor light anddark incubations, Labels on the x-axisdesignate tank trcatmcntsfor not!-enriched ! and enriched +! conditions, and for PAR = 100%, 2 = 60'i , 3 = 40% of ambien ligh !. Fluxesinto sedimentsare negativeand fluxes out of sedimentsare posi ivc. July dcnotcsinitial prc-treatmentrneasuremcn a. DIG Flux Ut bt Tra binant s AmbleiiPA ! i ixi v 60"i 4c+ 60% 40'I'e ~ LlGHT 0 ii, R E g DARK O 5 8 ~E -10 i, Q JULY4 g JULY' -15 0 0 G 0 0 JULY + + + 4 + + Nut nant Treatment Ftg.2. MeanDIC f!uxcs mmolm ' h '} " standarderror of sedimentsfor light anddark incubation s. !abc!s onthc x-axis designate ank treatments for non-enriched ! and enriched + i conditions, and for PAR = ! 00%, 2 = fi0%, 3 =40% o ambientlight!. Fluxesinto sedtmentsarc negativeand fluxes out of sedimentsare positive. July denotestni ialpre-treatment measuremen s. Sediment-Water Material Fluxes t05 Ammonium FIux LightTrsatrttartt %, Amtttsttt PAR! t ari",. fi0' MN ail "~ 150 Q LlGHT 100 R rsr 8 E II DARK 50 i 8 g JULY-L Q JULY-D -50 0 0 0 0 JULY + + + Nutrient Treatment Fig.3. Mean ammonium fluxes ltmol m h- '!" standarderrorolsediments forlight and dark incubations l.abel» onthe x-axis designate tanktreatments fornon-enriched ! andenriched +!conditions, andfor PAR l I= lN'», 2 =60%,3 =40% of ambient !ight!. Fluxes into sediments arenegative andfluxes nut of sediments arepositive. Julydenotes initial pre-treatmentmeasurements. Phosphate Fiux LttttttTreatWWnt SS Amtusnt PAR! t QQ's 40s, so". 20 ~ UGHT S c 10 8 E + DARK R R 0 0 ~ JUL Y4. I JULY-D -$0 -20 0 JULY 0 0 0 0 0 + + + + Nutrient Treatment "ig.4. Mean phosphate fluxes lsmol mh - '>"standard errorofsediments forlight and dark incubations. Labels onthe x-axis designate tanktreatments fornon-ennched Oland enriched +!conditions, andforPAR l i= 1t l%, 2 60%,= 3 40%= ofambient light!.Fluxes intosedimenLs arenegative andfiuxes outof sediments arcpositis c. Julydenotes initial pre-treatment measurements. 108 Rizzo and Boustnny Nitrate+Nitrite Flux LightTreatment 0 ambient patt! 100% sp!'o 40'0 00 1 00'5 ~ L.IGHT 0 5 rv 5 E Q DARK Z x$0 Sh Z Q JULY< Z II JULY-D -100 0 0 0 0 0 JULY + + + + + + Nutnent Treatinent Fig.5. Meannitrate + nitritefluxes ltmol m -h'! ' standarderror of sedimentsfor lightand dark incubations. Lahelson the x-axis designate tank treatments for non-entiched ! andenriched +! conditions,and for PAR = I00%,2 =60%, 3 =40% of ambientlight!. Fluxesinto sedimentsare negative and fluxes out of sedimentsare positive. july denotesiniual pre-treatmentmeasurements. Chlorophyll a LightTreatment Q AmbientPAR! 40'X 100 sGwc 00 0a 40 i 20 + 0 + July Nutrient Treatntent Fig.6. Mean sediment chloro p h yll a m g metn0!" "sstandard error of sedimentsfor light«nd dark incubations Labels on the x-axis desi. gn ate tank treatm treatmentsfor non-enriched ! andenriched +! condirions,and for PAR = 100% = 60%,3 =40% of ambientlig.ht!. Ju!y denotes initial pre-neatment measurements. Sediment-Water Matenal Fiuxes t07 additionsdeclined. Similarly, nutrient addition in productivitywith light reduction but no effect of increaseduptake of DIC in thelight, but dark DIC nutrientenrichment. However, Dailey l995! points releasewas not significantly affected even though out that ambient nutrient concentrations werc releaseswere almost two-fold higher in thehigh and probablysufficiently high in herstudy to alleviate lowlight nutrient addition vcatments. Pre-treatment nutrient limitation without enrichment. Our light uptakein t.helight was nearly 3-fold higher than reductiontreatment for thc benthicmicroalgal pot» anypost-treatment value, while dark DIC release mayhave been negated by the extensivecanopy wasless than half the value of any post-treatment formationachieved by the Vallisneriawhich was reachingpeak biomass in all themcsocosm tanks. flux. Sincebenthic microalgae respond rapidly to light Therewere no significantdifferences in any reduction Dailey J995!,even a weekunder full nutrientfluxes due to experimentaltreatments for plantcanopy may have nullified the effects of our eitherincubation condition. After treatments NH, light treatments.Unfortunately light levelswerc wasgenerally released in the light and taken up in onlydetermined for thewater surface, so we cannot thedark at fairly lowrates. In contrast,pre-treatment determinewhat actual light levelswere reached at fluxesshowed highrates of NH, release inthe dark, the sediment surface. whilerelease in thelight was about half that in the dark.Fluxes of PO,and NO werelow and erratic Nutrientenrichment significantly increased exceptfor a highrate of NO uptakein thedark for DICuptake in thelight, similar to theresults of the the enrichedlow light treatment.Pre-treattnent oxygenfluxes, but the results for thedark incu- fluxesshowed release of PO,in boththe light and bationswere not significant though the same trends dark,but flux rateswere still low. Underlight wercpresent asin the oxygen data. Stitnulation of' incubation,NO wasreleased athigher rates before nitrificationin dark-incubatedcores could have treatmentsbegan, while darkincubations also actedantagonistically in nxiucing the increase in showedrelease of NO in contrasttouptake under darkDIC efflux expected based on stimulationof oxygenuptake. Nitrifical.ion could have been all post-treatmentconditions. increasedby thc directaddition of NH, subsvatc Agreeingwith the net production data, nutrient andby increased sediment oxygenation fron! the additions significantly increased chl. a increasein benthicmicroalgal productivity. concentrationsbut were unaffectedby light reduction.Control concentrations ranged from 55 Nntrieat Iluxes - 70tng m ',while enriched treattnent concentrations Pre-treatmentNH, fluxeswere similar to rangedfrom 72 - 80mg m '-,about 30% higher than othersreported for the literature, especially for meancontrol group concentrations, and similar to heterotrophic dark!conditions Rizzo ct al. 1996k pre-treatment.values, Benthicmicroalgal production in thepre-treatment coresreduced release of NH, substantially 09c! DISCUSSION overdark-incubated cores, but ratesof re!easewere stillhigh compared toother studies which showed Community Productivity muchgreater reduction ofNH, release, orreversal of flux direction Nowicki and Nixon 1985; Ourresults clearly detnonstratc anincrease in Sundbackand Graneli 1988; Rizzo l 990;Rizzo et benthicmicroalgal nct production, chl. a biomass, al. l 992;Reay et al. 1995!.The high NH. release andsediment oxygen uptake, the latter probably inthe light also differs from the results of anon- coupledto theincrease in system autotrophy. The goingstudy ofspatial flux patterns onboth the north nutrienteffigy:t was not surprising considering the andsouth shores of Lakepontchartrain which have low ambientnutrient concentrations at this site consistentlyshown removal of' NH, with positive typically 2 pMfor all nutrients!, and agree with netproduction Rizzo, unpublished daiakMicrobial Nilrsonand Sundback 991! andNilsson ct al. responseto an organic loading event inay have 991!. Dailey 995! founda significantdecrease 10B Rizzo and Bou stan y stimulateda heterotrophicresponse in excessof that would also be poisedto rernovcNO from the over- supportedby autotrophicmetaholisrn, s milari to the lying water-column. Light-inhibition of nitrifi- effeclsof bivalve culture Barranguetet al, 1994!. calion, discussed above, may have limited Suchan event may havebeen caused by loading dcnitrification and resulted in release of NO in the from houseboatsand septictanks within a few lightas we! l asNH,. Thc highdark uptake and light hundredmeters of thecollection site; or possiblyas uptakein the enriched low light treatmentmay have a responseto senescenceof a recentcyanobacterial resultedfrom build-upof added NO in the water bloom JohnBurns, pers.comm.!. column.Concentrations were l7 pM in this treat- ment,compared lo 1-4 ItM in lhc other treatments, Thepost-treatment fluxes of NH, aremuch and may have afforded additional subslralc for lower than those reportedfrom other systems, denitrification,Removal of NO by sedimentsis especiallyfor the prevailingtemperature ca. 30 C! widelyreported when water column concentrations andalso differ from mostflux studies in showing arehigh Boyntonand Kemp 1985;Van Raaphorst consistentNH, uptakein thc dark 'Kamp-Nieisen et al. 1992; Rizzo and Christian 1996!. 1992; Vidal et al, 1992; Yoon and Benner 1992; Rizzoand Christian 1996!.Since sediment oxygen ln summary,both rnicroalgal net productivity consumption,and henceNH regeneration was as and biomass,and coupled aerobicrespiration were highas in other studies showing NH, release Kamp- increased by nutrient enrichment in Lake Nielsen t992; Vidal et al. 1992; Yoon and Benner Pontchartrain sediments. Further research would 1992!, uptakemust havebeen dueto an NH, bcdesirablc to determineif such a responsewould demandingprocess which bccarne dotninant during occur in the presence of competition from phyto- thestudy. Nitrification is themost likely processto planktonblooms. It is also interestingto note that explainthe dark uptake,since it hasbeen shown to despite substantial microalgal productivity and an be very important in nitrogen fluxes in other apparentlynitrogen-limited system, there was no estuaries Risgaard-Petersenet al. 1994!. The significanteffect on DIN fluxesfor thesesrxiiments, observedreleases in the light coutd have been or those supporting submersed macrophytes inducedby suddeninhibition of nitrificationby the Roustanyand Rizzo,this volume!. This points out high incubation light levels. the substantial contribution of other microbial processesto nutrient cycling in this systemand Ruxcs of PO, were low 20 Jtrnol rnih '! underscoresthe need for studiesof eutrophication and erratic under all treatments and incubation effectson othermicrobial processes. conditions, Such findings are typical of both autotrophicat1y- and heterotrophically-dominated ACKNOWLEDGMENTS sediments under oxic conditions Rizzo and Christian 1996, and discussion therein!. Ratios of We thank Dr, Hilary Neckles for contributions N:P based on NH,, are typically 5 Rizzo, to the experimental design, and review of the unpublished data!. indicating little liklihood of manuscript. We thank Mr. Darren Johnson, Dr. phosphatelimitation, and little reasonto suspectan Rebecca Howard, and 3 anonymous reviewers for autotrophicimpact on PO, f1uxes. commentson the manuscript.We also thank Mr. David Meaux and Ms. Martha GriAis f'or assistance Similarly, NO fluxeswerc alsogenerally low with the experiment. < 20 Jtmol m '-h '! and enatic as reported in other studies Rizzo and Christian 1996, and discussion LITERATURE CITED therein/, but there were consistent incubation difference in flux direction. In the dark NO was BaiutAisoun, C., E. ALLror, avo M.-R, PLAsm-Ct>~. takenup under al I treatmentconditions, vs hite it was 1994. Benthic microphytic activity at two generallyre!eased in the light. ThcNO fluxescould Mediterranean shellfish cultivation sites with be explained by coupling of denitrification to referenceto benthicfluxes. OcearroIogica nitrification. An active denitrifyingcommunity Acta 17: 2t 1-221. Sediment-Water Matenal Fluxes 109 BDYNToN,w. R. Ain w. M. KI:sIR 1985. Nutrient Nowlcxr,8, L, Ai'n S. W. Nllxoi. 1985. Benthic regenerationand oxygen consumptionby nutrient rernineralizationin a coastal lagoon sedimentsalong anestuarine salinity gradient. ecoiystem. Estuaries8;182-190. Marine EI alogy ProgressSeri es 23;45-5,i. Rt:AY,W. G D. L. GALLAolu'Jt,AND G M. SIMstoxs, CORMu;R,L, s., J. Sill.l:IIAi', M. B. I LI.MINiL ANt>A, JR 1995. Sediment-watercolumn oxygen and HINI!RI IIS. 1994. Ixlulslana Waterquality data nutrient fluxes in nearshorcenvironments of summary 199 -1993. LouisianaDepartment the lower DclrnarvaPeninsula, USA. Marine of Fnvironmental Quality.Office of Water Fco ogyProgn ss Series 118:215-227. Resources,Baton Rouge,LA. RIsOAARDPETEXSEN N. S. RYSOAARI!L. P.Nr'.SS[:,, DAILEY,S. K. 1995, lntcractions of benthic ANDN. P. REvSIIi.cat.1994. Diurnal VariatiOn communities and material fluxes across thc of denitrification and nitriticiation in sediment-water interface in North Carolina sedimentscolonized by benthicrnicrophytes. and Virginiaestuaries. M.S. Thesis. East Limnotogyand Oceanographv 39:573-579. CarolinaUniversity, Greenvillc,NC. RIzzo,W. M, 1990. Nutrientexchanges between DoEruNo,P. H., C. A, OvrATr,B. L. Nowlcxt, E. G. the water column and a subtidal benthic Inicro- KLos, Ain L. W, RIIEI>.1995. Phosphorus and algalcommunity. Estuaries 13;219-226. nitrogenllrnitation of primaryproduction in a Rrzzo,W M.. G. l. LAcxEY,AND R. R. CHRIs>IAN. simulatedestuarine gradient, Marine Ei ologv 1992. Significanceof euphotic, subtidal ProgressSert'es 124: 271-287. sedimentsto oxygenand nutrient cycling in a EsTRADA,M., 1. VALIELA,AND J, M. TEAt 1974. temperateestuary. Marirte Ecology Pmgress Concentrationand distribution of chlorophyll Series 86'51-61 in fertilizedplots in a Massachusettssalt RIZZO,W. M, Win R. R. CIIRlsnIAN. 1996. marsh. Jourrral vf ExperimentalMarine Significance of subtidal sediments to Biologyand Ecology 14:47-56, heterotrophically-mediated oxygen and KAMP-NIELsFN,L. 1992, Benthic-pelagiccoupling nutrient dynamicsin a temperateestuary. of nutrient metabolism along an estuarine Estuaries 19:475-487. eutrophicationgradient. Hydrobiologi a 235/ SMARr,R, M. ANDJ. W. BARKO.1985. LabOratOry 236: 457-470. culture of submersed freshwater rnacrophytcs KEvIP,W. M., R. R. TwlLLEY, J, c. STEvr:.isox. w. R. in naturalsediments, Aquatic Botany 21:251- BOYNTON,AND J. Mt:ANs.1983. The decline 263. of submerged vascular plants in upper STANLIY, D. W. 1992. HiStOriCaltrendS; water ChesapeakeBay; Summaryof resultscon- quality and fisheries, Galveston Bay. cerningpossible causes. Marine Technology University of North CarolinaSea Grant Society Jo«mal 17:78-89. CollegeProgram Publication UNC-SG-92-03, LAPOINTE,B. E, ANDM. W. CLARK.1993. NutriCnt Institute for Coastal and Marine Resources, inputsfrom the watershed and coastal eutro- East Carolina University, Greenville, NC. phicationin the FloridaKeys. Estuaries SI:LLIvAN,M. J. AliaF. C. DAIBER.1975. Light, 1 5:465-476, nitrogen.and phosphorus Brnitation of edaphic NILssoN,C. ANDK, SIJNDBAcx.1991. Growth and algaein a Delawaresalt marsh.Journal of nutrient uptake studied in sand-agar ExperimentalMarirte Biology and Ecology rnicrophytobenthiccommunities. Journal of 18:79-88. ExperimentalMarine Biology and Ecology SL'iDBActC,K., V. ENOxssoN,W. GRANI. ANDK. 153:207-226. PETrERssox, 1991. Influence of sublittoral ¹ssoN, P.. B. JoNsspN,l. I . SwANBERD,AND K. microphytobenthoson theoxygen and nutrient SUI'DB*cx. 1991. Responseof a marine flux between sediment and water: a laboratory shallow-watersediment system to an increased continuous-flov' study. Marine Ecology loadof inorganicnutrients. Marirre Ecology Progress Series74:263- 79. ProgressSeries 71:275-290. SI:NDBACV,,K. Ain W, GRA.iELI.1988. InfluenCeOf microphytobenthos on the nutrient flux 1$O Rizzoand Boostany betweensediment and water: a laboratory study.hfarirIe EcologyProgress Seri es 43:63- 69. VALIELA,l., K. FDRExIAH,M. LAMONTAGNE,D. HFRSH,J COSTA, P. PFcxOL,B. DrMEo- ARDERSOS',C. D-AvANzO, M. BARIOvE,C.-H, SIIAvl,J. BRAwcEY,A'vD K. LAJTHA. 1993, Couplingsof watershedsand coastal waters: Sources and consequences of nutrient enrichmentin Waquoit Bay, Massachusetts. Fstaari es 1 5;443-457, VARRAAFHORST, W, H. T. KLOOSTERIIUIs,E. M. BI»GHG Is,A. J. M. GIELZS,J. F, P. MAtSCIIAERT, Ar'nG. J. VAv NOORr. 1992. Nitrogen cycling in twotypes of sedimentsof thesouthenI North Sea Frisian Front,Broad l.ourteens!:Field dataand rnesocosmresults, lIletherlands JoarnIdof Sea Research28:293-316, Vu!AE.M.. J. A. MDRGI'I,M. LAtAsA,J. RoxIERO, Av»J. CAMt, 1992. Factors controlling spatial variabIlityin ammoniumrelease within an estuarinebay AlfacsBay, EbroDelta, NW Mediterranean},Hydrobiologia 235/236;519- 525, WiusCHMEYI», N.A. 1994.Rourornetric analysis ofchlorophyll a in the presence of chlorophyll b andpheopigrnents. Limnologv and Ocean- ograplIY 39:1985-1992. WIIvri:I.,R, G. Axi> G. E. LIRI-.vs, 1991. LimnologicalAnalyses. Springer-Vcr}ag. xlcw York. Yotxv,W. 8, Atv»R BEHNER.1992. DenitriJIcation andoxygen consumption in sedimentsof two southTexas cstuarics. kfarine Ecology ProgressSeries 90:157-167, UnpublishedM xtterialS RIzzo,W. M., U.S.G.S NationalWetlands ResearchCenter, 700 Cajundotne Blvd lafayette, LA 70506. BI.'Rvs,J.W., St. Johns River Water Management DIstrict,PO. Box 1429,Palatka, FL 32178- 14'9 WholeSystem Material FluxesItithin Meadowsof Vaflisneria americana from Lake Pontchartrairm,LA: Effects of Light and Nutrient Manipulations Ror ALrs G. Bot;sTA>y United StatesCreologtcal Suet eylBi WILLIAM M, Rtzzo United StatesCseologica Suri ev/B«rlogica Resrtunes Di vtsiorr Universityrtf itrI'issouri-Crrlurnbia,30l Gentry Ha l,Cr>lurrtbirt, MO 652 /f; TFL 573-884-628lt email: ri oC<'misstruri.edu ABSTRACT:The importance ofSAV submersed aquatic vegetation! communities tocoastal andinland aquatic ecosystems iswidely recognized, anddramatic loses of SAY habitat have beenwefl documented throughout the entire lvlothern Gulf of Mexico,lmsses of SAVhabitat havebeen primarily attributed tothe adverse ecological effects of nutrientenrichment and lightreduction induced byincreased deveiopment ofthe coastal zone. Successful management andrestoration wfll largely depend on understanding theresponse ofSA'V communities to widespreadenvironmental changes. The objectives ofthis study were to determirsc the whole system macrophytes, epiphytes, sediments! response of an SAVcommunity to nutrient enrichmentandlight reduction onfluxes of dissolved oxygen, dissolved inorganic carbon, and nutrients.Intact sock of Vallisrrerttttrtnerscatur were collected from Lake Pontchartrain, LA, andgrown in a greenhouseduring the summer of1995 under three light leveLs IN%, 60% and40% of ambient!and two nutrient levels ambient, and enriched at 3-6X ambient!.ln September,sodswere subcored, andwhole system rnacrop bytes + epipbytes + sediarsents!Boxes ofdissolved oxygen DO!, dissolved inorganic carbon IDIC!, ammonium NH,!, phosphate PO,h andnitrate+nitrite NO ! weredetermined intight and dark incubations. Netproduction and respirationaveraged 2148.17 mg O, m' b' and-915.67 mg 0, mah', respectively lviegative valuesdenote uptake!. Ail other constituents, onaverage, were taken up in the light and released in thedark. lVIean !ight/dark flux rates for DIC, NH,, PO, and VO wereA3~.49 mM m-sh tl ~ Ii7t75$p-I23.60tt45.97, and-37.9Q/2329 lpmol m-t h t! respectively.Treatments producedsigniTicant differences in whole systetn net production. Wbo!e system oxygen productionwas enhanced bynutrient additions under high and low light, bnt reducedat intermediatelight. Variable epiphvte growth msy have confounded some treatment effects. INT ROD UCTION food sourcefor many itnportant commercial,recrea- tional,and endangered species. of fishand wildlife. The importanceof SAV submersedaquatic sediment and shoreline stabilization through the vegetation!communities to coastaland inland bafflingof waveand current energy. facilitation of aquaticecosysteins is widely recognized. The detrital food webs, and amelioration of water quality benefits of SAY conununities include habitat and by nutrientuptake and recycling andpromotion of sedimentation. Therefore, cltanges in the distri From the SymposiumReeerit Research in Coastal Cauisurna bution and abu.ndanceof SAV have widespread SaturateSystem Funriion and Restronseto Humantnlt uertre imlilicationsto fishand wildlife resources,shoreline RoZaS,L.P., J.A. Nyrnan,L,E. PrnffirCbl.N Rahalttis,D.J. Reed,and R.E. Turner editors!, 1999. published by Lotustaua geomorphology,and biogcochernical cycles. SettGrani CoBege Proprntn. Boustany and Rizzo Extensive losses of SAV habitat have been well oxygen DO!, dissolved inorganic carbon DICk documentedfor many coasta!areas of the United ammonium NH,!, ortho-phosphate PO,'!, and States. Seagrassescover less than ! 0% of their nitrate+ nitrite NO !. In addition, wc determined original areain GalvestonBay Pulichand White the responseof the epiphyie community and the 1991!, less than 30% in Mississippi Sound benthicmicron!gal community to thc studyvariab!es EleuteriusI987!, less than 20% in Tampa Bay Rizzo and Bousiany,ibis volume!. Lewiset al, !985!, andonly ca. 1% in Pensacola Bay Livingston 1987!. In contrast,the statusof MATERIALS AND METHODS SAY speciesin inlandestuarine and freshwater river systemsand bays is very poorlyknown. Significant Intact sediment plug», ! 5 cm in diameter, losses have been documented for Lake Pontchartrain containing Vatlime ria amerii anawere col!ectedon Steller!985; Turnerei. al. 1980!,and Mobile Bay June I, 1995 from the north shore of Lake Stout 1990! while tremendous f!uctuationsof both Pontchartrain adjacent to Big Branch National biomassand speciescomposition have been noted Wildlif'eRefuge, Plantswerc brought back to the in Currituck Sound Davis and Brinson ! 983! and greenhouseand p!aced in large mesocosintanks. thetidal Potomac Ri ver Rybicki andCarter 1986!. The tanks werc filled with a micronutrient solution ln thc Indian River lagoon lossesof SAY coverage Smart and Barko 1985!. Waterdepth wasadjusted havebeen highly variable over the past20 years, to achievelight levels typical of the depthat the but in someareas losses have exceeded95% Morris col!ectionsite m!. Nutrients NH . PO,.and NO,! and Toinasko 1993!. were addeddaily in sufficient amountsto maintain theambient nutrient concentrationsof the sampling Most losses of SAV habitat can be attributed area of Lake Pontchartrain. Each week one-third to effectsof coastalzone populationgrowth and of thewater was replaced and the tanks werescraped accompanying municipal, industrial, and and the water filtered with a diatomaceous earth agriculturaldevelopment Neckles 1994!.Although pool-filtering system to limit periphyton and direct causes of local declines can sometirncs be phytoplankiongrowth. identified, the majority of habitat loss has been attributedto widespreadchronic deterioration of On July 25, we began the experimental water quality Livingstott 1987, Kenworthy and treatments and continued them for 2 months. Haunert 1990!. Increased concentrations of Enriched tanks received daily 3-fold additions of suspendedsediments, dissolved inorganic rnatter, NH, andPO, and a 6-fold additionof NO,, based anddissolved nutrients in the watercolumn promote on the nutrient enrichment documented for poor light conditions and stirnu!ategrowth of light- GalvestonBay, which suffered extensive SAV losses absorbing algae both in the water column and in the 1970's Stanley 1992!. In the absenceof attachedto SAV leaf surfaces. Consequently,light historical data for Lake Pontchartrain, wc used transmission to the leaves of submerged Galveston Bay as a comparable model of conditions macrophytesis lessthan that necessaryfor plants that could have similar effects on Lake Pontchartrain to achievenet photosynthesis. and theplants begin SAV communities. Nutrient concentrations were to die. Therefore, successfu! managcrncnt, determinedprior to additionsin all mesocosmsand mitigation, and restoration efforts depend on within 20 min following, additions in all enriched understandingthe environmentaltolerances and tanks to monitor uptake and/or accumu!ation, We requirements of SAV cotninunities to these found that addeddissolved inorganic nitrogen was widespreadenvironmental changes.The object i ves being removed between additions, with the of thisstudy were to determinethe whole system exceptionof the lowest light treaunent,where NO macrophytes,epiphytes, sediments!responses of concentrations increased during the experiinent, an estuarine SAV community to 3-6 fold nutrient reaching values near 40 pM. Mean ambient enrichment and 40-60% light reduction, and to concentrations + standarddeviation! of NH PQ, determine the effects of the nutrient enrichment and and NO were0.92*0.! 4!iM, 041 + 0.05 AM, and light reductionon systerrif!ux ratesof dissolved 1,41 + 0.45 !xM. respectively and mean treatment WholeSystem Matenai Fluxes 1t3 concentrationswerc 3.97 + 1.52, 1,50+ 0.61. and from initial and finalconccntration» of DO, DlC, 1!.60+ 12.13!rM, rc»pectively, Therefore,actual NH,,PO, and NO fora»cquent i«i 3hlight and 1Sh enrichment»«vcragcd approximately 4.3X NH,, dark incubation, Afterward». cpiphytc» werc 3,7XPO,, and 8.2X NO ol ambient.The light »crapcdtrom the plantsand both thc plant»«nd reduction trcatrncnts werc basedon secchi disk epiphytcswere dried and weighed for biont«»» monitoringdata Corrnicrct al. 1994!,which wc determination. usedto calculatethc degreeof light reductionin area»where SAV was f'orrnerly present in Lake Dissolved oxygen wa.smea»ured polaro. Pontchartrain. These analy»e»suggested impacts graphically Ye! low Springs ln»trumcnt» Model SS! would occur «t 40-609clight reduction, and DIC was mcasurcdby infra-redgas analy»i» CapniCon 4 TotalCarbon Dioxide Analyzer!. Followingtwo monthsof treatntent,randomly Automatedanalysis A1 pkcm Flow Solution 1 fl selectedpots wereremoved from the mesocosrn autoanalyzcr!wa» used for thc nutrientanaly»e». tank»and»ubcorcd using 10 cm plexiglass cores Two-wayanalysis of variance ANOVA! w«» used [70crn-'surface area, 2.5 L volumeI. Thecores were to comparethe effectsof light, nutrientenrich- thentaken to the laboratoryand filled with thc same ment,and their interactionon fluxc». Resultsv:ere micronutrient solution used in the mesocosrns, consideredsignificant at «0. probabilitylevel. Coreswere placed in a laboratoryincubation system consisting of thermally controlled aquaria, receiving RESULTS saturatinglight 00-800 umol m -sec '! atambient <rx trteasttrernents mesocosmtemperature 5-30 'C!, Thecores were stirredthroughout the duration of theexperiment. Netproduction Fig. 1! rangedfrom 1635 to Totalsystem flux measurementswere determined 3213,45mg mr h ' andrespiration ranged from LightTreatment /c Antbient PAR! 3000 PAR 2ppp E Ll 1 fl 1PPP g DARK p 0 + 0 + 0 + D + nutrient Treatntent Fig.1.Mean oxygen fluxes tmg O. m h-' + ' standarderror!ofwhole system forhghl and dark incubation». Label» designatetanktreatments forambient to!and enriched +!nutnerns andlight !00%, 60k, 4 !~~ofambient light PAR!!.Huxes into sediments arenegative andfluxes out of sediments arepositive. 414 Boustany and Rizzo -650 to -1162.88 mg m' h '. Surprisingly, the with the oxygen data, the highest fluxcs for both highestrates of primaryproduction and respiration light and dark experiments were observed under wererecorded under the lowestlight and highest 60% light reduction and nutrient-rich conditions, nutrient treatment, while the lowest rates occurred andthe lowestf]ux ratesoccurred under low light/ underambient {high} light and nutrient treatments. ambientnutrients treatments in bothlight and dark Therewas a significantinteraction between]ight experimems. However,thc treatment effectsdid andnutrient treatments on disso] ved oxygen fluxes not produce significant differences. in the light. but no significanteffects underdark conditions{Table I }, In thc light, nutrientaddition Similarly, there were no significant effectsof increasedphotosynthesis under both high and low treatmentson anynutrient fluxes, Generallynutrient light, but not at the intermediatelevel of light fluxes were highest in hc low light treatments. reduction. Ammonium and phosphate fluxes tended to be higher in enrichedtreatments, but NO fluxes were f}isso]ved inorganic carbon DIC! fluxcs I'ig. higherin ambienttreatments, In the light,NH, {Fig. 2! rangedfrom -0.14 to -73.9I mM m ' h' in light 3! was takenup at ratesranging from -2].92 to- and !. I 2 to 50.23 mlv] m ' h ' in dark. Consistent 138.83p.mol m 'h ', In thedark, NH, wasgenerally rc]eased from sediments,except for slight uptake in treatments receiving moderate 0%! light rcxluctionand nutrientenrichment.. F]uxes ranged TableI. Results{F prob}of two-wayanalysis from -9.13 to 137,91 ltmo] m-' h '. The who]e of variance {ANOVA!. systemremoved PO, Fig. 4! in the light at rates ranging from -44.75 to -233,81 Itmol m' h ', and VARIABLE WHOLE SYSTEM released it in the dark at rates of 11.87 to 126.04 Light Dsrk lt.mo]m- h'. Thewhole systemrernovedNO Fig. 5! in the ] ight,at ratesranging from -15.52 to -62.11 Oxygen Light 0.0014 0.3580 Itmol m-' h', Dark flux rateswere morevariable {mg m'h '! Nutrients 0.27]7 0.7259 showing from slight uptake {-7.31 pmo] m -h' '! to fairly large re]cases{121,47 Itrnol m -'h'!. Interaction 0.0]50 0.2819 Lpiphytc biomass was not significantly Light 0,1426 0. 1390 different amongtreatmenLs. Nevertheless, epiphyte mmo I rn 'h ' I Nutrient s 0.9693 0.7403 biomass{Fig. 6! compriseda substantialpercentage of total systemaboveground biomass, 26-31% under Interaction 0.0942 0.3875 high light, Under moderatelight reductionand enriched conditions,epiphyte biomass contributed NH, Ligh 0.9489 0.5858 more {52% ! to total system biomass than did urnol m-'h ! Nutrient s 0 8713 0.6920 Vallisneria. This may haveheen responsiblefor the inconsistent results of nutrient enrichment at the Interaction k6139 0 933 I intermediate hght level versusthe significant enhancementof total systemproduction at the other PO, Light 0.8467 0 5223 two light levels. Under ambient nutrient con- umol rn-'h '! Nutrients 0.6838 0.6299 centrationsand moderate light, andunder both high Interaction 0.4780 0.5673 shading treatments, epiphytes contributed only about 10% to total systembiomass. Including epiphytebiomass as a covariatedid not change thc NH Light 0.8467 0.5223 results of the I]ux rate ANOVA's, {umol rn 'h'! Nutrient s. 0.6838 0,6299 Intei dctlorl 0.4780 0.5673 WholeSystem Material Fluxes 115 1.ightTreatment ciaAmbient PAR! 60 %0 -10 -60 -80 0 + 0 + 0 + 0 + 0 + 0 + hlutrient Treatment Fig.2. Mean dissolved inorganic carbon DIC! fluxes rnM DIC m -h ' ' +standard error! ofwhole system forlight anddark incuhations, Labels designate tanktreatments forambient o!and enriched +!nutrients and light ! 0 !A, 60%,40% of ambient light PAR!!. Fluxes into sediments arenegative andfluxes out of sediments arepositive. LightTreatment % AmbientPAR! 200 100 t 0 0 Ll CiHT Z -100 g D.a.a! 0 + 0 + 0 + Nutrient Treatment I ig.3.Mean ammonium fluxes !tM ."41 $,m h'-'+ standarderror!ofwhole system forhghi and darl; incuhations Labelsdesignate tanktreatments forambiern o!and enriched +!norrients andlight 0%, 60%, 40% ofambient hght PAR!!, Boxes into sediments arenegative andfluxes out of sediments arepositive. 115 Boustanyand Rizzo Light Treatlnetlt % AmbientPARI 140 E C40 PAR -60 Ll il I I' - I 60 DARY 0 + Q + 0 + 0 + 0 + 0 + Nutrient Treatment Fig. 4. Meanphosphate fluxes ItM PO, m-h ' ' + standarderror! of wholesystem for hghtand dark incuhadons. Labelsdesignate tank treatmemsfor ambient o I andenriched +! nutrtentsand light 0%, 60%,40% of ambient light PAR!!. Fluxes into sedimentsare negative and Iuxesout of sedimentsare positive. Light Treatment % AmbientPAR! 150 l00 PAR C0 I .I ! O'I' 0 t 0 IMRk 0 -%0 - l 00 -la0 0 + i» s C + Nutrient Treatment Fig. 5 Mean nitrate+nitrite fluxes !tf»»»Ih»0 m -'h ' + standarderror! of whole systemfor light and dark incuhations. Labels designatetank treatmentsfor ambient p! and enriched +! nutrients and light ! 00%. 60%, 40% of antbi cot hght PAR!!. Fluxes into sedimemsare negativeand fluxes out of sedimentsare positive. Whale SystemMaterrel Fluxes 117 Light Treatment % AmhientPkk! 70 cp C 40 3p pp jv Ambient t;ttriched AmbientKttrtt;hqd Attthtunt I tttScttv lV tttrient Treatment Fig.6. Pcccnr oftotal system aboveground biomass +standard error!consisting afcpi phyres fornutrient andlight treatmcnls. DISCUSSION 1'atlisrteria,which acclimateswell to low light conditions Twilley and Barko 199 !hA numberof earlierstudies have shown significanl increases in Fffeetsof Experimerttalhatjrtents epiphytcbiomass at highnutrient concentrations, Weexpected increased productivity as a result to thedetrirncnt of themacrophytc hosts Philips et of nutrientenrichment, as in thehigh and low light al. 1978;Borum and Wium-Anderscn 1980: Tw illey treatments,given the low ambientnutrient et al. 1985;Jensen and Gibson 1986; Viaroli et al. concentrationsin this system.The depressionof 1996'I.If ourValtisrreria plants were adapted to low nct productionat the intermediatelight levelis lightthere rrray have been photoinhibition within probablydue in partto theheavy epiphytc load. thehigher light rnesocosrn treatments asevidenced Macrophytephotosynthesis isfrequently limited by bythe highest rate of production atthe lowest light DICdiffusion through the leat'-water boundary, and/ levelunder nutrient enrichment, The impairment orby competition with phytoplankton f Sand-3ensen trf photosynthesi~ hy super-saturatinglighl and Borum 1991!, effects which would be intensities photoinhibition! is well documented exacerbatedby a thick epiphytelayer. Heavy Lurid92965; Tailing 1971; Vymaza! 1995!. Given foulingcan also severely limit light penetrationto thehigh ambient light in the greenhouse, theshading the leaf surface Twiliey et al. 19g5!, an effect levelsmay have acted to facilitate pr otcclion to plant probablyoverridden inthis experiment at thehigh photosysternsratherthan impose light limitation. lightle vel. Jt is possible that actua.! light penetration In sucha stronglyautotrophic system, the lack to theleaf tissuein our enrichedintermediate light of treatmenteffects Onnutrient fluxes was treatmentcould haveactually been lower thanin surprising.We expected to sec some autotrophic the 60% reduction treatment,though we could not impactsonnutrient fluxes as a resultofboth foliar make that determination. Shading effects would haveto be severeto induce light limitation in uptakeand forcing nutrients into the sediments by 116 Boustanyand Aizzo creatinga favorableconccntrat!on gradient by plant One obvious result of the impact of SAV uptake in thc root anne Wigand et al. 1997!. autotrophy vn material fluxcs was evident in the Althoughthese pr mcs»csarc probably occurring, magnitudeof the fluxes. Fluxesof all constituents othermicrobial and physicalpmccsscs apparently werean ordct of magnitudegreater than fluxesfrom dominatedmaterial exch«nges in this.systemunder unvegctatcdsediments Rizzo and Boustany,this all experimentalcondition», Secondarily, there may volume!. Presumably these higher flux values have beenan epiphytcin eraction, since nutricn reflectthc highmetabolic capacity of the sy.stern,a fluxcs,particu larly in D1C, NH,. and PO,, were also comb>nattonof rnacrophyttcproduct>vtty and consistentlylow in thcintcrmcdiatc ligh trcatments coupled heterotrophic response, and possibly second only to thc low ligh and low nutrient enhanced exch«ngesfrotn the presenceof a trcatmcnt!, in both light and dark incuhations. substantialrhir ospherc. Finally, even in cnr chcd treatmcn s, nutrient concentration»werc usually very low because of Consparisonof Material Fluxes with rapidup akcof thcnutricn addi ion»and werc very Other Studies often reducedto near detectionlim>ts by thc time Thc rclativc contributions of primary each»uh»cqucntaddi ionwas made. Const uently, producers to the metabolism of SAV communities replica cvariability increases, «nd that fact coupled areshown in Table2. Thesestudies encotnpass huge with vanabihty inducedby proccsse.swt'thin the diffcrcnccs in»cale, speciesand environment, an cores,probahly contributed to suchhigh variability con»cqucntly show great variability atnong in the calculated flux rates that significant comrnunitie» of SAV. Generally, sediments and differences could not bc shown. epiphytcsmake a greatercontribution to total system Table2. Relativecoutributiou ofautotrephic components tototal system primary production %!. Scale Plants I:.piphytcs Sediments Phytoplankton Mississtppi Sound' Annual 24 indian R iver' Sp indian Rtvcr' Quarter 72 Dravuni 1»land.Figi'. Fall 25 Tcrmmo»Lagoon' Annual 65 30 Marion Lake' Annual o4« 53 Chc».Bay - /~istcr«' Anno«1 15 Ches. Bay - Ruppta' Annual 26 Grevelingen i~ster«' Annual 24 38 Veer»e Mecr L' I va" Annual 17« 55 PresentStudy Su 87 «Plan »+ Fpiphyte» 'Daehnick et al. 1992 »D«yet al. 1982 -Heffernan k Gib»on 1983 "Hargrave1969 'Jensen k Gibson l986 'Murrayk. Wetzel 1987 'Pollard k Kogure1 993 "Nienhuis 1993 Whole Systemh/latenal =luxes 119 productivity,upto 50Vr, than wc found ! O'er!, ponentsare probably a result ofdifferences betw ccri Sincerates of benthicrnicroa!ga! net production systems,especially regarding species ol dominant wereas high as many other sediment rnicroaigal inacrophyte,andof therc!ativc importance o other systems Rizzo et. al. 1996!, our low va!uc may have microbialprocesses withi~ thosesystems. ln resultedfrom lack of inc!usionof seasonalityin our particular,flux.es of NH,and NO areaffected by nitrificationand denitrification, which cari 1 c assessrncnt.In our study, benthic production wa» cotnparcdto total system productivity only at the expectedto vary strollg!yaIHong systems 111 seasonalpeak biomass of Vallisneria, and therefore responseto environincntaldifferences such as representsa minimum contribution rather than a oxygenconcentration, salinity. light pcnctrat ion into typicalone. Thc particular growth and decompo- sediments,sulfide concentrations,and other sitionpatterns of inacrophytespecies result in variables Risgaard-Pctersen ct al. 1994!.Q'hi!c tremendousseasonal changes in themagnitude and most studiesshow much greaterwhole system nutrientfluxes compared to unvcgctatcdsediments directionof oxygenand nutrient fluxes Viaro!i et Table2k there is often very little difference inNO al. 1996!. fluxesbetween who lc system and sedirncnts Fa! cao Thecotnparisons of nutrient fluxes Table 3! andVale 1990, this study!.This differcricc riiight areeven more variab!e than oxygen fluxes and there beexp!ained by a preferencefor ammonium asa arefewer studies. The variability of nutrientfluxcs nitrogensource for scagrasses Mori arity and Boon andrelative contributions of autotrophiccorn- 1989!. Table3.Comparison ofliterature onrelative contribution ofautotrophic components tonutrient fluxes. Nutrient Whole System* Sediments* 0.004 to 0.03 ! 0-33~ii ! PO, Indian River' Spring 0.04 to 0.09 -58 to 121 ntax. -23~ 906 to 911 0 to 566 -62%! -34 to 29 max, 200%! New Caledonia-'- Summer - -4 to 66 -189 "All va!ues p,mo!m-2 h-1 '7immetmanetal. 1985. Theoretical diffusive flux. Halodule vvrighrii. Range O'1 site. 'I'a!cao2 Vale. 1990,Zosrera sp. Rangemultiple sites. 'Boucheret al. 1994.S pecies not given. Mud sediments. 120 Boustanyand Rizzo Althoughmacrophytes may bethe dominant effectivelypredict the responseol the community snucturalfeature in anSAV cominunity,the relative to c hangesin the light and nutrient environment. contributionof macrophytesto total system productionis highly variable. Suntmerprimary ACKNOWLEDGMENTS productionby Vallisneriaaniericana from Lake Pontchartrainis dominatedby the macrophyte The authorswould like to thankDr. Hilary Neckles, componentand is equivalentto we11-developedfor herassistance throughout all aspectsof thisstudy. seagrasssystems Duntonand Tomasko 1994!. This We also thank Martha Griffis and David Meaux for systemresponded to nutrient enrichmentbut not to coordinating and maintaining all fi e1d and lightreduction. The lackof significanttreatment greenhouseoperat.ions for this project, Darren eflectson nutrientfluxes suggeststhat nutrient Johnsonptovided statistical assistanceand review- fluxesin this system are not as strongly coupled to oxygen dynamicsas in other systems i.e., to LITERATURE CITED oxygenicphotosynthesis and aerobic respiration! andunderscores the needto assesstnicrobially- BoRI~M, J. ARn S, Wiulvl-A~»r;RSOR. 1980. BiOmaSS mediatedprocesses in thesesystems as well. and production of epiphytes on eelgrass However,part of theobserved responses may have Zosrera marina L.! in the Oresund, Denmark, beendue to cpiphyte/rnacrophyteinteractions, Ophelia. Suppl, I:57-64. underscoringtheneed to accountfor changesin all BoucHt-;R,G., J, CLAYIER,A'ND C. GARRIGI;i.. 1994. autotrophicco mp o nents w henevaluating the Estimation of bottom ammonium in the New ultimateeffecLs of eutrophicationonthese systems. Caledonialagoon. Coral Reefs13;13-19. Forexample, Jcnson and Gibson 986! compared COILMIER,E. S., J. SBEEHAR,M. B. FLEMiNG,Avu A, threedifferent SAVcornrnunities representing a HtsiwIGIIs. 1994, Louisianawater quality rangeof nutrientregimes and varyingdegrees of datasummary 1992-1993. Louisiana Dept, of humanaCtiVity and impactS. By COtnpariSOntn a Environinental Quality, Office of Water studyby P Proceedingsof thc symposiumon subtropical- MORRts,L.J, Av» D A.TostAsxo eds.!. 1993 tropicalscagrasses of thc southeastern 1.Jnited Proceedingsand Conclusions ot Workshops States.Florida Marine ResearchPublication. on: SubmergedAquatic Vegetationand lsio. 42, PhotosyntheticallyActive Radiation. Special FALcAo,M. AxriC. vALt:. 1990 Studyof the Ria PublicationSJ93-SP13. Palatka, FL: St. Johns 1-ormosaecosystem: Benthic nut.ricnt re- RiverWater Management District. mincralizion and tidal variability ot nutrients MtiRRAY,L. Awt>R. L. Wt rxat.. 1987. OXygcn in he water.Hyrlrobiofogia 207: 137-146. productionand consumption associated with HARoRAvE,B.T. 1969.Epi benthic algal production the majorautotrophic components in tv ii andcommunity respiration in the sediments temperateseagrass coinmunities. Marine of Marion Lake. Journo of the Fisheries EcologyProgress Seri es 3b:231-239. Researrh Board of' Canada 26;2003-2026, NEcxt.Es,H,A. Ed.!. 1994. indicator development; HEPPERvAv,J. J. Avn R. A. GtttSOV.1983. A COm- seagrassmonitoring and research in theGult parisonof primaryprtxluction rates in indian of Mexico. USFPA Office of Researchand River, Florida seagrasssystems. Florida Development,Environmental Research Scientist 46;286-295. Laboratory.Gulf Breeze,FL. EPA/620/R-94/ Jt:.vsEK,P. R. Avu R, A. GtttSOi.1986. Primary 029, productionin threesubtropical seagrass com- NtENttt.ts, P. H. 1993. Nutrient cycling and inunities:a cotnparisonof four autotrophic foodwcbs in Dutch estuaries.Hydrohiologta. components.Florida Scientist 49:129-141. 265: 1544. KexwoarttY,W. J. AVOD. E, HAt.'vERT edS!, 1990. PHtLtPS,G, L, D, EMINsov,Avn B. Moss. 1978.A Thelight requirementsof seagrasses;Pro- mechanismto account for rnacrophytedecline ceedingsof a workshopto examinethe in progressivelyeutrophicated freshwaters, capabilityof waterquality criteria, standards ArIuaticBotany 4:103-126. andmonitoring progratns to protectseagrasses. PoLLARn,C. P.AND K. Koot RE.1993. The role of NOAA Technical Metnorandum NMFS- epiphyticand epibenthic algal productivity in SEFC-287. a tropicalseagrass, Syringodium isoerifoliunr Lrv iS,R. R., M. J. DuRAKO,M. D. MoHaER,AvnR. Aschers.! Dandy, cornrnunity.Australian C. Piiii t.trs, 1985. Seagrasstneadows of Journalof hfarine and FreshivaterResearch TampaBay - areview, p, 210-246,In S.F. 44: 141-154. Treat, J. L. Simon,R, R. Lewis 111.R. L, PoMERoY,L. R. 1960. Primaryproduction of Boca Whitman,Jr. eds,!,Proceedings, Tampa Bay CiegaBay. Florida. Bulletin ofMarine Science Area Scientific Information Symposium, of theGulf and Caribbean]0:1-10. Florida Marine ResearchPublication. No, 6S. PuLtctt,W. M. AxoW, A. WttrtE, 1991.Decline of Ltvr.'OSTois,R. J. 1987. HistorictrendS of human submergedvegetatio~ in the GalvestonBay impactson seagrassmeadow» in Horida.p. system:Chronolog y and relationships to phy s- 139-15L In M. J.Durako, R, C. Philips,and icalprocesses, Hourrtal of CoastalA'esear<-h R. R, Lewis 111 eds.!, Proceedings of the 7: 1125-1138. symposiumonsubtropical-tropical seagrasses RYBicxi,N.B, ANDV. CARTER.1986. Resurgence of of the southeastern United States. Florida submersedaquatic rnacroph>zes in the tidal Marine ResearchPublication. No. 42, PotoinacRiver. Maryland, Virginia, and the Luau,J.W. 1965.The ecologyof the freshwater District of Columbia. Estuaries9:368-39S. phytoplankton.Biological Reui eiv. 40:231, RtsOAARD-PETFRSttv.X.. S. RYSGAARD.L. P, NID-SE- MORtARITY.D. J. W. Avo R. J. Boov. 1989. Avn N. P. REvsaacn. 1994. Diurnal variation interactionsof seagrasseswith sedimentand of denitrification and nitrificiation in se"i- water. In A. W. D. Larkum,A. J. McComb, ments colonized hy benthic inicrophytes- S.A.Shepherd eds.!. Biology of Seagrasses. Limnologyand Oceanography39' S73- S79. Aquaticplant studies 2. Elsevier, Amsterdam, New York. 122 Boustany and Rizzo RtzzO,W. M S. K, DAII.EY,Ci, J. LAcrtav,R, R. VIARDEI, P M. BARTDII, C. BDNDAvALI.I,R. R, CHRIsTIAN.B. E. BERRY,ANI3 R, L. Wt-:rZEL. CHRISTIAN,G. GIDRl!AsII,AND M. N ADDI.1996. Metabolistn-basedtrophic index for Macrophytccommunities and their impacton comparingthe ecologicalvalues of shallow- benthic fluxes of oxygen, sulphide and nutri- water sediment habitats. EsrrrarI'es 19:247- ents in shallow eutophic environrncnts. 256. II vdrvrbiologi a 329: 105-119, SAND-JErSFss, K. AND J, BoatIst. 1991, interactions VvstA7wL, J. 1995.Algae and clcrnental cycling in amongphytoplankton, periphyton, and Inacro- wetlands. Lewis Publishers,Boca Raton, FL. phytesin temperatefreshwaters and estuaries. WIOAND, C., J. C. STrvENSDN, AN» J. C. CORNwELL. Aquatic Boranv 41: 137-175, 1997. Effects of diocrcnt subrnerscd Inaczo- sMART,R. M AND 3. W. BARxo. ]985 Laboratory phyteson sedimentbiogeochemistry. Aquatic cultureof submersedfreshwater rnacrophytes 8 >tanv 56:233-244. in naturalsediments. AqrraricBIrtarI> 21:251- ZIEMAN,J. C. ANDR. T, 7H:MAN.1989. The ecology 263. of seagrassmeadows of the west coast of STANDI:v, D. W. 1992. Historical Trends: Water Florida: A communityprofile. U.S. Fish and Qualityand Fisherics,Galveston Bay. Univer- Wildl. Serv.Biol. Rep.85 .25!. si y of North Carolina Sea Grant College ZIMM1..RsIAN,C. R., J. R, MONTOoMFRY, ANn F. R. ProgramPublication UNC'-SG-92-03. Insti- CARISIIN. 1985. Variability Of diSSOlvedre- tute for Coastal and Marine Resources,East active phosphateflux rates in nearshore Carolina University,Greenville, NC, estuarine sediment~: Effects of groundWater STEILER, D.L, 1985, Production and nitrogen flow. Fsrrrari es 8:228-236. dynamicsof a Valli.cneriaamericana grass bed in Lake Pontchartrain,LA. Ph.D. Dissertation. Louisiana State University, Baton Rouge, Lou i sian a. STDI.T,J.P. ! 990. Estuarinehabitats. Pp. 63-88. In lVlobi!c Bay: Issues. resources, status, and management.NOAA Estuary-of-thc-month Seminar Scric» No, 15, Alabama Marine I'.nvironrncntal Science Consortium. Tech- nologyRcport No. 894X!l. TAEIux i,J.F. 1 971. Theunderwater hght clitnateas a controllingfactor in thc productionecology of freshwater phytoplankton. Mire Internat. Vi'rein. I.imnaI. 19:214. TI'RNI:R,R. E., R, M. DARut-t.i.,AND J, Boyn. 198O, Changes in thc submergedmacrophytes of Lake Pontchartrain Louisiana!: 1954-1973, %or!beast GuIf Science 4:44-49, Two EEY,R. R. ANDJ,w. BARxII. 1990.The growth of submersedrnuvophytcs underexperitnental salinityand light conditions.F sruariesl 3:311- 321. TwILLEY,R, R IVv M- KI-ssF,K W. STAvER,J, C, STEvENSON. ANO W. R BOYRTON, 1985, Nutrient enriChtnent Of eStuarine subtnersed vascularplant communitics. 1. Algal growth effect~on productionof' plants and associated commun ities. Afarine Ecology Progress Seri es 23: 1 79-19 1- Effects of the 1997 Bonnet Carre Spillway Opening on Lake Pontchartrain Submersed Aquatic Vegetation 1VIICHALtLA. POIRRIER,BORIS MACUC. Jtnr's C. FttAsiCia, CARrit. 13. FR.».'ZL, HVUX-JU~<; CHO Departtnen of Bi vltsgi ABSTRACT:An ongoing study of environmental factors that affect I.ake Pontchartrain sub- mersedaquatic vegetation provided information onthe efl'ects ofthe March 1997 Bonnet Carre SpiBwayopening. I'st Risneria americana snd Rttppia matitima abundance wassurveyed using theline-intercept method at Pointeaux Herbes, Lacombe, Goose Point, and Fontainebleau StatePark during late summer and fall nf 1996 and 1997. A AfyriophyRamspicartttn bed near themouth of Bayou St. John was also monitored. Temperature. salinity, dissolved oxygen, pn, andPAR were measured at mostsites before, during, and after the Spillway opening. There wasa significantdecrease in PAR due to blue-green algal blooms. There was no change in Vallisneria,butsignificant decreases inRttppia occurred between surveys. Abundant growth ofthe alga Ckrdophora occurred onRtappta and ftfyer'aphyllum, butnot onVallisnena. Cladophrsra growthon Rappia may' have made it moresusceptible toshading from phytoplankton and uprootingby wave energy. This could have resulted in Rrrppia being selectively lost from grassbeds.Large surface mats of Clmfophora, increased turbidity from blue-green algal blooms, andpoor water quality from algal decomposition eliminated theAfyriophyDuttt bcdin Bayou St. John. Introduction LakePontchartrain is a large,shallow, estuarine embayrnent Fig. 1! that hasa meansalinity of 4 The Bonnet Carrc Spillway runs from the ppt,a meandepth of 3.7rn anda surfacearea of MississippiRiver to Lake Pontchartrain Fig, ] k lt 1,630km' - Sikoraand Kjerfve 1985!. Thc discharge wasdesigned to divertwater from the Riverto of MississippiRiver waterthrough the Spillway preventflooding. Spillway constructionwas producesshort-term effects including freshwater completedin 1931,and the Spillway was opened conditions, increasedturbidity and plant nutrients, in 1937, 1945, 1950. 1973, 1975,1979. 1983.and and decreasedwater temperature. Higher nutrient 1997,Flow throughthe Spillwayoccurred during loadingproduces long-term cf'feet» by increasing an experimentalopening in 1994 and an the growthof phytoplanktonand epiphyticalgae unauthorizedopening in 1995, During 1997,the thatreduces light availabilityto SAViDennison et Spillwaywas opened on March17 andclosure al, 1993!.Blooms of thc blue-greenalgae Anabaetra beganon April 2. This studywas originally andMicrocystis occurred after the 1997Spillv ay designedto evaluatethe effectsof a breakwateron opening. Blooms began in May, reac,hcd a grassbeds submersed aquatic vegetation or SAY!, maximum with cell counts of 10' 1' in June, and butit providedan opportunity toobtain information declinedin July Dortch andAchee 1998!. Turner onthe effects of the1997 Spillway opening on SAY. et al. '1998! attributed these blooms to the introductionof nitrogencompounds that are high FromIbe Sytnposiutn Recent Researctr tn Cnarta! Mttisiatra: in MississippiRiver water,but arc usuallylow in tttatvralSystem Fttnction atsd Respottse to Human In fluenc. Lake Pontchartrain. They reportedChlorophyll a Rozas,L.P.,J.A. Nyrnan. C.E. Protfttt. Ist.h. Rabaiais. DJ. Reed. andR.E. Turner editorsu l 999. Ptrbltshedby LouisianaSea valuesof 5 - 15 lsg1 in yearswithout the diversion GrantCollege Program andvalues up to 800ling 1' afterthe diversiorr. 123 '$24 hl. A. Pnirner et at Fig,.1, Mapof LUtePontchartrain showing theseven SAV study sites. LakePnntchartrain SAV i» dominatedby 1973 Spillway opening. He did not find any Vallisncriuamerii.una Michx., a freshwaterspecies observable effects on SAV. Burn» and Poirrier thatoccur» in brackishwater, and Ruppia maririrnu 996! repoitecithat SAV nearFontainebleau State L., a hracki»hwater species that occurs in freshwater Parkwas lost during an alga! bloom after the 1995 Davisand Brin»on !980!. rajasguudalupensis Spillway opening. Persistentblue-green a!gal Spreng!, Mvriuphy'llumspiccaum L., Zartnirhell'ta bloom» did not occur after the 1973 Spillway palastri.sL., Potamngetnrtperfoh'urtis L, and opening, but have occurred after more recent Fleeprhari i parvula R.&S.!Link alsnoccur, hut are openings Poirricr and King 1998!. Burns and notabundant Montz 1978!. The focus of thisreport Poirrier 996! expressedconcern that River i» ori Ruppinand Valli.meria. dischargesmight causeSAV dec!ine fromreduction of light neededfor photosynthesis,and that higher LakePontchartrain SAV has beenin a stateof pH va!uesas»ociated with algal growthmight decline»inccfirst studiedby Suttkuset al. 954!. adverse!yaffect 1'allisrteria by reducingfree carbon Vegetationcoverage during 1953-1954 has de- dioxide. creased25 to 35% between1954 and !973 Turner et al, 1980!,50'7i bet v een1973 and 1984 Mayer Har!in 995! presenteddata that supporteda 1986!,and 17%. between ! 985and 1992 Burns et genera!izedshift in the biomassof major plant al. 1993!.Many explanations for thedec!ine have groupswith increasing nutrient input in»hal!ow been suggested!'Mayer 1986!, but modification ot marine systeins. As nutrients increase, the naturalshoreline,s and degraded water quality are abundanceof macroalgae,especially ephemeral theprincipal causes1 Burn~ et a!. 1993!. green taxa, increases, while SAV declines. ClaChrphorais an epiphyte on SAV in Lake Montz 978! conducteda qualitative survey Pontchartrain Burns et al. 1993!,Episodic blooms of SAV in Lake Pont.chartrainbefore and after the of this inacroalgamay be a factorin SAV decline. Elfects of Spittway Opening t25 Materials and Methods Data Ana! vsis The foliar coveragesum for eachspecies on a Study bites transectwas convertedto a pmportionby dividing Becausethc originalstudy was designed to the sutnby transectlength. For statisticalana!ysis, obtainbaseline data on theeffects of a proposed proportionswerc transformedwith thc arcsinc shorelinestabilization structureon SAV at transformationto ensurenorma! i tyof the data. Data FontainebleauState Park, three study sites A, B, wereanalyzed by three-wayana!ysis of variance andCl were established atthe Park. Single reference ANOVA! andafter-ANOVA unplanned contrasts. siteswere established at Pointeaux Herbes, Residualswere analyzed to test for normalityand Lacombe,andGoose Point. Another study site near homogeneousvariances. A one-wayANOVA of thcmouth of BayouSt. John was added to monitor PAR data was conducted to determine whether a Myriophvllurrtbed in January1997 Fig. 1!, valuesafter the Spillway opening Apri! 3 through July 10. 1997!were significantly diflcrciit from valuesobtained at othertimes September! 99 i- SAY March! 997and July 24, 1997- December!997 t. Speciesfo!iar cover was ineasured bythe line- interccptmethod Gertz 1984! with continuous Kpiphytes observationsalong thc transect. At eachsite. five random!yplaced line transects were extended 200 Cladophornabundance onrepresentative SAV m perpendicularfrom the shore, Water depths at sampleswas deterrnincd from Fontainebleau Aand whichSAY occurred were recorded as one of five C, Lacombe,and Pointc aux Herbes on May30, intervals;0 - 0.3! m; 0.31 0.62m; 0,62- 0.93rn; July3, and September 3, !997, from depth~ of0.3, 0,93- 1.24m; and1.24 - 1.55m 5 ft! oneach 0.6,and 0.9 m. Threecategories were established. transect. Fieldmeasurements were made from absent no Cladophora observed under a dissecting Septemberthrough October of 1996 and 1997, The microscope!,present {Cladophora wet weight< sizeof theBayou St. John Myriophyllitm bed was 509 10 9.5 8.5 Z 7.5 7 6.5 6 Aug-96 Oct-96 Dec-96 Feb-97 Apr-97 Jun-97 Aug-97 Oct-97 Dec-97 Date A - ~- FontainebleauC Fig. 2, pH measurementsfrom four water quality study sitesfrotn September13, 1996 through December 22, 1997. 200 +~180 ~ ~ + 160 acti140 ~ 120 c ~O100 80 60 Aug-96 Oct-96 Dec-96 Feb-97 Apr-97 Jun-97 Aug-97 Oct-97 Dec-97 Date eu A ~ FanteinebleauC ~ Leaambe ~ Painte aux Herbes Fig, 3. Dissolved oxygen measurements from four water quality study sites from September 13, 1996 through December 22, 1997. Effectsof SpiiiwayOpening 127 12 10 CL 8 CL >6 ~ ~ fl 0 Aug-96Oct-96 Dec-96 Feb-97 Apr-97 Jun-97 Aug-97 Oct-97 Dec-97 Date ~- Pointeaux Herbes Fig.4, Salinitymeasurements fromfour water quality study sites from September 13, f 996through December 22, 1997. Fig. 3!. Oxygenvalues were higher and more higherin dissolvedsolids than north shorestreams variableafter the Spillway opening due to increased Cormieret al. 1992!.Salinity did notreturn to the phytoplankton Dortch andAchee 1998;Turner, seasonalnorm until October 1997. Dortchand Rabalais 1998!, photosynthesis and respiration. PAR Salinity Measurementsof PAR expressed as a percentageof surfaceirradiance at 1-mdepth are Therewas an overall trend of decreasing salinity presentedin Fig.5. Low PARvalues' mean6.3%! tofreshwater conditions after the March 17 Spillway occurredwhen Mississippi River waterreached the opening Fig. 4!. Differencesamong sites were sites,and later during phytoplankton blooms; higher related to the direction of freshwater flow and values mean24%! occurredat othertimes. Values distancefrom tidal passes Fig. 1!. Flow from the fromthe turbid period April 3 -July 10, 1997! were Spillwaymoved along the southshore, and water significantlydifferent p<0.01!than values from atPointe aux Herbes was fresh < 0.5ppt! by April othertimes September1996 through March 1997 3. Freshwaterconditions persisted at this siteuntil andJuly 24 - December1997!. April 26. Salinitygradually decreased at thenorth shoresites after April 3, but freshwaterconditions SAV did not occuruntil April 26. Jncontrast, salinities at Pointeaux Herbes increased during this time and Vallisneriafoliar coverage Fig. 6! was analyzed laterfluctuated with rainfalland tidal exchange. bythree-way ANOVA with fixed factors sampling Northshore sites were fresh through July, On July period,sampling site and water depth!. The 1996 3 and 10,discharges from Bayou Lacombeand and1997 sampling periods were not significantly BayouCastine lowered salinities at threenorth shore different p = 0.658!.Mean foliar coverage differed sitesmore than when Mississippi River water was amongwater depths p 0.001!,and foliar coverage present.This is becausethe MississippiRiver is was greatest at depths of 0.31 0.93 rn. The inter- t28 M. A. Poirrier et al. 60 ~450 1 / g 30 I a.4 I a 0 Aug-96 Oct-96 Dao-96 Feb-97 Apr-97 Jun-97 Aug-97 Oct-97 Oec-97 Date , ~- FontanebtnliiA -~ r.nritanebtoauC ~ taenrnte ~ pOrde iiux HefbeS Fig. 5. PAR PhotosyntheticallyActive Radiation!measurements at a depthof one racierexpressed as % of surfaceirradiance from September13, 1996through December 22, 1997. action f'aI isneria americana ! Herbr> t'Icrhrs ! U>. In t!I' I acomhr Depth mi Gr>ogcI' t. P !0 Gl~sc I t -0r FontA QQ t>9 FontA 09-i ! Font8 Il I ' I = F ln H ! I-IIII!r' .">nl! Mean FOliarCOver trt! Fig,6. Differences inVallisneria americana abundance at0.3 depth intervals, between 1996 and 1997 surveysat six sites. Ruppiatriari ti ma ! Hcrbcs Hcrbcs L rearbr t i>con bc Depth rn! GooseP 0-03 Go useP 0 3-0.6 ! FonA [fg '.6-0 9 FontA ! faintR r>.9-I ' g I:-I: F!n tB I l>n' F~lnt Mean Foliar Coser Irrt! Fig.7. DifferencesinR ppt'amartyima abundance at0.3 depth intervals, between 1996 and 1997 surveysat six sites. 190 M. A. Palmer et al. Small amounts of Najas were present at Discussion Fontainebleau C in 1997, and small amounts of Najasand Eleoc/Iris werepresent at Lacombeand Despitethe seemingly adverseconditions for GoosePoint in 1996 and 1997, Bothspecies SAV growthafter the BonnetCarry Spillway occurred in shallow water, and our data did not opening, there was no significant change in indicatea changebetween sampling periods. Vallisrreriatotal coverage, or changewith depth at any sites between 1996 and 1997. However, there Kplphytes were significantdecreases in total Ruppia abundanceand changes in depthdistribution at all Cladophorais generally present throughout the sites. year in Lake Pontchartrainwith episodesof extensivegrowth during spring, summer, and fall. Of theenvironmental factors monitored, light In our study,Cladophora was absent in the0.6 rn reductiondue to blue-green algal blooms and growth samplefrom Lacombe and 0.6 and0.9-m samples of Cladophoraon Ruppiaare the best explanations fromPointe aux Herbes in May,but present in most for the Ruppiadecline, Temperature was not othersamples Table 1!. Cladophoraovergrowth important because there was no decrease when onRuppia occurred in 0.3 and0.6-rn samples from MississippiRiver water was present at the shallow FountainebleauA and C in May, 0.6 m Ruppia study sites, Limitations due to a decrease in free samplesin Septemberand 0.3-m Najas samples in carbondioxide from increased pH Titusand Stone September,and 0.6-m Valli,sneria samples from 1982!cannot explain the persistence of Vallisneria Lacombeand Pointeaux Herbesin September and the decreasein Ruppiabecause Ruppia is Table1!. Cladophorawas present on Myrio- conunonin alkaline brackishwaters. The freshwater p/iyllumin BayouSt. Johnduring Februaryand conditions that occurred after the Bonnet Carrb March,overgrowth occurred in April, and with Spillwayopening differed from typical seasonal 1-m'floating surface mats developing during May trends.Salinity is generallyhighest, 5 6 ppt,in and June. Novemberand generally decreases during winter TABLEl. Relativeabundance of Ciadophora on subtnersed aquatic vegetation SAV!. A =Cladophora absent P =Cladophora present OG= Cladophoraovergrowth Date Depth . FontainebleauA FontainebleauC Lacombc Pointe aux Herbes 5/30/97 0.3 m OG-Ruppia OG-Ruppia P-Ruppia No SAV 0,6 I m OG-Ruppia OG-Ruppia A A 0.91 m P-Ruppia P-Ruppia P-Ruppia A 7/3/97 0.3 rn P-Ruppia P-Ruppia P-Ruppia No SAU 0.61m P-Ruppia P-Ruppia P-Ruppia P-Ruppia 0,91 m P-Ruppia No SAV P-Najas P-Vallisneria 9/3/97 0.3 m P- Vallisneria OG-Najas P-Ruppia No SAV 0.61 m OG-Ruppia No SAV OG-Ual1isneria OG-Vali isneria 0.91 rn No SAV No SAV P-Vallisneria P-Vallisneria Ettectsof SpittwayOpening 131 andspring to a low of 2 - 3 pptin May Franciset decreaseoccurred in shallow water 0.62 m!. al.1994!. However, as demonstrated in this study, Althoughany Rtrppia present in deepwater in 1996 freshwaterconditions from local stream flow can > 0,62rn! was general! y absentin 1997,thc greatest persistf'or relati vely long periods atnorth shore SAV reductionin Rappiafoliar coverageoccurred at sites.Freshwater conditions might be regardedas intermediatedepths .31- 0.9 rn! where l 996 anexplanation for thedifferent response between coveragcswere greatest,Light availabiltty was speciesbecause Ruppia iscommon inbrackish water important,but the growth of Cladophoraon Rappia andValli sneria is commonin freshwater Orth and alsoblocked light. and may have contributedto Moore1983!. However,Rtippia also occurs in Ruppia loss in shallowwater. inlandfreshwater habitants Davis and Brinson 1980! andsurvives periodic freshwater conditions inLake The effect of waveenergy was also important. Pontchartrain Burns et al. 1993!, Rappiawith heavyCladophvra growth was found uprootedand washed ashore at Fontainebleauand Lightreduction was an important factor, A Lacombeafter storm~in April and May 1997. significantdecrease in PAR occurred ata depthof HeavyCladophora growth may make Rappia more 1 mfrom April 3 throughJuly 10, 1997. The April susceptibleto uprooting by waveenergy. Wave decreasein PAR was due to the introductionof energycould also explain Rrrppia loss from 0 0.3 MississippiRiver water that is high in suspendedrnwhere, even with Cladophora growth. light was siltand clay. Algal blooms were thc main cause of probablynot a limitingfactor, The growth of the decreasein PAR after May 1997, Values Ruppia,and Cladophora onRuppia, was dynamic averaged6.3 % ofsurface irradiance during this TableI !. Rttppiamay have been more abundant «t period,compared with an average value of 24%at FontainebleauA and C during the spring and othertimes, Minimum light requirementfor SAV summerthan during the 1996 and 1997 quantitative rangesfrom 4.4 % to29.4 % Dennisonetal. 1993!, surveys.The presence and episodic overgrowth of A minirnurnvalue of 8.2 % hashen reportedfor Cladophoraon SAVsupparts Cladophvra as a Rappiamaritirna Duarte 1991!. Minimum light causeof Ruppiadecline. requirementsfor Vallisneria are unknown, but it is anefficient carbon fixer at lowlight intensi ties Titus The cause of inore Cladophoragrowth on andAdams 1979!. Meyeret al. 943! reported Ruppiathan Vallisneria is unclear.Cladophora Vallisneriato be the most shadeadapted of five growsan Vallisrteriaand can bc abundant in areas submersedmacrophytes, and found in short-term protectedfrom waveaction. This difference in experimentsthat Vallisneria can maintain 25% of Cladophoragrowth in thelinoral zone couM be its surfacephotosynthetic rate at 0.5% of surface causedby differences in grazing activity related to light Meyer et al. 1943!.The average value of 6.3% differencesin plantmorphology However, if afterthe spillway opening may have been sufficient Vallisneriais not easilyuprooted by waveaction, to supportVallisneria, but not Rappia,This waveenergy could rernovc Cladcphora from differencein shadetolerance may have contributed Vallisneria. Weisneret al. 997! found that to the decreasein Rappia and not Vallisneria. hfyriophyllttmspicaram growth was reduced atsites However,heavy Cladophora gmwth on Rtrppia also withless wave energy due to increasedepiphyte decreasedlight availability to Rappia, Vailisneria growth. maybe able to survi velow light intensities by using energyreserves in largeroots and tubers. Tertninalgrowth in Mvriophvl andamRtrppta, butnot Vallisneria, tnay tnake new surface growth lf lightavailability was the cause of SAV pronetoalgal overgrowth. Cladophora overgrovth decline,one would expect that more SAV would onMyriophyllarn and the formation of largesurface have been lost from deeperwater. Significant matsover the plants was the primary cause of the decreasesin Rappia occurred in deeperwater ,3 1 lossof the1997 Myriophyllum bed in BayouSt. - 1.55m! at Fontainebleauand Pointe aux Herbes, John.In 1995,a Myrtophyllambed present at. th» but at Goose Point and Lacotnbe the greatest samesite also died becauseof Cladvphora 132 M A. Poirner et al overgrowthafterthe Spillway opening Burns and UrbanWaste Management and Research Cente Poimer1996!. ln LakePontchattrain, growth of Universityof New Orleans,No. 92-05, RuppiaandMyriophyllurn occursin late winter and Bnv's, J. W., Jir. Avo M. A. Pottuusii.1996 The earlyspring Burns etal, 1993!, but new growth of Restorationof SubmersedAquatic Vegetation Vallisneria occurs with increasingwater in the Lake PontchartrainF.stuary, ImuisiatuL temperaturesinApril. The earlier surface growth Final Reportto the Lake PontchartrainBasiri ofhfyriaphyllurir andRuppia may also have made Foundation,Metairie, Louisiana, themmore susceptible toCladophora fouling, CORMtat,E. S., A, Hn~irtCHS,J. SHEE~v,Avo S. SvirrH. 1992. LouisianaWater Quality Dats Conclusions Summary]990-1991. Louisiana Departtnentpf Environmental Quality. Baton Rouge, Basedon a comparisonof SAV foliar coverage Louisiana. presentin 1996and 1997, the 1997 Bonnet Carte DAvis,G. J. Avu M. M, Birnssois.1980. Responses Spillwayopening did not affect Vallisneria areal of Submersed Vascular Plant Communities to coverage.However, a significant decrease inRuppia EnvironmentalChange. Report for Fish and arealcoverage was observed, and a Myriophyllurrr Wildlife Service, Bio log ical Services, bedin BayouSt. John died, Decreasesin light Kearneysville,West Virginia. availabilityto Ruppia from blue-green algA blooms, DENt~t', W. C., R. J. OitrH, K. A. MOOnE,J. C. heavyCIadophora growth, and the uprooting of STEvENSOII',V. CARTER,S. KOLEAR, P. W. Ruppiawith heavy Cladophora growth by wave BEsosrirOM,ANti R. A, BATtvic,1993. AssesSing energyappeared to bethe main causes of Ruppia water quality with submersedaquatic decline.The loss of a Myriophyllurnbed was caused vegetation,Habitat requirements asbarometers byphytoplankton shading, Cladophora overgrowth, of ChesapeakeBay Health. BioScience 43:86- andadverse water quality from algA decomposition, 94. DORrCH,Q. AwoS. AcHEE, 1998, Lake Pontchartrain 1997AlgalBloom; Identification, Toxicity, and ACKNOWLEDGMENTS Similar Occurrences Elsewhere in Louisiana CoastalWaters. "Clean Enough' ?", p. 19. A This work wassupported by a grantfrom the ConferenceonMississippi River Water QuAity LakePontchartrain Basin Foundation JBC Project 19-20September 1997, ¹ 12! throughEPA Assistance Agreement No. X- DuARTE,C. M. 1991.Seagrass depth limits. Aquatic 996097-01-0. We alsoacknowledge the generous 8otany 40:363-377, financial supportof FreeportMcMoRan, Inc. for FirAvetS,J. C M. A. POtttntFR,D. E. BAnee,V. portionsof this work. WuEsvNnERAAM3 M. M, MtrLtNO.1994. HiStoric Trendsin theSecchi disk transparency of Lake LITERATURE CITED Pontchsrtrain,Gulf Research Reports 9'.1-16. GERTz,S. M. 1984. Biostatisticalaspects of APHA. 1992. Standard Methods for the macrophytonsampling, p. 28-35.In W M. Examinationof Water and Wastewater,18th ed. Dennisand B, Cr. Isom eds.!, EcologicA AmericanPublic Health Association, Inc., New Assessmentof Macrophyton: Collection, Use York, andMeaning of Data, ASTM STP 843. B vtrNs, J. W., Jit., M.A. PouuttFSt,ANO K .P. PREsrOtr, AmericanSociety for Testingand MateriaLs- 1993, Effects of urban runoff on the New York. environmentalquality of Lake Pontchartrain, HARLtN,M. M. 199S.Changes in majorplant groups Louisiana,p, 127,Sub-project: Effects of New followingnutrient enrichment, p. !73-188- In Orleans urban runoff on the distribution and A. J. McComb ed,!, Eutrophic Shallow structureof submerged aquatic vegetation Fstuariesand Lagoons CRC Press, Boca Raton communities'm Lake Pontchartrain,Louisiana. Florida. Effectsot SpillwayOpening 133 LNo,O. T. 1974,Handbook of CommonMethods Conferenceon Mississippi River Water Quality in Limnology.The C. V. MosbyCompany, Saint 19-20 September 1997. Louis, Missouri. Wasett, F.. B., J. A. Srttxisn, wwi J. Sws:nsTn~.1997. Maven, M .S. 1986, The submerged aquatic Mechanisms regul at in g abundance ot vegetationof the LakePontchartrain estuarine submerged vegetation in shallow eutrophic system,Louisiana. M. S.Thesis, University of lakes. Oecologt'a109:592-599. New Orleans. MevEtt,8, B., F. H. Bat.t.,L, C, TttoMesois,AtsD E, 1, CLAY.1943. Effectsof depth of immersion on apparentphotosynthesis in submersed vascular aquatics.Ecology 24:398-399. Movrz, G. N. 1978.The submergedvegetation of Lake Pontchartrain,Louisiana. Casranea 43;115-128. ORTH,R. J. ANDK. A. MoottE.1983. Chesapeake Bay:an unprecedenteddecline in submerged aquaticvegetation. Science 222:51-53, PIRRKR,M, A. ANDJ. M. KrNo.1998. Observations on LakePontchartrain blue-green algal blooms and fish kills, p. 53 In Abstractsof 4th Bi- Annual Basics of the Basin Research Symposium:Addressing the Condition of the Lake Pontchartrain. StKORA,W. B. ANDB. KJERFVE.1985. Factors influencingthe salinity regime of Lake Pontchartrain,Louisiana, a shallow coastal lagoon:Analysis of a long-term data set. Esruaries 8:170-180. Strrrxus,R.D R, M. DmNF~, axo J. H. Dmvzm. 1954.Biological Study of LakePontchartrain. AnnualReport for theYear July 1, 1953 to June 30, 1954. TulaneUniversity, Zoology Depart- ment, New Orleans, Louisiana. Trrvs, J. E. mD M, S. An~s. 1979.Coexistence and the comparative light relationsof thc submersedmacrophytes Myriophy blunt spicarumL. AndVa lisneriaamericana Michx, Oecologia40: 273-286, Trrvs,J. E. ANoW. H. Sro~+. 1982.Photosynthetic responseof two submersedrnacrophytes to dissolvedinorganic carbon concentration and pH-li rnnology and Oceanog raphy 27:151-160, Tt ONER,R. E., R. M. D~u., mDJ, Boi'o. 1980. Arealchanges in the submergedmacrophytes of LakePontchartrain Louisiana!:1954-1973. ItlorrheastGulf Science4:44-49, TvRslER,R. E., Q. DotrroH,~ N. RaBALAls.1998. Controlof Algal Populationsin Lake Pontchartrain."Clean Enough?", p. 18. In A What ls the Threat of HarrnfLII Algal Blooms in Louisiana Coastal Waters? Q. DottTcHt, M. L. PattsoNS',N. N. RABALAls-',R. E. TURNER' 'LouisianaUniversities hfart ne Consortium, 8l24 Highway56, Chauvin, LA 70344; TEL: 504-853-2821t FAX; 504-85/-2874 emaiL qdortch@lurrtcon,edu litrarine Science Departtnent, Natttra Sciences Division, University of Hawaii-Hilo, 200 W. Kawili St.; TEL: 808-974-7596:FAX 808-974-7693; email: mpars ABSTRACT: Harmful Algal Blooms HABs! have increasedworldwide, at least in part in responseto escalatingcoastal eutrvsphication. Siam nutrient inputs and eutrophicationhave increasedsaabstantially in Louisiana coastal waters, the available data on the occurrence of HABs were assembledto assessthe threat in this region. Twenty-four HAB speciesare present, rangingln effectsfrom water discoloraSon toanimal mortality. Fourtypes of toxinswhich can potentially affect human health have beendetected in algae or oysters,irtcluding brevetoxins, hepatototdns,domolc add, and okadaicacid, although no knownhuman illnesses have occurrvtd. At least two the HAB groupsproducing these toxins are stimulated by high nutrient ava0ability and others ruay be as weL ln order to k~ HAB problems from escalating in Louisiana coastal waters, it is essentialthat nutrient inputsto eoastatareas not be increased. INTRODUCT1ON visually obvious bloomsare not always necessary for deleterious impacts to occur. Thus, the term Harmful Algal Blooms HABs! refer to what HABs refersto complexphenomena defined by their used to be known as "red tides" but now include a impact rather than their appearance. greatervariety of organismsand phenomena. -Red tides" describedred waterdiscoloration, usua]l y, but There has been a global increase in both the not always,caused by dinoflagellates,some of which numbers of incidents of HABs and the type of produce toxins that cause human illness antVor fish organismsthat causethe problems Shumway 3 990; kills. Blooins are now known to rangein color from Hallegrae5l 993;ECOHAB 1995!. Severalreasons red to brown to green or blue-green and include other have been given for this increase: l! escalating a]gal groups besides dinoflage]tates and also nutrient enrichment of coastal areas, which stimu- cyanobacteria and autotrophic cil.iates. Not all lates blooms; ! growing global shipping, which b]oom organismsare harmful beyondcausing water transports organisms to new areas; ! increasing discoloration or episodic hypoxiatanoxia Further, aquacultureand mariculture,which provides micro- environments, magnifies transport opportunities, From the SymposiumRerent Rereatrh tn CaastatLouisiana: and enhances surveillance; and ! increasing tvatttrat SystemFtsnrtitrn atut Responseto Human Inft/ttenrr. numbers of scientists aware of the problem. Rozas, LP., J.A. Nymart,C.E. Proffitt, N.%. Rabalais, DJ. itecd.atttt tt E. Turocr Mttors!. l999. Publishedby Louisiana Although all four areprobable factors, it is generally SeaGrattt Collage Probata. felt that escalatingcoastal eutrophication is the main 1S5 Q. Dorich ei al. tactorand that future increases in nutrientinpuLs to by the LouisianaState Departments of Environ- coastalareas will magnify the threat. mentalQuality, Hea!th and Hospitals,or Wi!d!ife and Fisheries.Some of the data are from inicmal Nutrient inputs to Louisiana waters have agencyreports Latapie 1969. Morrison 1980 increasedto bothshe!f and estuarine environtnents Ance!etet al, 1981,Bejarano et al. 1981!and some with concomitantenhanced eutrophication Turner havebeen published Rabalais et a!. 1995;Dortch and Rahalais 1991, 1994; Rabalaiset al. 1996; et al. 1998!,but a!!are in databasesat LUMCON Parsons1996!. Redtides havebeen documented in thenorthern Gulf of Mexico Perryet a!. 1979;Perry ! Systematic,routine sampling co~ducted at 1980;Perry and McClellan 198!a, b; Eleuterius et LUMCON. Theseinclude monthlysampling ar a al. 1981;Maples 1983b, Rabalais et al., 1995!,but shelfstation 20 milessouth of Cocodriesince 1990, Louisianahas not sufferedthe dramatic impacts weeklysamp! ing «t a stationin theTerrebonne Bay observedelsewhere. In generalit hasbeen assumed estuarysince 1993, sampling during approximately that the low salinities and high turbidities of 18 cruises covering various segments of the Louisianacoastal waters prevented blooms. Several Louisianashelf since 1989 described in Dortch ci recent blooms, resulting in fish kills near the al, 1997!,and samp!ing over oyster beds east of the Louisiana/lcxasborder Robichauxet al. 1998!, MississippiRiver in conjunctionwith thcLouisiana closureof oysterbeds to commercialharvesting Departinentof Health and Hospitals Oyster Dortchet al. 1998!, and advisoriesagainst Monitoring.All of thesedata are availablc as recreationaluse of Lake Pontchartrain Dortch and databasesa LUMCON and most are available from Achee' 1998!, combined with growing public the NOAA Nutrient Enhanced Coastal Ocean awarenessof problems e!sewhere, have increased Productivity NECOP! Data Manageinent Program concernabout HABs in Louisiana coastal waters. Hendec1994! and/or the National Oceanographic Thepurpose of this paperis to compilewhat is Data Center. Some of these data have been knownabout HAB speciesand to assessthe threats published Rabalai set al. 1995;Dortch et al. 1997; thatthey pose, The long-term goa! is to determine Parsonset ak 1998in press;Robichaux et al. in whetherthe threat is severeenough to warranta press!, regular monitoring program and how that monitoringshou!d be conducted.Although the Phytoplanktonwere preserved in 0.5% g!u- focusis on Louisiana coastalwaters, pertinent taraldehyde,size fractionatedonto po!ycarbonate informationfrom other low salinity areasof the filters .2, 3, and 8 mm!, and identified andcounted northernGulf of Mexico will also be included in usingepif!uorescence microscopy Dortch et a1. this evaluation. 1997!. Someidentifications were confirmed with ScanningE!cctton Microscopy Parsons etal, 1998!. METHODS RESULTS AND DISCUSSION Thereare three sourcesfor the datacompiled in thisreport. Harmful Algal SpeciesPresent in Louisiana Coa!~~ Waters ! Publishedreports Housely 1976; Perry et aL 1979;Perry 1980; E!euterius et al. 1981;Perry Twenty-fourpotentially harmful species have andMcLe! land 198!a, b; Maples1983a, b; Rabalais been identified so far in Louisiana waters, repre- et al, 1995; Dortch et al. 1997,1998; Dortch and senting five taxonomic groups Tab!e 1!. Achee'1998; Parsons ct aL 1998;Robichaux et al. criteriafor choosingthe organismson the list are 1998!. thatthey occur in Louisianawaters and that they cause at least one of three deleterious effc«s ! Unpublishedb! oom/fish kill investigations. somewherein the world: water discoloration/ Thesewere conductedat LUMCON on samp!es hioluminescence,animal mortality, or human broughtinby individualsor as part of investigations illness,PotentiaL impacts arc givenfor eachspecies Threat Of Harmful Algal Bloorrls in Louisiana 0 tti k tw rtI Ng C0 a C I0 ~v o" C C C W C~m ~'o >~ cg ops OO~ 0'uo" ~ t 0 0 0 O 04 Q E 0 t g t C4 p tLi caphd ~ W I 0 a 8 Cl i- e o Ot 5 5 ci 0 0 CO0 ~-U j! V UUVV o>O < o~ o C ~. KpjA QAAu3 e~ o~ Hm="~ rrrtp. r/J C vl g ti Yl C K K rtt C" Ok 0 ~0 O.h.a o 0 g 0 v Ov rhea% c/l Or g!M ch ch - Li g,+~ 0 5 t.'aaa a,Ca<4< 5 Q F4 4t v ru a <. C C C 2 $~ a~ j5 ~ ~ w C4~ 0 C . k 5 4 - ~ 5 k tS 7 0 000 ooooow ohio 0 0 0 0 0 0 -oc c c c c C c 0 5 C C C C C C 5 aaaaazacg aaaaaa 8 ti 5 0 l5 0 .. P~ C p g 0 Q 00 r. tN o KBooKRp rrt 0 P P s - "0 KR~ p p O ~ 2 P. 2 P. 2 5 5 28,< 5,»=" Ql W ttt Clt o ~~o o" o /~M + C k 5 h -." B P. 2 E! P. 4t ~BEEBB e- Ch c' Wan. Waa, o 137 O. Dortch et al. Table1!: an iinpactwithout a? .signifiesthat the 1990,Ho andHodgkiss 1993!, and is in thc same impacthas been documented in Louisianawaters genuswith knownokadaic acid producers, andan impact with a? indicatesthat the impacthas not been clearly documented in Louisiana waters Suchan extensive list, includingmany bloom- or that there is some questionabout the impact fortningspecies, indicates that the low salinities and elsewhereas well. Thus, the? can have several highturbidities of Louisianacoastal waters do noi different meanings,as the following examples preventblooms. In fact,many of theorganisnts have indicate. ! Alexandriurnosrenfeldii hasonly been sufficientmotility that they canposition theinsclv e s tentativelyidentified and samplesare beingsent at the water surface, thereby avoiding any light elsewherefor confirmationbecause of the possibility limitationthat might result from the high turbiditics. thatit is toxic Steidingerand Tangen 1996!, ! Thehigh turbidities maymake it morediiTicult for kfesodiniuin rrabrurn, a ciliate with cryptomonad untrainedobservers to recognizeblooins, since symbionts,causes massive red tides in manyareas many are the color of suspendedsediment, The Lindholm 1985!, but althoughit is abundant in locationswhere the speciesare found Table 1! Louisiana waters, it has never been observed to indicatethat many are adapted to lowsalinity waters. discolor the water. ! Anabaena spp. and Even Gymnodiniumbreve, the red tide organism Microcysris spp. can produce both hepatotoxins and whichcauses major problemsin the high saliniiy neurotoxins Sivonen 1996!, but in samplesfrom waters off of Florida and Texas Tester and Louisianaon! y hepatotoxinswere tneasured Dortch Steidinger1997!, has now been found at relatively and Achee' 1998!. ! Okadaic acid has bccn low salinities off Louisiana Dortch et al, 1998 !. measuredin oystersin Louisianaand elsewhere in thenorthern Gulf of Mexico Table2!. Somespecies The long-termgoal of this researchis to of Dinophysisand many benthic/epiphytic species determinethe seasonsand places whereHarmful of Prorocenrrumproduce okadaic acid andits Algaeare likely to occur in orderto design a derivatives, which cause DSP, None of the monitoringprogratn if the frequencyof blooms p!anktonicspecies abundant in Louisianawaters is warrantsit. In Table 1, all the available information knownto produceit, but a numberhave not been aboutthe temporaland spatial occurrence of each adequatelytested. While it is possiblethat okadaic speciesis given. A? indicatesthat there is some acidinay be produced by P,rnexi canum, this benthic uncertaintyin the distribution of the organism, speciesis relativelyrare in watersamples. It i.s althoughthe uncertainty can arise from several possiblethateither one of themore abundant known causes.For example Prorocentrwn mexiconum has speciesis producingokadaic acid or thereare been identified only recently and is too rare to benthiclepiphyticspecies that are getting into water describe its distribution. In the case of Pseudo- samples. ! P.minimum is a specialcase, whose nitzrchia,the genusis easyto recognizewith light threat is difficult to assess. It causes massive red microscopy,but identifying the toxin-producing tides in a nuinberof areas,like theChesapeake Bay speciesrequires either molecular methods or SEM, Luckenbacket al. 1993!, with no immediately which we have only usedfor the last two years obviousdeleterious effects, However in Japanin Parsonsetal. 1998!, Finally, a numberof organisms 1942 bloomsled to venerupinpoisoning from are seenin low to moderateabundance all year shellfishconsumption, with many deaths Okaichi round,but a carefulquantitative analysis ofthe entire andImatomi 1979!. It hasbeen implicated as the dataset is necessaryto determinethe tiines of the causeof other less serious outbreaks of DSP-like yearwhen they are most abundant, humanillness Tangen 1983, Freudenthal andJijina 1985,Silva 1985!, but no further work has been done The color of blooins and the ocrurrence of on thehuman toxicity of thisorganism. Finally, it biolurninescenceare also indicated Table 1! siricc, maycause problems with shellfishmortality or sometimes,al! of the informationtogether can bc development Luckenback etal. 1993,Wikfors and diagnosticof theorganism present. Because many Smo«witz1995!, is sometimes associated with fish incidentsof waterdiscoloration or bioluminescence "ills Perryand McLelland 1981 b, Rabanniet al. arc not a causefor concernfrom a publichealth Throatof Harmful Algal Blooms in Louisiana perspective,it would be helpful todevelop infor- BrownTide" Stockwellet al, 1993!. A yearlong mationwhich can be used to reassure thepubhc an d studyin TerrebonneBay and the Louisianashelf helppublic officials make decisions about has shownthat the organisin is not presentin monitoring.Forexample, a bloom which discolors Louisianawaters, although it is present in Florida thewater "tomato soup" color, is bioluminescent at Lopezand Villareal, pers. comm.!, Similarly, night.and occurs inthe spring can only be Nocriluca pfiesteriapiscicida and similar organisms do not sp.,which isprobably harmless, although Ashtend nowappear to posea significantproblem in tobe absent when it is presentin largenumbers. Louisianawaters becausefew fish with the typical Mostblooms, however, will requiresome rnoni- lesionsare present, even in fish kills. However, toringto rule out organisms that are a threat. pfiesteria-likeorganisms have been isolated froni MobileBay Burkholderand Glasgow 1997! and Onedifficulty with establishinga listof sinceproblems with Pfiesteria are enhanced byhigh HarmfulAlgal species present inLouisiana coastal morganicand organic nutrient inputs Burkholder watersis thatmany are noi observedin routine andGlasgow 1997!, it is possiblethat Pftesteria- sampling.but appear to occuras sporadic blooms. likc blooinscould occur in Louisiana. Heferasignia akashi wo, Li ngulr>di niurn pa lyedrum, andMicrncysris sp. havencvcr been present and Water lNscolorationand AnitxtaiMortality Alexandrium monilatum,A. osrenfeldii, Ceratiurrr hirrus,Gynrnodinium breve, and liocriluca sp, have A number of speciesproduce large scale onlyrarely been counted during regular sainpling. bloomsin Louisianawaters that are quiteevident, Theyare either not present ut all or arebelow the evento untrainedobservers, including Alexandri unr limits of detection in our routine methods, 100 to monilarurn,A. osrenfeldii, Gymnodinium breve, G. 1000cells 1' dependingon location, time of year, sanguineum,Hetemri gnra akashiwo, Lingulodinium andprimarily, suspended particle concentration. polyedrum,and Prorocentrum minimum. Of these, Most of the samplescontaining these organisms onlyG. breve and, maybe P. minimuni, are known have been brought in as special samples by to causehuman health problems, which will be individuals or state agenciesbecause of water discussedbelow. Two othersare suspectedof discoloration, biolumincsccncc,or fish kills, and causinghuman health problems, A. ostenfeldiiand abundanceswere in therange of 1 x 10' to 1 x 10' L. polyedrum,but the evidenceis quite scant celIs 1', dependingon thc size of the organism. Rabalaiset al. 1995;Steidinger and Tangen 1996!. Bloomsmay alsocover large or small geographic However,animal inortality is well documentedfor areas.Thus, it is highlylikely that,despite our long severalofthese species, A.monilarum, G.breve, G, termsystematic sampling >4000 samples!,there sanguineum,H. akashiwo, and P. minimunr areother Harmful Algal specieswhich have not yet summarizedin TableBl in Rabalaiset al, 1995; beendetected. This problemalso magnifiesthe Dortchet al, 1998!. Themost usual inanifestatiou dNiculty of determining the spatial and temporal is fishkills, but invertebrate,bird, turtle, and marnie distributionof bloomsof a particularorganism, mammalmortality can also occur. In somecases is becausethe available information is dependenton notknown whether a toxinis producedorwhether "chanceencounters", An effort is underwayto thedeaths are due to oxygendepletion during the expand the spatial and temporal coverageof both decayof thebloom e.g. Robichaux et al. 1998!- regular samplingand 'chance encounters." Finally,more subtle ecosystem effects are also possible Smayda 1992!, For example, consumption HAS SpeciesWhich Are Not Now a Probleni of toxicalgae by larvalfish can effect recruitment althoughthis process would bc difficult to detect in Thereare several groups of organismsthat are thefield Smayda1992!. Thus, even when blooms notin Tables1 and2 becausethey maynot presently donot have a humanhealth impact, they may have bea significantproblem in Louisianawaters. Some a significantimpact on the ecosystem. estuariesinTexas have been plagued with the "Texa s 139 Q. Dortch et al. Human Health Impacts Tester and Steidinger 19971, hut its nutrient requirementshave not be exainined systematically. Four toxins, that can cause human illness and, Atthoughcoastal blooms may hc initiated h> in some cases death, have been measured either in transport events, their continuation niay hc phytoplanktonor shellfish in Louisianacoastal dependenton the availability of nutrientsin those waters Table 2!. Two of these,brevetoxins and areas. Finally, very little i» known about thc hepatotoxins,were measured during algal blooms physiologicalecology of the known okadaic acid and resulted in actions to protect public health producers,including their nutrient requirements, including closureof oysterbeds to harvestingeast because most cannot be cultured. Further, it is of the Mississippi Riverfor up to 5 monthsin 1996- impossible to determine their relationship to 1997 Dortch et «1. 1998! and issuanceof an ad- nutrients in the northern Gulf, since it is unclear visoryagainst recreational use of LakePontchattzain what speciesare producingokadaic acid. in the sumner of 1997 Dortch and Achee' 1998!. Two other~, domoic acid and okadaic acid, have Historic Changesin Harmful Algal Blooms beenmeasured during routine sampling. Evaluation of the huinanhealth implications of the occurrence The hypothesisthat increasingnutrient inpuis of all of thesetoxins requires a betterunderstanding to coastal areas has caused the increase in HABs is of thefrequency of blooms,the temporal and spatial an attractive hypothesisthat has beenvery difficult variation of their occurrence,and the factors which to test, because of the lack of historical data on causel.oxin production. At presentthere have been nutricntsand algal spccics composition. increasing no knownhuman illness or deathdue to toxicalgae eutrophicationhas been well docuinentedboth on in Louisiana. the Louisiana shelf and in estuaries, with large increasesin nutrientmputs since the 1950's Turner The abundanceof two of thetoxin-producing and Rabalais 1991, 1994; Parsons 1996} and it groupsis clearly stimulated by nutrients. The would be an excellent area to test the hypothesis. Aaabaenaspp. and Mi crocysrissp, bloomsin Lake The first tecordof an algal blooms date~io 1969 Pontchartrain in the summer of 1997 occurredafter Latapie1969!. From1969 to 1990there were 6 the diversionof high nutrientriver water intothe reports of red tides Perry 1980; Perry and Lakefor floodcontrol purposes Dortch and Achee' McLelland, 1981a; Morrison unpublished, 1980; 1998!. Analysisof algal abundanceand nutrient Ancelet et al. unpublished, 1981; Bejarano ci al. dataindicate that increasedavailability of nitmgen unpublished,1981; Eleuterius et al. 1981;Maples andphosphorus stimulated the blooinand that 1983b!and after 1990there are 18 reports.The nitrogenlimitation ettdedthe bloom. A similar apparentincrease in frequencymay, however, be blooin occurred in 1995 when river water leaked duesolely to increasednumbers of observers e.p. intothe Lake andlocal runoffwas high Dortchand LUMCON, startingin 1989!. Achee'1998!. Pseudo-riirzschia spp. abundance on the shelf reachessome of the highestlevels ever The only groupfor whichthere are pood observedanywhere in the world in theplurne of the historical data is the diatom species Pseudo- MississippiRiver during peak river flow Dortchet nitzschia,in whichsome species produce domoic ah1997!, suggesting nutrient stimulation. Now that acidwhich causes ASF. Studiesconducted in 195S- individualspecies can be identifiedon a routine 1957 {Simmonsand Thomas 1962!, 1972-1974 basis Scholinet al. 1994; Parsonset al. 1998!, it Fucikand El-Sayed 1979!, and 1990-1994 Dortch willbe possible to determine how nutrients stiinulatc et al. 1997!are directly comparable and showa 1 argc growthand toxicity of each species, Elsewhere, increasein the abundanceof this genus since the bloomsof this groupare stimulatedby nutrients 1950's Rabalais et al. 1996;Dortch et al. 1997!, Dortchet at. 1997;Fryxell et al. 1997!, Forthe Becauseit is thoughtthat growth of this pn!upof othertwo groups, the role of nutrientsis notclear, organisinsis stimulatedby nutrients,the increase Physicaltransport isthe mechanism most fmqucntty canbe attributedto incre-asingnutrient inputs since cited as leadingto Gymnodiniumbreve blootns thattime. Investigationsof algalremains preset ved Threatof Harinfu! Algal Blooms in Louisiana 140 Table2. Sumsssssyyofoutbreaks oftoxic algae with human health impacts in the low salinity waters of the northera CuIf of Mexico. Brevetordtssin Oysters Neurotoxic Shellfish Poisoniug, NSP! Gyrrrrrodinr rrmbreve Dortch et al. 1998! Fail, ]996 in Louisiana,Mississippi, Alabama coastalwaters Oyster bedsclosed for harvestfor 1 to 5 months First confirmed bloom in low salinity waters Cornmori HAB speciesin Gulf of Mexico Testerand Steidinger 1997! Normally occursat high salinities Causes fish kill» and humanrespiratory problems aswell as NSP Link to nutrientinputs unclear, but beingre-e valuated ~ CyanobaeterialHepatotoxins in Phytoptauktou A rrabaerrcispp. and Mr'crucysrissp. Dortch and Achee' 1998! Strmrner, 1997, Lake Pontchartrain Probably resultedfrom increasednutrients due to diversionof MississippiRiver water Ad visory issuedagainst recreational use Present in other fresh and very low salinity water bodiesin Louisiana Lake Pontchartrainbloom Ju]y ]995 Lake Salvadorebloom January ]995 Lake BorgneJuly/August 1997 B]oom» of cyanobacteriaand impacts increasing worldwide due to eutrophication Pearl 1996! ~ Domoic Ac]re in Phytophsnkton Amuesie Shellfish Poisoning,ASP! Pseudo-rrircrrhia spp. At ]east 4 toxin-producingspecies Parsonset al. 1998! High cellular domoic acid concentrationsmeasured Doucetteet al. 1997! All coastal and shelf waters Dortch et al. ]997; Parsonset al. 1998! Most abundantin winter in estuaryand in spring/fall on shelf On shelf peakin abundancecorresponds to peakin riverflow Link with nutrient inputs irr Louisiana and elsewhere Dortch et al. 1997! ~ Okadaic Acid ln Oysters D]rsrrheticShellfish Poison]ng, DSP! Measured at 2 locations in Northern Gulf of Mexico Mobi]e Bay, Fa]], 1990 Dickey et al. ]992! Terrcbonne Bay, Jan,-Mar, 1995 Dickey, pers, comm.! No species clearlylinked to eitheroccurrence Dine p/iysiscarrdara and Pmmcerrrrrrm spp. frequently present but noneshown definitively to produceokadaic acid / ~rrr cerrrrrrrrrrrrexi radiumknown okadaic acid producer,rare]y present ]» ot Possibleto eva]uatelink to nutrients at present 141 O. Dortch et al iri sedimentsare being usedto directly testthe link DtctcEv, R. W., G. A. FRvxwL, H. R. Gtt+~wtu:,. Fuctx,K. w., ANDS. Z. EL-SAYED,1979. Effect of speciesin thecoastal and estuarine waters of oilproduction anddrilling operations onthe Louisiana,USA, p. 184-187. In B. Reguera ecologyof phytoplankin on the OEI study J, Blanco,M. L, Fernandez,and T. Wyatt eds,! area.RI'ce Uni versity Studies 65;325-353. Hartnful Algae. junta de Galicia an4 HALLEORAEFE,G. M. 1993, A reviewOf harmful IntergovernmentalOceanographic Commis algalblooms and their apparent global in- sionof UNESCO,GRAFIS ANT, Santiago de crease,Phycologia 32;79-99, Compostel a, Spain. XENDEE.J.C, 1994. Data managetnentfOr the PEARL,H. W. 1996, A COmparisonof cyanObaeterial NutrientEnhanced Coastal Ocean Pmductivity bloom dynamics in freshwater, estuarineand Program.Estuaries 17:900-903. marineenvironments, Phycologia 35: 25-35, HOUSLEY,H. L. 1976.Distribution, periodicity, and PERRY,H. M. 1980. Dinoflagellateblooms occur identiftcationofthe phytoplankton inthe Bay off Loutstana. Coastal Oceanographyand of St,Louis, Mississippi, and the Northeastern CltmatologyNews 3.3. Gulf of Mexico. Ph.D. Dissertation,Univer- PERRY,H. M. ANDJ. A, MCLELLAND.1981a. First sityof SouthernMississippi, Hattiesburg, MS, recordedobservance of the dinoflagellate 208 pp. Prorocentrum minimum Pavillard! Schiller LINDHoLM,T, 1985. Mesodinium rubrum a unique 1933 in Mississippi Sound and adjacent photosyntheticciliate. Advancesin Aquatic waters.Gulf ResearchReports 7:83-85. Microbiology3:1-48, PEMtv,H, M. ANDJ. A. MCLELLAND.198 lb. Blooms LIICXENBACII.M. W., K. G. SELLrm S, E. SHutevAY, contmue to cause red tides in coastal waters AND K. GREEN. 1993. EffeCtS Of two bloOm- of Mississippi.Coastal Oceanography and fornungdinoflagellates, Frorocentrum mini- ClimatologyNews 4:1-2. mum and Gyrodiniumuncatenum, on the PERRY,H. M., K, C. STttcx,AND H. D, HowsE, 1979, growth and survivalof the easternoyster, Firstrecord of a blootnof Gonyaularmani lata Crassostreavirginica Gmelin 17911, Journal in coastalwaters of Mississippi.Gulf Research nf Shellfi sh Reseatch 12:411-415. Reports6: 31 3-316. M*vt.es, R, S., M, D, CauzE, AND R, DDNAIIDE. RABALAIs,N.N., Q. DORTCH,D, JUSTICE,M. B. KILoeu, l 983a,Observations on "RedTide" organisms P. L. KLERxs,P, H, TEMPLET,R. E, TuRNER,B. in coastal waters of southwestern Louisiana. CoLE,D. Duper,M. BEAcHAvI,S. LENm,M. Northeast Gulf Science 6:157-160. PARsoNs,S. RABAI.AIS,AND R, ROBICIIAux. MAvLEs, R.. R. DoNAIIoE AND G. J. FISTER. 1983b. 1995. Statusand Trends of Eutrophication, Seasonalvariability of chlorophyll a in the PathogenContamination, and Toxic Sub- nearshore marine waters of southwestern stances in the Barataria and Terrebonne Louisiana. Proceedingsof the Louisiana EstuarineSystem. BTNEP Publ.No. 22, Academy of Sciences46:53-55. Barataria- Terrebonne National Estuarv OKAIctn,T., ANDY, IMATDNII.1979. Toxicityof Program,Thibodaux, Louisiana, 265 pp. plus Prorocentrum minimum var. Mariae- Appendices. Lebouriaeassumed to be causativeagent of RABALAIs,N.N., R.E. TuRN~,D. JusTIc,Q. DDIITcII short-neckedclam poisorung, p. 385-386. In WJ,WtsEMAN, Ja., ANm B.K. SEN GLVrA. 1996. D. L, Taylorand H. H. Seliger eds.!Toxic Nutrientchanges in the Mississippi River and Dinoflagel late Blooms, Elsevier/North systemresponses onthe adjacent continental Holland, New York, shelf. Estuaries 19:386-407. PARsoNs,M. L, 1996.Paleoindicators of changing RABBANI,M. M, ATIqu-uR-REHMAN,AND E- water conditions in Louisiana estuaries. Ph.D. HARMs,1990. MaSS mOrtality offiShCs cauSed Dissertation,Louisiana State University, B aton by dinoflagellatebloom in GwadarBay. Rouge,LA, 302pp. southwesternPakistan, pp. 209-214. In E.M. PARSONs,M.L., Q, DORTcN,AND G.A. FRYxELL, 1998, Cosper,V.M Bricelj,and E J.Carpenter eds-!, A multi-year study of the presence ofpotential Novel PhytoplanktonBlooms Spring~~- domoicacid-producing Pseudo-nit-schia Verlag,Berlin. 143 Q. Dortch et al. ROa!cHAvx, R., Q. DORTcrl.ANTi J,H, WRENN. In TANGEN,K. 1983, Shellfishpoisoning and ihc press, Occurrenceof Gymnndiniumsan- occurrenceof potentially toxic dinofl ageI!ates guineum in Louisiana and Texas coastal in Norwegianwaters, Sarsia 68:! -7. waters, 1989-1994. In R. Zimmerman ed,!, TESTER,P. A., AN» K, A. STErnrNor:R. 1997. Characteristics and Causes of Texas Marine Gymnodinium Irrer e red tide blo Ho, K. C. ~ I. J. HoDGKISS,1993. The occurrence and environmentalsignificance of red tides causedby Prorocentrurnrnininuun Pavillard!. Presented at Sixth International Conference on Toxic Marine Phytoplankton, Oct. 18-22, 1993, Nantes, France. L~~iE, R. 1969. Fish kill of June 16, 1969, near EmpireCanal rock jetty. SpecialReport of Louisiana Wild Life and Fisheries Commis- sion Source: R. Ancelet, Marine Fisheries Division, Louisiana Departmentof Wildlife and Fisheries, 1600 Canal St., New Orleans, LA 70112!. LopEz, T,, Environmental Sciences Department, University of Massachusetts-Boston,100 Momsey Blvd, Boston,MA 02125-3393and T. Villareal, University of Texas Marine Laboratory, Port Aransas, TX. MoRRisoN,T. 1980, Fish kil} in Bayou Lafourche. Memorandumto Mr, Harry Schafer,Chief, Seafood Division, Louisiana Department of Wildlife and Fisheries. Source: Jim Hanifen, Marine Fisheries Division, Louisiana Departmentof Wildlife and Fisheries,2000 Quail Dr., Baton Rouge,LA 70898!. Nitrogen Losses in Water FlowingThrough Louisiana Swamps R, EUGENE TURNER CoastalEcology 1nstitute and Deparrntent of Oceanographv and C ttasral Science» Louisiana Slate Universiry Baton Rouge, Louisiana 70803 USA TEL 225-388-6454 FAX 225-388-6326 email: eutu me@''lsu.edu ABSTRACT: A comparisonwas made of rutrogenconcentrations entering and leaving two ecosystemswith well-defined input and outlet channels: l! the Atchafalayo River basin, a relatively natural and large ,662 km'! alluvial swamp receivingabout one-third of the MississippiRiver discharge,and, ! the 8onnetCarre spillway,a 13~ ha flood peak reduction spillway near New Orleans.Six percentof the total nitrogenwas removed from the Atchafalaya River during the transit downstreamthrough the basin.D sso vcdnitrate concentrat on,a major constituent of concern, remains essentially unchanged +4%! l'rom upstream to downstream monitoring stations. Tbe Bonnet Carrc spillway discharge resulted in a comparativelylow total uitregenloading rate of < 0.01g N m' d' and inconsistentpatterns in uptakeand releaseamong the nitrogenForms. The uptakeof nitratein 7 of0 examples,contrasted with the net releaseof TK.'t and TN, in S of6 and of 4 of6 examples,respectively. Them wasa generalinverse relationship between the amount of nitrogenretained and loading rates. These results were comparvntito literature valuesfor sewagetreatment systemsand otherswamps. Natural andalluvhd swamp Forests retain a muchsmaller atnount of these elementsflooding them than do wetlandwastewater flowing overland or belowground.The low retention rates for theselarge natural systemsis attributed to the relatively low nutrient concentrationcompared to sewagetreatment systems, the short duration of the overlandflow weeks!,large sixe,and the generalahsence of belowgroundflow. Diverting mainstem MbtshnippiRiver water through a floodcontrol spillway part of a proposedwetland restoration project!wiH apparently remove a relativelyinsigniTicant amount oF the total nitrogen loading. Thereduction of overhankfloodin fromflood protection levees did not significantly diminish nutrient loading to the continentalshelf. Keywords:wetland, nutrient cycling, nitrogen, overland flow, swamp, louisiana, nitrogen, phosphorus. suspendedsediments Introduction Nixon and Lee 19g6! and potential nitrogen reduction rates lnay range 10 fold over a 20 nC ti'aterquality may changewhen water flows temperaturerange Fig. 13-10 in Kadlecand Knight t"roughor over wetlandsbecause of the various ]996!, The effects of variation in the hydrologic diverseelemental pathways and ecological pro- regimeare quite robustand pervasiveacross all cessesintegrating water fluxes with the wetland wetland types. For wastewater treatmentsystems, structttre.Forexample, the nitrogen assimilation rate which are especially well docutnented,there are fornatural vegetatiOn ranges from 0. 1 tO2 kgha' d' severalaspects that are particularly important and interrelated:constituent concentration. loading rates, Font the SymposiumRecent Research in CoastalL>ttisiana: retention time, and water depth Kad lee and Knight +aturatSystem r'uttctiott and Resrtonseto Humanrefluenc. 1996!. The nutrient quality and loading rates in outs.L>., J.A. Nyman, C.E. pro fitt, V.N, Rabelais, D J. Reed, relatively undisturbednatural systemsarc usual ! d R 1:.Turner editors!. l 999. publishedby Loutsiana Sea quitedifferent from that of wetlandwaster,atcr ratttCollege program. ]45 t46 R. E. Turner ~nt systerrts.The former spread comparatively duringunusually high flood stagesthrough a low concerttrationnutrients in largevolumes over spillway and into the Atchafa!aya basin. These !argeareas; the !atterinvolve engineered systems actions are meant to reduce water heights oversrnallez areas typicallyless than 2 ha!and at downstream,especially for the benefitof thecity nutrient concentrations typical of sewage, of New Orleans, which is most!y at sea level, or agricu!turn!runoff, or indusnia!sources. Economic below, considerationsand predictability are the major concernsof wastewatertreatment systems, not The BonnetCnrre Spil!way tlatural sy stetrus, The Bonnet Carry Spillway Fig. !! diverts 1 evaluated thesedifferences in water flo wing MississippiRiver waterinto Lake Pontchartrain intoand out of naturaland engineered systems using duringexceptiona!iy high water.The 1,325 ha water quality data from a large swamp the spil!way was completed in 193]and is locatedabout Atchafalayaswamp, southLouisiana, USA! andan 33 miles 9 km! upstreamfrom New Orleanson alluvialfloodp!ain spillway Bonnet Carre, near the!eft descending bank. The spillway'sdesigned New Orleans!, and also data for wastewater capacityis 7080 m'sec'and was used to reducethe treatment systems from the North American floodwaterheights in 1937,1945, 1950, 1973, 1975, WetlandTreatment SystemData Base NAWTDB! 1979, 19S3and 1997.There is a proposalfor an and Danish Wetland TreatmentSystem Database additiona!spillway of 10,000ha to divert256 nr' DWTSD! summarizedin Kadlecand Knight ! 996!. sec ' into the watershed Day !997!. Another In the process, I describethe low percentageof diversionis proposed and authorized,but without nutrient retention for a natural riverine swamp approval;Connor ! 996!whose design and operation system.These data arethen usedto estimatethe scheduleis known as the New General Design nitrogen retention rates for a proposedriver Memorandum NGDM; conducted after a re- diversion near New Orleans. analysisin 1996!.The proposed diversion schedu!e in the NGDM proposesan average monthly flow of Site Deser!pt!ons 546, 850, 612, and 122 m' sec' during February, The Atchafa!aya Swamp The Atchafalaya River forms from the confluence of the Red River and the one-thirdof the MississippiRiver that is divertedinto the AtchafalayaBasin near St. Francisvi!!e. LA Fig. !!, Thereare no permanent settlementswithin the depressionalbasin that is almostentirely an a!luvial s warrlp.Towns located on the edgeof the basin whosedrainage enters the basin ha ve a total population estimated to be less than 100,000. The 4,662 km'-swamp basin is a reservedfor occasiona! use as a floodway. Con- structedlevees on both sidesof the main channelconstrain waterto a largelynorth o southflow. F1oodwater does not flow over these constructed le vees and out of the basin.Additional amountsof water from the Mississippi Riverare diverted Fig. 1.The locan on of placesmentioned in thetext. nitrogenLosses During Overland Flow 147 March, April and October, respectively. The Fertilizeruse within the basinon agricultural spillwaywould be operatedin perpetuity,The landis certainly less than 10% of theba.sin's surface purposeof thesediversions is to influencethe area based on an inspection of aerialphotographs 1, salinitvregime in thereceiving watersand perhaps but the preCiSepercentage ls not avai}able.1 positivelyaffect fisheries and wildlife habitat, estimatedthe fertilizer input to thebasin by using restoreand create wetland habitats. These projects anaverage fertilizer use for croplandin theGulf of haveunclear or scicntiflcallycontentious effects on Mexicowatersheds for l 987 Turnerand Rabalais wetlandrestoration Turner 1997! and swamp forest 1999!and applying this to 10%of the basin's area productivity Megonigalct al, 1997!.If such diversions could reduce the concentration of Waterfrotn the Mississippi Riverleaks into the nitrogenand other nutricnts in waterflowing over BonnetCarrc spillway whe> the riverstagerises thembefore reaching the lake,then the occasional abovethe river leveeat the spillway structure.The noxiousand dramaticalgal bloomssustained by volutneof thisleakage is enipiricallyrelated to the nutrientsreaching the laketnight be lessof a threat, heightof theriver, and describedby an equation andthe projectappear more appealing. A central developedby theNew rleans District,US Army questionof this analysis is howmuch nitrogen could Corpsof Engineers,Water sampleswere collected beremoved frotn overlyingwaters during an average withinthe spillway at two placesduring two leakage diversionand with how much land area. periodslasting 3 to 4 weeks each.One sampling location was on a road running parallel to the Methods spillway,near where riverwater entersthe spillway. The other location was at the railway crossing just I analyzeddata from monthlywater quality beforewater leavesthe spillway and entersLake monitoringstations at the upstream northern! end Pontchartrain Figure 1! Sampleswere collected 8 of thebasin at Sirrunesport,LA, andalso at the timesin spring,1998, at dischargesranging from downstream southetn! end southof Morgan City, 9.4 to 55.5 m' sec . These satrtpleswerc frozen and LA Fig. I!. Bothcities hada populationof less later analyzedfor dissolved inorganic and organic than 15,000 in 1990. The samplingprogram is constituentsusing EPA Methods 350,1,350.2, and organizedby the Departmentof Environmental 353,2. Quality,State of Louisiana,Data for various forms of nitrogenwere for monthly satnpling trips, which The North Atnerican wetland TreatmentSystem wereusually within a fewdays of each other. Water Data Base NAWTDB! and Danish Wetland takesless than 7 daysto travelfrom Sinunesport to TreatmentSystem Database DWTSD 1 summarized MorganCity during normal river stages. I used data in Kadlecand Knight 996! include information fromthese two stationsto cotnpletea comparison onnutrient loading rates, concentrauon, volume, and of theconcentrations of variousforms of nitrogen other pertinentinformatiott for 189 wastewater for thcperiod 1980 o 1993.Subsets of thedata were treatmentsystetns in North America and Europe. compiledthat includedonly data for whenthe These data were compared with the nitrogen A'tchafalaya.River would be out of itstnain channel, removalrates for the Atchafalaya basin developed The nitrogenloading rate frotn the human popu- in thispaper, and other ex ample s for Louisianafrotn lationliving the Atchafalaya was estimated at 4.4 literature sources, kgN y' byusing per capita estimates Vollenweider 1968; cited in Howarth et al. 1996! and a rather Kadlecand Kmght 996; Example 13-1.page generouspopulation estimate of 100,000persons 437!provide a simpleformula to estimal.ethe land ltv»g within and aroundthe basin. An average necessaryto retnovc various percentages of total di«bargefor the Atchafalaya River of 17,545tn' nitrogenin watersflowing over wetlands.Th>s s 'was used to calculate average loading rates. which formulawas applied by usingan averagetotal is theaverage 1980 to 1990flow measured by the nitrogenconcentration iri the MississippiRi>er USGeological Survey at Simmesport,Louisiana. from 1980to 1990!. 14g R. E. Turner noticeablyfrom upstreamto downstreamlocations, andthe paired samples show a slightincrease %! at MorganCity. The total nitrogenconcentration AtehafalayaBaaljtt decreasesslightly %!, primarily becausethe A comparisonof the concentration of nitrate, Kjeldahlnitrogen concentration isreduced by 14% Kjeldahlnitrogen and total nitrogen Kjeldahl There was no difference in the result if the data set iutrogen+nitrate! atthe upstream Siminesport! and wasconstrained to samples taken during flood stage downstream Morgan City! monitoring stations is or below flood stage. shownin Fig.2. Table1 providesthe average concentrationsforall years and the ratio of nutrients The contribution of sewerage from the atthe upstream and downstream station for paired populationinthe basin .4 kg N y' perperson! is samples,The nitrate concentrations donot change only0.07% of the totalnitrogen flux throughthe basin, and thus cannot be the source of the excess nitratedownstreain. If all fertilizer applied in the basin was leached as nitrate into the river, then that loadingwould equal about 1 %of the nitrateflowing intothe basin's northern end. This is certainlya high estimate,because not all of the appliedfertilizer will enterthe river, Howarth et al. 996!, for example, estiinated that only about 20% of the applied fertilizer nitrogenends up asnitrate in largertvers, Theapptoximate 4 % gain in nitratein water passing throughthe swamp, not statistically significant, does notappear to be a resultof nitrateadditions from sewerageor fertilizerreleased into the basin. 0 0 Thetotal nitrogen loading for theAtchafalaya Upstrearm basinwas calculated using an averageflow and concentration.This value was compared to loadings for thewastewater treatment systems listed in the NAWTDBand DWTSD Fig.3!. Theconcentration of TN enteringthe Atchafalaya River basin is about at 1.75mg N 1'. ThcTN loadto theAtchafalaya Basinis about0.38 g N m d '. Theproposed diversionthrough 10,000 ha of a proposednew BonnetCarre diversion will resultin a TN loadof 0.39g N m d '. Comparedto the NAWTDB and DWTSD systems,the naturaloverland flow systetn in theAtchafalaya basin represents ahigh load for a surfaceflow system but low load for a subsurface flow system!,and has a relativelylow inflow 0 0 1 2 3 concentration.Thisis an important observation, for Upslream it revealsdistinctions between the hydrology of engiiieeredwastewater systems and natural syst" Fig. 2. Theconcentration of nitrate and total nitrogen TheAtchafalaya basin loading rates are relatively totalKjeldahl nitrogen + nitrate;mg 1'! at Simmesport,Louisiana upstream! and Morgan City. high,although for water with relativelylow nitrogen Louisiana downstream!.The data arefrom 1980 concentrations,because the water dischargeis to 1993 and are collected ona niostlymonthly basis. relauvelyhigh. Further, there is generallyan inverse A polynomial fit of the data is shown. relationshipbetween the percentage of nutrients NitrogenLosses Dunng Overland Flow 149 Table1. The concentration ofnutrients rng 1'! in the Atchafalaya River at Qmmesport LA upstream! andMorgan City, LA downstream!for 1980to 1993.Data are from various agency water qualitv monitoringrecords the numbers in theparentheses isfor the sample size n! and +1 stant}ard error; nSX.!.The column for 'Change'is for thedifference inthe average values for paired samples the numberof paired samplesis in parentheses!, 8 iintnesport MorganCity Change upstreatn! 'downstream! percent! Total Kjcldahl Nitrogen TV V! 0.90 0.77 -14% mg N 1 '! 97/0.030! 21/0.019! 89! Nitrate NO,! 0,86 0,90 +4% mg N 1 '! 99/0,040! 18/0.036! 89! TotalNitrogen TN = TKN+ VO3! 1.79 -6+ tng N 1'! 92/0.053! l 925/0.047! retainedwithin a systemand loadingrates. because keyeco/ogical pathways become saturated at high 100 loadingrates, Wastewater managers, for example. design and operate their systems to avoid the ineNicienciesof highloading rates. 18 The total nitrogen load for surface water tto wastewatertreatment systems and the removal rate areshown in Fig. 4 forthe NAWTDB andDWTSD Z andthe Atchafalayabasin. The uptakerates for thc I basinare clearly verylow in comparisonto the 1 engineeredsystems. The averageloss of nitrogen leaving the AtchafalayaRiver basin .02 g N m -'d'! is about .1 one-halfthc averagefertilizer application rate for 001 .81 .1 1 10 croplandinthe Gulf of Mexico estuarine watershed TN load {gNm ~ d ! .013 g Nm -d ' '; Turnerand Rabalais 1999!. Thus thenitrogen retained by the ecosystem, although a lowpercentage of the total amount flowing through Fig.3. Therelationship between thc total nitrogen thesystem, can be a relativelysignificant nutrient TN!concentration mg N 1 '!in theinflow and outflow of surface flow wetland waste water treatinent sourceif theecosystem is nitrogenlimited. systemscompared to theTN load g N m d'!. The dataare from Kadlec and Knight 996!. The Bonnet Carre concentrationof TN enteringthe Atchafalaya River basinis about1.75 mg N 1'. TheTN loadto the A plat of the percentretention of nitrate, AtchafalayaBasin is about0.38 g > m.=d-' andthe Kjeldahlnitrogen, and total nitrogen Kjeldahl ptuposeddiversion through 10,000 ha of a newBonnet Carr6diversion will result in a TS load of 0.39 g V m nitrogen+ nitrate}versus water volume flawing d' markedwith an 'X' in the figurc!. acrossthe Bonnet Carre is in Fig. 5. The spillway 150 R. E. Turner is y 1 Std. Dev. CMS 28 2 19.2 % TKN loss -85.1 88 % TN loss -12.8 31.2 % Nits'.te loss 18.5 17.5 00 0 -50 .01.01 Thl load gNrn~ 4 ! -150 Fig 4. Thetotal nitrogen TN! loadlg N m s d'! for -200 surfacewater wastewater treatment systems and the 0 10 20 30 40 50 60 uptakerate g N rn ' -d'!. The dataare from the CMS NAWTDB andDWTSD presentedin Kadlec and Knight ! 996!. The TN loadfor theAtchafa!aya and Fig. 5. The relationshipbetween nutrient retention proposedBonnet Carr6 is 0.38 and0.39, respectively, total Kjeldahl nitrogen TKN'!, total nitrogen TN!, g N m - d'! The removal ratefor theAtchafalaya and nitrate! andthe dischargevolume m' sec'; CMS! systemis 6% of the total N load,or 0,019 g N m ' d '! of Mississippi River waterleaking through the Bonnet and shownwith ao 'X' on thefigure. Carry spiHwayin spring.1998. Negativereduction means that there was a net release. The mean i 1 Standard Deviation are shown for the variables. dischargeresu!ted in a comparativelylow nitrogen PmposedBonstet Carre River Diversions loadingrate of 0.01 g N in ' d'. The uptakeof nitrate in 7 of 8 examples,contrasted with the net A graph preparedby Richardsonand Nichols release of TKN and TN in 5 of 6, and in 4 of 6 985! hasbeen used to estimate the area necessary examples,respective 1 y.There was a generalincrease o remove50% of thenitrogen load from a proposed in retentionwith lower loadingrates. This inverse diversion of Mississippi River into Lake relationshipbe weennutrient retention and nutrient Pontchartrain Day 1997!. The average loadingrate is commonly described in the literature. concentrationof nitrogenin the MississippiRiver What is not generallyappreciated is that some rng I'! andthe proposed diversion amount C S! natural overland f!ow systemsrelease nutrients, were used to estimate that 10,000 ha were needed ratherthan take them up. Devitoet al, 989!, for to reachthe loadingrate g N m ' y'! where50% of example,reported that iiitrogen retention rates for the nitrogen was retained in the Richardson and five Ontariowetlands were insignificant to negative, Nichols 985! graph,The graphRichardson and and Sorannoet al. 996! showedthat some alluvial Nichols 985! usedwas basedon data presented systeinsmay release phosphorus. The landscape by Nichols !983! that showedthe relationship scale is important,too. Arheimer and Wittgren betweenthe percentagenitrogen removed during 994!, makethe point that nitrogen removal over!andflow and the loadingrate of wastewater efficiencyper area tends to decrease with increasing sewerage secondaryeffluent! over 'natura!' watershedsize. In somecases, what appears to be freshwater wetlands. Nichols 983! nicely denitrification,may be Oleresult of groundwater summarizedthe data andoffered exainples of net dilution e,g., Pinay et a!. ! 998!, uptakeand release of nutrientsthat depended on hydrologicflows, nutrientloading history, and soil NitrogenLosses Dunng Qverland Flow 151 chemistry.The original data used by Nichols 983! swampinitially droppedand then bcgaii to rise, werc based on g temperate and 1 Florida wetlands especially«mrnonium. However, thc avcragc of all thatwere in peatsoils i.e., nonehad the inorganic measurementsof total nitrogen and phosphorus mineral»of the MississippiRiver!. The datawerc concentrationat 8 stationswithin the swamp werc from 1977 or earlier, and most data were for the essentiallyidentical, indicating that there was no periodof tnaxirnurnvegetative growth. The Nicho}s net loss in these two elements. Kcmp and Day's 983! data set ruight be used to providea estimateof thcnet loss of TN andTP wasexplained preliminaryestimate of thcnitrogen retnoval rates asthe resultof atmosphericdeposition. which was for a proposedMississippi River diversion.but estimatedwith iri situsampling, The average total further analysis seetned useful for when one nitrogenconcentration in the swatnp water was considersthe cost of the proposedBonnet Cams about1 tng1 ',and in therainfall. 0,35 mg 1 '. The diversion $US 214 million!. I used the data logicof addingthe TN andTP weightin rain, but generatedhere to provide an alternative estimate of not the volume in rainfall was incorrect incom- therelationship betweenthe loadingand retnoval plete!mathematical.summation of inputs. TheTN of nitrogenfor the projectarea. andTP arrivesin a lowerconcentration in rainwater thanin thereceiving water, so thc additionof TV A nitrogenbudget was prepared for theDes and TP as rainwater should dilute thc.cwamp water AllemandsSwamp by Kemp and Day 9R5! that concentration.Further, they did not considerthe has data that could be used to estimate the net amountof TN and TP that was intercepted by amountof nitrogenand phosphorus retained as water vegetationbefore it reachedthe swamp water. ln flowedthrough a swampsystem, The nitrateand effect,there was no net TN or TP uptake. There ammoniumconcentration water flowing through the mayeven have been a netrelease of TN andTP as waterflowed into andout of the study area. These datawere compared to thosecoflected during an experitnentalrelease of river waterthrough the BonnetCarry spillway, There was negligible uptake of either nitrogenor phosphorusduring various MississippiRiver diversions into LakePontchattrain Demchecketal. 1996!.The data generated by the analysisfor theAtchafalaya basin have a lower retentionrate and a higher loadingrate. A com- parisonof thesedata with those of Nicho]s 983! suggeststhat a 20%reduction innitrogen loading is posstblefor a BonnetCarre diversionwith spillwayof 100,000ha. However, the analysis of short-term releasesof waterover the existing Bonnet 0.00i 0.0 i 0, I 1 fG Carrespillway suggests that thc n.itrogenuptake in divertedwater may be negligible,or, if it occur;, N Load NNtn d ! will be at very,very low loadingrates Fig.6. The relationshipbetween the percentage reductionand loading rates for TN for several Kadlecand Knight 996; example 13-1, page Louisianaoverland flow swampcmites filled circles!, 4371provide a formu!a thattnay be usc-d to estimate wastewatersystetns of natural peat soils unfilled the land area necessaryto remove nitrogen at squates!and leakage through the Bonnet Carte spillwayin 199R unfilled cire! es!. Data ate frotn this differentretention percentages in surfaceflow over study Atchafalaya basin!, the Bonnet C~ spillway wetlandwastewater treatment systetns. Kadlec and Demchecket al. l 996;data col!ected as patt of this Knight 996! tnakethe point with this formula, study!,Nichols 983! and from Day and Kemp 9R5!. whichis empiricallyderived, that overlandflow A linearfit of thetransfortned data is shown,together systemsoperating at the lower concentrations e.g.. with the 95% confidence intervals for each data set. naturalsystems! behave differently than waste w ater Negativeteducuon means that there was a netrelease. 152 R. E. Turner treatmentsystems, I changed one input variable to beforeengineering works Kesel 1988!.Therefore, useit, because the background ratethat Kadlec and a 6 % reductionin the total mtrogenload fromTable Knightused .5 mgN 1 '!was higher than after the I! in the= 3%of theriverwater no longer flowing targeted50% reductionin the proposednew overlandis a very small changein the nitrogen diversion i.e., it waschanged from the observed loadingto the sea. The results of theseanalyses do I 76 toO,gg mg N l 'l.In other words, the formula not supportthe view that constraining the suggeststhat a 50% reductionin nitrogencannot be MississippiRiver by flood protection levees caused achieved at the existing conditions, lf the low oxygenzones to form offshore,or lastlonger, backgroundrate is loweredto 0.75 mg N 1', then or be more severe. thearea necessary toachicvc a 50%reduction in TN is I 29,605 ha. A 25% reductionin TN load and Conclusions a 1.25 mg N 1' backgroundconcentration would require106,450 ha using the satnc assumptions. Thenitrogen loading rates of thealluvial system examined here arc relatively high, but the N % Thereis clearlya lowerretention rate fol' river- retentionand nitrogen concentration are relatively water flowing over riverine swampsthan for inuch lower than observed for wastewater treattnent wastewaterflowing over and ihrough peaty wetlands systemswith surface flows. Estimatesof nitrogen Fig. 6!, A plausibleexplanation for this difference removalrates for naturalsystems that are based on is that the peaty systctnshave more of the nutrient wastewatertreattnent systems are thereforeinappro- loadflowing belowground,compared to thealluvial priate.Peaty wetland systems seem to have a inuch systems,and thereforea highernitrogen retention higherrate of nitrogenretention than afluvial rate systems,which may release nitrogen during flooding eventsof a few weeks,or less.The prospectsthat a Furthermore,the natural systems have a rela- significant percentuptake of nitrogen as water tively very low nutrientconcenu ation compared to flowingover large man-made diversion spillways that in wastewater, which makes the uptake will occurarc unsubstantiated, if not rejected.The mechanismsin the soilless efficient at strippingout meagerlevels of nitrogenretention that will occur elements from the overlying water. if thesediversions are built, implies a significant increasein nitrogen loadingto the receiving basin. Nitrogen Lotsdlttgand Low Oxygen Finally, re-routingMississippi River floodwaters Zottes ONshore over thepresently-leveed swarnplands and former floodplains,although desirable for otherreasons, These results can be used to evaluate the will notsignificantly reduce nitrogen loading to thc influence of flood protectionlevees, which reduced continental shelf, overlandflow, on the flux of nitrogento thecoastal zone and subsequentI'ormation of low oxygen ACKNOWLEDGMENTS zones.Nutrient loadingin thcMississippi River has been linked to the causesof the low oxygenzones This paperis basedon a tnanuscriptpresented of 18,000 km' formingnear the MississippiRiver at the Workshopon Nutrient Cycling and Retention delta on the continental shelf in most summers in Natural and Constructed Wetlands at Trebon, Rabalais et al, 1996!. Organicmatter from Czech Republic,1997. The review commentsof J. phytoplanktonproduction sinks to bottoinwaters Kastlerand H. Brix are gratefullyappreciated. The consumingthe oxygento formthese zones u~der analyseswere supported by theLouisiana Sea Grant stratifledconditions. The phytoplankton production CollegeProgram and the Lake PontchartrainBasin is at presentriver concentrations!limited by the Foundation. riverine nitrogen loading Turner and Rabalais I994!, which havedoubled in thelast 30 years Turnerand Rabalais 1991!. Only 2-3 % of the annuityMississippi River discharge flowed overbank hlitrogerIl oesee Durrng Overland Flow 153 L1T ERAT URE Cl TED Ntxox,S, W, ANDV, Lu:, 1986.Wetlands and water quality.A regionalrcvievv of recentresearch in CoNNDR,W. L. 1996, Reportto Congresson the thc United States on thc role of freshwater and BonnetCarre freshwater diversion project status saltwater wetlands as sources, sinks and and potentialoptions and enhancements,13 transformersof nitrogen,phosphorus, and December1996. Distributed by C Earl, VS variousheavy metals. Tech Rpt.Y-86-2. U.S. ArmyCorps of Engineers,New Orleans District Army Corps of Engineer», Waterways Louisiana!. ExperimentStation Vicksburg MS DAY, J. W., JR, 1997. An evaluation of four PINAY,G., C. RvarluoNI,S, WDNDzEUL,AND E. alternative scenarios for the Bonnet Carre GazwULE.1998, Change in groundwaternitrate Diversion.Report to the Lake Pontchartrain concentrationin a large river floodplain: Basin Foundation, New Orleans, LA. denitriflcation,uptake, or mixing".Journal of DAY,J. W JR. AND P. KEMP. 1985. Long-tertn impacts the Worth American Benthulogical Society of agriculturalrunoff in a Louisianaswamp 17: 179-189. forest,p. 317-326, In P. J. Godfrey,E. R, RABALAls,N,N., R. E. TURNER,D. Jl"srlc, Q. Haynor,S. Pelczarski,S. and J. Benforado DORTCH,W. J,WIsaslAN, JR AND B. SENGULA. eds.!,Ecological Considerations in Wetlands 1996,Nutrient changes in theMississippi Rrver Treatment of Municipal Wastewaters,Van and system responses on the adjacent Nostrand Reinhold Co., New York. continentalshelf. Estuaries 19.386-407. DEMcrtEK,D. K., C, R. GARRlsoN,AND B. D, Mt& RICHARDsoN,C. J. AND D. S. Nlcllol s. 1985. 1996,Seated water-qualitydata for the lower Ecologicalanalysis of wastewatermanagement MississippiRiver, BonnetCarze spillway, and criteriain wetlandecosysterns, p. 351-39L In Lake Pontchartrain area, Louisiana, April P.J, Godfrey,E. R. Haynor,S. Pelczarski,S. through June 1994 and 1974-1984. U.S. and J, Benforado eds.!, Ecological GeologicalSurvey Open-File Report, 96-652A. Considerations in Wetlands Treatment of BatonRouge, Louisiana. MunicipalWastewaters. Van Nostrand Reinhold HOWARTH,R. W, G. BIULEN,D. SwANEY,A. Co., New York. TowNsEND, N. JA'WORSKI,K. LA>TIta, J. A. SORANNO,P.A., S, L. HUBUER,S. R. CARPENEER, AND DowNP G, R. ELMGREN,N. CARAco,T, JORDAN, R, C, LArHROP.1996. Phosphorusloads to F. BERENDSE,F. FRENEY,V, KUDEYAROv,P. surfacewaters: A simple mode! to account for MURDocH,AND Z. ZHAO-LIANG.1996. Regional SpatialpatternS of landuse, Ecological Applr'- nitrogenbudgets and riverine N & P fluxesfor cations 6:865-878. the drainagesto the NorthAtlantic Ocean: TUJLNER,R. E. 1997,Wetland loss in the northern Naturaland human influences. Biogeochemistry Gulf of Mexico:Multiple workinghypotheses. 35:75-139. Estuaries 20:1-13. KADISC,R, H. ANDR. L. KNIGHT.1996. Treatment TURNER,R, E, 1998.A Comparativemass balance Wetlands. Lewis Publishers,New York, budget C, N, P and suspendedsolids! for a KESEI R,H. 1988. The decline in the Suspended natural swampand overlandflow systems,p. load of the lower MississippiRiver and its 1-11.In J. Vyrrtazal ed.!. Nutrient Cycling and influenceon adjacent wetlands, Environmental Retentionin Natural and ConstructedWetlands. Geologyand WaterScience 11:271-281. BackhuysPubl. Inc., Leiden. MrxWNaGAL,J. P., W. H. CONNER,S, KROEGER,AND TURNER,R. E. ANDN. N. RABALArs.1991. water R. R. SHARrrt'..1997. Aboveground production qualitychanges in the MississippiRiver this in southeasternfloodplain forests: A testof the centuryand implicationsfor coastalfood webs. subsidy-stresshypothesis, Ecology 78:370-384. BioScience 41: 140-147. NrcrsoLs,D. S, 1983.Capacity of naturalwetlands TURNER,R, E. ANDN. N. RARAI.AIs.1994. Evidence to remove nutrients from wastewaters. Water for coastaleutrophication near the Mississippi Polluti on Contrrrl Federation Journal 55:495- Riverplurne. Wature 368:619-621. 505. R E. Turner Tutum,R,E. ANo N.N, RAa~, 1999. Suspend& particulateanddissolved nutrientloadings to GulfofMexico estuaries, p.89-107. lrrT. S. Bianci,J.R. Pennock andR, W. TwiHey eds!, BiogeochemistryofGulf of Mexico Estuaries. J.Wiley and Sons, Inc. Hew York, Vouevamoea,R.1968. les bases scientifiques dc Peutmphisationdeslacs et des eaux courantes sons1'aspect particulier duphosphores etde pazotecomme facteurs d'euttophisation. Rept. DAS/CSI/68-27Paris, OCDF A Reviewof Recent Studies of the Ecologicaland Economic Aspects of the Application of SecondarilyTreated Municipal Effluent to Wetlands in Southern Louisiana J. W. DAv, JR.',J. M. RvBCzyx2,L. CARDoctt-',W. H. CoistslER', P. DELGADO-SANCHEz-',R. I. PRATT,A. WESYPHAL' 'CoastalEcology Institute, Louisiana State Uni versity, South Stadium Rd., Baton Rouge,LA 70803, TELr 225-388-6508;FAX: 225-388-6326; emai 1: cei day Lblsuvm.sncc, lsu. edu 'Departmentof Biologicaland Environmental Sciences, California University 250 University Avenue,California, pA I5419; email: rybc-yk@cup,edu 'CoastalFcology Institute, Louisiana State University, South Stadium Rd., Baton Rouge, LA 70803; email: cardochCtlsu.edu 4BaruchForest Science Institute, Clemson University, Box 596, Georgetown, SC 29442 'CoastalEcology Institute, Louisiana State University, Baton Rouge, LA 70803 aCoastalEcology Institute, Louisiana State University, Baton Rouge, IA 70803 7CoastalEcology Institute, Louisiana State University,So~th Stadium Rd., Baton Rouge,LA 70803; email: [email protected] ABSTRACT: Insufficient sedimentation,coupled with high rates of relative sea level rise RSLR!, are two important Factorscontributing to wetland loss in coastal Louisiana. We hypothesizedthat addingnutrient-rich treated wastewater eNuent to selectedcoastal wetlands results iu four benefits: I! improv& efHuentwater quality; ! iacreasedaccretion rates to help offsetsubsidence; ! increasedproductivity of vegetation;and ! financial savingsof capitalnot investedin conventionaltertiary treatment systems. To testthese hypotheses, we sre currently monitoringseveral forested wetlands that are receiviugsecondarily treated wastewaterin coastai Louisiana. At one site where sedimentation accumulationwas measured, ratesof accretionincreased signfricantly after wastewater application began ia thetreatment site from 7A to 1L4 mmyr'!, andapproached the estimated rate of sugionalRSLR 2.0 mm yr'!. No correspondingincrease was observed in an adjacentcontrol site. In thesame site, surfacewater nutrient reduction, from the effluentinlaw to outflow 600 m!, rangedfrom l00% for NO -N to 66% for total P. At another site, a forested wetlandthat hssbeen receiving 3 wastewatereffluent for 40 years,dendrochronological analysis revealed that stem growth increasedsignificantly in the treatmentsite after waste~ster water applicatious began, snd wassignificantly greater than an adjacent controL Prehminary results indicate that these sites havethe potential to assimilate alleffluent nitrogen and varying percentages of phosphorus. Resultsof avoidedcosts analyses to evaluatethe economicimplications between conventional treatmentund wetland treatment at three sitesiudicate savings range fsvsm $500,000 to $L5 miNon. I tatrodnction effluent Kadlec and Knight l 996!.Previous studies indicate that both natural and constructed wetlands Numerous studies have shown that wetlands have been successfully used to purify effluent canbe effectivetertiary processors of v.astewater Richardsonand Davis l987: Conneret al. 1989; Reed !991; Kadlec and Knight l996L Wetlands "nn theSymposium Recent Research in CoastaiLoucsntna: are efficient at removing excess nutrients and ~V«a~atSystem Funcrtnn and RespOnSeto unmantnft ttenre. pollutantsby physicalsettling and filtration, L-l" J.A. hiysnan,C.E. Proffitt, N.h1. Rabalais. M. chemical precipitation and adsorption, and sett,andR.E. Turner editors>.l999. publishedby Louisiana 5 aGrant College Program. biologicalmetabolic processes that result in burial, l55 storagein vegetation anddenitrification Conner in greaterroo productionleading to organicsoil et al. 1989;Kadlec andAI vord1989; Patrick 1990!. formation which can enhance the accretion neces- Thesewetland functionscan be especiallycritical sary to oftset the subsidence that is contributing to forthe coastal regions in Louisianaaffected by wetland loss. degradedwater tlualitycaused, in part, by inadequatesewage treatment Louisiana OEQ Since1988, the CoastalEcology Instituteat 1988!. LouisianaState University has been workingwith the U,S. EnvirontnentalProtection Agency EPA!, Wastewater effluent may also serve as a thcLouisiana Department of EnvironmentalQuality restorationtool in coastalwetlands impacted by high DEQ!, andseveral dischargers to assessthe impact rates of relative sea level rise RSLR!. Wetlands of forested and marsh wetland wastewater havebeen shown to persistin theface of RSLRwhen assimilationprojects in coastalLouisiana for a vertical accretion and elevation gain equals or general policy review see Breaux and Day 1994!. exceedsthe rate of subsidence Delauneet al. 1983; The dischargersinclude two municipalities, Cahoonet al. 1995!, Historically,seasonal overbank Thibodaux and Breaux Bridge, and one food floodingof Mississippiriver deposited sediments processor,Zapp's potato chip factory in Gramercy and nutricnts into the wetlandsof the delta plain. Fig, I !, 7 o additionalmunicipalities Amelia and Not onlydid these floodsprovide an allochthonous St. Bernard!are in the final stagesof the EPA- source of mineral sediments, which contributed mandatedUse Attainability Analyses prior to formal directly to vertical accretion, but the nutrients dischargepermitting. A feasibility study was associatedwith these sedimentspromoted vertical recentlyconducted for wetlandtreatment of shrimp accretionthrough organicmatter production as well processingeffluent in Dulac,Louisiana, All of the as deposition Nyman and Delaune1991!. This potentialand actual receiving wetlands have been sediment and nutrient source to most forested hydrologically altered by some combinationof wetlands in coastal Louisiana has been eliminated levecs,spoil banks, highways, oil and gas access sincethe 1930s with thecompletion of leveesalong roads,or railroad I ines.In addition, priorto wetland the entirecourse of the lowerMississippi River, treatment,all effluent wasdischarged directly into resuhingin vertical accretiondeficits accretion< open water bodies. Wetlanddischarge provides RSLR!, prolonged periods of inundation,lowered additionaltreatment by removingfurther nutrients productivity and a lack of regeneration Conner and from theeIIIuent before entering open water bodies. Day 1988!. Inthese stressed systems, we hypothesize four primarybenef t tsderived fromwetlands wastewater treatmentin Louisiana: ! improvedeffluent water quality; ! increasedaccretion rates; ! increased productivity of vegetation; and ! the financial savingsof capital not investedin conventional treatment systetns Bteaux 1992;Breaux and Day 1994!.The high rateof burialdue to subsidence and higherthan nationalaverage rates of deni- trification due to warm temperaturesare additional reasons for the U«of wetland treatment in Louisiana.Increasing vegetative productivity is bernard especiallycruci a-I in manyparts of Louisianawhere coastalsubsidence in theMississippi Delta results ina relativesea levelrise nearly ten times greater thaneustatic sea I«el nse Conner and Day 1988; Penlandetal I 988!-Increasing productivity results Fig, I. Wetlandsu'eatmcnt study sites. WetlandWastewater Treatment in Louisiana 157 To examine the effect of wetland treatment on Measuremenistaken at Thiboda«by Zhang effluent water quality, seditnent accretion, 995! indicatethat effluent water quality was productivity,and economicsavings, we review improvedas nutrientswerc significantly reduced results of studies conducted at Amelia, Breaux andassimilated. The efflucni stream was highly Bridge.Dulac, Thibodaux and St. Bernard Conner nitrified,with NO,-Nbeing the dominant furmof N andDay 1989;Day et al. 1994;Day et al, 1997a,b; andsoluble PO,-P accounting for about77+ « the Dayet al. 1998;Cardoch et al, 2000!. Throughout totalP inthe effluent, After Passage through the thisreview, when we use the term significant, it treatmentswamp the concentrations of many water implies a statisticalsignificancewhich is docu- qualityparameters at the output station were rnentedin the references. Sampling of benthic significantlyreduced coinpared with theinfluent invertebrate and nekton communities did not indi- concentrations.Frotn 1992 throtrgh 1996. the mean cateany clear effectsdue to wastewaterdischarge annualreduction from inflow to outflow!of NO, and results are not presented here. For more N thedominant form of nitrogen in thcefflueni, information,refer to Conner and Day 989!, 8reaux rangedfrom 96% to 99%: Fig. 21, At the outpu~ and Day 994!, Day et a!. 994!, Day et al, station,the NO,-Nconcentration was belov,thc 997a!, Day et al. 997b! and Pran ]998!. detectionlimit .1 mg 1 '!during most sampling Additional projectinformation can be found in periods, indicating that the swamp systeni was Breaux 992!, Hesse 994!, Delgado-Sanchez removingNO,-N, Figure 3 illustrates reductions of 995!, Zhang X, 1995,Blanick 997!, Boustany NO,-Nconcentrations asa function of distanced et al, 997!, Rybczyk 997!. traveledin theswamp. Within 800 m, concentrations werecomparable to thosefound in the control site. Improved KNlueritWater Quality NO,-Nwastakenupbygrowing plartts, immobilized to organic N, or removedby denitrification We hypothesizedthat effluentwater quality Boustanyet al. 1997!. Concentrationsof total P in will he improvedthrough efficient nutrient uptake the treatmentsite varied during the study period. andremoval pathways within forestedwetlands. From 1992 through 1994,the rneart annual reduction Loadingrates and percentnutrient reductions for of total P in the treatment site ranged froin 33% to municipalwastewater treatment wetlands are listed 71% froin inflow to outflow I=ig. 4, Zhang 1995!. in Table 1. Data from the Point au Chene treatment wetlandfor theCity of Thibodauxoffers an example Zhang 995! described the effects of for the impactof effluenton waterquality. wastewatereffluent on effluent water quality. sediment nutrient concentrat.iona, and the chemical The Thibodaux site consists of two almost compositionof floating aquatic vegetation at the pertnanentlyflooded, subsiding, forested wetlands, Pointe au Chene site. This study assessedthe long separatedby a slightlyelevated bottomland hard- termability of theswamp to treat secondarily treated woodridge. Since1992, thc 231 ha wetlandon the wastewatereffluent from the city of Thibodaux.In westernside of the ridge hasreceived secondarily generalZharig found that, withiri the immediate231 treatedmunicipal wastewater atthe average rate of ha treatment zone, N «nd P concentrations in the 15,140 m' d ', The wetland on the eastern side of waterwere reduced100% atid 66 7r.,respectivclv, the ridge, which is not impactedby the effluent, from effluent inflow to outflow Table 1. In a related servesas a controlsite. Baselinemonitoring of review,Rybczyk et al. 996! concluded that the vegetation,soils, surfacewater, hydrology,and effective tertiary processingof effluent at t}iis site fauna, at both sites, began in 1988. Extended could be attributed to the following: I ! The domi~ inundation was documented during the baseline nantspecies of N in the effluen wa» the oxidized studies Conner and Day 1989!,A comprehensive NO,-Nform and not the reducedspecies, NH,-N. sitedescription is providedby Breauxand Day These naturally dystrophic wetlands readily 994! andRybczyk et al. 995!. denitrifyNO,-lsl, resulting in a net los«f N to the systemas N, or N,Ogas see8 otrstanyet al. 1997!' 15S J.W.Day, Jr. et al. 10 0.1 0.01 0.001 1992 ! 993 1994 1995-96 SantplittgYear Fig. 2. Meanannual concentrations of It 0, forthe eNttent inflow pipe, the treatmentoutflow, and within the first ]00 tn of thecontrol site. Inflow concentrations arereduced 96-99%. Note:Logarithmic scale. 12 10 z' 6 0 0 200 400 600 600 1000 1200 1400 Distancefrom ENttetttlrtpot Pipe tn! Fig.3, Meanconcentrations of NO,-N alongsample transects in the treatment site during sample years 1994 and l995, andin thecontrol site for saxnpleyear l995. Nitrate concentrationsare reduced99%. Wetland Wastewater Treatment in Louisiana 2,5 0.5 1992 1994 SamplingYear Fig. 4. Meanannual concentrations of Total P forthe effluent inflow pipe. the treatment outflow, and within the first 100 m of the control site. Inflow concentrationsare reduced 35-71%. ! Loading rates are low cotnparedto other are3 mg1' and 1 mgI', respectively.For many of wetlandstreatment sites. For example,the Stateof these sites, nutrient concentrations have. been well Florida has adopted regulations for wetland below that limit, indicating that tertiary treatment wastewatermanagement that establishedmaximum was achieved, P loadingrates of 9 gm' yr' for hydrologically altered wetlands Harvey 1988!, an orderof Increased Sediment Accretion magnitudehigher that at mostof oursites, and; ! Highrates of accretionand burial of sedimentsin Currentevidence indicates that rising water thesesubsiding systetns provide a permanentsink levels are leading to wetland loss, coastal erosion, for phosphorus.Two other studies also documented and salt water intrusion in a number of coastal areas thehigh rates of denitrificationatthis site Crozier Stevensonet al, 1988; Scstini 1992!. If coastal et al. 1996; Bousumyet al. 1997!, wetlands,especially those in deltas,do not accrete vertically at a rateequal to the rate of RSLR, they Similarwater quality improvements have been will becomestressed due to waterloggingand salt documentedfor the treattnent wetlands at Amelia, stress.and ultimately disappear Mendelssohn and BreauxBridge, and St. Bernard Table 1!. High McKee 1988!. Many wetlands in Louisiana suffer reductionrates of N and P indicatethat the wetlands fromaccretion deficits; that is, theyare not keeping ere act as a net nutrient sink and that the sites are pacewith RLSR- Discharge of secondarilytreated effectiveproviders of tertiarytreatment. For effluent can stimulate biomass production and comparison,in Florida, the tertiary ad vanced waste enhance sediment accretion rates. Matntainino e treatment AWT! standardsfor tata!Jvl and tots.l P vegetationis crucial to wetlands survival. 1M J.W.Day, Jr. et a!. Table l. Loadingrates and percentnutrient reductionsin at four wastewatertreatment forested wetlandsin coastalLouisiana. All concentrationsare sported as mg 1'. Treatment Nitrogen Phosphorus ENuent Basin Loading Loading Concentration Site ha! g m'yr'! g m'yr'! Nutrient Discharge Outlet Reduction Amelia' 1012 9,8 to 19.6 1.] to 2.1 TKN 2.98 66' Total P 0.73 0.06 92' Breaux 1475 1.87 0,94 NO3-N 0.8 ,1 100 Bridge' PO4-P 1 02 80 Total P 2.9 03 87 St. Bernard' 1536 0.42 TKN 13.6 1.4 89.7 Total P 3.29 0,23 95 Thibodau x' 23] 3,1 0.6 NO3-N 8,7 100 TKN 2,9 0.9 69 PO4-P 1.9 0,6 68 Total p 2,46 0,85 66 'Day ct al. ]997a!. 'Day et al. 993!, 'Day et al. 997b!. 'Zhang 995!. -'Reductionscalculated for averagesofstations T 1 and LW stations for 4/96 sampling Day et al. 1997a!, There was no consistentdifferent betweenthe treatmentsand control sites at Amelia. Subsidenccin deltas leads to a relativesea level rise in thesoil profile seeDe]anne 1978 for a description RSLR! rate that is oftenmuch greater than eustatic of methods!,it was estimatedthat background rise,For example, while the currentrate of custatic accretionrates in theThibodaux site averaged only rise is between1-2 min yr' Gornitz et al. 1982!, 0.44 k 0.04 cin yr ' for the sameperiod, leading to RSLR in the Mississippidelta is in excessof ]0 anaccretion deficit of 0,79 cmyr ' Rybczyk1997!. mm yr ', thus eustatic sea level increaseaccounts for only 10-15% of total RSLR in thisdelta, We To determinewhether wastewater applications hypothesizedthat adding nutrient rich eNuent can stimu/atedaccretion, a feldsparhorizon marker increaserates of seditnentaccretion by proinoting technique Cahoon and Turner 1989! wasutilized productionof organic matter and trapping of minera] to estimateaccretion rates in the site receiving matter. Evidence from the Pointe au Chene treatment efTluent and in an adjacent control site, both before wet]andat Thibodaux, supports this hypothesis, 988 - 1991! and after 992 - ]994! wastewater applicationsbegan in the treatmentsite, Pie-effluent There]ative sea level rise RSLR! rate at the accretionrates averaged 0.78 cm yr' in thetreatment Thibodauxtreatment wetland Fig. 5! derivedfrom siteand 0.52 ctnyr' in thecontrol site and werenot tidal gaugeanalysis Penlandet al. 1988!, is 1.23 significantlydifferent Fig. 1!. After application cm yr' for the period ]962 through 1982. To began,accretion rates in thetreatment site , 1 cm maintainelevation, soil accretion must equal this yr'! weresignificantly higher than accretion rates rateof RSLR. However, by analyzing "'Cs activity measured at the control site .14 cm yr '!. Wetland Wastewater Treatment in Louisiana 151 16 14 12 k ! 10 C e 8 15 > e ftacktsrEEinit Pre-4ffliierit PEEWEEefflorni t E961 - i9881 !988 - 1991! i 199l 1994 i Fig.5. BaCkground from ' "Csmeasurements!, pre-eNuent. and post-effluent aCCretiOn rateS, relative sea level rise RSLR!and accretion balance deficits for treatment T! andcontrol lC! at thc Thibodauasite. T andC werenot significantlydifferent during thc pre-treatment period, but T wassignificantly greater during the post-effluent period. 25 2 4E0 Tiis 0i e 0 5 0 1920 1930 1940 '950 Vss Fig, 6 . The ratratio treatment/control!h t/ 1!o f' annua ual wwood stem growth measured asgrowth indiameter! forhald cypress~ treesat BreauxBridge. Before wastewater t ppljc~iOnsapp ications too the t atmentsite b gmin the late 194 kor eely 195th growthin the control 1site f was signiticantly t1yhigher ' erthant an growt h ErEthetreat ment sit e ~f ! 0 5! .A fter w staevE uter applicationsbegan, stem growth was significantly higher in thehe treatmenttieatme site. Bo'lhsites werc similar Ensize and structure Hesse et al. le !. t82 J.W,Day, Jr. et ai. Additionally, estimated accretion rates in the abovegroundproductivity Fig. 6'}. Stem wood treatment site fell within one standard deviation of growth from 1920 to 1992 was measuredat the theestimated rate of RSLR in the region Rybczyk treatment site and an adjacent control site. An 1997!, annualdiameter increment ratio was calculatedby comparingstern wood growthfrom the treatment Using an integrated field and modeling siteversus thc stemwood growth at thecontrol site. approach,Rybczyk et al. 996!, Rybczyk 997! Recordsindicate that the city begandischarging into and Rybczyket al. 998! focusedon the use of the forested wetland between 1948 and 1953. wastewater effluent at Pointe au Chene for wetland Before wastewaterapplication began, Hcsse et al, enhancement and restoration. Their studies revealed 997! foundstatistically significant highergrowth thatneither aboveground tree production nor annual in the control site than at the treatment site. ratesof decompositionwere affected by wastewater However, after onset of treatment, there was effluent. Becauseof increasedfloating aquatic increasedgrowth in the treatmentsite, resulting in vegetationproduction, however, rates of sediment statistically significant higher annual diameter accretionincreased significantly after wastewater increnMntratios Hesseet al, 1997!. A spike in the applicationsbegan and fell withinone standard enor annual diameter increment ratios coincides with the of the estimated rate of relative sea level rise. A site- onset of treatment. The sustained elevated trend of specificwetland elevationmodel revealedthat ratiosin thetreatment site illustratesthe long term wetlandelevation in thissubsiding region was more benefits of wetland treatment in this site. sensitiveto the uncertaintysurrounding estimates of eustaticsea level rise anddeep subsidence than Short term records at this site also confirm to possibleeffluent-related changes in autogenic these findings. In January 1994, the effluent processessuch as decompositionand primary dischargewa.«.witched from the historicwetland production Rybczyk 1997!, The model also old treatment site!, to a new site that had not indicated that nutrient addition alone was not previouslyreceived effluent new treatmentsite!. sufficientto lead to longterm restorationof thc ln 1992, permanentplots were established at both forested wetland and that some mineral sediment sites to measureannual littcrfall and stemgrowth inputwas necessary. Table 2!. There was no statistically significant difference in thc total abovegroundproduction IncreasedPrxidsactivlty between the old treatment site and the new treatment site during 1993 Delgado-Sanchez 1995!. Secondarilytreated effluent deli vers nutrient- However, during 1994 and 1995, when effluent rich waterto wetlarlds,stimulating vegetative dischargewas switched to the new treatment site, productivity. Long term impactson forested total productionwas significantly higher at thenew wetlandscan bc assessedby evaluatingdata from treatmentsite comparedto the old treatmentsite theBreaux Bridge treatment wetland. The treatment Delgado-Sanchez1995!. Most of this difference wetlandat BreauxBridge is uniquebecause of its was due to increases in stern wood biomass in the longhistory of dischargeto the receivingwetland. new treatment site and not leaf production. Thetown of 6.%Nhas been discharging itseffluent froman oxidation pond ,785 m' d'! to a 1475-ha Similar results have beenreported for the other cypress-tupelowetland for almost 50 years Breaux treatment wetlands.For example, a study conducted and Day 1994!, Ivlonitoringof the effluen impact at Amelia also indicatesan increaseof primary siteand an adjacent reference site began in 1992.A productivity.The City of Ameliais investigating comprehensivesite descriptionis providedby Day theecological feasibility of incorporatingthe Ramos et al. 993! forestedwetland aspart of its treatmentsystem io polishsecondarily treated sewage effluent Day et A dendroecologicalanalysis was conducted aL 1997a!.A yearlong study on primary productivity Hesse 1994; He,sse et al, 1997! to determine the indicatesenhanced growth in the treatmentsites long term impacts of wastewatereffluent on Table 3!. Productivity, as expressed in mean Wetland Wastewater Treatment in Louisiana fable2. Abovegroundproduction g m'yr' + se!measured at BreauxBridge treatment site.' Stem Wood Leaf Total Aboveground Year Site Production Product ton Production 1993 Old Treatment* 780 2 358.5 420 1200.9 1993 New Treatment 677.9 + 69.21 514 1191,9 1994 Old Treatment 593.2 4 46.8 547,3 * 9.2 1140.5 1994 New Treatment* 1383.4 + 186.4 745.8+ 8,2 2129.2. 1995 OM Treatment 574.8 X 187.4 705.2 X 81.] 1280 1995 New Treatment« 847.7 i 200,1 763.6 + 45,5 1611.3 'FromDelgado-Sanchez 1995. «Indicatessite receivingwastewater eff!uent, ~Indicates statistical difference. litterfall for one year,was statistically significantly papers,Breaux 992!, Breauxand Day 994! and higherin thetreat tnent site than in one of thccontrol Breaux et al, 995!, conducted economic cost bene- sites{Day et al. 1997a!, fit analysesof the wastewatertreatment operation at BreauxBridge and Thibodaux Table 4!, They EconomicSavings conservatively estimated a capitalizedcost savings, usingnatural wetlandwastewater treatment rather Conventional wastewater treatment is often than conventionaltertiary treatment. At 8reaux veryexpensive for the loadsgenerated from many Bridge, the estimated costs savings wa.s of the small communities in southern Louisiana. approximately$1,4 million, over a 30-year period. Wetlandassimilation can providean affordableand At Thibodaux, there is a potential savings of effectivewaste treattnent option. In a series of approximately$5 N,0 N, However, it ts further Table3. Total mean litterfall g m'! collectat Table 4. Cost comparisons for three wet}ands the Amelia treatment wetland from Sept. 1995- treatment projects Sept.1996. Thosemeans with diKemnt letter are statisticallydifferent Day et al. 1997a!. Ctmventiona! Wetland Cost Treatment Treatment Savings Sne Mean Litterfa! 1 g m '! f s.e, Breaux 1,500AXN 125,000 1,375,000 Bridge' Control 1 581.09 k 35.68 Thibodaux' 1,650,000 1,150,000 500 0 N Control 2 42,45 + 38.24 Dulac' 2,200 000 700,000 1,500,000 Treatment 716,65+ 38.08 Lake 1 Site I 546,06 ab + 47.24 'Costsreported in 1992dollars as pcr Breaux a.nd Day Lakel Site 2 666.35 + 49.52 994! and Breaux et at. 995!. Capitalized costsare discounted at 9% for 30 years. 'Thetreatment site is adjacentto LakePalourde. Lake 'Costsreported in 1995dollars as per Cardoch et al Site2 is connecteddirectly to the treatmentsite by a 000!. Capitalizedcosts are di scounted at 8e~for 2~ small channel. Thus measurementswere taken at the years. lakeedge where there i spotential influence from the eNuent. 164 J W. Day, Jr. et at notedthat capitalized savings could be as»gh as less available, i will be increasingly difficult for $1,300.000over a 30-yearperiod, depending upon smallcoastal communities to meetthe waterquality the disinfect.ionsystem employedprior to wetland standards. Wetland wastewater treatment could discharge. provide an econotnically viable and effective alternative to expensive conventional tertiary Non-toxic. industrial processors,such as treatment, Additionally,it potentially servesas a shrimpprocessors, can benefit from using wetlands means for wetlandrestoration in the subsiding for their highlyseasonal loads. A studywas recently coastal zone. conductedto determinethc feasibilityof using wetlandsfor treatmentof shriinpprocessing waste- LITERATURE CITED water in Dulac, Louisiana Cardoch et al. 2000!. The avoidedcost estimateapproach was usedto BLArtrrtx,T, P,1997. Effects of variedhydraulic and comparecosts from conventionalon-site treatment nutrientloading rates on water quality and of he shrimp processing effluen with costsfor hydro]ogicdistributions in a naturalforested wetlands treatment. Conventional treatment would wetlandreceiving waste water. Masters Thesis. costapproximately $200, XX!per yearfor 25 years, Departmentof Oceanographyand Coastal ascompared to wetlandtreatment costs of $64,000 Sciences.Louisiana State University, Baton pcr yearfor 25 years.This is a potentialcost savings Rouge,Louisiana. of $1.5 mi ll ion doll ars over 25 years Table 4!. BOUSTANY,R. G., C. R. CRozrER,J. M. Rvnczvx, xisti R, R, TwtLLFv, 1997, Denitrification in a South Much wetland treatment has focused on Louisianawetland forest receiving treated constructedwetlands primarily to provide a high sewageeffluent, WetlandsEcology and degreeof controlfor treatment.In Louisiana,the Management 4:273-283. densenetwork of canalsand leveeshave left many BRe*t:x,A, M, 1992. The use of hydrologically wetlandshydrologically isolated andconfer the altered wetlands to treat wastewater in coastal same degree of control as constructedwetlands, Louisiana,Ph,D. Dissertation,Department of With many natural systems plentiful, it is Oce anography and Coastal Sciences, unnecessaryto build artificial wetlands in Louisiana, LouisianaState University, Baton Rouge, althoughmany have been built. These isolated Louisiana. wetlandsprovide a practicalcconornic solution for BitsAux,A. M., ANDJ. W. Dxv, JR. 1994. Policy the smallcommunities that arc widely dispersedin considerations for wetland wastewater the coastal zone, treatmentin the coastalzone: a casestudy for Louisiana.Coastal Management 22:285-307. Conclusions B~ux, A., S. FxRaErt,xisn J. Dav. 1995. Using naturalcoastal wetlands systems for waste- Resultsfrom severalongoing and completed water treatment:an economicbenefit analysis. studies of wastewater treatement in wetlands Journal of Environmental Management indicatethat theyare achievingthe ecological goals 44:285-291. of enhancingeffluent water quality, stimulating C~oon, D. R, xtsoR .E, TctusaR.1989, Accretion vertical accretion, and increasingproductivity. and canal impacts in a rapidly subsiding Economically,the savingsare substantial for small wetlandIi. Feldsparmarker horizon technique. communitiesand non-toxicindustrial processors, Estuaries 12:260-268. Calculations of nutrient retention and loss via CaHooN, D., D. REED ANoJ. DAv. 1995. Estimatirig denitrification, plant uptake,and burial indicate that shallow subsidence in rnicrotidal saJt tnarshes the receivingwetlands should assimilate all of the of the southeasternUnited States:Kaye and NO,-Nand more than 50% of thephosphorus given Barghoornrevisited. Marine Geology130;1- the current loading rates, As water quality 9, regulationsbecome more stringent,and federal CxaoocH, L.. J. %. Dav, Jtt.,J, M, Rvnczvx, ANnG, grantsfor sewagetreatement improvements become P.~. 2000. An economicanalysis of using WetlandWastewater Treatment in Louisiana 565 wetlandsfor treatmentof shrimpprocessing 3 W L CAR ~Ktt J Q. RYBczYK,ANn G. wastewater: A c asestudy tn Du lac, Louiaiana. p. Kt.'stp. 1998, pood Processor Ecological Econontics,in press, CommunityDeve]optnent of RuralCoastal Cols>ta,W. H. ANoJ. W. DAv,JR, 1988. Rising water Areastltrough th.e Applica'tton of Wetland levels incoastal Louisiana: implications for Wastewater Trc atmc nt Sy stetns. RePort two coastal forested wetland areas in submittedto National Coastal Resources Louisiana,Jnurnal nf Coasrai Reseals.h4:589- Rcsean.hand Development Institute Coastal 596. EcologyInsutute. Louisiana State University, ColsNER,w. M, AKn J. w. DAv, JR. 1989. A use BatonRouge, LA 70803 attainability analysisof wetlandsfor receiving »LAt'tsn,R. D.. w. H. 3R.PATtttcK AND R. J. BL'REslL treated municipal and small industry 1978, Sedimentationrates determinedby Cs wastewater:a feasibilitystudy using baseline datingina rapidly accreting salt marsh. Xarure data from Thibodaux. LA. Center for Wetlands 275:S32-S33. Resources,Louisiana State University, Baton DELAUNE,R. D., R. H. BAtrMAYK, ANDJ. G. Rouge, Louisiana, Gossnttlsx. 1983.Relationship amongvertical Co~trER,W. H., J. W. DAY JR., AwnJ. D. BERGFttoN. accretion,coastal submergence, and erosion 1989, A useattainability analysi~ of forested in a Louisianagulf coastal marsh. Jourrtal of wetlands for receiving treated municipal SedirrtenranPerrvjlog, 5 3; 147-157. wastewater.Report to theCity of Thibodaux, DELGAoo-sAhlctnL,P. 1995 Effects of longterrn Louisiana. wastewaterdischarge into the Cypiere Perdue CRoztF+,C. R., J. M. Rvnczvx, ANoW. H. PAratcx, forestedwetland at Breaux Bridge. Louisiana JR. 1996.Spatial gradients of dissolvednitrate Maste'sThesis, Department of Oceanography andnitrou s oxidein a wetlandforest receivmg and Coastal Sciences, Louisiana State treatedsewage eNuent, p. 65-68. In Kathryn University,Baton Rouge, Louisiana. Flynn ed.!, Proceedingsof the Southern Gon~n7., v., S. LEBEontF, ANo J. HANSEN. 1982. ForestedWetlands Ecology and Management Global sea level trend in the past century. Conference. Clemson University, South Science 215:16H -16! 4. Carolina, HARYEY,R, 1988. Interoffice memo. Rc: Revisions DAv, J. W A, M. BREAUX,S. FEAGLEY, P, KEMP,Also to Chapter 17-6 pursuant to wetland C. CounvtLLE.1994. A useattainability analysis application.9/28N8, 5 pages And Reclaimed of longterm wastewaterdischarge on thc Waterto WetlandsRule. 17-6.030. 19 pages. CyprierePerdue Forested Wetland at Breaux Stateof Florida, Department of Environmental Bridge, LA, Coastal Ecology Institute, Regulations. Lousiana State University, Baton Rouge, HF>sE,I,. T. DGYLE,A~u J. DAY. 1997, Long-term Louisiana. growth enhancement of ba!dcypress DAY,J. W., J, RVBCZVX,R. PRArr,A. WESrpnAL,T. Taxodittmdisrichum! from municipal BLAHNtx,G. GARSOi,A~ P, IQ:Me.1997a. A wastewater application Fnvirortmenral use attainability analysis for longterm itfanagemerrr22:119-127, wastewaterdischarge on theRamos Forested HEssE,I. D. 1994.Dendroecologicai deterrnina.tion Wetland at Amelia, LA. Coastal Ecology of municipal wastewater effects on Taxodium Institute,Louisiana State University,Baton distichum L.! richproductivity in a Louisiana Rouge,Louisiana. swamp.Ivlasters Thests Departtncntof DAY,J. W., J. RytKZyx,R, PRArr,M, ScrtrLA,A, Oceanography and Coastal Sciences. WEsTPHAL,T. BLAHNIK, P, DELGADo,P. KEstP. LouisianaState Un i versity, Baton Rouge, A.J.~mE, C,Y. Hu, G. Jv,,Asm H.W. Jt~'G. Louisian.. 1997b.Ause attainabilityanalysis for longterm KADLFc,R. H. Aso H ALvono, JR. 1989. wastewaterdischarge to thePoydras-Verret Mechanismsot water quailty imporvements Wetlandin St, BernardParish, LA, Coastal in wetlandtreatment systems, p. 489-498.In EcologyInstitute, Louisiana State University, D.W. Fisk ed.!. Wetlands: Concerns and BatonRouge, Louisiana. Successes.Proceeding sponsoredby 166 J.W. Day, Jc et nl. American Water ResourcesAssociation, Rvncrvx,J. M., J. W. DAv, l. D. Hassi.,ANn p, September17-22, 1989,Tampa, F!«da. DzaoADoSAIvcnaz. 1996, An overviewpf KAuux:,R, H. ANnR. L K st K. J. Gauthreaux et al. SampleSites werethen sealedin plastic containersand stored in a cabinet at room temperature. All satnples were The Calcasieu River/Lake complex contains digestedwithin 3 rnoof collection. the sites where the samples were collected. Sedimentsthought to be contaminatedwith parti- A procedureclosely following thatof Tessier culate metals were used to create a marsh habitat at et «l. 979! was employed for the sequential the Sabine National Wildlife Refuge in southwest extractionprocedure, After drying, a fractionof the Louisiana. The habitat reclamation sites, control sedimentsamples was crushedinto a fine powder site,sampling locations, and dredging locations are by usinga mortarand pestleand screenedthrough shownin Figurel. A briefhistory of therestoration a 20 meshsieve, Specimens of powderedsediments sitesusing Calcasieu Ship Channel dredge spoil at .5 g! were placed into 250-ml Erlenmeyer flasks the Sabine National Wildlife Refuge is as follows: andsealed using parafilm. The flasks werelabeled Site I was createdin 1981 andis the oldest of the andthe samples were ready for immediatedigestion, sites and had a homogeneous environment at the time of sampling.Site II wascreated in 1993and I! Exchangeable,The exchangeabletnetals wa» three years old when sampling began. It had a were extractedfrotn the sediment sample by morehetetogeneousenviroiuneni thanSite I in terms digestingthe samplewith 20 inl of a 1.0 M MgC1, of topographyat theti meof satnpling.The creation solutionadjusted to a pH of 7.Oatroom temperature, of Site lll was completedin early 1996. Site IV The tnixtutewas continuously agitated for I h using was the natural "reference marsh" and was similar a magnetic stirrer. This solution was then to Site I in environment. S ite Ii had areas similar to centrifugedin a 50-ml polypropylenecentrifuge Site lV whichcould be usedfor comparison.Site tube at 7000 rpm for 30 min. The supernatantwas V wasthe Calcasieu Ship Channel from which the pouredinto a 50-ml volumetricflask and brought sedimentwas taken to create the marshfor Sites I, to volume usingdeionized water. This solutionwas II, and III, placed in a 40-ml plasticbottle prior to analysis. The residuewas washed with approximately20 tn! Materials and Methods of deionizedwater and the solutioncentrifuged at 7000 rpm for 15 min. The supernatantwas dis- Sediment samples werc collected at the carded. samplinglocations discussed previously usinga tefloncoated scoop. The upper 1 cmol' topsoil was ! Metals Bound to Carbonates. Metals collectedfrom a 10 crn diametercircle and placed bound to carbonates were extracted from the residue in a plasticcontain.er. Three replicate samples were of the first extraction with 20 inl of a 1.0 M randomlytaken at eachsample site. At Sites I, III, NaC,H,O,solution, adjusted to a pH of 5,0 with and IV sampleswere takenfrom the interior IN! aceticacid, Following continuous agitation at room abovenorma! water levels and near the waters edge temperaturefor 4 h usinga inagneticstirrer. the OUT! to monitor these different environments. mixturewas centrifuged in a 50-ml polypropylene SiteIII wasthe proposed fi/1 site andsamples were centrifuge tube at 7000 rpm for 30 nun. The takenprior to PRIOR! andafter AFTER! thesite supernatantwas pouredinto a 50-ml volumetric was restored.Site II was sparselyvegetated and flask andbrought to volumeusing deionizedwater, sampleswere collected near clutnps of vegetation This solutionwas stored in a 40-ml plasticbottle NONVEG!and within the vegetated areas VEG! prior to analysis,The residuewas washed with to monitorthe impactof plant activity on metal approximately20 ml of deionizedwater andtlte concentrations,The ship channelsediments Site solidsseparated by centrifugationat 7000 rprn for V! were taken using a 0.1 rn'-Ekman grab. All 15 min, The supernatantwas discarded, sedimentsamples were stored at 4'C for lessthan 3 d, weighed,and dried in a forcedair ovenat. <95'C. ! Metals Bound to tron and Manganese Uporl drying,dry masseswere measuredso that Oxides.Metals bound to ironand manganese oxides percentwater could be determined,The samples were extracted from the residue of thc second Migrationof SpeciatadMetals in ReeiairnadSoils 169 Fig.l. A mapof the sainpling area including the locations ofthc five sampling sites and the types of samples collectedat the sites. extractionwith 50 mlof a 0,04M NH,OHXCU25% residue from the third fraction with 7.5 ml of a 0.02 XC,H,O, solution.The solutionwas kept at a M XNO, solution attd 12.5 m] of a 30% H O. temperatureof 96'C y 3'C for a 5.5-hperiod and solution, adjusted to a pH of 2 0. Following agitatedcontinuously for 30 min.using a magnetic continuousagitation for 2 h usinga magneticstirrer stirrer,The mixturewas thencentrifuged in a 50- at a temperatureat 85'C + 2 C, an additional7.5 ml ml polypropylenecentrifuge tube at 7000rpm f« of 30% H,O, solution was added. The pH of the 30 min.The supernatant was poured into a 50-m! mixturewas adjusted to a pH of 2.0 andthc agitation volumetric flask and brought to volume using continued at a temperature of 85'C + 2"C for 3 h. deionizedwater, This solution was stored in a 40- After allowing the mixture to cool to roonl ml plasticbottle prior to analysis.The residuewas temperature approximately 45 tnin.l, 12.5ml of a washedwith approximately20 rnl of deionized 3.2M NH,C.H,OJ20% HNO, solutionv asadded. waterand the solids separated by centrifugation at This mixturewas diluted to approximately50 ml 7000 rpm for 15 min, The supernatantwa.s usingdeionized water, agitated continuously for 30 discarded, minand the solids extracted by centrifugationin a clinicalcentrifuge at 7000 rpm for 3 }min. T"c ! JH'eratsBound ro OrganicAfarrer. Metals supernatant was poured imo a 50-m! volumetric hound to organicmatter were extractedfrom the flaskand brought to volume using deionized water 170 K. J. Gauthreaux et ai, This solutionwas then stored in a 40-ml plastic StatisticalGroupings of Sampling Stations bottle prior to analysis. The residue was washed with approximately20 ml of deionizedwater and Samplingstations were placed in threegroups the solidsseparated by centrifugationat 7000 rpm based upon observed differences in metal for 15 min. The supernatantwas discarded. concentrations,The stationgroups were: ~o~- S ite 1 OUT!, Site III PRIOR!, and referencemarsh ! Residual. Metals in the residualform were Site IV!; @gag - Site I IN!, Site I I NONVEG!, extracted from the residue of the fourth extraction Site Hl AFTER!, and Site V; pi~re~ - Site Il by placingthe residuein a microwavedigestion VFG!. Totest whether the selectedgroupings could bomband adding 10 ml of concentrated70% HNO,. be separated and distinguished by metal The botnbwas then placedinto a microwaveoven concentration,a multivariate analysis of variance for 30 s atfull power,The bombwas then taken out MANOVA! was used. Group differences with andallowed to cool to room temperaturefor I h. respect to metal concentrations were highly The residuein the botnbwas placedin a 50-ml significant p 0.05!. polypropylene centrifuge tube, diluted to approximately20 ml usingdeionized water and Since no information is obtained to determine centrifugedfor 30 min. The supernatantwas poured theindividual metalscausing the differences within into a 50-ml volutnetricflask and broughtup to groups, a univariateanalysis of variance ANOVA! volume using deionized water. This solution was was used to examine the effect of each metal. The storedin a 40-mlplastic bottle prior to analysis.The concentrationsof Fe, Mn, andZn werefound to vary residue was then discarded. significantly between the station groups. The remainingmetaLs showed no group differences. To Metalconcentrations were detertnined using furtherunderstand the relationshipof the metalsin FlameAtomic Absorption Spectrophotometry Cr, eachgroup, a discrirninantanalysis was run using Cu, Fe, Mn, Ni. and Zn! and GraphiteFurnace Duncan'smultiple range test to confirmthat group AtomicAbsorption Pb!. Duplicatesamples, matrix means were different, The results Table I! indicate andreagent blanks, and standard additions were used that an individual observation could be correctly to checkfor reproducibility,contamination and placedin the predictedgrouping 91% of the time, possiblematrix effects. Contaminationwas not ioundin any blanksamples, and the samplematrix did notaffect the analysis. Table 1. Diseriminantataalysis of metal data daasifyingmetal concentrationsin each station groupltsg. PtedictedGroup Membershipa Actual Group No, of Cases 2 45 38 5 2 85.0% 10.5% 4.5% 105 2 95 8 1.8% 90,6% 7.6% 133 0 10 123 7,8% 92.2% Percentof groupcases correctly classified were 91.22%. Migrationol SpeciatedMetals irr ReciaiiriedSoiis t7t SabineNational Wild]il'e Refuge sediments Arrnv Corpsof Engineers1987; Beck ct al. 1990 The samplescollected were selected based Cunninghamet al. 1990;Derouen and Stevenson upontheir locationand the dif'ferentcharacteristics 1987; Schul tz I 991; Wad c 1 994; 3. Sncdd on pf thc samplesites i.e., vegetatedsediment, non- unpublisheddata!. The mean metal concentrations vegetatedsediment, ship channelsediment, etc.!. measuredin thisstudy are comparedin Table2, The mean concentrations for Cr, Cu, Fe, Mn, Ni, Concentrationsof Cu, Cr, Mn, and Zn for ship Pb,and Zn arc given in Table 2 for eachsampling channel sedimentsfound in these studies ranged station. The valuesreported are meansfor sumsof from10-59 ppm for Cr, 7-27 pprnfor Cu, 0.8-2~8 thefive separatedfractions for eachstation. Figure for Fe,590-670 for Mn, 6-] 8 pprn for Ni, 8-'22for 2 showsthe variation of mean metal concentrations Pband 36-84 ppm for Zn. The means1'or all totals ateach sample site. Elevatedconcentrations of Mn performedin the currentstudy compare favorably werefound at Sites I, II, and V compared to the and fall within the rangesmeasured previously referencesite Site IV!. A similar patternwas found Table 3!, for Fe concentratronswith the inclusion of elevated levels at Site 111,while Zn concentrationswere found To further test the reliability of thc method to be elevated at Sites I and II. Figure 3 shows the used,a subsamplewas digested to yieldtota! metal effect on the Fe arrd Mn concentrationsafter ship concentrationsin the sample Table 4!, The channe]spoil hasbeen placed on Site III. It is clear agreementbetween the measurements is within the that verticalrmxing has not occurred. variation between samples. Tolal rnctal concentrations,however, are generally higher, The results obtained using the sequential perhapsreflecting observedlosses of sampleduring extractionprocedure and summingthe fractions transferfoHowing centrifugation or othersystematic yieldresults that agree well with earlier studieson errors. Table2. Mean metal concentrationsand standarddeviations by samplingsite in ppm unlessnoted. Numbersin parenthesesare the number of samplesused in calculatingmeans. S ite Chrorniurn Copper Iron %! Manganese Nickel Zinc 18.5 ! 11.0 ! 1.82 ! 2] 0 ! 20.4 ! 6.4 ! 47.1 ! m.O %3.] +.61 WO M.S +.7 +~.4 21.8 2! 14.5 2! 1.95 1! 640 2! 19.5 1! 83 9! 55,5 2! &,9 M.2 +.55 X]20 W,o +9 +]] 5 III 19.5 ! 10.0 ! 0.4] ! 151 ! 10.4 ! 6.8 '4! 36.5 e! before! +~,5 +3.5 +.22 k 30 M.8 +.8 +4.1 III 18,] ! 13,6 ! 1.9] ! 648 ! 12.1 ! 5 e > 41.0 i after! +&.8 +1.8 +,35 +145 +U.2 +4 +8,1 IV 23.6 4! 10,6 ! 0.35 ! 56.2 ! 17.8 ! 4.3 ! 33.0 ! +1. 8 Mr.7 +.11 W.] w.5 +.6 +]0,] 21,4 4! 9.9 4! 2.10 2! 580 4! 14.6 2! 5.6 9! 4].e 41 +4.5 k3.2 +.6] M20 +3.5 +8 +15.6 172 K. J. Gauthreaux et al. 2.5 15 II saa IV V Fig,3. Thevariation of meanconcentrations of Fe %! 2.5 and Mn ppm! acrosseach samplingsite after Site Ill was restoredusing dredgespoil. manganeseoxide and organicpha.ses and a small increaseinthe residual phase, This change in pattern is uniquefor SiteII and maysuggest uptake of Mn by thelocal vegetation and subsequent buildup in detritus. Discussion III IV V SI5e Concentrationsof Cu, Cr, Pb, and Ni are not Fig, 2. The variatinn of Incan.metal concentrations significant!ydifferent among Site II VEG!, SiteI! acrosseach sampling site. NONVEG!, and Site V sediments, This trend shouldbe expected in typicsoils for the sampling Table5 givesthe mean concentrations pprn! area. Coppertends to be immobilein soils witha forthe studied metals for each fraction separated pH lower than6 andchromium usually existsas the andfor eachsample site, Forexample, copper at chromic +3! ionin soilswith a lowpH, allowingit Site1 OUT!varies from 0.3 pprn in fractionI ion to complexwith organicmaterials and adsorbto exchange!to a highvalue of 4.7 pprnin fraction5 clays and other minerals, which renders Cr residual!.Table 6 givesthe same results for the immobile.The pH of thesoils at the sampling sites metalsFe, Ni, and Pb, averaged5.3 C. E. Proffitt unpublisheddata! for the surficial sediments and could cause the observed Concentrationsof Cr, Cu, Mn and Zn are trend Gambrell !994!. comparedfor Site V, Site II VEG!, and Site II NONVEG!samples in Table5. ForSite II VEG! For Site V sediments,a definite correlation for samples,greater than 85% of Cu is boundin the manganesecan be seenbetween samples collected organic and residual fractions, while 50% of Cr is before dredging BD! and those collectedafter containedin the residual fraction, with the remainder dredging AD!. The highestconcentrations of Mn spreadevenly throughoutthe otherfractions. Site are containedin fraction2 for BD samplesand in V and Site II NONVEG! sampleshave fraction4 forAD samples.The most probable cause approximately 50% of the Mn bound in the for this variationoccurring after dredging would carbonateand manganese oxide fractions, whereas appearto resultfrom differencesin grain sizeand Site Il VEG! sampleshave over 75% in the compositionof the sediments Wade 1994!. Migrationof SpeciatedMetals in ReclaimedSoils 173 Tab!e3. Comparisonof metal concentrationsfrom previousstudies ott Ca!casieu Ship Channel ~;ments takenin thevicinity of SabineNational WIM!ife Refuge. investigator Cr Cu Fc Mn Ni Pb Zn pprn! ppm! %! { ppm! ppm! PPm! ppm! DeRouen 986! 10 45 !CF Kaiser 989! 36 Cunningham 990! 17 1.97 589 36 Schu1 tr. 991! 1.71670 15 84 ArmyCorp. 993-94! 10 14 12 36 Wade 994! 59 0.77 20 Sneddon ! 995! 17 18 70 Averageal! Investigators 1.48 630 13 13 53 SITE V This Work! 10 2. 580 15 The total Mn concentrations for Site I indicate Table 5!. PR-L samples have higher Mn a differencein the INNER 32 pprn! and OUTFR concentrationsin the exchangeable fraction, with a 92ppm!sampling sites. SiteI OL'T! sampleshave marked decrease in Mn for carbonate fractions. For significantlylower Mn concentrationsthan Site I PR-W, the trend is reversed; fraction 1 containslow IN!. Completecoverage of Site I by dredgespoils concentrations of Mn with fraction 2 containing fromthe Ship Channe!occurred during the same higher concentrations.Manganese exists in soils dredgingperiods, indicating that the variationsof primarilyin the divalent state whichis mobileand Mn shou!dnot be aslarge as observed.One possible predominatesin acidicsoils; but whenthe pH rise~ explanationfor this discrepancymay bethe location above 6, Mn i combines with carbonates. Thus, the of the satnplingsites. Site 1 OUT! is locatedjust greatestconcentration of Mn should occur in westof the ShipChannel, very near Long Bayou fraction 1 for FR-L and fraction 2 for PR-W because andadjacent to severalminor streams Figure 1!. f!oodingof marshsediments should buf'ferpH to 7 Site I IN! is located in thc center of Site I far frotn Gambrell 1994!. openwater or any waterways.The soi!s at Site I atetypic regionalsoils and have a veryacidic surface Site III AFTER! sampleswere collected six !ayer US Dept.Agriculture 1995!. This may allow monthsafter the site wascovered with Ship Channel actdleaching to occurat Site I OUT!, causing dredgespoils Table 3 indicates that Mn resides dep!etionof Mn. Leachingappears to haveoccurred mainlyin fraction2 at SiteHI AFTER!compared at Site I IN! sincethe meanMn concentrationhas to SiteV whichhas high concentrationsin fraction~ decreasedfrom typical spoil concentrations ofabout 2-4, Site III PRIOR! shows high concentrations 900ppm to thecurrent mean concentration of about of Mn in fractions1-4. The pronouncedshift of 3 PPmAnother explanation may be that Site I Mn from fraction1 samplescollected at Sit.eIII OUT!was never covered by spoils, thus measured PRIOR!and fraction 4 of the SiteV samp!esinto Mn may reflect concentrationsin typic soils fraction2 of SiteII! AFTER! can be explained rePresentcdby SiteIV, the referencemarsh. using the same reasoning as that for Site IV-L and IV-W. A fraction of Mn contained in fraction 1 of SiteIV referencesite! contained two sampling Site III PRIOR! sedimentsshould be converted into !ocations,PR-L aboveambient water levels! and fraction2 when Ship Channe!dredge spoil are PR-W covered by water!. Pronounced differences placedon Site III. Watercovered the entire site as «Mn concentrationsexist for thefirst twofractions sedimentssettled and dewatered resulting in a shift 174 K. J. Gauthreaux et at Tahk 4. Theconcentrations ppra! of' metals except Fe in percent!in subsampiescolnpared tp concentrationin the summedfractions in parenthesis!measured in the sequentialextractions. SAMPLE REPLICATE Cr Cu Mn Fe Ni Pb SITE NUMBER ppm! ppm! ppm! %! ppm! ppm! ppm! SITE I 20.1 12.5 162 19200 19,1 6,7 60 6 1.0! 0.6! {155! 8600! 3,2! 4! {545! OUT-A 19.5 11.1 104 12100 17 4 7 2 31 9 7.4! 0,8! 94.4! 2500! 7.3! .8! {32,6! SITE [I NONVEG-B 24.1 24.9 455 14600 20,7 6.8 55.4 {20.4! 3.0! 24! 6900! 9.8! .1! 8.4! VEG-C 30.0 20.7 709 22000 21.1 6.4 61,9 8,2! 8.4! 88! 0300! 9.7! .7! 4.4! SITE Ill PRIOR-A 17.4 8.5 128 16100 16.2 6.4 35.3 8.2! 8.4! 22! 4000! 7,2! ,2! {34.2! AFTER-A 16,7 16.6 591 9100 14.9 7.2 39.4 0.8! {15.2! 89! 8700! 1,8! .5! 6.0! SITE IV IN-A 22.4 9,0 79.4 2600 10.8 6.7 33.0 2.0! .0! 0.8! 400! 8,6! .6! 9.2! OUT-C 30.1 14.9 50.8 4100 14.1 5.9 42 7 2.4! 2.6! 3.6! 500! 2,4! ,3! 7.0! SITE V 31,1 8,0 978 9000 12,9 5A 36.9 8.4! .6! 998! 8700! 1,8! .5! 0.6! AD-A 24.7 5,6 461 7100 13.1 5,8 35 4 9.6! .8! 53! 800! 2.8! .8! 8 2! of Mnfrom fraction 1 in the Site III PRIOR! Shiftingof Mn in theSite HI PRIOR!and Site V sedimentstofraction 2. Asstated earlier, Mn' can samplesfrom the exchangeableand organtc combinewith organic matter when the pH is above fractionsshould produce the measuredinrt» 6, inferringthat some of theMn in fraction4 increasein Mnin fraction2 for Site Di AFTER! organic!in Ship Channel dredge spoils will be satnpies,Theoretically, some Mn in fraction2 w>11 shiftedinto fraction 2 when encountering the beshifted into fraction 1 as water levels fa! I andPH increasedpHin water into which it was placed. is loweredby the acidicsoils. Migiafionof SpeciatedMetals in AeclaiinedSoils t7S The data ln Table 5 illustrate a shift in Mn from of themechanisms which aid or hinderIran s location. action 2 of Site II NONVEG! samplesto fractions PlantScan only uptake metals in specific ionic forms 3 and4 of vegetatedsamples at the samesite. A orcertain chemical compounds orcornplexcs. Metal plausib!eexplanation forthe shift of Mn into fraction speciesthat arevery insolubleand arc «dsorbcd onto 3 iron/manganeseoxides! is that oxidation of Mn i surroundingminerals greatly hinder bioavailability. increasesin aerated soils having initially low pH Soluble meta! speciesthat do not adsorb on thatare periodically floodedwith alkaline, saline surroundingminerals tend to be transportedmorc water Gambrcll1994!. When vegetationbegins to quicklythrough the soil in forms that arc morc growon thc soils, the root systemsa!low better readilyadsorbed by plantroots and are thus more aerationand, thus, greateraccess to 0, by soil Mn. readily availableto thefood web. Plants also can alter the nearby soil chemistry "rhizosphereeffect"! by changingthe pH and/or As manganeseoxides are producedthey are redoxpotential by exuding protonsor chelating precipitated and acceleratethe oxidation of Mn. agentsnear the roots Otte et al. 1995;Simmers et Mn" is selectivelyadsorbed by manganeseoxides al, !98!!, This allows for higher solubility of andas manganese oxides are formed surfacearea is deficient meta!s resulting in chelation and increased,thereby increasing the rate of adsorption complexationof toxic metalsinto a chemicalform of Mn", The shifting of Mn intofraction 4 of the thatcan be absorbedby the roots Otte et al. 1995; vegetativesamples is probablydue to an increased Sitnmerset al. 1981!, Changes in pH and Eh in the supplyof organicrich surface matter resu!ting from rhizosphereby the roots of Spanina anglica play decayingvegetation, When the pH is above6, Mn'-' important roles in determining the chemical ions form complexes with organic matter causing speciationof elementsand theirresulting mobilities an increase in Mn concentrations in fraction 4 for Otte et al. !995!. Eh values were found to be 400 tile vegetativesamples. mV higheraround the rootsof Asteriripolianr than for S. anghca Otte et al. 1993!. They conc!uded Strmrnary thatthis effectresults from the greaterflooding in the areasoccupied by S. anglica due mainly o The use of sequentialextraction procedures differences in elevation. This conclusion was to studymetal distributions in sediinentscan yie!d supportedby high salinities foundin soi!saround useful information related to bioavailability to S,angiica . organisms, The reproducibility of the method correlated we!l with previous measurements of The bioavailabilityof metalsis alsoaffected inetal concentrations in thc study area and with by thetrans!ocation of the metalsfrom the rootsto results for digestions of collected subsamp!es the steins and !eaves Ottc et al. 1993!. This may suggestingthat this methodcan provide accurate notseem to be within the realm of effects causedby and useful results. No evidence was found Io chemistryoccurring in soi!. However,certain metals suggestthat Ca!casieuShip Channelspoil would cannotbe transportedfrom the rootsto the plant contaminate restored marsh with heavy metals at tops resultingin accumulation near p!ant roots the SabineNational Wildlife Refuge. However, in unlessfactors in soil, suchas alkalinity, phosphate areasthat are heavi!y vegetatedthe concentration levels,or basecation concentrations,allow for a profilesfor Fe, Mn, and Zn become modified when changeul metal speciation. Otte et al 993! have comparedto shipchannel spoil and in nonvegetated reportedthat Cu andZn are higher in theroots of S. areassurrounding vegetation. The concentration anglica than in the shoots;however, the opposite changesappear to berelated to changesin pH and/ wastrue for A. /ripolirrrn. Differencesin soil or Eh causedby thealteration of soi! chemistry by chemistrydue to frequent flooding appears to have vegetation,The roots of Spanirraspecies have been an importantrole in this difference. found Sirnrners et al. 1981; Otte et al. 1995! to changethe pH and/orEh in the rhizosphereby the A final factor leading to bioavailability is the releaseof hydrogenious or chelatingagents. This speciationof metals, This factor is related to some mayresult in changingthe chemicalspeciation of K,J.Gauthreaux etal. ~! gag ofC Mn,gr, andZn in each fractionateach suppleaite. Mi9lationof SpociatedMetals in ReclairnettSoiis 177 Tableg, Themean coacentrations +/-SD! for the metals Fe, Ni, and Pb for each fraction separated and for each samplesite. Migrationof Specieted Metalsin Reclaimed Soils 179 TIO K, J, Gauthreaux et al. tnetals and mobilities in soil and perhaps menziesii!.as affected by nitrogensource, p. bioavailabil ity. Other changes in tnetal 45-61, /n M. L.. van Beusichem ed.!, Plant concentrationsappear to be relatedto thelow pH of IVutritivn-Phvsiology and Application, regionaltypic soilsand the periodic ]ooding of the Kluwer Acad. Publ., Amsterdam. samplearea. The metalsCr, Cu, Ni and Pb werc HAL'TER,R, ANDK. MENGEL. 1988, Measurement foundto be essentially immobilized by the localsoil of pH at the root surface of red clover chemistry Trifolittmpratense! grown in soils differing in protonbuffering capacity, Biol. Fertil. Soils ACKNOWLEDGMENTS 5:295-298. JENNY,H. ANuK, GRossENEACHER. 1963. Root soil We would like to thank the Ututed States boundaryzone as scen by electronnucroscope. EnvironmentalProtection Agency for supporting Soil Sci. Soc. Am. Proc. 27:273-277. this work under contract number R-824-143-01-00. ChvE, M. L, M. S. HAARSMA,R, A. BROEKMANAND We would also like to thankDrs. StearnsRogers J. Rozi:MA. 1993. Relation betweenheavy andMark Dclaneyfor theirassistance. tnetalconcentrations in salt marshplants and soils. Environ. Pollat. 82: 13-22. LITERATURE CITED Orn, M. L., C. C. KEARNsAND M, O. Dove. 1995. Accuinulation of arsenic and zinc ]N! thc ARMvCORPS OFENGrNEERs. 1987. Ranking Potential rhizosphere of wetland plants. Bulletin Contatninantsin thc LowerMississippi River Environ, Contamin. ToxicoL 55: 154-61. de]ta.Tech. Rep. DACW 29-82-D-0187.New ScHOLTz,T. w. 1991. Sabine National wildlife Orleans, Louisiana, Refuge 1988, U.S, Fish and Wi!dlife Tech. BECK,J. N., G. J. RAsIELow,R. S. TIIOMPSON,C. S. Rep,R4-86-022/R4-88-4-120. MuFLLER,C. L. WEBRE, J, C. YoUNGAND M. P. SIMMERs,J. %, B. L. FOLsoM,JR., C. R. LEEAhID D. LANGLEY.1990. Heavy metal COntentof BAThs,1981. Field Survey Of Heavy Metal sediments in the Ca]casieu River/Lake Uptakeby NaturallyOccurring Saltwater and complex,Louisiana, Hydrobiolngia 192:149- FreshwaterMarsh Plants,Tech. Rep,EL-81- 165. 5. U.S. Army Corpsof Engineers,Waterways CtINhIhcitAM,P., R. WILLIAMS,R. CHEsstN,K. LrrrLE, ExperimentStation, Vicksburg, Mississippi, P. A. CROCKL'R,M. ScituRlz, C. DEMAS,E. TESSIER,A., P. G. C. CAMPaiar.AND M. BissoN. 1979, PETRocELLI,M. REDMOND,G. MORRISONAND Sequentialextraction procedure for the specia- R. K. MANtIAL,1990. ToxiCsStudy Of the tionof particulatetrace meta]s. Analyt, Chem. LowerCalcasieu River. Tech.Rep. prepared 51: 844-850, for EPA WaterQuality Management Branch, UNITED STATEsDEPARTMENT Oi' AGRlcULTURF,SOa. RegionVI, Dallas,Texas. ConsERvATIONSERVtCE, in cooperation with the DAvtFS,B. E. 1992 Trace meta]S in the environ- LA Agricultura]Experiment Station and the tnent;Retrospect and prospect. pp. 1-17. D. Louisiana Soil and Water Conservation C. Adriano ed.!, Biogeochenustryof Trace Committee.1995. Soil survey of Cameron Metals, Lewis Pubhshers,Boca Raton, R. Parish, Louisiana. DEROEEN,L. R. ANn L. H. STEvENsohI, ] 987, WADE, R. 1994. Calcasieu Ri ver Sediment Reinoval EcosystemAnalysis of the CalcasieuRiver/ Study,Tech. Rpt. EL-94-9, U,S. ArmyCorps LakeComplex. Tech. Rep. U,S,DOE contract of Engineers.Waterways Expcritncnt Station, No. DE-FGO]-83EP31]1 ]. Chapter2. Vicksburg, Mi ssissippi. GAMeRELL,R, P. 1994. Trace and toxic metals in wetlands a review. J. of Environ, Qua/. 23:883-89], GusMAN.A. J. ] 990.Rhizosphere pH alongdif- ferentrOOt zOnes of Doug]as-fir{Pseudotsaga COASTAL LAND LOSS AND WKTLANB RESTORATION tSI R. E. Turner estuaryare causallyrelated to the landlosses this sealevel ri se,climate change~, soil type,geomorphic century." I then comparethe strengthof this frameworkand age, subsidence or tnanagement. hypothesisto someof theother hypothesized causes of land loss on this coast, There are laboratoryand Four Hypotheses small-scale field trials that support various hypotheses,It seemsto me thatthe mostreliable Four hypothesesabout the causes of indirect interpretationsare basedon what happensin the wetlandlosses in BaratariaBay will be addressed field, andnot on the resultsof computermodels, here adapted from Turner 1997!: laboratorystudies or conceptualdiagrams. H l. i ct n ences of The test results discussed herein are derived t !tin oil banks v d solelyfrom data derived at a landscapescale. The 'ori of 1 loss sin h data set is restricted to a discussion of the Barataria watershed. This watershed is a significant H2. componentof theLouisiana coastal zorie 14,000 lv ha!and there are a varietyof habitatdata available i tl on it. Its easternboundary is the MississippiRiver from whichoccasional overflowing waters are v n.vi hypothesizedto deliver enoughsediinents and on 1 v tno I freshwaterto significantlyinfluence the balanceof rit f i land lossor gain in the receivingwatershed, and whosere-introduction would restore the estuary's wetlands. Improvingour understandingof the H4. w rin si ecologicalprocesses operating in this watershed h ' ' of mightassist in the managementof others. The effect of geologicalsubsidence and sea DIrect and Indirect Causes of Wetland Loss level rise are not included in this list because both factorshave remained relatively stablethis century Wetlandloss is essentiallythe same as land loss when the land-loss rates rose and fell, Local on thiscoast Baurnann and Turner 1990!. We can subsidencecaused by oil andgas fluid withdrawal discriminatebetween wetland loss that is a direct in Louisianahas been estitnatedto be relatively consequenceof humanactivities, and the lossesthat insignificant comparedto soil sttbsidencerates arean indirect consequence of various other factors. Martin and Serdengecti,1984; Suhayda 1987!. The initial habitat conversions from humati Thereare clearlyIong-term variations in wind, and activities,or "direct impacts", are about 12% of the therefore sea level. However, the trend in water- total land lossesin the Louisianacoastal zone from level rise for the last 80 yearsis essentiallylinear, the1930s to l 990 Britsch and Dunbar 1993!. These and there is no acceleration in relative sea level rise directimpacts are almost exclusively the resultof at any tide gagesite with a long-termrecord up to dtedgingfor oil and gas exploration and recovery, the 1990s Turner 1991!. as well as navigationchannels, Additional direct itnpactsarose from failed agricultural impound- The four hypothesesidentified above were ments.The 'indirect losses' make up the retnaining examinedusing data on a varietyof habitatchanges 88% of all landlosses. Some of thecauses of these obtainedfrom photo-interpretationsof both7 I/2' indirectlosses, or impacts,include reductions in and 15' quadranglemaps that cover the Barataria sedimentsupply, dredging, from subsurface fluid watershed. These analysesinclude documentation withdrawal,or hydrologicalterations. The ratio of of the numberof new pondsforming nearcanals, direct:indirectimpacts resulting frotn human the numberof pondsfilling in near canals.,and the activitiesmay vary under influences such as global amountof landloss and canal density over various BaratariaEstuary Wetiand t-oss 185 time periods. The major question asked is: "Docs land lossresult from the hydrologic changesarising from dredged canals and the consequentialspoil 80 bankparallel to the canal?" 60 Spatial RelationshipsBetween Land i~ and HydrologicChange; 7 l/2' Quadrangle Maps A newlydredged canal is typically >20 m wide and is 5 rn deepand has a spoil hank built from the 'IG dredgedmaterials that is several meters wide and many times higher than a natural levee. If 0 hydrologicchanges cause wetland loss,then land- 0 3 lossrates should be higher ncarcr,rather than farther, Distance nl from a dredgedcanal and spoil bank. Wetland fragmentationinto ponds is presuinedto bethe first 800;. stage of wetland loss. This hypothesis was Y = 0.<6x+ 14.1 e I examinedusing data on thc spatial distributionof c 6001 k- -0.58 different sized ponds found in 1955/56 and 1978 c fromsixty-three pairs of USFWS 7 1/2'quadrangle e 400' habitatmaps Turner and Rao 1990!. Pondsthat hadmerged or enlargedto becamepart of a larger zimI open-waterbody during the intervalwere identified 0 0 00 400 600 800 lOGO 1 00 and not included in the analysis. The total land loss l978 Canal Area ha1 examinedrepresented 38% of thetotal landloss for the coastalzone in the sameperiod. Someponds Fig. 1. Top:The re!aiionshipbetween the percentof foundin 1955/56were not presentin 1978,and the pondsthat arenew, persisting.and ephemeral for the vast tnajorityof pondswere new. The pondsin interval 1955/6 to 78 ! and distance to the nearesi Baratariawatershed and elsewhere! between I and canal. Bottom: The re}arionshipbetween the areaof 50 ha were the most numerous n = 1104! and tnostly new ponds<60 ha formed between1955/6-78 and canalsurface area ha! in Baraiariaestuary adapted formed after 1955/56 n=935!, from Turner and Rao 1990!. The appearanceof 'new ponds and the persistenceof existingponds waspositively related to the distancefrom the canal Fig. 1, top panel!- regressionof'the two variables pond area and canal Morethan half of all new andpersisting ponds, but area!gave an intercept statistically indistinguishable lessthan 10 % ofthe ephemeral ponds, were within from zero p = 0.03!. Thesepatterns were also 1 km of a canal. If canals had no effect on new documentedin the neighboringSt. Bernardand pondformation, then the distributionpattern of new, Terrebonnewatershecls Turner and Rao 1990!, The persistingand ephemeral ponds should overlap. The hypothesisthat canals and spoil banks caused new frequencydistribution of these pondsdo overlap pondformation is notrejected. withinthree kin of thecanal. The greatestdisparity betweenthe distributionof ephemeraland new TemporalRelationships Between Land Loss pondswas within 1 km of the canal. andHydrologic Change: Salt Marshes The area of new pondsbetween 0 and 60 ha Thetemporal relationships between canal area that formed between 1955/56 and 1978 in each and landloss for the St. Bernard,Barataria, and quadranglemap was positivelyrelated to the area Terrebonnewatersheds were investigated by Bass «canals in 1978 Fig, 1, bottompanel!. A linear and Turner 997! using aerial photographs. BaratanaEstuary Wetland Loss lIT /pat}a} and Temporal ~ 1930s to 195ps;R,- = 0,aq geh}tionsh}psBetween Land 01930s to 1974 R2 0 95 Lossand HydrologicChange: 01930s to 1983; R- =0.93 15' Quadrangle Maps 12000 v1930a to 1990 R2 0 91 Data from 15' quadrangle mapsare available Britsch and 8000 Dunbar 1993! to test for a spatial and temporal relationship betweenlandloss and hydrologic ~g 4MN changes.Britsch and Dunbar's land inventories for coastal 0 Louisiana from the 1930s to 1990 0 500 1000 1500 MOO 500 3000 were derived from colored Direct ha! overlays on 15 base tnaps approximately63 X 10' ha!. They usedthese 0.3 overlaysto map the open-waterhabitat changes betweenmapping intervals. Theseauthors used a consistent photo-interpretationmethod that is slightly differentfrom methodsothers have used, The data set is based on grossland-loss rates, rather thannet land-loss rates, and represents the only data setof its kind for Louisiana! that goes back to the 1930s and that covers the whole coast in a consistent manner.The }nappingdates were from the 1930s 0 0. 0,01 0.02 0,03 0.04 0.05 range 1931 to 1949; p,=1934!, the mid-1950s range Direct Loaa 1951 to 1958; p.=1957!, 1974, 1983 and 1990, Land Britschand Dunbar 993! classified Man-made loss Fig. 4. The relationshipbetween direct land lossand as land that became open water as a direct indirectland loss primarilycanal density!in the consequenceof hurzummodification. Natural loss 8 aratanawatershed for eight 15' quadranglemaps was all other land loss. The 'Man-made loss' in the analyzedby Britsch and Dunbar 993!. No data was Britschand Dunbar 993! analysisis the sameas excluded. Four different mapping intervals are what1 consideredto bedirect land loss in this paper. coinpared: 1930sto 1950s,1930s to 1950s,1930s ro The 15' quadranglemaps included all of the 1974, and 1930sto 1990. Top: Area of direct land loss vs. area of indirect land loss ha!. A linear regression Barataria watershed. of the data is showntogether with the Coefficient of Determination R'!. p < 0.01 in all cases!. Bottom: T~er 997! usedall of thesedata except those The percentindirect land loss vs. the percent indirect niapswith >85% openwater, or <10' ha land within landloss. A polynomial fit of the data is shown a 15'quadrangle map. Only oneof nine mapsthat togetherwith the R'-for eachdata sei p c 0.01 in ail cases!. included the Barataria watershed was excluded in thatanalysis. This one map includedthe Delta Farmsregion, where an agricultu}alimpoundment failedin the1960s and the area became open water. Thisdramatic conversion toopen water represented the Barataria watershed and the indirect land loss Aevast majority of landloss from the 1930sto 1990 Fig. 4; p < 0.01 in all cases!.The interceptv as fortllat quadrangle map. zero,or less,indicating that no significant nct land losswouM occur withoutdredging. identical results There was a strong,positive relationship wereobtained for theneighboring Terrebonneand bet eenthe direct land loss within each 15 mapin St. Bernard watersheds Turner 1997!. 1M R. E. Turner Thisdata set was also used to plot the relative a low signal-to-noiseratio. ln otherwords, if the changesin land loss since the 1930s. The first competinghypotheses are individually strong or derivativeof thepolynomial regression equation interactwith each other, then a plotof directand describingthe cumulative land loss as a function indirectland losses should look like the scatter-plot of time yielded an instantaneousland-loss rate of datapoints shown in thebottom side of Fig.6, whosetrajectory approached zero in the 1990s, notthe rather strong linear regression shown in the land-lossrates declined as rapidlyas theyrose. top panel, which is the result for the Barataria These estimated instantaneous land-loss rates watershed R' = 0,98;p =0.001!, This result sug- paralleldredging activity. but land losslagged geststhat the cft'ect of canaldredging and hydrologic dredgingactivity by several years Fig, 5!. changeon land loss is quite robust. Testsof CompetingHypotheses HO: Thereare many reasons why it isnot easyto Hydrologic Change developlandscape-scale data andthen usethem fruitfullyto test competing hypotheses about how n 0.3 hydrologicalterations of the landscapeaffect the N 0 area ol coastal wetlands. Underneaththe surface 7 0.2 of theLouisiana coast are deltas of differentages V iti andcomposition. Theamplitude and energy of the 0.j. tides within and amongwatersheds is not C homogenous.Thedensity and timing of dredging activity variesamong watcrsheds because of economicand anciently-defined geological factors. 0 025 0.05 Furthermore.ifthe four hypotheses identified earher Direct Loss in thispaper are compiemcntary, or if the causal Land significantterms interact, then the effectsof dredgingshould be difficult to tease out because of HO: Salinity, Suspended Sediments and Flood e mrect t and ass ' total Landlossr10 o Permitted Direct t andloss! ~ 8 M O X 0.025 0.05 Direct Loss l 960 >980 year Land Fig 5 L d lossand cmg d Kgng over t me for the Fig.6, TopPaneh the hypothesizcdrelationshipbetween Louisianacoastal zone from Tutner 1997!. Permitted indirectand direct loss if thehydrologic change area open squares! isbased on the area dredged each hypothesisiscorrect. Bottom Panel: the hypothesized yearthat is permiued bythe State's coastal zone relationship between indirect and direct loss if the managementprogram. The other two estimates are hydrologicchange hypothesis isnot correct or if several basedona statisticalfii of the Brit sch and Dunbar hypothesisare significant individually or actingin l993>land loss data for the whole coast. concert.The left panel from Fig. 4 in Turner1997! is the actualdata for the Baratariawatershed. BaratariaEstuary Wetland Loss 189 Another test of competing hypotheses is to the reducedsediment loading. There are at least comparethe relationship between land-loss rates and three linkedassumptions if this hypothesisis true: hydrologic changein the Baratariawatershed for I! saltwater changesmust occur,throughout the theyears before and after the significantdrop in watershed,and not just in onesmall part of it, ! suspendedload occurred in thc mid-1950s. If this thesechanges must be significant plant stressors and sediment-loaddecline was an additional cause of lead to vegetationlosses, and, ! otheremergent wetlandloss, then theintercept of theland-loss and plantcommunities do not successfullyre-colonize canal-densityrcgrcss ion line shouldbe higherafter any newniche created. the 1950s, han for data for beforethe 1950s Fig, 7!. If the decline in sediment loading were an The 'saltwater intrusion' and the 'sediment insignificantinfiuence on land loss during the deprivation'hypotheses were tested by assigning mappinginterval!, then there would be no difference each 15' basemap a numberto denoteits relative in theslope of the regressionlines for the two data position inland from the estuarine entrance sets.The hypothesized influcnced was not observed describedin Turner 1997!. The quadranglemap see Fig, 4!, so we shouJdreject this competing closest to the estuarine entrance was the lowest hypothesis. numberedmap, and the quadrang Je inap furthermost from the seawas nurnbercdthe highest. The relative effects of increased estuarine salinity which are tLttlgenerally observed on this Thesetwo hvpotheses salinity stressand coast;Wiseman et al., 1990! and flood protection sedimentdeprivation! can be rejectedfor several andnavigation levees on land-lossrates can also be reasons,in additionto the previously described testedwith the data setof Britsch and Dunbar 993; relationships.The estuarineheadwaters are where Turner1997!. The hypothesissuggests that land- overbankflooding previouslyoccurred but not Joss rates will increase if freshwater fiow into everyyear!. Plant stressresulting from sediment- estuarineheadwaters is restrictedand plants become deprivationor salt water intrusionshould be: I ! stressedby an increasein salinity,or, becauseof lowestfor theplants that are inost adaptedto high salinity and nearest the reinaining suspended sedimentsupply the estuarinecrttrance!, and, 2! Ho: Hydroloqic Change highest for thoseplants least adapted to salt, i.e., thoseplants located in the freshwaterrnarshes. 1f and Suspended Sediments salinity stressoccurs, and if it leads to land loss. After then the amountof indirect land loss per direct land 1955 loss shouldtheoretically have been highest in the tn 0.3 lowest salimty zone bottom panel in Fig. 8!. This Ol ef ore result was not observed, The indirect:direct land 955 loss ratio declines, not increases, going from salt to V c 0.2 freshwaterzones along a gradientfrom the estuarine mouth to inland. This ratio does not decline in the regionwhere plant stressesshould bemost sensiti ve t 0.1 to salinitystress Fig. 9; R' = 0.80;p =O,G] 6!, There is moreland lossper dredgedchannel in the high- 0.025 0.05 salinityzone of thc estuarythan in the low-salinity zone, and land loss with dredging where flood Direct Loss protectionlevee s aremost likely to reduceoverbank Land flooding. Although saltwater intrusion may be significantlocally, it doesnot appearto be a major Fig, 7. The hypothesizedrelationship between indirect anddirect land lossfor two mappmgintervals if indirect factor driving land loss this century in this suspen~ sedimentloading in the l950s hasan effect basin,These two hypothesesare therefore rejected. on landloss. This patternwas not observed see Fig. 4l. Ho: Hydrologic Change 5 hig O V 4 OV 3 5 7 Distance{relative! seaward! landward! low Fig.9. Therelationship between the land loss per w Distance W areacanal Y axis! andthe distanceto the coastin Seaward Landward 15' quadranglemaps. Land loss is from Britschand Dunbar 993! and is for the 1930sto 1990. The distancemeasure is a simplemap sequence from coast to inland, Coatelusiosts HO Increased Salinity or Sediment Oeprivation Thchypothesis that hydrologic change is the hig primarycause of wetlandlosses in the Barataria watershedwas tested in variousways using data on V landscape-'scalehabitatchanges. Comparati ve tests ofcompeting hypotheses were also made to exainine the relativestrength of theinfluence of salinity O8! V changes,suspended sediment load reduction, and flood protectionlevees on land-lossrates. The resultswere consistent among several tests. The formationofponds is highestnear canals, whereas pondsthat revert to wetlandsare relative!y scarce t low nearcanals. When canal density is high,land-loss ~ Distance ~ ratesare high, and when canal dredging slows, then Seewnrd Landward land-lossrates stabilize or decrease.Thc amount of landloss per area of dredgedcanal is highest wherethe hydrologic gradient is highest from Fig,8. Thehypothesized re!ationship between the tides!,and not in the estuarineheadwaters. The indireiclossrates Y axis! vs. direct losses Xaxis! hydrologicchange hypothesis isthe only acceptable fromthe 1930s to 1990 for each estuary asa function hypothesisofthe four that were tested. lt explains of distancefrom the coast data are for the ] 5' therise and fall of' land-loss rates in time and space quadranglemaps examined byBritsch and Dunhar l993!.Only quadrangle mapswith <85% open water in the Baratariawatershed and is a moreefficient and>8 ! 00ha are included. The top panel indicates the explanationthan alternative hypotheses t"e resultsnecessary tosupport thehydro!ogle change applicationof Occam'sRazor!. hypothesis.andthe bottom panel isthe anticipated resultif increased salinity, decreased suspended Theseconclusions obviously h»e som sedimentsorboth is significant. Theactual resuhs are thatshown in the top pane! and Fig. 9. consequencesforconserving theexisting wet!~+ and for their rehabilitationand restoration. BaratanaEstuary Wetland Loss %91 consequenceis that thc role of plantsin wetland Universitycourse -Wetland Loss. Restoration and stability should be consideredas more than a Managetncnt"are especially thanked for their reactionto patterns in inorganic sediment rates. patienceand wiHingness toleam, sharc, and critique planbare major contributors to wetland accretion, thevarious ideas that survived here, and for helpin plant ecologists could contribute to wetland buryingothers, restorationby investigating belowgroundplant organicstorage pools; wetlandhydrologic studies LIT ERAT Li RE C1TED should be expanded to include landscape-scale interactions. We have much to learn. BAss,A. AhoR. E. TuRRRR.1997. Relationships betweensalt marshloss and dredged canals in Landscape-scaleanalyses bring a uniqueset of three southLouisiana estuaries. Journal r>f complicationsto ecosystemscience. Obviously Coastal Research 13:895-903 landscapesare not homogenous, and therefore BAUMANN,R, H, AND R. E. TDRhnR. ]990. Direct variability is introduced when comparing one impactsof outer continentalshelf activities on watershedto another. Further, varying the size of wetland loss in the central Gulf of Mexico. the measuringunit tnay confound detectionof the EnvironmentalGertlogy and 8'ater Resources actualpattern. An analogymight be the exatnpleof 15:189-198. tryingto determineif theearth i.scurved. Although BOESCtl,D. F., M. N. JOSSFJYh, A. J. MeirrA, J. T. the earth's surface is easily seen as curved when Moaxis, W. K. Nt,TTLF., C. A. SIMnh'sTAD,AVt! flying long distances, its shapedoes not appearto D, J, P. Swum. 1994. Scientific Assessment ol be round when walking, One cannot quantitatively Coastal Wetland Loss, Restoration and detect this curvature with ordinary surveying Managementin Louisiana.Journal of Coastal instrumentsas easilyalong a 10 m path, as alonga ResearchSpecial Issue. No. 20. 10 km path. If a 100 km measuringpath or 100 BRrrscii, L. D AND J, B, Duh'uAR, 1993. Land loss km'plot! hasa mountainrange, then aneven longer rates: Louisiana Coastal Plain. Journal of path may be neededto compensatefor the local Coastal Research 9:324-338. variation introducedby geological history. The MARrtv, J. C. ANDS. SHtnelsoacn. 1984. Subsidence relationshipbetween hydrologic change and land overoil andgas fields. Reviews in Engitreering lossmay not seem evident by analyzinga 1-hapixel, Geology6:23-34. insteadof a 100-ha pixel. or if the wetland is ScAtFE,W. W., R. F. TDRNeR,Ahio R. COSTAvzx. encompassedby stranded beach ridges, or 1983. Recent land loss and canal impacts in embeddedwithin the Mississippi River delta, or coastal Louisiana, EnvirorrmentalAfanagetnent isolatedby remnantchannel leveesburied a few 7:433-442. meters below the surface. This situation leads one SuHAYDA,J. N. 19g7. Subsidenccand sea level. to understandthat the interrelationships between Chapter10, 1n: R. E.Turner and D, R. Cahoon wetlandhydrology and plant health may extend over eds,!: Causesof WetlandLoss in the Coastal kilometers,and that evaluatingthese connections Central Gulf of Mexico. Voh 2: Technical mayinvolve some ratherinnovative and humbling Narrative.Final reportsubmitted to Minerals failuresbefore we fully appreciatethe proper scales ManagementService, Contract No. 14-12-001- necessaryto investigateand quantitatively predict 30252. OCS Study/MMS 87-0119, New theconsequences of coastal wet.land management. Orleans, LA. TuRhrER,R. E, 1990. Landscapedevelopment and ACKNOWLEDG MENTS coastalwetland losses in the northernGulf of Mexico, American Zoologist 30:89-105. Theseanalyses accumulated over tnany years, TL~zR, R. E. 1991. Tidegage records, water lc vcl andespecially through the often vigorous discussion rise and subsidencein the northern Gulf of withcolleagues and the hardwork of the variousco- Mexico. Estuaries 14:139-147. authorsand studentswho sharedthe researchefforts TtnthrER,R. E. 1997. Wetlandloss in the northern escribedherein. Students of the Louisiana State Gulf of Mexico; Multiple working hypotheses. Estuaries 20:1-13. 192 R. E. Turner Tva~ R. E. ~n Y.S. Rao. 1990.Relationships hetweenwetland fragmentationand recent hydrologicchanges in a deltaiccoast. Estuaries 13:272-28 ] . WtSmae, W. J., JR.,E. M. SwENSOt',mn J. PowER. 1990, Salinitytrends in Louisianaestuaries. Estuaries 13:265-271. Pattern and Process of Land Loss in the Louisiana Coastal Zone: An Analysis of Spatial and Temporal Patterns of Wetland Habitat Change' JOHNW. DAv,JR.', GAttv P. SHAFFEtt', LoUls D. BRITSCH-', DFN1SEJ. REED, SUZANNF. R. HAWES, DONALD CAHOON" 'Depanrnentof Oceanographyand Coastal Sciences and Coastal Ecology Institute, Loui.sianaState University,Baton Rouge,LA 7N303, TEL: 225-388-6508;email: johnday Otlsu. edu 'Departmentof BiologicalSciences, Southeastern Louisiana University Hammond, LA 70402-0736;TEL 504-549-2865; email: shafe@selu,edu 'U.S.Army Corps of Engineers,New Orleans District Engineering Division P.O, Box 60267, New Orleans, IA 70I60-0267; TEL: 504-862-2995;email: louis.d bri tschC+mvn02.usace. army,mil 'Departmentof Geology,University of NewOrleans, IVew Orleans, LA 70148; TEL: 504-280-7395; emai L dj [email protected] 'U.S,Army Corpsof Engineers,New Orleans District Engineering Divisiort P.O. Box 60267, New Orlearts, LA 70I60-0267; TEI.: 504-862-25I8; email: suzanne.r.hawes@'mvn02. usace.army. mi I National WetlandsResearch Center, U.S. GeologicalSurvey, 700Caj undome Blvd., Lafayette 70506; TEL: 3I8-266-8634; emaiL. don cahoon@usgs,gov ABSTRACT:An earlierinvestigation Turner 1997! concluded that auostof thecoastal wetland loss in Louisianawas caused by theeffects of canaldredging, that loss was near zero in theahsence of canttlsvand that land loss hect decrettsed to nearzero by the late 1990's. This analysh was based on a 15-minutequadrangle approximately 68,000 ha! scalethat is toolarge to isolateprocesses responsiblefor small-scalewetland loss and too small to caphtrethose responsible for large-scale hrss.Herein, we conduct a furtherevaluation of therelationship between direct loss due to canal drcdghtgand all other loss From 1933-1990 using a spatialscale of 4,100ha that accurately captures localland-loss processes. Data sets for the Pontchartrain and Breton basins did not meet the criteria for parametricstatistics. Regressions of other wetlami loss on canalarea i~., directloss! for the Blrdfoot,Terrebone, and Calcasleubasins were not signlHcant. Significant positive curvilinear relationshipswere isolated for the Baratarla RMAO! and Mertnentau R0.29! basins,indicating that tbeextent oF canals is signi6caatly related to wetbmd loss in these basins. A significantnegative relationship R~~l! wasfottnd for theAtchafalaya coastal basin which had statisticaHy lower loss rates than the otherbasins as a whole. Whenthe data werecombined for aH basins,92% of the variation in other wetland loss was attributabieto cana!s. AHsignificant regressions intercepted the Y-axisat potdtiveloss values indicating that smne loss occurred m theabsence of canals. We agree with Tttrnerthat canalsare an importantagent in caushtgwetland loss in coastalLouisiana, but stronglydisagree that they ase responsible for the vast majority of this loss. We conclude that wetland lossin the Missimippidelta is an ongoingcomplex process invoiviag several interacting factors and that efforts to create and esture Louisiana'scoastal wetlands ntust emphasizeriverine inputs of Fresh water and sedbnents. Fromthe SymposiumRecent Research in CoastatLouisiana: 'This paper ia s condensed version of an article thol can tttaturatSystem Function ansi Response ta Humantnfluence. be Foundin Vohsme23 of Estuariestutd is printed here Rozas,L.P., !.A. Nymao,C.E. Pro%tt,V.N. Rabalais,DJ. with the permiaaiooof the Estuarine Research Reed,attd R,E. Tumor editors!. 1999. Publishedhy Loutstaoa Federtstion. SeaGrattt Co/lege Program. 193 104 J,W. Day et at. Iatrodtsetlots 3. Land I ossis highestnear the coast and decreases Turner 997! analyzedwetland loss in coastal inland. This implies that land loss is highest in Louisianawetlands from 1932to 1990 using salt marsh and lowest in fresh marsh and that statisticalanalyses of landto waterchanges in 15- sal waterintrusion has not been an important minute quadranglemaps. He concluded that factor in land loss. virtuallyall of the losswas causedby canals,that land loss was near zero in the absenceof canals, 4, Restrictedriverine input has had little impacton andthat land loss rates declined to nearzero by thc landloss. A corollaryto this i» that land lossin late 1990s, Turner explicitly excluded saltwater wetlandsin the AtchafalayaDelta region,which intrusionand the leveeingof the MississippiRiver is not leveedand receivesapproxiinately one as important factorscontributing to land Joss thirdof the totaJAow, of the Mississippi River, becauseland losswas highest near the coastand has been the saine as that of other basins with becauseregressions of direct versusindirect land similardensity of canals. If land loss in the losshad zero intercepts. In thispaper and in Turner Atchafalayadelta region is low, it wouldsu ggest 997!, direct land loss refers to wetland which that~bile lack of riverineinput may not have becomeswater when canals are dredged and indirect directly caused land loss, riverine input is land loss refers to all other wetland loss. Turner' s essentialto building newwetlands and reducing conclusionscontradict PenJand et al. 996!, who lossof existingwetlands, concluded that about 46% of wetland Jossin coastaJ Louisianahas occurred through natural processes. Materials and Methods The objectiveof thispaper is to catTyout a Data Base further evaluation of the causesof land loss in the Louisianacoastal zone, particularly with respect to 8ritsch andDunbar 1993!quantified wetland the efFectsof canals, A more detailed version of to water changesduring four snappingintervals: thispaper Day et al. 2000!may be found in the early-1930sto rnid-1950s referredto in this paper journalEstuaries. This reduced version has been as 1932-1955;the actualdates of thedifferent snaps printedwith permissionof Estuaries, usedvaried slightly!, 1956-1973, 1974-1982,and 1983-1990.They aggregated their direct and indirect Turner 997! statedfour hypotheses about the landloss data to the standard15-minute quadrangle coastwide causesof landloss and testedthem with map scale -68,000 ha or 168,000 acres!, This is a variousstatistical analyses of directand indirect Jand convenientscale for mapsbecause it is largeenough Jossrates from 15-minute quadrangle snaps which to presenta considerableamount of detail but small containabout 68,000 ha. Wehave incorporated the enough so that the number of maps which essenceof thesein thefollowing hypotheses which encompassthe entire coastalzone about50 maps! we testin thispaper. is notexcessive, Britsch and Dunbaralso produced six spatial maps that were color coded for each Hypokhetses mappinginterval Britschand Dunbar 1996,Fig 2 of Day et al. 2000! 1. Directland loss i.e., dueto canals!is quan- titativelyrelated to landloss in general,both for However,the 15-nunutequadrangle scale is individualhydrologic basins and for thcentire generallytoo large for statisticalanalysis of site- coast.indicating that most land loss can be specific patterns of wetland loss in coastal attributed to canals. Louisiana.The patch sizeof mostof the land loss that hasoccurred in the coastalzone is considerably 2. Whenshrect land lossis zero,other land lossis smallerthan the scaleof a 1 5-minutequadrangle. closeto zero i.e.,the intercept in regressions of An exatninationof the mapsof Britschand Dunbar otherland losson directland lossis zero!. 993! shows that most 15-minute quadrangles RelaionshlpBetween Canals and Wetland}l QM $95 containseparate patches of wetland lossthat arenot wetland habitat type in each cell, we overlaid spatiallyor functionallyrelated to eachother see vegetationc}assification maps on the habitatlos» Fig,2of Day etal. 20 N!. For example,in adetailed nMps. For the 1932-1955loss period, we usedthc studyof the proximityof canalsand wetland land 1949 mapof O' Neil 949!. In a similar manner, loss Leibowitz 1989!,no relationshipexisted for for the 1955-1973, 1974-1982, and 1983-1990 }os }andlos» greater than 5 kin froin the canals. intervals,we used vegetation classification map» for 1968 Chabrecket. al, 1'968!, 1978 Chabreckand Data Analysis Linscombe 1978!, and l988 Chabreck and Linscombe 1988!, respectively. To better approximatethe locationand scale of manyof the land loss processesand patterns Regression and ANOXIA analyses w ere including oil and gas fields where most canals performedusing the SYSTAT 6,1 general linear occur!, we subsampledthe tnapsof Britsch and rrxx}e}.Specific hypothesis tests between direct }and Dunbar 996! at a 4,}00 ha 0,100 acres! or 6,4 loss i.e., due to canals! and other land lossi nc1ude: by 6.4km ce}l size, which approximates the size of ! otherland loss in the entire coastalzone and in an average oil field network or a large marsh eachhydmlogic basin is statistically relatedto direct managementimpoundnient Cahoon and Groat land lossand ! when direct land loss is zero, other 1990!, A priori, the total number of cells n=121! land loss is zem; ! land loss is highest near the wasdetermined by budget constraints,These cells coastand in salt rnarshes for this test,distance from werearranged along 19 transectspositioned nearly the coastwas defined by the sequenceof each cell equidistantfrom eachother, such that the number in the subsamplingtransects!; and ! land loss in of cellsper unit area of thecoast was roughly equal. theAtchafalaya Delta hydrologic unitis not different We did not include transects which would have been froin that in other hydrologic units. HypothesesI practicallyall water eg transectsin LakeCalcasieu and2 weretested with regressioninode}s, wherea.s or Lake Pontchatrain!.However, to ensurethat each 3 and4 were testedas separateone-way ANOVAs basinreceived at least n=7 cells, it was necessaryto usingbasin, cell number in thetransects, and marsh place some transectscloser together e.g., the typeas categoricalvariab}es. birdfoothydrologic unit is verynarrow compared to the others!. The transects were positioned We did not eliminate cells containingless than perpendicularto the localcoastline either the 6u}f 15% lard in 1933 as in Turner 997! becausethis shoreline or interior bay margins as in the potentiallycreates two biases. First, by definition, Terrebonne,Barataria, Breton, and Pontchartrain these cells are located on shorelines where the basins!and variedin lengthbecause they extended priinarycause of landloss is waveerosion, Pen}and to theinland extent of the mappedwetland, bui did et al, 996! reportedthat about35% of landlos» notoverlap one another.While this processwas wasdue to wave erosion Second, very few oil field not completely random, the placetnentof the canalnetworks arc located directly on the Louisiana transectswas inadc without. regard to overa}lland coastlineand henseelimination of coastal cel}» may losspatterns and, once the coastalcell of each improvethe regressionfit, transectwas p}aced, a}l ccl}s along the transectwere fixedin place. Log transformationsof the dependentor independentvariable, or both, wererequired in In eachcell, direct dueto canaldredging! and several instances when the data did not meet the all other ]andloss termednatural loss by Britsch criteriafor parainetricanalysis and when relation- and Dunbar 1996! was determined for each shipswere curvilinear. Nonparametric regression samplinginterval. SinceBritsch and Dunbaronly wasrequired for the Pontchartrain andBreton Sound classifiedchanges from land to water,the change datasets Burkesand Dodge 1993! Whendata frommarsh to spoilbank adjacem to eachcanal is contained an observation with excessive le'veiage not counted as loss. Britsch and Dunbar did not i.e., > 0.55!the results are presented with and classifyland loss by habitattype. Todetermine the withoutthat observation Hair et a}.1998!. For ihe 18' J.W, Oey at al. Barataria,Atchafalaya, and combined data set, one for the Birdfoot, Terrebonne, and Calcasieu observationrequired omission because it produced hydrologicunits bestfits producingp>0,12, Fig. an excessive >+3.0! Studentized residual Hair ei 2!. Positiverelationships existed for thc Breton al. 1998!. Unlessspecified, differences were Sound F,,=10.37,p=0.023, Fig. 3a!, Barataria deemedstatistically significant at alpha= 0.05. F, =56.97,p<0.0001, Fig, 3b!. andMerinentau An attempt was made to analyze the data basins F~~ 1073 p 0004 Fig. 3c!, producing standardizedto the amountof landpresent at each R -0.675,R'=0.721, and R'=0.349, respectively. site in 1932 as in Turner 1997!. That is, the direct For the Baratariadata set, omission of thcsingle andother loss values were propottianalized io the observationonthe Y axis with leverage&.57,Fig, amountof hmdin eachtx:11 at the beginningof the 6aj decreased the R' from 0.721 to 0.470. study.These data required an arcsinesquare root Interestittgly,in the Atchafalaya,which is a basin transformationtomeet norma!i ty andhomogeneity characterizedby high input of riverineinorganic of varianceassumptions Sokal andRohlf 1995!, sedimettts,a significant negative relationship existed 4000[ A I Rggggitt!lt:For all the data standardizedto the amountof land presentin 1932, no significant Blrdfoot relationshipsoccurred, regardless of transforination Fig, 1!. interestingly,when cells were reinoved 2 3000 thatcontained less than 15% land in 1932 seeFig, 4 of Turner. 1997, for comparison!,the fit did p becometnarginally significant F, rr3 4.16, p<0.044!albeit weak RM.036!. Forthe analyses $ 2000- by basin,standardization did not itnprove the fits; therefore,all subsequent interpretations are hmited to the non-standardized data. tDOO Statisticallysignificant relationships between 0 400 200 300 other land lossand direct land losswere not obtained Direct Loss ha! 9- 06 B. Terrebonrt e sI- rrr 0.5 p 7" 4- rn zs 03| Ca p E 0.2~. P ~ J . 5- z 0 14 4'" 0~ 0 1 00 200 300 400 0.0 0.01 0.02 0.03 0 04 0.05 Direct Loss ha! Normalized Direct Loss Fig. 2. Direct land !oss and other land loss for the A-! Fig. l. Directwetlands loss and otherwetlands loss Birdfoot and B.! Terrebonehydrologic unib from forall basins normalized tothe land present in each 1933-1990. Data for Calcasieu Basin are not shown as quadratin 1933 as in Fig.4 ofTurner 1997!. n = 121. directloss was zero for all quadrats. RehionshipBetween Canalsand WetlandLoss t tlat between other wetland loss and direct loss cti F W,93, p=0.041,Fig. 3d!, producingRa=0,236. 3 7 Forthe three parametric fits Barataria,Merrncntua, andAtchafalaya!, the intercept b ! wasstatistically g 56 greaterthan zero, indicating that there was wetland 4 loss in the absence of direct losses. The regressionof otherwetland loss on direct wetland loss with all of the data combined could 0300 1 2 23456 78 accountfor only 9.29oof wetland loss attributable tocanals F, = .00,p=0.001, R'=0.092, Fig. 4!. Rank of Direct Loss Theintercept of b.=644ha was highly significantly 9 differentfrom zero t=6.60, p .0001!. 87 >~VI.: The data set with all basins combined was also used to test for diffetences in h 6 other wetland loss from 1932 to 1990 due to effects is! 5 of basins,the distance from the coast, and marsh type Fig. 5!. The basineffect washighly significant for theraw F, ,=9.56, pc0.0001,Fig, 5a! and F40 12345 678 standardized F, o,=g.71,pc0,000! data and thc a prr'orilinear contrast of theAtchafa! aya versus other Log Direct Loss ha! 8 ~ ~ basinswas highly significant F~nz 12 9 Cl pc0.0001and F, , =11.37,p<0.0001 for the raw C, and standardizeddata, respectively!, despite relativelylow lossrates in the BretonSound and Pontchartrainbasins Fig. 5a!. Land lossdid not differ from the coast inland for the raw data 5 F =l.32, p&.247!, butdid for the norlnalized O 4 ' Mermerttau data F,,~=2.68, pW.014! with the highest losses occurringin bothcoastal and the mostinland cells F 0 1 234567 Fig.5b!, Wet!andloss did not differ for different Log Direct Loss ha! marshtypes F,, =2,72,p=0,069!, but displayed a similarpattern as that of distancefrom the coast D. Fig. 5c!. 8 6 Discussion I Theresults of ouranalysis indicate that canals ~ ~ w ~ havebeen an importantfactor in landloss, but that 0 therelationship with land loss varies between basins. F Atchafalaya ForBarataria Basin, up to 72% of otherwetland 4 2 3 4 5 6 losswas statistically associated with direct losses dueto canals. However, omission of a singleouther Log DirectLoss ha! decreasedthe R' to0.47, or by 35%. Frolnboth an ecologica!and statistical perspective, webelieve that Fig. 3, Regressionsof other wetlands loss on direct a singleobservation with thatmuch leverage war- wetlandsloss for A,! BretonSound. B.l Baratana" C.! Mermentau,and D.! Aichafalaya basinsfrom rantsomission. There wasno significantrelation- 1933-1990 95% confidence interval s of the mean are shipbetween direct land lossand other land lossfor included. foe J,W. payat al. 4000~-r r r All Sites Combined Q 0 300 Ci ~ 0 8 ~ 2 M N ,, 0 Fig. 4. Regressionof otherwetland loss on direct c, C3 wetland loss lor «ll hydrologicunits combinedfor penod af 1933-1990.95% confidencelimits of the 5 meafl are Included, E 01 several of the basins Pontchartrain,Birdfoot, Terrebonne,and Calcasieu!. This does not mean, of course,that land loss has not been caused by i 0 1 2 3 4 5 6 7 canalsin thesebasins, Rather, it indicatesthat other processesarc also i tnportant and inaskthe potential &stance from Coast cell ntimter! statisticalrelationship, orthat insu%cient statistical 15 powerexisted due to low sample sizes. There was no clear patterrtin landloss with distance from the coastor fordifferent types of marsh, and in general 10 theAtchafalaya hydrologic unit, with the highest C! D Q! riverineinput. has had a significantlylower rate of l4 wetland lossthan the other basins. io E05 Althoughthe t5-minutequadrangle is a convenientmapping scale for a varietyof purposes, i t commingles i.e.,aliases! the functional processes responsiblefor coastal wetland loss in Louisiana. 00 In a detailedstudy of theproximiry of canalsto patchesof high wetland land loss, Leibowitz I989! ~G concludedthat canals were not the prirrtary cause Marsh fype ofthe loss. In addition, when positive relationships betweencanals and land lossexisted, the Fig, 5. Differencesin wetlandloss rates from 1933-1990 relationshipdecomposed within 5 kmof thecanal. among A! basins, B! disumccfrom the coast Cell 1 is Our quadrNswere 6.4 krn ona sideand therefore neamstthe coast!. and C! marshtype. Standarderror shouldhave captured positive relationships crisply, barsare included.For basins,BA is Barataria,BS is had they existed. BretonSound, CS is Calcasieu,lvlo is MississippiDelta, ME is Mennentau, PO is Pontchartrain, TE is Terrebonne,and TV is Atchafalaya ReiaionsbipBetween Canals and WetlandLass 199 We found that direct land loss that is, dredged patternof landloss acrossthe salinity gradient, canals!ranged from beingnot statisticallyrelated There are documented cases, however, where wc to other land loss in several basins to accountirtg believesaltwater intrusion was responsible for !and for 47% and 68% of the variation in other land loss loss.For example, huge marsh losses occurred west in the Barataria and Breton Sound basins, respec- of the northernpart of Lake Calcasieuduring the tive!y.Based on regressionana!ysis, Turner ! 997! 1956-1973mapping interval, These losses occurred conc!udedthat canals arc responsiblefor the afterthe completion of theCa!casieu Ship Channe! majorityof wetlandloss and that whendirect !oss in 1941 and fol!owed the passageof Hurricane is zero,other land lossis zero. Our analysis detnon- Audreyin 1957. The hurricaneapparently led to stratesthat this is not the case. The scale of the 15- massivesaltwater intrusion and widespreaddeath minute quadrangles used by Turner leads to of the heshwaterCladium marsheswhich previously statisticalre!ationships betv ccn canals and other occupiedthe area Morganet a]. 1958!. The land !osswhich is clearly unrc!atedto cana!s i.e., remainingmarshes are now intertnediate tobrackish. shorelinewave erosion!. Pcn!and et a!. 996! also The constructionof the MississippiRiver Gu!f concludedthat land loss was due to multiple Outlet !ed to sa!twater intrusion and caused the death interactive causes and indicated that about ha]f of of almost all of the Taxodium swamps which the land loss was natura! and that thc total amount formerlyoccurred east of the MississippiRiver of! and loss indirectly due to "submergence"because below New Orleans Coastal Environments 1972!. uf human modifications was about 35%, Among Someof this area is now openwater, but much of the causes of land loss other than canals were wave the swamp has converted to Spartina marsh erosionand tectonic fauhing. scatteredwith ghostcypress trunks, In general,we found a loweroverall statistical Turner 997! conc!udesthat the isolationof re!ationship between direct and other land loss than mostof thedeltaic plain from riverine input by f!ood is suggestedby theresults of Pen!andet al. 996!. control!evees has not played a significant role in Forthe combineddata sct. the R'-was on]y 0.092, wetlandloss. This contradictsa long historyof Onereason for this is that the re!ationshipwithin research that demonstrates how the river built and eachbasin varies from linearto log-linear to log- maintainsthe delta Fisk et al. 1954; Kolb and Van !og to no re!ationshipto a negativerelationship in Lopik1958; Day et al. 1995,1997; Roberts 1997 I. the Atchafalaya Delta area. The mostobvious example of this are the marshes in the Atchafalayadelta region, a non-]evecdcoastal An importantdetrimental impact of canalspoil bay wheresubaerial land buildinghas continued banksis thatthey lead to the reductionof sediment since 1973 Roberts et al. ]980!. Our analysis inputand poor drainage of marshsoi!s Reed 1992; demonstrates that land loss in this area is sig- Boumansand Day 1994;Cahoon 1994; Cahoon et nificant]ylower thanthat of anyof the othercoastal a]. 1995b; Reed et a!, 1997; Swenson and Turrter basins. !987!.The pmgressive waterlogging due to reduced sedimentinput can interact with existing salinity to Turnersuggests that there is a "needfor tnuch producedeleterious effects on vegetation.A number greaterecological understanding" of wetlandsand of studieshave shown that multiple stresses,such thatthere is litt]eappnxiation of therole p]ants play as salinity and waterlogging,have a much more in "dotninating the accumulation of sediments detrimentalimpact on coasta]vegetation than a throughtheir contributionto soil organicmatter sing]estressor Grime 1979; Mendelssohnand be]ow ground."We certainly agreeon the needfor McKee 1988; Mc Kee and Mendelssohn 1989; Grace further study on the functioning of these systems. and Ti!man 1990; Shaffer et a!. ]992]. But it haslong beenrecognized that soil formation and accretion in much of the Mississippi deltaic We foundno c!earpattern in land lossrates plainis dominatedby organicsoil formationfrom with distance from the coast, or across different rootproduction and managetnent suggesuons have tnarsh types, suggestmgthat there is no general explicitlyincorporated this function Hatton et a!. 200 J.W. Oay et al, 1983;Temp]et and Meyer-Arendt 1988; Cahoon restoration,specifically with reference tocana] spoil 1994;Cahoon et al. ]995a;Day and Temp]et 1989; banks,should be a necessarycomponent of a Dayet al. 1995,1997; Nyman et al, 1993a,b!. holistic,integrated delta restoration p]an. ~s a]one Organicsoil formation often accounts for70%-80% however,will haveminimal impact if it is not of accretion,but additionof mineralsediments coupledwith reintroduction of river water.Mincra] resu]tsinstimulation ofp]ant production and health. sedimentswill begenerally necessary to re>ui]dand Mineralsediment addition, especially in riverwater, maintainthe coast,It is notlikely thatremoval of has several positive impacts on marsh plant spoilbanks will resultin revegetationona large communities.The rrunera]sediments add strength scale.Several studies have shown that there ts rapid «ndbulk to the sediments,for example,and they lossof elevationof 10-15 cm whenp]ant death carrynutrients that stimulate productivity and iron occurs Nyman et al, 1993a,b;Delaune et a], 1994. whichcomplexes with sulfidephytotoxins. Fresh Kernpet al. ]999!. In addition,soil strengthin water also reducessalinity stress. highly stressed,low elevation wetlands is very low andthere is verylittle elevation gain even with high Basedon his analysis,Turner 997! con- accretionrates Cahoon et al. 1995h;Kcrnp et a]. cluded that land loss rates in the coastal zone will 1999!. A nutnberof actionscan help reduceland be closeto zero by theyear 2000, But land loss loss,but only riverine input can leadta major ratescontinue to bc high,with measuredloss rates creation of new land. This agreeswith our rangingfrom 65 to 9] km'yr' in the 1980sand the fundamentalunderstanding of how deltas function 1990s Barras et al, ]994!, ln addition,landscape bothspatially and tempora]ly Roberts 1997; Day modelingresults Reyes et al. ]999! andstatistica] et al. 1997!. If Louisianais ever to achieveno net pmjectionsbased an past land loss rates J. Suhayda, loss of its coastal wetlands, we believe that it wi]] Dept.Civil Engineering,LSU, personalcom- be necessaryto expandrestoration strategies to munication! indicate that ]and loss rates will includemajor river diversions. continueto behigh aver the coming decades. For his modeling,Turner used a second-degree ACKNOWLEDGMENTS polynomialregression to fit wetlandloss over time andto extrapolateloss rates from ]991-1995. This Wethank Bruce Pugesek and Darren Johnson typeof regression canfit only a symmetricparabola, for statisticalcomments, and Donald Boesch, James andextrapolation with polynomial regression in Gosselink,Martha Hixon, Andrew Nyman and four generalis cautioned Zar ]996!, anonytnousreviewers for critiquingthe manuscript. Supportfor this effortwas partia]]y provided by the Conclusions LouisianaSea Grant College Program and by the U.S.Artny Corps of Engineers. We concludethat wetland loss in the MississippiDelta is a verycomplex process and that LITKRATURE CITED lassis causedbya dynamicand interacting setof processes.We agreewith Turnerthat. canals have B~ J A p E BouaGIKNsAND L. R. HA~~ '. been,and continue to be,an important agent in 1994 Land loss tn coastal Lou>siana 1956 contributingtothis land lass, We disagree, however, 1990, NationalBiological Survey, National thatcanals are responsible fora majority ofthe land WetlandsResearch Center Open File Repn lossand that land loss iszero when canal density is 94-0] 4 pp 10color prints zero.The exclusion of sediments, freshwater, and BocMAvs,R. M, ANDJ,W. DAv. 1994,Effects « nutrientsof the Mississippi River from much of the coastalzone has elinunated a major land building twoLouisiana marsh management plans on andmaintenance mechanism which historica]l water and material f]ux and short ter> counteractedmany of the processes responsible for sedimentation. Werlands14: 247-261- landloss and thus is a major factor in coastal land BRrrscH,L D, ANDJ, B Dtns~AR 1993.Land lo lossinLouisiana. Wea]so agree that hydrologic rates:Louisiana coastal plain. Journal af Coasral Research 9: 324-338, RelaionsiIIpBetween Canals and Wetland Loss 201 D. AND J, B, DL'NBAR, 1996. Land loss DAY,J,W., D, PONT,P.HENSEL. ANo c. IBAr'Fz.1995. in coastal Louisiana. A series of seven color Itnpactsof scalevel rise on deltasin thc Gulf mapsof coastalland loss. Tech, Rept, GL-90- ofMexico and the Mediterranean.. Thei tnpor- 2, Maps 1-7. U.S. Army EngineerWaterways tanceof pulsingevents to sustainahility. ExperimentStation, Vicksburg, MS andU,S, Estuaries18: 636-647. ArmyEngineer District. New Orleans, LA. DAY,J,W. JR J.F, MARTIN, L. CARooclt.ANn P. H. BIIRKES,D. ANOY- DODGE-1'993, Alternative TEMPLET.1997. System functioning asa hasis Methodsof Regression.Wiley, New York. 228 for sustainabletnanagetnent of deltaic pp. ecosystenLsCoastal ljrfana gement 25: 11S-153. CANOON,D, 1994. Recent accretion in twOmanaged DAY,J,W. JR G,P. sNAF»st, I..D. BRITscH,D.J. Rluux tnarshimpoundments in coastal Louisiana. S,R, HAwEs,ANn D. CAHOON,2000. Pattcm EcologicalApplications 4: 166-176. andprocess of land loss in the Louisiana CANooN,D, R., ANDC. G. GRoA7,EDs., 1990. A coastalzone: an analysis of spatial and studyof marshtnanagement practice in coastal tempondpatterns of wetlandhabitat change. Louisiana, 3 vols, Final report submitted to Estuaries23: in press. MineralsManagetnent Service, New Orleans, DELAum, R, D J. A. NYMANAND W. H. PATRlcK, Louisiana. Contract No. 14-12-0001-30410. JR. 1994.Peat collapse, ponding and wetland OCSStudy/MMS 90-0075. lossin a rapidly submergingcoastal marsh. CAnooN, D D.J. REED, Avo J.W, DAY, 1995a, Journalof CoastalResearch 10, pp.1021- Estimatingshallow subsidence in microtidal 1030. salt tnarshes of the southeastern United States: Ftsx, H, N., E. MCFARLAvJR., C.R. KoLe, ANoJ. L, Kaye and Barghoorn revisited. Marine WILBFsrrJR. 1954. Seditnentaryframework Geology128: 1-9. of the modernMississippi delta, Journal of CAIIooN, D., D. REEO, J.W. DAY, G, STEYER,R. Sedirnentary Petrology 24: 76-99. BOUMANS,J. LYNCH, D. MCNALLYANo N. LATIF. GRACE,J.B. ANoD. TILMAv,1990. Perspectives on 1995b, The influence of Hurricane Andrew on Plant Competition.Academic Press, San sediment distribution in Louisiana coastal Diego,CA. 484 pp, tnarshes,Journal of Coastal Research 18: GRnvtE,J, P. 1979. PlantStrategies and Vegetatio~ 280-294. Processes.John Wiley, New York.222 pp. CHABRECK,R. H. ANo G. LINSCOMBE. 1978. HAIR, J. F., R, E, ANOERsoN,R. L. TATHAM,Avn W. Vegetative-Type Map of theLouisiana Coastal C, BLAcK.1998. MultivariateData Analysis Marshes.Louisiana Department of Wildlife with Readings,Fifth Ed. Macmillan,New and Fisheries, New Orleans, LA, York, Inc. 745 pp. CHABRECX,R. H. ANO G. LINscOMBE. 1988, HATtoN,R., R. DELAONE,ANo w. PATRICK.1983. VegetativeType Map of theLouisiana Coastal Sedimentation,accretion, and subsidence in Marshes.Louieiana Department Of WIIditfe tnarshes of Barataria Basin, Louisiana. Lim- and Fisheries, New Orleans, LA. nologyand Oceanography 28: 494-S02. CHABRECK,R, H., T. JOAv~, AlsoA. W. PALMISANo KEMPP., J.w. DAY, D.J. Rrro, D.R, CAHOON,Axo M. 1968. Vegetative Type Map of Louisiana WANo.1999. Predictingeffect.s of sea level CoastalMarshes. Louisiana Department of riseand sediment supply on surfaceelevation Wildlifeand Fisheries, New Orleans. in anorganic rich salt marsh. In: L.P.Rozas, COASTALENVIRoNMFNTs, INc. 1972. EnvirOnmen4d J.A.Nytnan, C.E, Proffitt, N.N. Rabalais,D.J. BaselineStudy, St. Bernard Parish, Louisiana. Reed,and R.E. Turner cds.!, Proceedings, Preparedfor St,Bernard LA ParishPolice Jury. Recent Research in Coastal Louisiana. 159pp. Unpublished. LouisianaSea Grant College Program, LS1;, DAY,J,W. AND p. TEMPLET1989, Consequences of BatonRouge, LA, sea level rise: Implications from the KoLa,C. R. AvDJ. R. vANLot tx. 1958.Geology MississippiDelta. Coastal Management 17: of theMississippi Dehaic Plain -Southeastern 241-257, Louisiana. US Army EngineersWaterways 202 J,W.Day et al. ExperimentStation. Vicksburg, MS. Technical ReED, D. J., N. DF. LucA ANo A. L Poove. 1997. Report 2: 3-482. Effect of hydrologic managementon marsh LElaowrrz,S.G. 1989.The patternand processof surface sediment deposition in coastal land tossin coastalLouisiana: A landscape Louisiana. Estuaries 20: 301-311. ecologicalapproach. Ph.D. Dissertation, REvesE., J.F. ManrtN, M,L. Wutrr:, J.W. Dav, G 3'. LouisianaState University, Baton Rouge, LA, KEMF,In Press.Landscape modeling of coastal 298 pp, habitat change in the Mississippi delta. MCKRR,K. ANDI, MEND~SOxN.1989. Responae Of Ecology. a freshwatermarsh plant communityto in- RORRRrs,H. H. 1997, Dynamic changesof thC creasedsalinity and increasedwater level, holoceneMississippi River delta plain: the AquaticBotarry 34: 30]-316. delta cycle. Journal of Coastalkesearch 13: MRNDELssxoN,I. AND K. McKER.1988, Spartr'na 605-627, alter@iflora die-backin Louisiana:time-course RORRRVS,H. H, R, D. AD*ass, axo R. H. W, investigationof soil waterloggingeffects, CuvxtNoxAM. l980. Evolution of sand- Journalof Ecology76: 509-521. donunatedsubaerial phase, Atchafalaya Delta. MOROax,J, P., L. G, XtcxoLs, ANDle. WatOHr. 1958. Louisiana. The American Association of Morphologicaleffects of HurricaneAudrey on PetroleumGeologist Bulletin 64: 264-279. theLouir iana coast. Technical Report No, 10, SttARTR,G, P, C. E. SasSER,J. G, GOSSELtgtt,aNn ContributionNo, 58-3, BatonRouge, LA: M. REtMANEK.1992. Vegetationdynamics in LouisianaState University,Coastal Studies the emergentAtchafalaya Delta, Louisiana, Institute,53 pp. USA. Journal of Ecology80: 677-687. NVSraN,J.A., J. C, CALLAWAY,axn R, D, DzLatjm.. SoxaL,R, ANDF. ROLxF.1995 BiOmetry,Third 1993a.Case Study of a rapidlysubmerging Edition. W.H. Freeman and Co., New York, coastalenvironment: relationships among 887 pp, verticalaccretion, carbon cycling, and marsh SwENsON,E. ANDR. TuRNzR.1987, SpOil banks' less in Terrebonne Basin, Louisiana, Pro- effectson a coastaltnarsh water level regime. ceedingsof the Hilton Head Island South Estuarine, Coastal, and Shelf Science24: 599- CarolinaU.S.A. InternationalSymposium 2: 609. 452-457. T~ruw, P. ANDK. MFYFRARENDT. 1988, ~iaiana NYMaN,J,A R.D. DFLauNR,H.H. Roantrrs,axo wetlandloss: a regionalwater management W,H. ParRtcx,JR. 19931, RelatiOnship approachto the problem. Environmental betweenvegetation and soil formationin a Management 12 !: 181-192. rapidlysubmerging coastal marsh. Marine TuRNFz, R.E. 1997. Wetland lOSsin the nOrthern Gulf FcologvProgress Series 96: 269-279. of Mexico: multiple working hypothesis. O'Natl, T, 1949. The muskratin the Louisiana Estuaries 20: 1-13. coastalmarshes with map of theSouthern Part ZAR, J. H, 1996, BiostatisticalAnalysis, Third of Louisianashowing vegetation types. Edition. PrenticeHall. Upper SaddleRiver, Louisiana Wild Life and Fisheries NJ. 662 pp. Commission.,Technical Rept. 28 pp. PFNLAND,S., J. MFNDHsSOttN, L. WaVNF.,aND D, BRrrscx.1996. Natural and Human Causes of Coastal Land Loss in Louisiana, Coastal StudiesInstitute and Wetland Biogeochemistry Institute,Louisiana State University, Baton Rouge,LA, 25 pp, R~>n, D. J, 1992. Effect of weirs on sediment depositionin Louisiana coastalmarshes. Envi ronrtrenta Management 16: 55-65. 2N E, Reyes et al. INTRODUCTION affectingit changethroughout time Boumansand Sklar1990!. This ypeof feedbackhas been tested Coastal wetlands across southeastern inaquatic modeling programs like LAPTER Reyes Louisianahave cotnpacted and are being lost as they et al. 1994!, and used in terrestrial simulation convertedto open water Wells 1996!. Annual prograinsPATCHMOD Wu andLevin 1994!and variability in mean sea level MSL! can be several ECOLECON Liu et al. 19941. centimetersper year Baumann1980!, and can result in in~ penetrationof salinityinto wetlands STUDY AREA Penlandet al, 1988!.Such changes are believed to underliethe generalpattern of displaceinentof The Barataria-Terrcbonncsystcin is an freshwatervegetation by tnoresalinity tolerant ittterdistributaryestuarine-wetland system located communities,and vegetationdie-off followed by in southernLouisiana. The Baratariabasin portion conversion to apen water Roberts 1997; Wells is located between the natural levees of the 1996!, MississippiRiver and BayouLafourche. It is roughlytriangular in shapewith an areaof 6100 Most wetlands in the Barataria - Terrebonne kin'. TheTerrebonne basiri is borderedby Bayou estuarinecomplex are losingelevation to MSL at Lafourcheon the east and the Atchafalaya River on variablerates Penlandand Ramsey1990!. Reed the westand occupies 5500 km' Fig. 1!, 995! calculated mean annual land loss rates in Barataria at 20.1 km' for 1958 to 1978 and 34.5 Bothbasins are dynainic systems undergoing kmi for 1978 to 1988, and for Terrebonneat 24.9 changedue to naturaland human processes, The and 31.6 km', respectively.Reed 995! also Baratariabasin hns been closed to direct ri ver inflow estimated that indirect land loss due to canal since1904. Precipitation provides its mainsource dredgingcould accountfor tnore than 30% in of freshwater;however, the Mississippi River exerts Baiatariaand 10% in Tetrebonne,It appears that an indirectinfluence on salinityin the lowerbasin local anthropogenic modifications have had by reducingsalinity in thenearshore Gulf of Mexico differenteffects in each basin and making it difficult Petretet al. 197I !. The Terrebannebasin is directly to assesschanges on a regionalbasis. influencedby the AtchafalayaRiver. As a resuh, the westernportion of thisbasin is one of thcfcw Understandingthese habitat changes iscritical locationsin southernLouisiana that has experienced to assessthe long-termeffects of proposed net landgain Boeschet al. 1994!. restorationapproaches, The objectives of thisstudy wereio ! constructa multiplescale process model The vegetativecornrnunities in bath basins for the Baratariaand Terrebonnewatersheds to reflect gradients in elevation and supply ot understandand predict regional habitat change and freshwater.Marshes occur as bandsof sah, brackish. ! assesslong-term indirect and cumulative impacts andfresh vegetation from theGulf inland Chabreck of managementalternatives asproposed for wetland and Condtey1979!. Fresh marshesgive way to restoration. swainpsand bottomland hardwoods at higher elevations,These communities have overlapping Wchave been addressing these issues using salinity tolerances when grown in the laboratory. spatially articulatedlandscape models Costanza et butgenerally competition leads to distinctzonauon al. 1990;Sklar et al. 1985;White 1991; White et al. in the natural setting Conner et al. 1987!. 1991!.These dynamic spatial interaction models havebeen called Coastal Ecological Landscape MKTHGDS SpatialSimulation CELSS! by Sklar and Costanza 991!. CELSS modelsincorporate location- A landscapehabitat prediction model was»dt specificalgorithms that allow feedback between the for eachbasin. Each is a dynamicspatial model localprocesses andthe landscape dynamics, sothat usingvariable time and spatial scales. Both models boththe landscape andthe intensity of the processes usca finitedifference, 2-dimensional and vertically Landscape4lodeiing in Coastei Louisiana 204 100 ktu scale Atchafal ayaRtv ~ upland 1 BayouPerot Grand IsLe »g.1, The State of Louisianashowing location for the Batataria and Teirebonne watersheds. Nutnbcrs indicate time senesslations. »tegratedhydrologic modulewith a time step dt! modulewhich redefines the habitatinosaic cell size of 1hour and a spatialcell sizeof 100km' coupled of I km'-!on a bi-annualbasis. The conceptual witha primaryproductivity module with a dtof ] frameworkof the four modulesis presentedin day and 1 km-'cell size. Output from the Figure2. The model was written in FORTRANand hydrodynamicand productivitytnodules are runson a UMX platfortnand specific details for subtnittedto a soilmodule dt of I yr cell sizeof 1 the modulesinteraction can be found elsewhere ktn'! andthen evaluated by a habita.tswitching Reyeset al in review.;White et al. 1997}. 20S E. Reyeset at Fig.2, Flow of calculations forthe landscape progrsni modules indicating time and spatial scales, Hydrodynatnics velocity,is determinedto depositon the marsh or resuspended,Deposition is calculatedas a netdaily The hydrodynamicmodule uses the diffusion value,and salinity and duration of floodingare wave approximationfor shallow waterto calculate averagedto daily values. watermovement and sediment transport Singh and Aravamuthanl 995!. This approximation requires Productivity thailocal acceleration, uniform flow, and Coriolis forceio be considered neghgible. This simplification The macrophytemodule was viewed as a is necessarybecause standard hydrodynamic representationof any portion of a givenlandscape equationsrequire smal ler time steps than is practical with homogenouscharacteristics. The biological for longterm predictions Cheng et al. 1993!.The moduleruns on a daily time-step,integrating nei effectof frictionis accounted for by a Manning productivity for the inacrophyte community coefficientthat is the 100 km' average ofal l I km' throughouta I km' cell. Althoughstructurally the habitatdependent Manning coefficients included in same, the biological inodule uses different that100 km' cell. Inputs include rainfall, pumping parametersand initial values for eachhabitat once outfall,and rivers. Outputs are limited toevaporation is spatiallydistributed, Specifically, two biological andtidal boundaryexchanges. Infiltration into components are modeled: non-photosynthetic groundwateris assumed negligible. carbon biomass roots and stems! and photosynthetic carbon bioinass leaves!. Gross Initialspatial inputs include a 100kin' land pmductionis a functionof biomass,maximum gross elevationmap and a suspendedsediinents field. productionrate and a limitationfunction Hopkinson Resultanthourly values for 100 km' water elevation, et al. 1988!. This limitation function includes watervelocity, salinity and suspended sediment responsesto waterlevel. salinityand temperature. distributionsarelinearly interpolated toyield 1 km-' The waterloggingfunction represents the different values.interpolated water and landelevations are tolerances of each habitat as determined by a usedto calculate water depth. Suspended sediment representative specie! to flooding conditions is evaluatedhourly, and according to the water Nyrnan et al. 1993!, Salinity stress is also LandscapeModeling in CoastalLouisiana 206 determinedby habitat type Pezeshkiet al. 1987!, Thc habitatswitcher module has two corn- The temperature response function varies ponents:a dailycounter and a switcher.Thc daily seasonally.Respiration rates proxy for metabolic counterqueries biomass density, sal inity and depth stresses!adjust to thesesame factors Burdick et al. of standingwater at each1 km-'cell. Basedon these 1989;Dai andWieg crt 1996;Hopkinson et al. 1978!, values, habitat type is determined according to Excessfixed carbon is translocated to the non- classificationcriteria Table 1!, and the counter photosyntheticstorage Howes et al. 1985!.The advancesby oneunit. At regularpredeterinined oppositeprocess occurs if respirationlosses offset intervals, the habitat counters for each cell are photosyntheticintake, submittedto the habitatswitcher component Th» algorithmevaluates if a habitatchange shouldtake Soil place under several conditionalrules. If more than half of thetime open-water conditions existed then The soil module includes three components: the cell type is assigrcdas open water Nyman et inorganicsediments, dead belowgroundbiomass al. 1993!.If not, the vegetativehabitat type with andtotal beiow groundorganic sediments dead the highestcount is assigned.When the habitat type biomassplus non-photosyntheticbiomass from the changes,new productivityand respiration rates biologicalmodule!, Both inorganic and organic appropriatefor thathabitat type are applied in the componentswere divided by a constantbulk density biologicalmodule. The habitat switching decisions to calculate elevation. aremade once every two yearsin this model version but any time interval could be defined. Total seditnent elevation was calculated by addingthe heights of inorganicand organic storage Table 1. Habitat typedefinition by salinity PSU! and accounting for percentage pore space. and biomassdensity kg OM m *!. incorporation of aboveground litter to the belowgroundstorage is assumed negligible Nyrnan et al. 1993!.The amountof inorganicsediments is conservedand a decompositionrate is appliedto belowgroundorganic sediments. Subsidence accounts for 85-90% of the relative sealevel rise RSLR;estimated at L2 cmfyr!within Louisianacoastal marshes Day and Ternplet 1989!. While subsidenceis notexplicitly includedwithin thesoil module,decomposition of theorganic stock partially simulatesshallow subsidence.Deep subsidenceof the Holocenelayer is accountedfor FprchttgFunctions by increasedrates of eustaticsea-level rise Fenland andRamsey 1990!. Forcingfunctions for the landscapemodel wereinput as time series, The time series necessary Habitat Switcher to run both models from 1956 to 1992 werc cotnpiledfrom 15 stationsfor 9 parameters wind This modulekeeps track of habitatcharac- speedand direction, inorganic suspended sediments, teristicsand environmental parameters for eachcell evaporation,rainfall, air temperature, salinity, tides, throughouttime Theseenvironmental parameters river discharge! aresummarized and evaluatedannually to determine if theyare representative of another habitat type. Daily tide stageswere obtained from thc The interactionof primary productivityand National OceanService NOS! at Bayou Rigard. environme.ntalconditions defines habitat type for 1955-1979and from EastPoint, Grand isle from Laurenrothetal, 1993!.Once a thresholdofchange 1980-1988.Daily salinity values at GrandTerre Lab isreached, the model simulates habitat change. collectedby Louisiana Wildlife and Fisheries were gtP E. Reyes et al. usedas the boundarycondition for the Barataria Salinity was calibrated by adjusting boundary basin.Boundary conditions for Terrebonnewere set conditions i.e., salinity initial conditions and usingthe salinity distribution reported by Murray diffusionrates!. Salinity results matched closely the andDonley 994!. availabledata Murray and Donlcy 1994! in the lower portionsof the basins. SpatialData Assembly Theinacrophyte production module was tested Habitatmaps for theBarataria and Terrebonne usingspecie specific parameters for eachwetland basinswere provided by USFWSin rasterized625 dominantcommunity type. Varying physiological m' georeferencedmaps. These digital maps were parameterssuch as, tlooding and salinity tolerance derivedfrom aerial photography for 1956and 1978 within reportedranges Howes ct al. 1986;Nyman and satellite imagery for 1988 and 1990, and et al. 1993;Pezeshki et «I. 1987;Visscr et al. 1996; «ggregated to I kin'. In additionto openwater and Wisemanet al, 1990!produced seasonal trends of developedupland, each cell was classifiedas a productivityand bioinass Conner and Day 1976; wetlandtype characterizedby a singledotninant Kirby andGosselink 1976!. species.Salt rnarshes were characterized by Spartina alrerniflora,brackish rnarshes by Spartinapatens, Spatial Calibration fresh marshesinclude Pariicsrnrheiniromon and swampsby Taxodirrm disrichiurri Chabreck 1972; The model was run for the 1978 to 1987 Conneret al. 1987;Tiner ! 993;Visser et al. 1996!. decadeusing the USFWS maps to set initial conditions and final spatial comparison.The CA LIBRATION objectives were: I! to siinulated ecological processesacross the landscape and ! to verifythat Recognizingthat a landscape model is a all the landloss processes were implicitin the complexsystem with non-linearresponses to landscapemodel. This second objective was stated different environmentalstimuli, a calibration to assurerhat although when the landscapemodel strategywas implemented to considerthe effects of doesnot explicitlyincorporate local processes e,g, differentscales and impactsof each moduleon canalsand spoilbanks!,it incorporateswhatever modelperformance, This strategy allowed us to regionaleffects these impacts might have.This increasethe model complexity as each module was calibration method thus compensatesfor local I irsttested individually and then combined into the effectsby loweringthe regionalresilience of the landscapemodel. The data set used for this habitats to land loss. calibrationonly included the parameters from 1978 to 1988, The landscapecalibration required a matchin habitat distribution. This implied consistencyamong TemporalCalibration the land use changes, land loss rate and habitat responseto climatic variability. Previoushabitat Resultingtime seriesfrom each module were modelingefforts in southernLouisiana Sklar and comparedagainst available data at specific Cos anza 1991! have utilized a goodness of fii locations.The model was run repeatedly until these parameter Ft; Costanza 1989! to evaluate the model time series matched the field data. The performance.This fit index comparestwo maps hydrodynamicinodule was tested using the 1994 usinga movingwindow technique and calculates elevationinap Alawady and Al-Taha 1996!, no the degree of accuracy between them in values windsand theoretical tides for 1987 and 1988. rangingfrom 0 no match!to 1.00 perfectrnatch!. Hourlywater levels were computed by the model For the calibration purposes, the model was at cellscorresponding to the locations of theNOS repeatedlyrun comparingresulting mapsfrom 10- dataand compared for consistencyand match. yearsimulations ending in 1988to theUSFWS 1988 Manningcoefficients were then adjusted for each map. This was doneuntil the overall fit improved of thehabitat types to produce the best match. to 0.85 for both basins. an~scapeModeling in CoastaiLouisiana lnitia] conditions salinity, elevation, and canbe answered using this cotnparatlvc approach. Manningcoefficients!, and biological parameters Whatwere the effects ofthc management alterna- such as salinity tolera.ncesfor each habitat were tives.'r WasW it positiveor negative with rcgardito manipulatedduring the calibration.The 1978- ] 988 landloss' Was there any associated change inhabitat calibratedsimulations yielded a fit of 0,89 for distribution? Baratariaand 0,85 for Terreborme.There was also agreementfor total wetland and water areas for the Normal ConditionsScenario two watersheds Ft = 0.96 for Barataria and Ft = 0 94for Terrebonne!. Table 2 presentsthe resulting TheNC scenarioconsisted of a 30-year fits andhabitat areas for eachof theruns, starting simulation for eachbasin. To run simulationsinto with the calibration,validation, and management the future,theoretical time series and boundary optionexperiments that will be discussedlater in conditionsneeded to bedecided. We repeatedthe ihe text. originaltime seriesin reverseorder, because climate tendsto be cyclic Thomson1995!, The forcing Anothercalibration was doneby comparing functionsand boundary conditions are actual data available land loss information. Annual land-loss for years1955-]992 butwhen thc year 1993 was estimatesfrom 1955/56, 1978 and 1990generated simulated, the climate from 1991 wai used, 1994 from the USFWS and USACOE Dunbar et al. simulationused climate from 1990, and so on. 1992!intervals are given in Table3 alongwith those createdby the model, TheresuJting habitat distribution for Barataria Fig. 3! converted1,105 km-' to openwater during Validation 1988 to 2018 Table2!, The largestdecline 98 km'! wasfor brackishmarsh, while only 5 km-' of To validatethe model, parameters settings for swamp were lost. The modeI iden t ified large the base case 978-1988! were used to simulate portions of the middle and lower brackish marsh 1956-1988conditions using the USFWS map as that convertedto open water, whereas the upper initial conditions.The model predictedland loss basin, dominated by swamp habitat, remained fluctuations for 1956-78 between 0 and 65 km' for relatively unchanged. Barataria and 85 km'-for Terrebonne, similar to reportedvalues of' 73 km'- Gagliano et al. 1981!. Thebrackish marsh sites of BayouPcrot and Habitatand goodness of fit resultsare presented in BayouL'Ours were subjected to time seriesanalyiis Table 2. Goodness of fit values for these simulations Fig. 4!, asthese sites underwent a changefrom were lower than the calibration values. The decrease brackishinarsh to open water. F igure 4a revealsthai. of accuracyin model predictionscan be attributed following 2005, the water level mcreasedand to the differentland Josstrends Table3! through remainedhigh as plant biomass decreased until the the30-years tested. habitat at BayouL'Ours changed in the year2017. At BayouPcrot Fig. 4b!, this habitatswitch MANAGEMENT SCENARIOS occurredin 2015probably because of risingsea level and increased salinity. Landscapemodels of this typeare one of the fewtools that canbe used to predictthe effects of ln Terrebonne, 1,204 km' of land werc complexspatial interactions and cuinulativc, long- convertedto openwater of which660 km- were terrneffects of global changes,Simulations, from freshmarsh! habitat Fig.5!, Thisoccurred moitly 1988to 2018,were performed for a seriesof in a largearea of freshinarsh at the northwestern inanagernentscenarios Table 2!, The first scenario, portiorrof thebasin, although some fragmentation referredto asNortnal Conditions NC!, simulated a of brackishand salt marshesalso occurredin the future continuation of current trends, Later southeast.These changes resulted on a water/land simulationsare evaluated by comparingresults ratio increase from 0.62 to 1.51 by 2018. againstthis NC scenario.The followingquestions 209 E. Reyes et al. Table2. Susnmaryof scenario results performed iu eachbasin. ResultingHabitat Coverage ktn'! Calibration Fit Fresh Swamp Brackish Salt Open Scenario Name Marsh Marsh Marsh Water Land/Water Habitat Terrebonne Basin 1170 432 828 576 2106 USWFS Base Case 1100 516 865 551 2080 0.9433 0.8508 calibration; 1977-87! Base Case 847 657 596 842 2170 0,8664 0.7274 validation; l 956-87! Normal Conditions 510 428 365 3310 988-201 8! Freshwater Addition 51] 428 362 3305 0.9829 Hydraulic Restoration 552 429 466 365 3300 0.9829 Barataria Basin 755 734 2952 USWFSmap Base Case 723 1002 722 634 2854 0.9597 0.8932 calibration; 1977-87! Base Case 1191 577 2883084 0.8648 0.7439 validation; 1956-87! Normal Conditions 396 1017 236 217 4057 988-201 8! FreshwaterAddition 521 1019 311 236 4057 0,9751 StoppingSaltwater 303 1015 226 247 4132 0.9645 Intrusion Note: Fit valuesfor BaseC asescenarios were computed against 1988 USWFS habitat map, Fit valuesues for ~age~nt opt ons were compute against the2018 no~~ conditions habitat map Additionof FreshwaterScenario inflow was simulatedat 301.4 m'/s I0,000 c fromDecember through March and 28.3 rn-'/s I,M Thisscenario simulated diversion of river cfs! for the remainderof the year.A hydraulrc waterinto theBarataria basin. The site for this connectionalready exists between Barata freshwaterdiversion was Davis Pond, an area that Terrebonneso the simulatedfreshwater addition encompasses6.6 km' of eastcentral Barataria. implementedinto Terrebonne by increastng Lanttscapa 4lodeling irt Coastal Louis taros 210 fable3. Annual loss rates km'! for the 1956-78 and 197848 periods inyerrebonne andBarat na Basins Source: Dunbar Reed US FWS Model Dunbar Reed USFWS Mode1 et al. 1992! 1995! output etal, 1992! 1995! oulput Note: '1958-74 and 'l 983-1990 intervals. 2018 Normal 'ondi tlons 2018 Added fieshsrater ArealEvent tktnli Patrertt Hahitat T!pe h;ortnat Fresh»ater trash nt~b 393 53 l ssramp l017 l019 hrackish marsh 336 3ll salt marsh 3 lt} 339 open water 40s9 3a33 ttplands l 7ll l 7' ttrnposid i «g 3.Resulting habitat distribution of Barataria Added Freshwater scenario compared ared vs. Normal Condntnns scenario 211 E. Reyes et al. a! BayouL'Ours 1.4 lp 1 2 1.0 0,8 0.6 0.4 0,2 0,0 1990 1995 2000 2005 2010 2015 1990 1995 7000 7005 2010 2015 Year Year b! BayouPerot 10 14 1.2 1.0 0.8 o 06 04 02 0.0 1990 1995 2000 2005 2010 2015 1990 1995 7000 2005 2010 2015 Year Year Waar Depth Biomass Fig.4, Time series of waterdepth and photosynthetic biomass for a>Bayou L'Ours and b! Bayou Perot satnple locations for Nortnal Conditions scenario. ratesthere by 84.9 m'ls ,000 cfs! duringpeak internalwater flow by redirectingflow ftotrtthe west discharge. portionof the basinfarther into the east.For this simulation,Manning coefficients were increased Results ftom this scenarioshowed that land locallyas a proxyfor the modiT~cations{Fig. 6a! lossin Barataria was reduced by l 13 ktrr'compared We assumedthat increasingwater friction in the to NC Fig, 3!. The preservationof freshtnarsh was selectedarea would result in increasedflooding and largely responsiblefor this difference. Habitat redirectflow towardsthe internalportions of the distribution effects were minor in Terrebonne and basin. resulted in almost no difference from the base case scenario Table 2!. The resulting habitat distribution in Terrebonne showed about 42 km' tnore- of fresh Restorationof tuternalHydrants ~nario marshand 33 km' lessof brackishmarsh compared to the NC Fig. 5!, This wasdue to a fresheningof Thesimulation of restoredunernal hydraulics the tnidwestportion of the basin,and fresh marsh wasdone only to theTerrebonne basin. The rnodifi- preservation Fig. 6b!, The scenariohad negligible cationsimplerrmnted in thisscenario in Terrebonne effectsupon the distributionand amount of swatnp include: ! Restorationof natutallevees at 15 sites and salt marsh habitats Table 2!, thathad been destroyed and ! lmprovetrtentofthe Landscape4lodeling inCnasta> Louisiana212 2'l3 E. Re!teeet al. a! hiodellmplenteuration h! D>ffcven W bra bra Fig,6. a! Manipulauonsimposed within tnodel to performTerrebonne Restore Hydraulic Conditions scenario. b!. Differenc habitatmap for Terrebonne Restore Hydraulic Conditions scenario vs. Normal Conditions, StoppingSaltwater latrstslon Scenario habitatchange in coastalLouisiana are j sealevel riseand subsidence, ! changesin theintroduction In this scenario,a barrierto saltwaterinfusion of freshwaterand sediments from the Mississippi into the upperbasin was simulatedfor Barataria, and AtchafalayaRivers, and ! modif!cationsto This levee crossesthe width of the Barataria basin internalhydrology Baumann et al, 1986;Boumans withonly one break in thecenter portion that allows andDay 1993; Cole tnan 1988; Day et al, 1997;Day flowfrom Bayou Perot and Bayou Rigoletts to Little andTemplet 1989; Gagliano et al. 1981;Reed 1995; Lake.The results showed anincrease inopen water Salinaset al. 1986;Turner 1997!. Our landscape Table2! comparedto the NC scenario,About 110 modelsare driven by thesesame dominant regional km' of fresh marshwas lost, 10 km' of brackish processesand were, therefore, sensitive to factors marshwere lost for a totalopen water gain of 88 that affect how land and water surfaces evolve km' Fig,7!, There was preservation ofan additional interactivelythrough time. This meansthat the 35 km-'of saltmarsh. The greatest amount of land models are less sensitive to local factors such as losstook place in fresh marsheslocated in the canal dredging, or natural ones like nutria eat outs northwest.This was duc to increasedflooding or fires. durationnorth of the simulated levee Fig. 7!. When only the western portion of the DlSCUS SION Terrebonnebasin was modeled in the original CELSS study Sklar et al. 1991!,a Ft = 0.&82for Othershave found that the principal regional the calibration run from 1956-1978 and Ft = 0.79 factorsdriving long-term trends in land-lossand for the validation run of 1978-1983 were obtained. Lan~ Modelingin Coastal Louisiana 214 2018 Normal onditions 2018 SaBwater Intrusion Areal Fmenx tun-! pauerri HahtxaxTape Normal Salvaaxer fresh marsh 393 303 sv amp l7 IOI5 hriickish marsh 336 i 36 [QiiiI salt marsh 1 l9 347 open wmer 4059 4iM uplands 178 l78 lunposedl Fig.7. Resultinghabilat distribution of BaratariaSaltwater Intrusion scenario compaxed vs. Norma] Conditions scenario. Theresults for bothpresent models which included predictablyinfluenced land elevation and habitat the area modeled by Costanza and his colleagues type. Thesemechanisms had their major impacts axesimilar Table2!. Theseresult s leadus to believe on the marsh communities, thus setting a trend of thatthe preseint tnodel satisfactorily represents the land loss in these areas. This was due in part to Baratariaand Terrebonne systems at a largescale differences in initial elevation, salinity, and water andpmvide with an adequatespatial and temporal levelsbetween upper and lowerbasins. resolutionfor the modelmanagement predictions, CONCLUSIONS The assumptions of the landscape models. paxticularlywith respectto thespatial resolution of Two region al model s that co xnbi ne the waterrouting IOO km'!, limited coxnparisons hydrodynaxnicand biological processesat different betweenadjacent areas, and made assessment of the time and space scales are presented. These iong-termpotential of small projects less than l mechanisticmodels includedfeedback amongfour km'! virtuallyimpossible. The landscapemodels different modules water. soil, plant and habitat shouldbe usedas reconnaissancetools to provide switching!.A -year calibration showedthat thc aninitial estimate of thetype and level of hydrologic processesmodeled are sufficient to explain up to changenecessary to achievea desiredresponse, 85% of the habitat distribution and 95% of the lan Jt' Plantand soil processes atless than l km'scale and water changes. hydrologicprocesses at lessthan IOOkxn' that have ttotbeen xnodeled may produce loca!ized changes. Scenarioresults dexnon strated the importance of increasing water flow into both basins. As these The biological module and habitat switching areas are subject to limited freshvvater inflov s, the algorithxnsfocused on those factors that directly or rate of land loss only increases. 2ts E. Reyas et aI, The adv antag e of usin g these land scape BOuMAvS, R. M. J. Avo F. H. SKLAR. 1990. A models is that they allow one to evaluate natural polygon-based spat i al P B S! model for processeswith a regional perspectiveand to simulating landscapechange. Landscape investigatecause and effect of the management Ecology,4 /3!; 83-97. optionsat any location. Burtntcx,D. M., !, A. ME'voELssoHis,AND K. L. McKEE. 1989. I.ivc standing crop and ACKNOWLEDGMENTS Metabolismof theMarsh grass Sparti na patens as relatedto Edaphic Factorsin a Brackish Financialsupport for this studywas provided marshcommunity in Louisiana. Estuaries by the Barataria-TerrebonneNational Estuary 12 !: 195-204. Program BTNEP! throughthe LA, Departmentof CttAnRECX,R. H. 1972.Vegetation, water and SOil EnvironmentalQuality. The authorswould like to characteristicsof the Louisiana coastal region. acknowledgethe assistance of theBTNEP Scientific BatonRouge, Louisiana: Sca Grant, andTechnical Cornrnittee members in reviewing CHAartEctc,R. H. Avv R. E. Coworu:v, ] 979. Common earlyresults. We alsowould like to thankPhillip vascularplants of the Louisiana marsh.Baton Atkinson,Hassan Mashriqui and James Hyfield for Rouge, Louisiana: Sea Grant. thelong hours they spent submitting jobs and post- CHE'vc,R. T., V. CASULLLAvv J. W. GAitrvEn,1993. processing.We acknowledgeMelissa Woods and Tidal, Residual,intertidal Mudflat TRIM! EmilyHyfield for editing and proof-reading. Weare Modeland its Applications to SanFrancisco gratefulto theeditors and two anonymousreviewers Bay,California. Estuarine, Coastal and Shelf fortheir comments and suggestions. Science 36:235-280. COtEMAri, J. M. I988. Dynamicchanges and E.ITERATURE CITED processesin the Mississippi River delta. GeologicalSociety of AmericaBulletin 100. ALAwADV,M. AivoK, AL-TAHA. 1 996.Elevation Data 999-1015. Gathering B arataria-Terrebonne National CovNEa,W. H. AvoJ. W. DAv.1976. Productivity EstuaryProgram BTNEP!. 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L, 1991, Spatial Modelling in Coastal 605-627. Louisiana.In S. Mathies Ed.!, DataInventory R, D. DELAt!rate, x!ro W. H. PaTRrcK Workshop,5 pp, 367-376!. Thibodaux,LA: JR.1986. Changes Occumng Along A Rapidly LouisianaState University and BTNEP, SubmergingCoastal Area: Louisiana, USA, WrnTE, M, L., J. F. MprtrlN, E. Rrtvr:s, G. P. KExrr, 3, JourrrraI of CoastalResearch 2 !:269-284. W. DAY,V. ARAVAMtrrrlAs, 3. N. ScHAYDA,Ar'D SrNGN,V, P ~Nt! 'V.ArtAVAMt!rrrAN 1995. Errors of H. S.MasHRlqVI. 1997. LandsCape SimulatiOn Kinematic-Wave and Diffustion Wave Model Upgrading; spatial-ecological Approximationsfor Time-Independent Flows, modeling of the wetlands of Barataria- Water ResourcesManager!rent 9 !:755-782. Terrebonne BTNEP Final Report No. 31!. SOLAR, F. H. w~n R, CosraNza. 1991, Thc CoastalEcology Institute, LSU. Developmentof DynamicSpatial Models for WrnTE,M, L., T. M~wEt.L, R.Cosrs NzA,~o T. W, LandscapeEcology; A Reviewand Prognosis, DovLr.". 1991. Fcosystem Modeling of ln M. G. Turner and R. H. Gardner EtLs.h BaratariaBasin, Louisiana: Utilizing Desktop Quantitative Methodsin LandscapeEcology Parallel Technology No. American Water pp. 239-288!. NewYork, New York; Springer- Resources Association. Verlag, WrsExs*rs,W. 3., E. M. Swr:wsow,ANo J. PowErt,1990. SrtLxrt,F- H., R. CosTxvzw,aNn J. W, Dxv, 3!t. 1985. Salinity Trends in Louisiana Estuaries Dynamic SpatialSimulation Modelling of Estuaries 13 !;265-271, Coastal Wetland Habitat Succession. Wu, J, G, !twoS. A. Lavrv. 1994. A spatial patch Ecological Modelling 29:261-281. dynamic modelingapproach to pattern and Sr'!ut, F. H., 1Vl. L. WHrrE, xNo R, CosTmz!s. 1991. process in an annual grassland. Ecological The Coastal EcologicalLandscape Spatial Monographs 64 !;447-464. Simulation CELSS! Model: Users Guide and Resultsfor theAtchafalayafI'errebonne Study Area Open File Report91-04 No, National We t 1ands Re search Ce nt er, US F ish and Wildlife Service, Trroxtsos, D. J, 1995. The Seasons, Global Temperature. and Precession.Science, 268 April !, 59-68, T+F>, R. W. 1993. Field Guide to Coastal Wetland Plants of the Southeastern United States. Arnherst.Ma~~achusetts: The University of Massachusetts Press. TuR~Ert,R. E. 1997. Wetland loss in the northern Gulfof mexico:multiple working hypotheses. Esrrusries 20 I !:1-13. Vrssrst,J. M., C. E. SxssErt,R. H. CrrABREcK,Avn R. G LtNscoxsar:.1996. Marsh Vegetation- Types of Barataria andTerrebonne Estuaries, No, 1.$ O'- C EI -96-11 !, B arataria- Terr ebonne Nat.ional EstuaryProgram. WELts,3. T. 1996. Subsidence,sea-level rise, and wetlandloss in thelower Mississippi River delta,In J. D. Millimanand B, U. Haq Eds.!, Sea-LevelRise and Coasral Subsidence pp. 281-3I I ! Netherlands:kluwer Academic Publishers. Salt Marsh Plant Colonization, Growth, anal Dominance on Large Mudflats Created Using Dredged Sediments C. EDwARD PROFFITr' AND JENNJFERYOUNG Louisiana Envirr>rtmentalResearch Center, McNeeseStare University, P.O. Box 90220, Lake Charles, LA 70609 Present addresses: 'Author i'orcorrespondence; U.S. GeologicalSurvey, Biological Resources Division. NationalWetland Research Center, 700 CajundomeBlvd., Lafayette,LA 70506 TEL: 3 l 8-266-8509; FAX: 318-266-8592; email: edward proNttC~usgs,gov 'LouisianaDeparttnent of NaturalResources, Nicholls State University, l07 Mead Hall, Thibodaux, LA 70310 ABSTRACT: Large mudhats up to e200 ha! created from sedimentsdtmlged from the Calcasieu Ship Channel are being colonizedby marsh halophytes.We comparedcolonization and gro»1h by dominant marsh vegetationat edgeand interior locationsof createdsites ranging in age from 6 mo to 14 yr and natural referencemsrshes. Unvegetated arcs declinedrapidly with ageof cited marsbes interior locations: 99.7% io the6 mo old marsh, 428% in tbe3 yr old marsh, and 0.1% in the 14 yr old insrsh!.This change occuicdprhnariiy as s resultof rapid colonizationand vegetativegrowth by smooth cordgrass, Spaesirsarzlterriijlortr, in sll sites. The first year's colonizationwas mainly by raMng of mats of roots and rhizoines,but vertkal growth of buried plants was also important m sotnemarsh edge locations. Seedlingscontributed to marsh grassrecraaitment in tbe secondand third years in the two youngestsites. Sptzrtinaalternijlnr» dominatedor ccwiomiuatedin our 1996 survey: a! 14.4% edge! - 2.7% interior! of site III created in 1996 and surveyedabout 6 inontbs after de-watering,h! 82.7% cdge!- 279% interior! of site 11created in 92993,and c! l00% edge!- 46 8% {interior! of site I createdin 1982, d! 100% edge!- 922% {interior! of referenceinsrsh 1, and e! 99% edge! and 100% interior! of referencemarsh 2. Other marshgrass species dominated or co- dominstedfess area. Dombtanceby S. pasensranged from 0- 15'% {createdmarshes! «nd t - 5.8% {rcfescncemarshes! depending on location andsite. Donunanceby Disrichlisspicutrr ranged from !- 600% crestcd inarshes! and 0 - 2.0% referencemarshes! depending on location and site. The annualsucctdent Ssiricorniu bigekvii exhibited thick growthbetween patches of grassin many portions of the interior of site IL Spartirraalterrtiflons wss shorter aad hsdgreater raxnet densities in siteI, the oldest created marsh, relative to the other tnarshes. Plant height and biomass was greatest in site Il. There wasuo significantdifference in plant heightand biomassdue to locationwithin marshes edge vs interior!. The numbers of floweringstems of S. altensiglorowerc not diferent in site II and tbe natural refeicncesmarsh 1. However,there wasno flowerin in siteI the 14 yr old createdmarsh!. The causeof these difl'erencesamong populations could be either environmentalor genetic. Spartina alterniflora cover reduced below-canopy air temperaturesdming summer,but had no significant effect iu other setisons.Sediment organic matter generallyincreased with the age of the created marsh. Key wordsand phrases: salt marshcreation and restoration, marshp!ants. dredge sediments.Spurtirtu aherrtiflora, Spartina paterts, Disrichlis spicatu, Sulicorm'ubigelovii Fromthe Symposium Recerrr Reseurck irr Coastall~utriarra. ktaruraiSysrern Function und Response ru Hurrrurr /rrfluertee. Rozas,L.P., 3.A. Nyman, C.E, Proffitt, N.N. Rabalais,DJ. Read,and R.E. Turner editors!. 999. Publishedby Louisiana SeaGrant Col!ege Program. 218 219 C.E. Proffttt and J. Young INTRODUCTION noted above. Studies of' colonization, growth, and speciesinteractions are required to assessthe rate Restoration of marsh structure and function is of marshdevelopment and patternsof succession. a criticalcomponent of the efforts to offset wetland We studiedthe colonizationand vegetativegrowth lossesin coastalLouisiana. One restorationmethod of thedominant grass species Sparri na alterrtiflrzra. involvesthe creationof rnarshhabitatin openwater We also characterizedthe percent cover of afl areasby usingseditnents dredged for either that abundantgrass species S. alternifloru,S. paterts, purposeor asa by-productof navigationchannel and Dr'sriehlisspicata L,! Greene! in 3 created maintenance. Marsh creation has sometirrtes marshesof differentages and 2 referencemarshes includedplanting one or more specieson the in order to assesspatterns of succession and dredgedsediments, However, in manyinstances, dominance. This effort was part of a larger large bare mud flats are created under the collaborative suite of studies that also included assumptionsthat plants wil I colonize"naturally," analysesof the geneticdiversity of S. alrerntJfara that the ensuing tnix of dotninantspecies is andthe levels of metaland organ ic contaminants in determinedtnainly by elevation and hydrology, and sediment and biota, thatthese "tnarshes"will have atl or mostecological functionstypically associatedwith tnarshes of that METHODS groupof species.These assumptions have not been fully tested,especially in largearea sites. Site Descriptions Environmental gradients, such as tidal Three large flats >40-200 ha! of dredged inundation, salinity, and soil anoxia, have been sedimentswere created by the U S. Army Corps of shown to affect tidal marsh plant growth and Engineersin 1982, 1993,and 1996 at the Sabine survival Ponnamperurna 1972, Mendelssohn et al, NationalWildlife Refugein southwesternLouisiana 1981,King et al. 1982, Nixon 1982,Mitsch and duringmaintenance dredging of the CalcasieuShip Gosselink1986, andmany others!.Interspeciflc Channel, All sites used in this study were on the competitionbetween dominant salt marsh grasses eastside of statehighway 27, southof thecity limits alongthe gradients establis,hes the typicalzonation of Hackberry, LA «nd north of the refuge patternsnoted in high and low intertidalmarsh headquarters.The flats werecreated by pumping a settings Bertness and Ellison 1987, Bertness 1991!, slurry of dredgedsediments and water into areas In low marsh, flooded soils are often anoxic and that hadhistorically been marsh, but which were the ability of Spartina alterniflara Loisel to openwater with occasionalmarsh islands at thetime oxygenateits rootsand rhizophereis a key factor of restoration. All of the created marsh sites have allowingthis speciesto becomedominant Gleason contaimnent berrns on one or two sides and are 1980,Mendelssohn et al. 1981!, High marshsoils contiguouswith naturalsalt marshor openwater aresometimes more oxygenated and consequently onother sides. Marsheswere open to floodingfrotn are often lessstressful in tertns of this physical either the Hog Island Gully canal site II and factor.Sparrina alternigora can colonize and grow referencemarshes I and2!, old Hog Island Gully underhigh marshconditions. However, it will be and West Cove site III!, or the Calcasieu Ship excludedwhen Spartinaparens Ait,! Muhl., a Channeland Long Bayou site I!. Our studywas strong competitor for space, is also in the site initiatedprior to constructionof site Ill in 1996. Bertness 1991!. Thus, this site was sampledfor certain variables percentcover, clone size, and sedimentorganic The southwesternportion of thc Calcasieu content!but was not includedin the quantitative estuarynear West Cove is strongly influencedby analysesof growth,biomass, etc, Naturalmarshes oceanicwater entering through the Calcasieu Ship adjacentto the flats were used as referencesites. Channel.Consequently, marshes on the east side Reference marsh 1 was located on the north side of of highway27, whereour studytook place, are theHog IslandGully canalto the west of the site II dominatedby halophytessuch as the marsh grasses createdtnarsh. This referencemarsh was sampled Salt MarshOeve!oprnent on Dredt!edSediments for cover, stern density, height, and flowering werecorded numbers of stems,!ength o fevery stern whenevercreated rnarshes I and II weresampled. asa measureof height, nutnbers offlowering stems, We establisheda secondreference marsh following andcollected all aboveground material for biomass creation of the l996 site. Thi» reference marsh 2 determination dry mass after drying at 70" C!. A! so, waslocated on the south side of the HogIsland Gully we recordedwater depth and salinity at eachplot- canalimmediately to the westof site III. Air temperaturewas measuredabove and below the S. alterniflor canopy Qunnhtativeaaa!yses of biomassand plant size and environmenta! conditions Biomass,height floweringand stem density datawere analyzedby repeated-measuresor two- In April 1996 we established stationsfor study wayANOVA asappropriate using Systat, Repeated- attwo locations "edge" near open water or adjacent measuresanalysis was used for temporaldata when marshand "interior" further from open water! in theassutnptions of thetest were met. Differenc s in two created marshes site I created in ! 982 and site air temperatureabove and below canopy was tested II createdin 1993! and a reference marsh reference usinga pairedt-test. 1,adjacent to site !I!.In site I andreference I, edge locationswere within 2 mof openwater and interior Percent Cover Determinations plotswere 50 m inland.Using 50 m fromopen water for interiorplots sufficed because these tnarshes We ran a minimumof 3 replicatetransects t 4 werean! y approxitnately150 - 200 tn wideand thus rn wide! across each marsh in all created and interiorp!ots actually represented marsh interior, reference marshes. We measured the distances of However, this was not the case in the much-larger open ground or water! and all vegetatedpatches siteII. This site wascontinuous with existingnatural fa!!ingon the transectline, The dominantspecies, marshon its westernmargin. As "edge"locations or co-dotninantspecies mixture assessedby visua! in this large 00 ha! site, we picked plots of estimationas approxitnately equal spatial coverage !, vegetationthat were c!ear!ygrowing on dredged was recorded for each section of vegetation. The sedimentsand were closestto the borderingnatural percentcover was calculated from the meansof the marsh.For the "interior" plots, we chosea location replicatetransects in eachmarsh. nearer marsh center about 400 m from the edge whichappeared representative of thetypical interior Sediment Organic Matter of the site. Thus, for all study marshes,interior locations were situated between about !/4 and !/2 As one metric of long-tertn effects of of the distancefrom open waterto the mostdistant vegetationon soil structure,we conducteda one- pointacross the marsh. time samplingof the studyplots for sediment organiccontent. Litter was removed from surface Three permanent p!ots were establishedand upper5 cm!soil samples and the stx!imcntwas markedwith PVC polesat eachlocation. In siteII, driedto constant temperature at7P C. Drysampies whereS. alterniflnra often existed as spatially wereusual ly veryhard and were crushed and ground separatedcircular patches, plots were locatedin priorto determiningorgaruc content via loss on separatepatches of the grass. The patch radius at ignition 00' C for 4 bours!. studyinitiation in April 1996 rangedfrom 3,06 to 7.49 m. Cominuousswards of grassexisted rather RESULTS thanseparate small patches,in site I and reference marshes.In thesesites, plots at a location edge or Knvironmentn! Conditions interior!were situated 50 m apart. E!evations in thernarshes range from 0 to + !,7 We sampledeach plot quarterlyover ! year. m with 0 defined as elevation at marsh-open water Ten quadrats 5 x 25 cm! were !ocated by interface C. Norman,unpublished data!. In siteI I, haphazardtoss at eachsampling. In eachquadrat elcvationsatthe edge plots ranged from o-! 5 to G,24 221 C.E. Pmffittand J. Young m andfrom 0.31 to0.46 m atinterior plots Because Historicdata provided by the SabineNational of logistical constraints,elevations were not Wi!d!ife Refuge show considerablewithin-and- gathered«t individual study plots in the other among-yearfluctuations in salinitiesin the Hog marshes.Whi!e thesites were relatively flat, there IslandGu!!y Cana! adjacent to restoredsites l!and werctopographic highs in sitesII andIII whichwere III andboth reference marshes Fig. 1!, From 1991 probablyassociated with theplacement of discharge - 1997,the mean 4 1 S,I:, salinity was10.7 i 0.51 pipeopenings during sediment deposition. mg1 ' n = 2, andthe range was 0.7 to 23.4mg 1 ~.The salinities of groundwater and surface waters Water depths varied seasonal I y, am ong in ourstudy ranged from A! to 32.0i 8.0 mg 1' marshes, and between !ocations within marsh es. The TableI !,and generally tracked patterns of change driesttime was the first co!lection spring !996! with of salinitiesin the canal. Salinityvalues in site I overa mean depths to groundwater below surface the yr old createdmarsh! were typica! ly a little valuesare indicated by negative sign! in created sites higherthan in other sites,This site is nearestthe of -66.3 k 2.62 cm Site II and -I8.8 4 2.1! cm in CalcasieuShip Channel. SiteI. !nreference marsh I therewas standing water at this co!lection ,4 2 2.20 ctn!. In the winter of At higher elevationsin two of the created !997,all marsheshad standing saline wa ter S ite II tnarshes sites II and III! surface sediments, 5,611,91 crn, Site .0% 1.89cm, Referencemarsh especiallyin unvegetatedareas, werc often hard, 1 8.92 1.90 crn, andReference marsh 2 18.8 2 2.10 dry,and cracked when there was no standing water cm!. Waterelevation data were notco!!ectedin the or recent rainfa , Under these conditions, surface youngestrestored marsh site III! because it was sedimentsalinities were substantially higher than notde-watered enough to al!ow walking access for thoseof the groundwater oftcn 20-60 cm below samplinguntil late intothe study, sedimentsurface!. Sedimentsalinities from site!I, 25 20 15 Ià > io tn 0 Fig.l. Historicbottom salinities frotn 1991 - l997in the Hog Island Gully Canal are shown. On the x-axis. the year labelis p!aced atthe start of a particularyear.Data collection varied but points were gathered approximatety bitnonth!y.Data were provided by R,Walters of theSabine National Wi!t!hfe Refuge U.S. Fish and Wildlife Service!. Salt MarshDevelopment on DredgedSediments 222 'Ihble1. Quarter!y measuresof mean + I S.E.! dredged sedimentswas not thick, buried S. saliaitiesin mg I' of standing or ground water alrerrtiflaracolonized by vegetativegrowth and 2! areshown for eachstudy site nM!. ND indicates overmuch of thesite numerous small generally data not collected. Zero values indicate fresh 0.5 mi! patchesof S. alrrr7iiflorawith intact roots water within the limits of measurement. and rhizomes rafted in with tides and storms, Sparrirtaparerts colonized by rafting and 0, spicara Mean Salinity Mg 1' I S E ! apparently by seed over those early months followingsite de-watering. However, relative to S. Site II S it c I Reference alrernillora,these latter two species did not co!onize yr old! 4 yr old! Marsh I extensivelyin termsof n.umbersof patchesand total area covered, Apr 96 22.0 .0! 32.0 8.0! Jul 96 21.7 .5! 20.0 .0! 16,3 ,4! Percent Cover Vov 96 19,3 .1! 21.8 .8! 17.2 .3! The unvegetatedarea in createdmarshcs Mar 97 2,2 .1! 0 0 decreasedwith tnarshage and increasedwith distancefrom open water Table2!. Datafrom sites II andIII createdin 1993and 1996,respectively! measuredin July 1996 aftermixing equal volumes showthat colonization was more rapid near the edge of distilledwater and dry sedimentand allowing 5 of thc marshcompared to theinterior of the marsh. hrto cometo equilibrium,were 50.2 2 4.1 Mg 1' Field observations in .site III suggest that a n = 5!. Sediment from reference sites, site I, and substantialproportion of thiscolonization near the near-open-waterareas in siteII that wastreated in edge was from vertical growth of buried S. the samemanner, had much lower salinities that alrerniflora. Both referencemarshes had nearly weresimilar to those.of groundwater, 100% vegetative cover Table 2!. Sparrina alrerniflora was the dominantor co-dominant The % organicmatter differed amongsites speciesin al! sites Table 2!. At edgelocations one-wayANOVA, P =0.0005, R' = 0.876!. Values within 2 m ofopen water! in createdsites, the area from site I created 1982! were not significantly coveredby S, alrernifloraalone or asa co-dominant di ferent from the reference 1 marsh 2. I and 9.5% increasedwith ageof thesite from14.4% site III, respectively!,The two youngestmarshes sites II created1996!, to 82.7% siteII. created1993!, and andIII! had less sedimentorganic rnatter .7- 100% site I, created 1982!. At interior locations 7.3%! than the reference marsh. Reference marsh 2 ! 50 m fromtnarsh edge! in the createdsites, area hadthe highest sediment organic content 9.3%!. with S. alterrtiflora as sole-or-co-dominantalso increasedwith site agef'orn 2.7% siteIII, created Air teinperaturcs above and below S. 1996!,to 27.3% site ll created1993!, and46,8% altrrrtifloracanopy were significantly different only site I, created1982! . Edge locations of the 2 duringthe summer t-test,P = 0.0005!. The overall reference marshes had 99 - 100% cover by S. meantemperature was 3.9" C cooler canopy in alrerniflor Table2!. DominancebyS, alterrt rflnra sulilinen in interior locationswas typically less than at marsh edge,but showedthe same increasing trend with Field Observations of Initial Colonization increasing age of createdmarsh; 2.7% site III, 27,3% site II, and46.8% site I, Referencemarshcs had 92.2 Field observations of site III, which was - 100% dominaceby S. alrerrtifloraat interior created and became de-watered during our locations. investigations,indicate that grasscolonization occurred within a few months of sediment de- In interiorlocations of the oldestcreated marsh wateringand as a result of two mainmechanisms: site I! the areadominated or co-dominatedby the 1! in thelow intertidalzone, where the layerof highmarsh grass D. spicata was about thc same as 2' C,E. Proftlttand J. Young Table2. Percentcover by the ruajorhabitat types in createdand naturalreference marshes. Values are tucanaof n=3 transectsper locationin eachmarsh and as suchmay nottotal to 100k. Mixed speciesgrou.pings Indicate numerical dominance by thespecies included. ~~ indicates open water at hightide ln tMsmarsh. Note that Salicortust bigelovii Is an annualand in thewinter, this portion of the habitatis aho bare ground with standingdead plants!. MIxed dotninancewas recorded when species coveredaplmosimately equal proportions of a patch.Ages of created sites at timeof sasnplingwas site Ill 8 yr!, siteII 0 yr!, and siteI I4 yr!. In eachmarsh, "edge" denotes the area from water'sedge to SOm Inland; and, '1nterior" denotesFrom that point on to the approximatecenter of the marsh. Created Marshes Reference Marshes Site III Site II Site I Ref 1 Ref 2 edge interior edge interior edge interior edge interior cdgc interior Bare Ground 85.1 97,0 2.4 42.8 0 0 0 0 0 l~' 0 Sahco rrrirs bigelovii 0 0 2.5 27,5 0 0 0 0 0 0 Spartinaalterrr rflanr 14.4 2.4 68.3 27.3 92.0 22.0 100 92.2 71.0 98,4 Spartina par eris 0.1 0.2 4.0 ],7 0 12,0 0 58 0 0 Distichlis spi cata 0.3 0.4 8.6 0.7 0 28.8 0 20 0 0 1vafrit tescerrs 0 0 0 0 0 0.2 0 0 0 0 S. alter7r.+S. patens 0 0 10,5 0 0 0 0 0 9.2 0 S. altern.+D, spicata 0 03 3.9 0 8.0 9.5 0 0 18.8 2,6 S alterrr.+B. frutescens 0 0 0 0 0 1,5 0 0 0 0 S. patens+ I vafrrr tescerrs 0 0 0 0 0 250 0 0 0 D. spicata+/. frtrrescerrs 0 0 0 0 0 7,6 0 0 0 0 D. spicata+B,frutescens 0 0 0 0 0 O.e 0 0 0 0 S paterrs+I.fry.+B.fru. 0 0 0 0 0 1.3 0 0 0 0 S. alt.+ D. spic.+[.fru. 0 0 0 0 0 138 0 0 0 0 +B. fru. that dominated by S. alterrtiflora Table 2!. This The annual Salicorrria bigelovii dominated speciescovered touch less area in other created ungrassedareas and displayedvery robust growth marshes,0 - 12.5%depending on marshand location duringspring and summerin the interiorof site II within marsh and 0 - I 8.8% in reference marshes Tab!e2!. Salicorrriabigelovii individualsgrowirlg Table 2!. In created site I, where it was tnost within grassedpatches were much smaller and abundant,the area dominatedby the third most occurredin low densities field observations!.It was abundantgrass species, S. parens, cvas about 3x less possibleto findoccasional S, bigelovii in theinterior thanthe greatestdegree of coverby D. spicata.In of the older site I created 1982! mixed in with the referencernarshes S, parens dotninated 0 - 9,2% of grassesbut plantsdid not attain the high density site area Table 2!. Patchesdominated by tnixturec and large stature seen in site II. In site III created of speciesincreased in frequencyof occurrenceand 1996! there was very little colonization by S. totalsite areacovered with increasing age of created bigelo vii the first year 996-1997 data! and no part marsh,but were iessprevalent in both reference of the site hadany degreeof "dominance"in terms marshes Table 2!, of coverby this species Table 2!. However.our Salt Marsh Development on Dredged Sediments 224 field observationsthc following year summer of 1998!indicate substantialcover by S, bigelvviiin partsof s ibeIII resultingfroin extensive colonization byseeds/seedlings in obvious natural low elevation 160i drift zones where seedscame in on the tide and in 106i apparent seedling shadows around the few 66q individualsthat did colonizethe firstyear. I-urthcr WNI96 lar99 field observationsin the springof 1999 indicatea veryhigh density of S, higelnr ii nowin siteIII. Thus, Sr99II thepattern of extensivecover of non-grassed portionsof interiorareas by S. bigelvvr'i recorded in site II created1993! is being repeatedin site III created 1996!. 'Ll DetMItlesof $. allerrtiflo ra 19996 nsf9 Spartirraalrerniflvra stem densities were 1.5 900 - 2 x greaterin the oldestcreated marsh site I!, thanin site Il, or in the referencemarsh 1 Fig. 2!. t7 9IXI Repeated-ineasures ANOVA showed that I 66 Iaa differencesamong rnarshes was significant P = 0,0005!. There were no significantmain effect ~ 9I96 atm96 I9996 ~ pr97 differencesbetween edge and interior locations Figure2. Rametdensines stems/[25 x 25 cm!! of 5. withinmarshes PW.693!, althoughthe significant alterniflvra are presentedfor restoredmarshes Sites l interaction P = 0.022! indicatedthat densities varied and II and the natural reference marsh by marshedge differentlyamong locations in thedifferent rnarshes and marsh kntenor locations. The x-axis is samphng Fig. 2!. times Apr. 96 Mar. 97!. Valuesare mean~+ l standard errxrr. Stem densities also varied significantly seasonally P = 0.0005!. Bothcreated sites I andII indicatedby a timex siteinteraction P = 0.0005t. showed continual increases in density over the The incanheights in siteI werealways less than 40 courseof one year, while densitiesin reference cm and did notvary substantiallyover the year Fig. marsh 1 irtcreased,and then decreased,a both edge 3!. Heightsin referenceinarsh I rangedfrom about andinterior locations. This resultedin a significant 60 - 80 cm and both edge and interiorlocations time x site interaction P = 0.0005!. showedgeneral decreases in heightover the year, Heightsin siteII rangedfroin about55 - 100cm Heigbtsof S. akernifbro and fluctuated dramatically over the year Fig. 3!. The tallestplants were at theinterior location of Stem length height! was significantly site II and were situatedfar from open water.The erent P = 0,0005!among marshes Fig. 3!. Site mean values exceeded ] 00 crn and some individual I, the oldest created site created 1982!, was stemsa!orig the outer portion of circularclones of dominatedby short-formS. alrerniflora,while site the grasswere 2 m long u.npublisheddata!. II created 1993! and reference marsh 1 were populatedby muchtaller S. aherniflora. Therewerc AbOve GrOttnd BiamaSSOf S. aLterr6iflorrr no significantdifferences P = 0.330! in height at edgeand interior locations within rnarshes Fig. 3!. Aboveground biomass is generallydependent Heightvaried significantly over seasonduring the on bothstem density and height. In ourstudy sites, studyyear P = 0.0005! and differencesamong differencesin plantheight tended to dcterininethe marshesin the pattern of change over time is differencesin biomass.The aboveground biomass Salt MarshDevelopment on DredgedSedrments 226 dominant or co-dominant over 27.3 % interior oj location!and 82.7% edgelocation! of' the marsh Table 2!.This speciesdominated or co-dominated 46,8% of marsh area a interior locations, and occurredin near mono-specificstands ai edge locationsin site I surveyed 14 years after site creation!. In the two reference marshes, S, alrerniflorawas dominantor co-dotninant over a tninimum of 92.2% of site area regardlessof nearnessto open water Table2!, Fig.5. Mean I S.E.! numberof floweringstems are Despite dominance by S. alrerniJl ora, the dry shownfor theearly Fall 1996collection, Values are conditionsfor portionsof the year in the interior depictedby differentmarsh site I, site II, andref I! portionsof sitesII andIII appearedconducive for andlocation within marsh. Solid bars are edge the establishment of high marsh species or locationsand open bars are marshintenor locations. Them was no flowering in site I. transitional species,In site III surveyedfor percent coverwhen 0.5 yearsof age!,occasional Salicornia bigeloviiexisted; and, in site II at 3 yearsof age! growth resultedin a high percentcover by this therewas a densespring andsummer 996! cover speciesin the marshescreated in 1982 site I! and by this succulenthalophyte over much of the non- 1993 site II!, For the interiorportions of the created grassedareas in theinterior of thedeveloping marsh sites,this tnechanism probably accounted for tnost Table 2!. This species is an annual and its of the first year colonizationby S, alrerrgiflora. colonizationwas by seed.In the youngestsite site Depositedsediment covered portions of theexisting III, created1996!, S. bigeloviiwas absent in the tnarshalong site edgesthat were continuouswith summer of I996 which is consistent with the fact existingnatural marsh and numerous patches of S. that the site was not yet dc-wateredwhen seeds altemifloraoccurred via vertical growth fmm buried wouldhave been establishing. In thespring-surruner rootsand rhizomes site III, field observations!. of 1997 we observed widely scatteredindividuals of S. bigelovii in site III. In 1998 and 1999 there has Sexualreproduction may havecontributed to beenincreasing dominance bv thisspecies over most colonizationof the site in lateryean. We observed of the non-grassed area of this site field a largeseed set by S. allerniflorain thefall of 1996 observations!.This speciesgrew well in bare areas insite H createdin 1993!and a numberof seedlings in sitesIl andIII, but wassparse and muchsinaller thefollowing spring. It is possiblethat some patches when it occurred within grassed patches. We of thisspecies also became establishedthrough conjecturethat the annualS. bi gelovii leadsa rather seedlingsthe previousyear sincethis site was 3,5 ephemeralexistence in thesecreated marshes, with yearsold when we first inade field observations.In its dominanceincreasingly litnited over the years siteIIL therewere seedling "shadows" around many by spreadof the perennial grasses. clonalpatches in the springof 1998 about2 years aftersite creation field observations!. Typicalhigh tnarshgrasses S. parens and D. spicara! only accounted for at most 14.5% and 8.6% Rapid vegetativegrowth of S. alrerniflora areacover respectively in site II and <0.5% in site resuhedin its dominancein all sitesregardless of III. Wherethese species have colonized, the patches theelevation and distance to marshedge Table2!. appear to be healthy and growing well field Sparrt'naalterriiflora was dominant or co-dotninant observations!. However, there has been little over2.7% interior location! and 14.4% edge colonization,We hypothesizethat this may be a location!in siteIII whenit surveyedat 6 tnonths result of a paucity of rafting propagules,or viable aftersite creation. Spanina alterniflora in site II seed,or both, BecauseS. alrerniIlora generally surveyed3 years after site creation! was the single dominatesnear water's edge in marshesin this 227 C.E. Protfittand J. Young portionof theSabine National Wildlife Refuge,this significantlylarger height and biomass!, lowerin is thespecies most likely to breakfree and raft into ramet density, and flowcrcd during the study. a newlocation. The other grass species are further Whether this is some function of sediment or other removedfront the waterand often S, alter jlora physical factors or is a difference in doininant occursbetween them and openwater, This result genotype s!is not yet known.We did observebut wouldtend to reducethe frequencyof rarnetsof did notquantify, more frequently water-loggal soils thesespecies breaking free, washing out of a marsh and apparentreddish iron depositsin site I where andfloating to newsites. Although we observedall short-formS. ai/erniflora dominated.Long tenn 3 grassspecies flowering, we haveno data on the studies of these sediments, during years of abundance of viable seed. We have observed S, compactionand/or other structuraland chemical afrerniflaraseedlings in both sites11 and III, but changes,and their effectson vegetationmay be not seedlingsof D, spirara andS, patens. If seed needed to shed light on this question. Also. set or seedlingsurvival is low,this too could limit transplantexperiments among sites and locations colonizationof thesehigh marshgrasses. These couldaddress questions of growthform. observationssuggest that further studies of seedset, viability, floatation, and colonization of the Full assessment of marsh function involves petenniaIgrasses «rc needed to resolvequestions ineasurements of such diverse items as sediment regardingcolonization by thesespecies. biogeochemistryand nutrients, productivity, food webs,population biology and genetic viability, and While the physicalconditions of the interior successionpatterns Such an undertakingwas nat of sitesII and Ill and studiesof competitive withinthe scope of thisstudy. However, in addition outcomes Bertness 1991! suggest that S, parens and/ to biologicaldata on colonizationand growth of the or D. spicarashould eventuawy come to be the doininantplant species,we did evaluatea few dominatepertenial grasses in interiorportions of physical parametersthat are affected by plant sitesII andI II. therapidity ofcolonization. degree communitydevelopment, These variables were: air af dominance,and robustness of growthof S. temperature above-and-below-canopy as an alterrufloraand the slowness of colonization by S. indicator of how plant cover can affect rnicro- parens and D, spica a in these locationsindicates environmentalconditions; and, sedimentorganic thatthis process may take many years. Interestingly, matteras a metric of long-term changespaJtially dominancebymixed-spec iesassemblages increased causedby plantgrowth and decay with «geof createdmarshes, and was lower in the presumablymuch older reference marshes Table The sedimentorgailic rnatter content of the 2!, Thepreponderance of patches dominated by oldestrestored marsh site I! was not significantly mixturesof speciesin siteI suggeststhat created different from tha in the reference marsh I, marshesof intermediateage thissite was 14 years suggestinglong-term effects of ma+.h grassgro wth old whensurveyed! may be fertilelocations for anddecomposition on soil structure.Sediment from futurestudies of species-speciesinteractions, theyounger restored sites si tesIl and III! hadabout 2/3 as much organic material %! as in the reference Contpstrisonof Marsh Structureaud Function inarsh1 9.5%!. Valuesfor organic matter in surface sedimentsof the reference marsh 2 9.3%! werc Thetwo created marshes sites I andII! studied similar to results froin a marsh terracingstudy for suchvegetation factors assize, growth, biomass locatedc0.5 km to the south L.A Departmentof and reproductionwere both dominated by S. Natural Resources Coastal Restoration Division altei'flora. However,the growthforms of this 1993! specieswere very different in thetwo marshes, The oldersite I wasdominated byshorter S.alterniflora Air temperatureis one metric of effectsof withmore densely packed ramets that did not flower vegetation on surface microenvironmenial duringthe study year. The younger site I was more conditionswhich could affect growing conditions similarto the reference marshes inthat plants were for otherplants or habitatquality for smallanimals. Salt Marsh Developmentan DredgedSediments 228 Cover by S. alrerniflora significantly reduced air ProtectionAgency to the LouisianaEnvironmental temperaturesjust above ground or water! surface ResearchCenter at McNeeseState University. during thesummer, but had no measurableeffect in the winter.Cooler conditions below gra.sscanopy LITERATURE CITED duringthe summer may reduce evaporationof soil moisture.This possibility is supportedby our BraTNEss,M. D, 199]. Zonationof Sparrinaparens qualitativefield observationsthat soil surfacesin and Sparrinaalrerniflora in a New England grassedpatches tended to bc less "dry and cracked" salt marsh.Ecology 72:138-148. duringthe summercompared to areasirnrnediately BEarNESS, M, D, AND A, M. ELi.isON. 1987. outside the grass patch. Other direct or indirect Determinantsof patternin a NewEngland salt effectsof reducedbelow-canopy temperatures could marshplant community.Ecological Mono- occur on seed/seedling viability, surface soil grapfrs57: I 29-147, salinities, invertebrate survival and foraging Gi EASON, M. L 1980. Influence Of tidal inunda- behavior,etc. In s udicsof restored marsh function, tiOn On internaloxygen supplyof Sparrirra moreemphasis should be p! aced on ascertainingthe alrerniflora and Sparrina parens. Ph.D. effectsof dominantvegetati ve cover on the physical Dissertation. Univ. of Virginia, Charlottesville, factors such as sediment organic matter and VA. rtucroclimatefactors affecting conditionsfor other KING,G. M., M. J. Kr i in, R. G, WIEoEitT,AND A, G. plartt speciesand marsh fauna, CHALMERs. 1982. Relation of soil water move m ent and s u 1fide concentraii on to While our study has shown that marsh Sparrinaaberniflora production in a Georgia vegetationdevelops on thesedredge sediment flats, sal t inarsh, Science 218:61-63. questionsremain about differences in S.alterniflora LOEISiANADEPARTMENT oF NATURAI RESOL'RCES, size andflowering among marshes,patterns of COASTALRESTOEATION DivisiON. 1993, Sabine succession,effects of and effects on! sediment TerracingProject Annual MonitoringRepon. parameters,long-term sediment ContpactIOrl rates, Departmentof Natural ResourcesProject No. fauttatuse, levels of export of plantproduction. and 4351089, the geneticvariability in the dominant species.In MENDELSSOHN',I. A., K. A. McKEE, ANDW. H. addition,further evaluatio~ of the amount and value PATnicic,1982. Oxygen deficiency in Sparrina of marshedge vs. interiorin termsof productivity alrerniflora roots: metabolicadaptation to and animalhabitat is neededfor largeareas such as anoxia. Science 214:439-441. the sites at Sabine National Wildlife Refuge, MrrscH, w. J. ANDJ. G. GossELINit.1986. wetlands, Furtherwork is neededbefore declaring these Van NostrandRemhold, Inc. New York, NY. marshescomplete "successes" in terms of the 539 pp. restorationor creationof fully-functioningsalt Nixox, S. W. I982. The ecologyof NewEngland marsh habitat, high saltrnarshes: a community profile,U.S, Dept,of the Interior, Washington,D.C. ACKNOWLEDGMENTS PONNAMIEauMA,F, N. 1972. ThC chCmiStry Of submergedsoils. Advances in Agronomy Weappreciate access to the studysites and 24:29-95. logisticalsupport by staff of the SabineNational WildlifeRefuge SNWR!. Roy Walters of SNWR provideddata on salinitiesand water temperature from theHog IslandGully canal station.Field assistancewas provided by G. Coto,D.J, Devlin, R. Lnwenfeld,M. Salter,and S, Travis. D,J, Devlin, E. Turner,and anonymousreviewers provided helpfulcomments on the paper,This study was fundedby a grantfrom the U.S. Environmental Low-Cost Wetllnd Restoration and Creation Projects for Coastal Louisiana R. EUGENE TURNER CoastalFcoiogy Instiritte and Departttrenrof Oceanographyand CoastalScience.s Lour'sana State Uni versiry BatonRouge, Lost tstutart 70&3 USA TEL 225-388-6454 FAX 225-388-6326 email; eurtsrne 0 lsts. edtt ABSTRACIt Wetlandrestoration and crestlion efforts are subject to differenteconomies of scale,lncludhrg scales of ecohrgical propor5ena An inverseeconomy of scaleapparently operates in thevarious smail and large wetla nd restorationprojects possible or implementedin coastal keuhlana.The S ha' gained averntge $12Jl thousand ha' created+restored!isinversely related to project cast,for projectsranging from $08 to $100 million. There is a 15-fold increasein $ ha' gainedas preject slee increases by a factorof ten. Thereappear to begeneric economies of scaleinherent to simlhtrenvironntental management approaches that represent a comprom- isee of at leastthree attributes:attempts to controlecosystem behavior predictability aad tasehecosystem complexity, and incompleteecosystem knowledge. Smail-scale projects are describedthat are very coateffective, including terracing, backfilling, restorstktn of abandoned agriculturalhtnds built br wetlandscirca 191 5k small crevassesand spoil bankmanagement. Thesmallest projects $2+NO eacb! create land at slowrates @ 5 ha yr'! andtend to be very costeffective $20 to MINIha'!. Thereappear to bemore than enough sites tn applythese small projectsat a rate that wotrldetiuni the anticipated restorationand creationrates resulting frtirmthe current CWPPRA program. Kr ywords: weiland creation, resutration, economy of scale,river diversion, Louisiana, coastal zone. jtstroduetion of the patternsin yield and agricutturalland cul- tivated to extendto otherendeavors in government, Effective wetland restoration efforts in coastal scientific research, and even household economies. Louisianashould be not only long-bsting decades!. Becoming aware of these economies of scale would but also economically'efficient, Economistshave seem to be a prudent aspectof both financial and longrecognized that there is aneconomy of scale political rnanagernentin anera of limiled resources operatingon agricultural lands, An English manand for wetl and restoration. Frenchman,almost simultaneously Sir James Steuartand Turgot ]761; in SchumpeterI9541 There are a variety of wetland creation, re- observedthat as additionalagricultural land was habilitation and restoration methods possible in newlycultivated, thatthe yields perarea eventually coastal Louisiana whose scale varies widely. Most decreased, presumably because thc new farm land of the Coastal Wetland Planing, Protection and wasof moremarginal value. Turgot,in particular, Restoration Act CWPPRA! projects are indi- recognizedan interval of increasingreturns before vidually large. For example,the 1995review of 4 the interval of decreasingreturns. Subsequent years of projects shows that the averageproject observationshave shown these general observations createdor restored203 haat an averagecost of 52. r million, or Sl2.8 thousandha" for thc avcr~g of From the S>mtros!umRcccat Rcscan tr irr CoasratLcrrrtsiatta: individual projects, The averagecost/area of all NataralSysrcrrr Faactr'orr and Rcspotrsc to ftrarrarr ttrflrtcncc. projects was $28.6 thousandha ' of restored or itozas,L,P.. J.A. trlytnan,C.E Protitt, .'V.N.Rabalars. D J. Recit.atNt R.E. Trtrtrer I artrrrrrs!. l 99rr publrs~ by Lour siana created land Anon 1995!. There are also sevetai SeaGrant College Prop.am. types of smaller projects whose costs and results 229 230 R. E. Turner are either well-docurncntcd or that have substantial projects and water diversionsrange from $12 estimatesto justify their implementation,These thousand to $76 million, the percentage river latter projects are nrtt common in south Louisiana, diverted variesfrom 0,06% to 19%, and the flow is tnostlyfor what seemt tomc! to be for sociological directedthrough a channelfrom 30 to 900 rn wide. or political reasons. They arc relativelysrnaHer The proposedor actualland gain ratesfrom these projectsthan those funded by CWPPRA becauseof crevassesrange from 5 to morethan 600 ha yr'. their individual cost or impact area. These srnaHer projectsare briefly reviewedhere andthen com- Land gain increaseswith project size or the paredto ourexperience with larger projectsin terms amountof water diverted, but not as fast as project of the economyof scale. costs increase. There is, therefore, an inverse relationshipbetween the costof landgained and the sizeof thecrc vassc Fig. 3!. Notethat updated cost Examplesof Low-Cost Projects estimates are included for the West Bank, Davis Pond and Caenarvon Diversion that were not Small Crevasses based on a summary in availableat the time of the paperby Turnerand Beyer et aL l997 and Turner and Boyerl997! Boyer 997!. Neither large nor smallcrevasses, of course,can be built everywhere, Constructing "artificial" crevasses,or cuts in the naturallevee of the Mississippi River, has been attemptedby the US Fish and Wildlife Servicein Agricultural ImposrndmeatRestoration the Delta National Wiidlife Refuge DNWR! to based ort Turner aad Neill i984 and build landwithin the Refuge Fig, 1!. The newly Trepagnier et ai. 1995! constructedcrevasses create emergent wetlands after two yearsof subaerialgrowth at about4-5 ha yr' Impoundments occur throughout south Pig. 2!. The presenttotal cost is <$200 ha' after Louisianawetlands Fig. 1!. Somewere built as six yearsand wiH decline to about $54 ha ' as wildlife refuges and others were formed by additional land builds. There is also documentation interlockingcanal spoil banks. The oldestare of the growthrate of largernatural crevasses, and probablythose built to "reclaim' land for agri- of the costsand anticipatedland gains restoration culture. Theseimpoundments are visible reminders or creation! from currently funded CWPPRA of the era,foHowing passage of the SwampLand projects Anon 1995!. The rangeof theindividual Acts of the last century, when publicly owned swamplandswere sold to individualsin transactions whichoften "lacked the characteristics of pristi.ne 60 honesty" Harrison and KoHmorgen1947!. Some areaswere promoted as having a veryhigh potential 50 for profitthrough agriculture. 40 Ten failed or abandonedcoastal agricultural impoundments circa 1915! were examinedby ra 30 Trepagnieret al. 995! to detemunerecent wetland O restorationrates in former agricultural impound- 20 o /+ mentsthat had failed. Aerial photographyfrom 10 between 1978 and 1988 u as used to determine the percentwetland area and levee length and changes betweenmapping intervals. Onesite gained wetland 0 2 4 6 8 $0 12 between19?8 and 1988,and four sites gained Years wetland between 19&5 and 1988. Wetland area in ling.2- Thegrowth of landin newlycreated crevasses the remainingsites were either stableor declining in theMississippi River delta from Boyeret al, 19971. during the study period. The average wetland Low Coast Restoration 231 Fsg.l. Photographsofvarious small resu!ration projects orpotent!al sites in south 1.ouisiana. Topleft: A recent]y- buihc«>'asse i 1990!. Bottom Left: A networkofspo>1 banks resulting from dredged canals. T !pright: the square !nthe center isthc Delta Farms open water area, which formed from a collapsedlevee during a hurricanein 19' . Tbearea !mmediately tothe north was dra!ned and farmed in 1915.but N astreshwater mars h on1930s aerial photos-M!ddle right: an aerial photograph ofthe Sabme terracing pro>ecn Bottom right: a groundview of a recentlycreated terrace <+s months ! !nthc Sabine terracing project. 232 R. E, Turner changerates for al! areas r,urged tron> -A.H to + Vegetationforms initially on the exposedspoil 2, ~c yr ' from I,q78 to ! egg. Although pan. of material. Laterthe vegetationextends into thewater. this varialbility in rates ii duc to rniipping inter- but at presently undetermined rates. The cost/ha prctatrrr'niliydfolr>glc factors urliqiic to eachsite gainedof thii type of project is in the neighborhood v erealso intportant. The reiults fr<»na multiple of $3.NN to $8,000fha after 5-! 0 years. regressionmodel indicitted that restoration ii inverselyrelated to impoundtncnt size and directly relatedto leveereduction, Trepagnieret al. 995! Spoil Bank Managementfbased un trsed thi» itatistical nrodel tu eitrrnatc thc costi of material in 'orner et aL 1994a! removing the lcvees and the potential land gaini. Levee. retnoval will enhance wetland restoration Thereis virtually no areaof the Louisianacoast rates at a very favorable cost <$1 ha '! and be that is without a dredgedcanal or channel nearby. suitainabie with little additional management, The These canals are built with various dredging recoveryrate, however, was estimated to be «bout methods to facilitate navigation, belowground l~~:yr ' if'10% of the levee were renrovcd. A rather mineral recovery, pipeline construction,. and clearexanrplc of thc pusiibilitiesare shown in thc trapping. Most canali, however,were constructed areanorth of the open water body known ai 1.!efta to servicethe oil and gasindustry, especially tu float Farms, in the Barataria Basin. The open water in drilling equipment. They arc occasionally re- forrnedlfrom a fornter agricultural impoundment dredged or 'swept'! when they fill in ln an aerial whose leveei collapsed in !960. The area on the view of the marsh, canals appear as straight lines northern border was drained and farmccl in 1 915, with a parallel man-made levee on either side but wa.s a.bandoned sornetirne thereafter, perhaps Fig. 1!. Somecanals are isolated,and othersare after a. hurricane. Thc land manager.C. Breaux, found in dense networks. The linear features of recall.sdragging a tractorout of the marshwhen he canals are in sharp contrast to the anatomising, v asa child pers.comm.!, Aerial photograph»show natural channels that form a dendritic drainage that it was mostly wetland by the 1930sbefore the pattern with naturally low levees. intracoastalWaterway v asbuilt. and it retnainsthat v ay trxiay. Thc material removed to create the canal is depositednearby in a continuous linc of dredged spoilmaterial. This tnan-madelevee, called a spoil Terracing basedon information in bank. usual!y hasdifferent. vegetation {c.g., shrubs } CWPFRA Planning docutnents! from the surrounding wetland. Spoil bank leveei havean averageli fetime of lessrhan 50 years{ Monte Terracing ii a wetland restoration practice in !978!. Gas right-of-way pipclincs may not have south Louisianathat involves pihng matcrialon a spoil banksbecause they are often fr lied in,wn.h the shallowand submerged surface to form an exposed previously dredgedmaterial immediately after the surfaceof dredgedmaterial. This new surface is pipeline is laid {backfilling!: theie 'backfilled not like atypical spoil bank dredgedfor navigation, canals frequently re-vegetateenough to make the which is continuous.in two parallel line», and rises new piant cover indistinguishablefrom the abovenormal high tidei, These terracesare more surroundingmarsh. The aggregatelength of these like a series of disconnected ridges arranged canalsand spoil banks i.i in the rangeof 9 to 1 LXK> perpendicularly to each other, whose surface is km and ] gto 2, XX!k.m, reipectively. trooded by high tides Fig. 1}. The natural Resources Conservation Service has constructed The cumulative impact oi conitructing many several of these in the Chenier Plain, and with iorne small individual canals and lcveei is to impound success.The purpose of the raisedbanks, or terraces, marshes, often unintentionally, and r:auie land loss. ii to dampen the waie energy to allow plants tu Spoil bankschange the flow of water into and out takeroot and suspendedmatter tu fall out in greater of the marsh t'Swenion and Turner I 'N7!, causeopen amounti, and to protect the adjacent shoreline. water pond~to fornr nearby Turner and Rao i 99 tu Low Coast Restoration 233 and are spatia!lyand tempora!!yrelated to the water habitat is, therefore, the general goal of conversionof wct!andhabitats to openwater e.g., backfilling.Canal backftlling i» generallyintended Bass and Turner 1997;Turner ! 997!. to directlyachieve four objectives: g impactsresult from the: ! longer !! To fill in the canal., wetlanddrying cycles. even in setni-impounded 2! Toreestablish emergent marsh vegetation wetlands,as a consequenceof altered water move- in the cana! tncntsinto and out of the wetland. Thc lengthened 3! To eliminatethe spoil bank, and, drying periodspromote soil oxidation and subse- quentsoil shrinkage; ! floodingevents that may 4! Toreestablish emergent marsh lengthenbehind spoil banks, presumably as a vegetationon thc spoil bank. consequenceofwaterbeing trapped behind the spoil bankonce water enters overland during very high Backfi!lingbegan to bc requiredin !979 as a tides Whenwetland flooding increases enough to conditionfor issuing a permitto dredge some canals. seriouslywaterlog soils and change soil cheinistry, Canalsmay be backfillcdafter thedrilling site is plantsmay becomestressed to thepoint where abandoned on-sitc mitigation!, or, anothercanal growthreduction or evendie-back occurs e.g., may be backfilled off-site mitigation! to obtaina Mendelssohnet al. 1981;McKce and Mendelssohn permitfor dredginga newcana! or otheractivity. 1989!; ! lowersedimentation rates behind spoil The spoilbank is leve!edas near to marshelevation banksin any wetlandtype, because of thereduced aspossible, and the spoiI bankmaterial that is moved frequencyand depth of tidalinundation; ! ln isused to fill inthc existing canal. The fill is placed addition,the spoil banks consolidate theunderlying evenly over the bottom of the canal, soi!s, Subsurface water movement isthus decreased, bothbecause of thereduced cross-sectional area and Whi!ethe backfilledcanal and adjacent berm the reducedpermeability of materialbeneath the westudied was not restored to a completelynatural levee Turner 1987!, condition,its status wasintermediate in many respectsto thatat a naturalbayou andan unfilled Thereis nosystetnatic manageinent plan ta canal Turner et al, 1994b!, restorespoil banks to wetlands byremoving them. We useda hydrolagicmodel and fie!d data to Thereduction in c!cvationof the spoil bankat estimatethat removing about ! 0%of the spoil bank thc backfilledcanal resulted in greaterwater wouldrestore hydrol ogic fl ows if thespoi/ retttovat movement in and ou of the marsh, redticed the werestrategicaliv pktc 10 EO~ -10 0 4 10 j' 3 10 EOIO 10 7 10 10 PejectCost $ j ProjectCost $! Fig,4, The re!atiottship betweenthe cost per ha land created orrestored andthe project cost for al! CWPPRA ptojectsinsouth Louisiana. ittcludlngdiversions, Left:$ha' cost vs. project cost.Right; Average AnnualCost perAverage AnnualHabitat Unit AAC/AAH 1 vs.! project c ost. Thedata arefrom Anon 995!. 1 00,000 10,000 1,000 a C 100 w 10 I 00 1 000 10,000 1 00,000 Project Size $1000s! "ig-5-The relationship betweenvarious small and large restoration projectsincoastal Louisiana implemented and uu-imp!ementedprojectcostsare averaged!. Therelationship betweeri restorationrcreation projectsizeand hecoat P hawetland restored orcreated. Theliterature sources arefrom: CWPPRA Coastal Wetland Planruog, Protee have inherent requirements that dictate, to some ACKNOWLEDGMENTS extent,where they can he implemented. These constraintsmay require adjustments in management This study was originally funded by two US efforts to achieve optimum uses of the available EPA grantsthrough the Gu/f of Mexico Program fundingand ecological resources, It is worthnoting, andEPA Region6, Dallas, Texas. We thankthe however,that thc vast majority of CWPPRAprojects National Marine Fisheries Service o%c e at LSU for are large projects. The first 4 years of the CWPPRA repeateduse of theiraerial photographs, progtamhadonly 1 of63 projectsthat costless than $5OO,GOO. LITERATURE CITED lt is worth askingif there is enougharea to use there smaller projects. Only preliminary numbers ANoN. 1995. CoastalWetlands Planning, Protec- are available,but they suggestthat smallprojects tion, andRestoration Act: Sutnmaryof Priority are a viable option for restoration efforts. The Lists 1-4. CWPPRA Report Series No. l. CWPPRAprogram has projects in placeto attempt LouisianaDepartment of Natural Resources. to create and restore wetlands at a rate of 479 ha BatonRouge, Louisiana. yr' Anon 1995!. A stnall crevasse builds at 4.76 BASS,A, ANuR. E. TURN>R.1997. RelatiOnships ha yr' Boyeret al 1997!, so it would take only betweensalt marsh loss and dredged canals in I OOsmall crevasses,at $48/ha, to create what costs three south Louisiana estuaries. Journal nf the CWPPRAprogram $28,000 h 'a, There are a Coastal Research 13:895-903. few hundred locations available to build crevasses Bxuxa~NN, R. H. AND R. E. TURNER. 1990, Direct Boycr and Turner 1995!, but land owner iinpacts of outer continentalshelf activitieson permissionis required something that may not be wetland loss in the central Gulf of Mexico, forthcoming, The open water in abandoned Environmerital Geology and Water Resources agriculturalimpoundments could be recoveredat 15: I 89-198. 10ha/yr, Trepagnier et al., 1995!,at a costof about $1ha'. Thereare at least 43 unpoundments,perhaps BovER, M. E. wNo R. E. Ttrxma. 1995 Data on 20of whichcould be restoredwith permission.The crevassesplays in the Delta National Wildlife averagesize is 2,352 ha. The potentialrestoration Refuge,Mississippi RiverDelta. Final Report to the United States Environmental Protection atea is, assuming50% recovery, 23,520 ha, at 50 years,or 470 ha yr', equivalentto the CWPPRA Agency,Dallas, Texas. landgain at .01% of theper hacost. The greatest BDYER, M., J. HARRts xNo R. E. Tuxr RR. 1997. opportunity to implement low cost restoration Constructedcrevasses and land gain in the projectshas to dowith restoring oil andgas recovery MississippiRiver delta Journal of Restoration canalsand reversing their negative impacts on Ecology 5:85-92, wetlandhydrology. There are tens of thousandsof HxatuSON, R, W xNn W. M. Komwoxoan. 1947. spoil banksand canalsthat could be backfilled, Pastand prospectivedrainage reclatnations in equaling 80,426 ha in 1978 Bauman and Turner coastalmarshlands of the MississippiRiver 1990!,There is a muchlarger area of impoundments Delta, Journal of Land Public Utility andsemi-itnpoundments that couM bemanaged, an Economics 23: 297-320. areathat perhaps exceeds 500,000 ha. It wouldbe MCKaa, K, L, axo L A. MRNoxt.SSOitN 1989. necessaryto convertonly 0.15 % yr' of the canals, Response of a freshwater marsh plant spoil banks,semi-impoundments and itnpound- conununity to increasedsalinity and increased mentsto wetlandseach year at lessthan $1000 waterlevel. AquaticBotany 34: 301-316. ha'!,to matchthe objectives of theprojected results MENDELSSOHN,1. A., K, L. MCKai= ANo W. H. of currentCWPPRA projects. PATRtctc.JR. 1981, Oxygen deficiency in SparrirtaalrerntIlora roots: metabolicadapta- tion to anoxia. Science 214;439-441. Low Coast Restoration 237 MOxTa,J, A 1978. Theimpact Of petrOleutn dredgingon Louisiana's- coastal landscape: A plantbiogeographical analysis and resource assessmentof spoil. Ph,D. Dissertation, LouisianaState University, Louisiana. NEtts.,C. ANDR. E. TURivEtt. 1987. BaCkfilling canalstomitigate wetland dredging inLouisiana coastalmarshes. Environmental Managemerrt 11:823-836. ScHUMpETER,I, A. 1954. History of Economic Analysis.Oxford University Press, New York. Svrpvsoz,E. lvl. ANn R. E.Titttxatt. 1987. Spoil banks;Effects on a coastalmarsh water level regime.Estuarine, Crrasral and Shelf Science 24:599-609. TttEPAGvttP3t,C. M., iv!, A. K Xths,A Yl!R. E. TL'RNER. 1995.Evaluation of wetland gain and loss of abandonedagricultural impoundments inSouth Louisianafram 1978to 1988. Resroratiorr Ecology3/4;299-303. Tt ttrtEa,R. E. 1987,Relationships between canal and levee densityand coastalland lossin Louisiana.United States Fi.ch and Wildlife ServiceBiological Report 85 4!. TURv'Ht,R. E, ANDC. NrttL. 1984.Revisiting impoundedwetlands after 70 years, p. 309-322. In R.3.Varnell ed.!, Water Quality and Wetland ManagementConference Proceedings New Orleans,LA., August 4-5, 1983 spon sors: LouisianaEnvirottmenta1 Professionals Asso- ciation!, Tuttrtatt,R, E. htvo!Vl. E. BovLR. 1997. Mississippi Riverdiversions, coastal wetland restoration/ creationand an economy of scale, Ecological Errgineering8:117-128. TUttstt:tt,R, E AxoY. S. Rho. 1990. Relationships betweenwetland fragtnentationand recent hydrologicchanges in a deltaiccoast, Estuaries 13;272-28 l. Ttjtt~~,R. E E.M. SwpvSO~,hr~ J.M. LPL,1994a. A rationale for coastal wetlandrestoration throughspoil bank rnanagernent in Louisiana. Envirnnrrrental hfanagerrtent 18, 271-282. TLtc~xtt,R. E, 3. M Li E. A~OC. NatLL. 1994b, Backtilling canalsas a wetland restoration technique in coastal Louisiana. Wetlands Ecologyand Management3:63-78. WETLAND MANAGKMKNT Effects of Weirs on the Depth and Duration of Flooding in a Louisiana Marsh JoHNA. BoURGEols' LouisianaDepartment of Xrztural Resources, Coastal Restoration Divisr'on. P,O.Box 94396, Baton Rouge, LA 70804 email:[email protected] ERIC C, WEBB' LouisianaDepartment of Natural Resources, Coastal Restoration Division, P.O.Box 94396, Baton Rouge,LA 70804 emaiI: etvebb@harveyecolr>gy.corn 'Presentaddress: H. T, Harvey & Associates,3150 Almaden Expressway, Suite 145, SanJose, CA 95118 ABSTRACT:This analysis examines the effects oftwo inarsh mtnusgement weirson the depth and durationof marshflooding, and utilizes the hourly water-level data at four of the real-time Data CogectionPlatforms DCP! for the period of September 1,1993 to August 1,199ti. The continuous water-leveldata on the inside and outside of' the water control structures at Mill Ctvsdcand Bayou ~Carpeindicate that the weirs significantly altered the nuniher and duration ofBoodhtg events on thesurrounding marsh Kolmogorov-Smirnov criticalvalues of O.14 and 0.10 respectively I, This resultedinfewer short duration F24 hr! flooding events and an increase inlong duration >2 wk! floodingevents. Subsequently, themarsh was intmdated toa greaterdepth and for hmger durations withthe presence ofwater control structu~ At Mi5 Crmk where theweir was the only link to the surroundinghydrology, these effects are inore significant thanat Bayou LaCarpe where the water is ableto hidirectly bypass theweir. Subsidence, complex drainage patterns. hnpr»per proj~ design. andinadequate structure manipulations arethe likely reasons forthe failure of the project at controlling hydrology. introduction Marshmanagement in Louisianabegan in 1954in theform of manipulatedtmpoundtnents in Louisianapossesses 41% of thetotal coastal anattempt to curb the effects of these natural and wetlandsin thecontiguous U.S. and these wetlands anthropogenicchanges Chabieck 1960, 19621. The arein a severestate of degradationdue to natural primarygoal of the.seearly tnarsh inanagement andanthropogenic causes Turner 1990!. Mass ventureswas to encouragethe growth of plant harvestiugof cypresstimber beginning in the early speciesdeemed "desirable" for waterfowl and fur- 1900sand dredgingof oil andgas access canals hearinganimals and I.o create "optimal" marsh/water beginningin the 1940sdratrratically changed the interspersionfor waterfowlby controllingwater landscapeof coastal Louisiana Niyerset al. 1995; leveland salinity Chabreck 1960k Structural wein. Reedand Rozas 1995!. Perhaps more important than were first usedin the early 1940sto gain accessto the direct loss of coastal wetlands from canal trappingareas by maimaining minimal water levels constructionis the resulting change in hydrology for thesafe paasage Ofboats. ThC use of weirsas a andsubsequent changes in marshcreation processes marshmanageinent tool did not begirt until a decade Cahoon 1994!, later Chabreckand HoA'pauir 1962!, >rorrrthe Symposium Recent Researelr tr Coastallr>uisiamr. Thoseearly passive tnethods were replaced tVaturatSystem I'rrrt erron and Respottse to Htrtttatrtnflttence with active techniquesas the goals of marsh Roztrs,L.P.. J.A. Nyrrrarr,C.E. Protein, N.N. Rahzlais. D J. managementchanged. Present marsh management Iteed,and R,E. Turner edtrors!. 1999. Publhhed by Louidsns techniquesinLouisiana include the use of levees. SeaGrtur t College Program. 241 242 J.A.Bourgeois and E.C. Webb pumpsand a varietyof structur'etypes in Canal HNC! to thc east,thc naturalridge of'Bayou ctimbination to cornrol water levels and salinitics. du Largeto the west.,and a naturalridge to the north ln adrlition to advances in the construction and I'ig. 1!. This inarshmanagement plan is located in operationof weirs,flapgatcs, culverts, and other the deltaic plain of Louisiana where wetlattd loss marshmanagement structures, the basicgoals have rates are cstirnated at 6S.6 km'-/yr Dunbar et al. shifted towarda preventionof the conversionof 1992!. The project area,which encompasses3 Q04 marshinto shallowopen-water areas. Active marsh ha ,423 acresk consistsof' cypress/tupelosw atTip managementindicates that water control structures lliving and dead!, fresh/intermediate rttarsh. are operatedto moderatewater level variability, brackish marsh, and open water. Anthropogertic reducesaltwater intmduction, and seasonally change changes, such as the constructionof navigation thc volume of water in the managementarea for the canaLsand their respectivelevees, have altered &e benefitof bothvegetation and wildlife. The results hydrology of I.hearea. These,changes allow for from previousstudies indicate that this type of greatertidal influenceand the introductionof saliate managerncetcan be successfulin enhancingplant watersinto freshwaterwetland areas Wang I9$fsl. gmwth whenproper drawdown is achieved,and in Salinities in the areacurrently range from 9 to 21 increasingwaterfowl and wildlife numbers Bess ppt. These anthropogenic changesto hydrology ct al, 1989k However, marsh accretion rates have coupledwith the high ratesof local subsidence G.H0 beenreported to be lowerin managedmarshes than em/yr to 1. 18 em/yr in Terrebonne parish!, in cotnparableunmanaged reference marshes contribute to the loss of marsh in the area Penjartcl iCahoon1994!. Achievingthe goals set forth for et al. 1988k activemarsh management project involves a seriesa tradc-offsin whichmanagers may not be In 19S6.95'7c of the project area was ertier- able to capitalize on maximum sediment and gent vegetation according to a soil survey rrtap err freshwateravailability in lieu of considerationsfor TerrcbonneParish U.S. DepartmentofAgriculture plantgrowth and wildhfe behavior patterns Cahoon 1956!. The dominant vegetation at that tinm was andGroat 1990!. Conflictingopinions on thc Atternattthera philoxeroides Martius} Grisebach impactsof activeman h tnanagementnecessitate our alligatorweedh C ephalarrthus occidentafis L.. continuedeffon to examine the available mtinitoring fbuttonbush!. Myrica cerifera L. fwaxmyrtle!, dataand evaluate the effectiveness of these projects Pontederian>rduta L. pickerelweed!and Taxetdittrri at meetingtheir management goals Covan et al. dLstirhttnr L.! Richard bald cypress! USDA 1956:t- 19881. Analysis of near-vertical, color-infrared aerial photography I:12,000! from 1989indicaM 60 to Wcreport thc results of approximately 3 years 70'7rof the areahad been convertedto open watet' ofhourly water level and salinity monitoring inthe and that 707' of the existing cypress swanapwas FalgoutCanal Protection project The goal of' this deador dying. studyw'as todeterrnine the effecti.veness of a marsh managementproject at meetingits target water The objectivesof the FalgoutCanal Pro«ct'on levelsand salinity. Specifically, weare looking at project are to preserveand cnhancc3' haf theeffects of twowcirs on the depth and duration acres!of marsh and cyprcssjtupelo swamp,redu~ of marshflooding. In lieuof anypre-project saltwater intrusion, and improve wildlife habitaL monitoringora suitablereference area, continuous The project consistsof three elements: I l levee data on the inside and outside of twowater control construction and maintenance, f2j seven water structuresare utilized to detertninewhether the control structures ie.g., variable crest wein!. and Pal'algoutCanal Protection project has mct its target 1 a pumping station Fig. I !. Constructionof the waterlevels in thefirst three years of operation. project began July 2, 1992 and ended on April 1993. Levee constructionoccurred along 5,73 I rn TheFalgout Canal Protection project is an 8,800 ft! of the noithern bank of Falgout tCana'. activemarsh management project bordered by the southern project boundary! and repairs svere FalgoutCaral to the south, theHouma Navigat»n tnadc to 10,516 m '34,500ft! of spoil baiik alon.- Weirs and Marsh Flooding 243 Ftg l - FalgotttCanal Protection TE-0'! projectlocation and feature~. 244 J.Jt.Bourgeois and E.C.Webb thewestern hank of theHNC theeastern project leveland salinity datacollected at thesestations were boundtuy!,Five water control structures are located usedto determinethc effectiveness of the two weirs alongFalgout Canal stations13, 14, 18,15, and at mCCtingthe project gOals of maintainingwater 16!, one watercontrol structure is locatedat the levelsbelow the marsh surface during the growing intersectionof'Forty Acre Bayou and the HNC season,achieving prescribed water levelsset forth station25!, and one watercontrol structure is in themanageinent plan, and reducing salinities locatedatthe intersection of Bayou Provost and insidethe project area. Targetwater levels were Bayouduhuge station 24! Fig, 1!. The pumping basedon marsh surface elevation, and range from stationislocated atthe structure inBayou duLarge 0.3tn LOft! belowto 0 05rn .167 f't!above the station24!, The pump is designed todraw fresh marshlevek For the majority of theyear, including waterfrum Bayou du Large into the project area theentire growing season, water levels are intended viaBayou Provost. However, it has never been to be below the marsh surface, There are no set activatedand the Louisiana Department ofNatural target salinities,but there are several safety Resources,Coastal Restoration Division LDNR/ provisionsin thc operationalschedule to close CRD!perMenel haveobserved storm water being variousstructures when salinities greater than 1.0. pumpedinto Bayou Provost from adjacent 3.0and 5.0 ppt respectively are detected outside of agriculturalfields on at leasttwo occasions. theproject area CoastalUse Pertuit P850732!. Operationof thesewater control structures contributestothe project objecti vesand its specific The structure at Mill Creek is a variable crest goals. weirwith two 1.83rn ft! bayswith a one-way llapgateon eachbay Fig.2a! Theflapgates are Theseven water control structures of the designedto facilitate water flow out of theproject FalgoutCanal Ptutecnon project are scheduled for whenthey are in thc operating position. The on.lv operationintwo phases. Phase I consists of a timethat these flapgates are to be operating isfrom drawdownperiod inwhich water levels are to be March1 to June15 of a PhaseI drawdown! year, drasticallyreduced toenhance revegetation of Thestructure atBayou LaCarpe is a vanablecrest emergentruntsh, Phase Il,or the maintenance phase, isdesigned tocontrol theflow of water through the weirwith eight 1,52 m ft! baysand one 3.66 rti project,keeping wateroff the marsh surface during 2 ft! boatbay Fig,2b!. thegnowing season, andsttategically flooding the tnarshatother times ofthe year. Thc project was The four DataCollection Platfortns DCPs! designedtobe in Phase I for the first year of utilizedin thisanalysis are located inside and outside operation,and at subsequenttimes if' deemed theproject area on eitherside of therespective necessary;otherwise, thcproject shall be in Phase water control structures!at stations le and» 11.When the project isin Phase 1 drawdown!, hereafter,Mill Creekand BayouLaCarpe, operationalchanges arescheduled atfour times n.spectively! Fig. 1 l.The DCPs record water depth. duringthe year 6 january,1 March, 16June and specificconductance andtemperature hourly with 2 November!,When the project is in Phasell Handar436A incrementalshaft incodersand maintenance!,operational changes are scheduled HydrolabH20s. TheU. S. GeologicalSurvey atthree tines dtuing theyear 6 January, 1 March { JSGS!,under contract to LDNR/CRD,services the and2 November!, DCPunits every 4 to6 weeks,and compensates the datafor biofouling when the margin of erroris greaterthan 5% whencompared to a newlycali- bratedhand-held instrument. When cotrtpensatton Thetwo structures ofinterest inthis analysis is necessary,a linear shift is appliedto thcdata; arelocated atstations 1$t'Mill Creek! and25 Bayou however,no shiftsin the data wereneeded for the LaCarpel Fig,1!. These are the only two weixs periodof this study,The data can be accessed thathave continuous DataCollection Platforms on througha directsateBite link or througha modern link to the USGS data base. Data were collected boththe inside andoutside ofthe proJect. Water from thesestations from Septetnber 1, 1993to August ], 1996. Weira and Marsh Flooding 245 Fig. 2. Weir designat a! Mill Creek and b! BayouLaCarpe. Fourteenstaff gauges,surveyed to National from March 1996 ta April 1996. Otherwise,the GeodeticVertical Datum NGVD!, wereinstalled project wasin Phasell maintenance! Table 1!. at the sevenstructures in June 1995. Additionally. marsh elevations in the southern, middle, and Mean marsh elevation is 0.341 m {!,12 ft, northernportions of the projectwere surveyed to SDM.10 ft! NGVD in the northern zone near lslGVD in June 1995. station 26, Bayou LaCarpe!, 0.411 m <1.35 ft. SD=0.15 ft! NGVD in the middlezone nearstation Resttlts 27!, and 0,539 m .77 ft, S~.12 ft! NGVD in the southernzone near station!8. Mill Creek! isee Operationalchanges at the structureshave Fig. ] for stationlocations!. Hourly water level at occurred on seven occasions since project Mill Crmk was < mean marsh elevation 29.7% of conapletion Table 1!. Six additionaloperational the 1994 growing season from March through changes were scheduled, but there is no October! and 40 2% of the 1995grow ing season. documentationfor any of thesechanges and it is Hourly waterlevel at Mill creekwas < meanmarsh thcmfore uncertainas to whether or not they were elevation39.1% af the growingseason for the entire actually implementeed,The projectwas in PhaseI dataset September1993 through August 1996} and drawdown! from March 1994 to June 1994 and was< theupper limit of the95% confidenceinterval 24$ J.A. Bourgeoisan et E.C. Webb Table1. Operatiortalchanges executed forFalgout Canal Protection TE-02! project structures atstations 18ttatd 25. Heightof stoplogs inthe bays are expressed in centimeters NGVD. Date Station 18' Station 25' Phase 2-Apr-93 -15 -0.5 ft! -31 -1.0 ft! Phase II constructionend! flapsraised bay4, -6 maintenance! -61 -2.0 ft! +46 +1.5 ft! Phase I flapsoperating drawdown! 4-Jun-94 -15 -0.5 ft! -31 -1.0 ft! Phase 11 flap~raised maintenance! 17-Oct-94 +31 +1.0 ft! -15 -0.5 ft! Phase II flaps raised maintenance! 21-No v-95 -15 -0,5 ft! -15 -0.5 ft! Phase II Aapsraised maintenance! 24-Mar-96 -61 -2,0 ft! +61 +2.0 ft! Phase I flapsoperating drawdown! I 3-Apr-96 -15 -0.5 ft! -31 -1,0 ft! Phase 11 fl aps raised maintenance! 25-May-96 -15 -0,5 ft! +6 1 +2.0 ft! SpecialRequest flaps raised partial drawdown! ' = 2 bays.2 one-way flapgatcs ' = 8 bays,1boat bay ofthe incan marsh elevation 40.7% ofthat period, of thestructures at both stations Kolmogorov- Hourlywater level at Bayou LaCarpe was < mean Smirnov critical values of 0.14 and 0.10, marshelevation 21.1% of the 1994 growing season respectively! Fig.3!, Fewershort 4 hr!flooding fromMarch through October! and 10.8% of the eventsand morc long >2 wk! floodingevents 1995growing season. Hourly water level at 1VIill occurredinside thc project area. Despiteno Creekwas < meanmarsh elevation 25.5% of the differencein thepercentage of timetnarshes werc growingseason forthe entire data set Septetnber Aoodcdinside and outside the inanaged area, the 1993through August 1996! and was < theupper presenceof weirs facilitatedlonger and deeper limitof the 95% confidence interval of themean flooding events. marshelevation 27.6% of thatperiod. Meanwater level insidethe project area was Forthe entire data set, the tnarsh surface was approximately0.15 m .5 ft! higherthan outside. Aooded57.1% ol thetime inside and 58.3% of the butthis difference was not statistically significant timeoutside theweir at Mill Creek. At Bayou pW,32!due to thehigh varianceof water levels LaCarpe,themarsh surface was flooded 54.8% of outsidethe structures.There was no signiflcant thesampling period inside the weir and 55,0% of difference in water levelsbetween stations 18 and thetime outside of theweir. However, he 25 p=0,12!.Water levels did varysignificantly distributionofthe duration ofAooding events was betweenthe insideand outside of bothweirs at any significant!ydifferent between theinside and outs ide given inonthand year side~station*year"month We!ra and Marsh Flooding 247 LBO t60 s t00 I 0BO 200 %0 rCV o' 'oss Xl I koelb of evsor boors! lso 160 t20 s V t, tOO a BO C 60 20 koerbSf ovooB boers! Fig. 3. Durationof floodingevents inside and outside the structures at a!Mill Creek station!8! andrb! Bai ou ~ station 25!. 2l8 J,A.Bourgeais and E.C. Webb interactionsignificant Lps.'0.0 l ]!. Thestructure at tothe unmanaged area Fig. 3!. Anincrease in marsh station18 appears todampen water level variabi 1ity submergencehas been shown to bemore detrimental morethan thc structure atstation 25 Fig.3!. thansomewhat elevated salinities to Strgrrrartri lanrifoliaL., a dominantmarsh plant in theproject Theproject was in PhaseJ drawdown!for area Webb and Mendelssohn 1996!. antythree months 8 March- 4June! in 1994,and lessthan one month 4 March- 13 April ! in1996. Undesireablewater levels within the project Tbcrttarsh managcmem plancalls for a targetwater areacould have resulted from improperoperation levelof 6 to12 inches approximately 15to 3Qcm! of thestructures, especially in emergencyhigh belowmean marsh elevation during the March to salinity/highwater cvcnts when rnanagetneni Juncdrawdown period, During the 1994 March to personnelcould not respond immediately because Junedrawdown period, water levels actually ranged of morepressing needs io protectinhabited areas. from15 to 30 crn above mean marsh elevation, thus However,even when operations were made as failingtomeet the target water level, Although water scheduled,the water levels were not reducedto levelswere lowered to 20 cm relative to outside levelsoutlined in themanagement plan. waterlevels!, they were not lowered to theextent calledfor in thcmarsh management plan relative Theseconclusions are basedon continuous tomarsh elevation! forthe brief period inwhich the datacollected directly in thevicinity of twoweirs. projectwas in Phase I drawdown! Table 1!, An Thelack of anysubstantial data on conditions that increaseinthe duraiion ol'flooding events generally existedin theproject area prior to constructionas correspondedtoan increase inthe depth offlood!ng wellas the lackof anyrnoiutoring in a nearby althoughthis pattern was not ex hib ited on the inside atlVfill Creek Figs, 4 and5!. referencearea, make comparisonsbetween preexistingand current conditions di%cutt. Future restorationefforts should place more of an emphasis Satinitiesinthe project were significantly on preconstructionmonitoring and simultaneous lowerinside than outside .09 pptdifference! monitoringof surroundingwetlands. p<0.0th andsalinitics at Mill Creekwere signilicantlyhigherthan those atBayou LaCarpe Observationsof landownersand LDNR/CRD .35 pptdifferenc> pcO.Ql l. The differencein personnelindicate that water in thenorthern portion saliniticsbetween inside and outside varied between of theproject area flows from station 24 towardthc stations station"side interaction significant eastand north to station 25 Fig,I!. Thisdrainage ~k05I!. Hourlysalinities were higher inside than outsidethcpmjcct 58.9% olthe period reported for patternis confirmedby the lowerinarsh elevations MillCreek and 34.0% ofthc period reported for in thenorthern portion of the project,and by an BayouLaCarpe, ongoinghydrologic survey Arthur Long, persorial communication!.The entirenorthern hydro/ogic unitdoes not appear to be included within the project area,as there is waterexchange between the HNC andthe project area through breaches in theproject ThcFalgout Canal Protection project hasnot boundary,and flows bypass the structure atBayou metthe goal of maintaining water levels below LaCarpe.The northernportion of the project marshelevation during the growing season. The sustainedw idespreaddamage from airboats, marsh structuresdonot prov ide adequate control of water buggies,and chain saws during seismic work levelswith the present operational scheme. Water performedinJanuary 1996. Much of thisdamage levelswere above mean marsh elevation a large completely destroyed the vegetation and percentageoftime during the growing season, as significantlychanged the hydrology of thearea drawdownswercinsufficient todewater theproject whennew channels were created and levees werc «rea.Although thenumber ofshort flooding events breached.A lackof hydrologiccontrol in the inthe managed areawas decreased, thenumber of vicinityof Bayou LaCarpe may account for theless longflooding event~ wk! was increased relative pronounceddifference in thedepth and duration of Weirs and hlarshFlooding 249 Mill Creek ir1side 100% 4 CP 8 0'/o cK 4 OAuJ 60% 40% ae: C20% I4 PILI L 4 ~ I ICI CII III III CC ID 4 lD Ol D D CIC CD CD O ID CIC v- CIC cn I I CD A Ouration of Floodlrcg Event Mill Creek Outside 0 f 00% Ul Cl 4 O4 n80/ 'g > l.9cnc 60/ OCC El 15.1-22.9 cm: ttt ,9 7.7-15.0 cm 40% IQ 1 G-7.6cm E r.20% 4 4 0/ CL l ~ ~ C OC lO l5 CD CV CCC CP CD CD O II1 I cn Cll CCC A CIC Duratlen of FloOct1ngEVent Fig.4. PropOrtiOnaldepth of flOoding fOreaCh dccratiOn Of flOOding event at Mill Creek inside andontccde, 850 J,A. Sourgeoisand E.C, Webb l oa.: 0 8py, Q. a 6OV. 4t 4p 4I4 F /Per g 04 Nl C% lO Cl 4$ O LA Cb Al P7 CV Duwflottof Floo4ngEvent r 5.Po ~ "g ~o'e 4"duration offlooding eventat Bayou LaCarpe insideand outside, Weiniand MarshFlooding 251 floodingevents between the insideand outside of redox McKee and Mendelssohn 1989}. The theproject area Figs. 3 and5! as comparedto Mill coinbina ion of increased submergenccand Creekwhere the weir is not bypassed Figs. 3 and increasedsalinity caused a greaterdecrease in plant 4!. growthwhen these factors occurred together Webb andMendelssohn 1996!. Organicrnatter makes up The water level pattern at the Falgout Canal a largeportion of marshsoils, so a decreaseio p1ant Protectionptuject is consistentwith thefindings of productioncan also cause a decreasein soil organic previousstudies of managedmarshes. Structural mattercontent Nyman et al. 1990b!.Low pritnary marshmanagement often reducesthe coupling of productivitycan create a feedbackloop in whicha themanaged marsh with the surroundinghydrology reductionin organicmatter inputs to the marshsoil Boumansand Day 1994!. A reduction of water leadsto inadequatemarsh accretion, which leatLs to level fluctuationsin managedmarshes can also still 1owerpriinary productivitythrough a further indicatea reductionin thenet exchange of nuttients increase in floodingstress Nymanet al. 1993!. and sediinents and lead to a decrease in marsh Thesepotential changes in marshelevation were accretion Cahoon and Turner 1989; Bournansand not consideredin the managementdesign of the Day1994; Cahoon 1994!. Furthertnore,the greater FalgoutCanal project, accretion deficit and lower marsh elevation relative to sea level observedin tnanagedmarshes may Marsh managementat FalgoutCanal using explai~why targetwater levels are seldomif ever weirsand flapgates is notmeeung target water level reached.In contrast,soine weir-managed marshcs goals.Under this management regime, Ihe project in the ChenierPlain regionof Louisiana have not area experiencesfewer shortflooding events and shownadditional marsh loss or changesin accretion morelong floodingevents even though the absolute Nymanet aL 1990a;Foret 1997!. This different time the managed marsh is flooded is not responseto managetnentby marshes in theChenier significantlyaltered relative to areasoutside the Plainmay be attributed to differencesin substrate project. Althoughthe weirsdid statistically andlocal hydrology,both of which influencethe significantlydecrease the salinity in theproject area, effectivenessof weirs. However, Cahoon 990! theabsolute difference of 0.09ppt overthree years showedthat inanaged marshes in boththe Chenier maynot be biologically significant, This minimal Plain and Mississippi River Delta regions of reductionin incan salinityinside the projectarea Louisianahave significantly lower vertical accretion likely doesnot offsetthe concotnitant negative thannearby unmanaged marshes. impactof theincrease in thedepth and duration of floodingevents over the surroundingmarsh. The exclusionof tidal energyfroin thesystein ntayalso contribute to degradationof theproject ACKNOWLEDGMENTS Fig. 3!. Seasonallyflooded cypress swainps showhigher productivity than swainps that are The authorswould like to thankthe many colleagues continuouslyflooded, drained, or thosewith a slow at the LouisianaDepartiTietit of NaturalResources tateof waterflow MiLschand Ewel 1979;Conner CoastalRestoration Division whocontributed to this andDay 1982!. In addition,impoundinent and levee effort. Specialthanks for comnicntsand statistical constructionhave been linked to lowernet primary advicego outto J, Andy Nyman,Greg Stcyer. Darin productivityin wetland trees Megonigal et al. Lee, Lawrence Rozas, and three anonymou.s 1997!.Ftuthermore, restoring the naturalhydrology reviewers. Assistance with data entry was of wetlandsby removinglevees has been shown to performedby Nancy Leiva. Funding for this havea positiveinfluence Trepagnier et al. 1995!. researchwas provided by theLouisiana Department of Natut al Resources Coastal Restoration Division. An increase in the incan water level over the ntarsh,such as hasoccurred at the FalgoutCanal Protectionproject, causes a significantdecrease in plautaboveground biomass due to reduced soil 2$2 J.A. Bourgeoisanst E.C. Webb LITERATURE CITED CowAN,J. H JR., R. I.. Tt:RNER,Aso D. R. CAHooN- ! 988.Marsh management plans in practice: BOtrrrtANS,R M ANn J,W. DAV, JR. 1994. Effects Do they work in coastalLouisiana, LrSA. oftwo Louisiana marsh management planson Environmental Management12:37-53. water and materials flux and short-term DUNBAR,J, B., L. D. BRrrscii, ANliE. B, KErvtrIH. sedimentation.Wetlands 14: 247-261. 1992, Landhiss rates, Report3 Louisiana CArtOON,D.R. 1990.SOil accretiOn inmanaged coastalplain. Technical reportGL-90-2, andunmanaged rnarshes, p.409-425. In D.R, IJSAEWaterways Experiment Station.. Cahoonand C. G. Groat eds!. A Study of Vickshurg,MS, MarshManagement Practice in Coastat FGRFT,J. D. 1997, Accretion,sedimentation, and Louisiana,Volume Ill, EcologicalEvaluation, nutrientaccumulation rates as influenced by Finalreport submitted toMinerals Manage- manipulationsin marsh hydrologyin thc mentService, New Orleans, LA. ContractNo. ChenierPlain, Louisiana. MS Thesis,Univer- 14-12-0001-30410,OCS Study/MMS 90- sityof SouthwesternLouisiana, Lafayette. 0075. Hr'-ss,T,J. JR R. F PArLLi.,R. J. MOERrLE, AvD K. P. CAHOON,D. R. 1994. ReCentacCretion in two Guir~av.1989. Resultsof an intensivemarsh managedmarsh irnpoundrnents in coastal managementprogram at Little PecanWildlife Louisiana.Ecological Applications 4:166- ManagementArea, p. 278-310. In W. G. 176. Duffy and D. C, Clark eds.!, Marsh CAHoov,D,R AvoC. G, GRoar editors!. 1990. A rnanagernentin coastalLouisiana: Effects and Studyof MarshManagement Practice in issues proceedings of a symposium. U.S. CoastalLouisiana, Volume I. Executive Fish and Wildlife Service and Louisiana Summary.Fmal report submitted toMinerals DepartmentofNatural Resources, Washington ManagementSer vice, NewOrleans, LA. D,C.:Govemmcnt Printing Office. U.S. Fish ContractNo.14-12-0001-30410. OCSStudy/ and Wildlife ServiceBiological Report M MS 90-0075. 89 2!, CAHOON,D,R., Axti R. E. TLRNER. 1989. Accretion McKt:i., K, L, ANt>I, A. Mt'.NPELssOHN,1989. andcattal impacts in a rapidlysubsiding Responseof a freshwatermarsh plant com- wetlandII. Feldsparmarker horizon tech- munityto increasedsalinity and increased nique. Estuaries12.260-268. waterlevel. AquaticBotany 34:301-316. CHABRECK,R. H 1960. CoaStalmarSh MEGONiGAL,J, P., W. H. CoNNERS, KROEGERS impoundmentsfor ducksin Louisiana. R, H. St bivtaxi, J. A., R, D. Dt!t At.'xi:,~it> W. H. PAratctt, JR, 1990b. Wetland soil forination in the rapidly subsiding Mississippi River Deltaic Plain; Mineral and organic matter rela- tionships. Estuarine. Coastal and Shelf Science 31:57-69. NYMAN,J. A R, D. Dt.l.Attivt,H. H. RORFRrs,AND W. H. Pwrtttc<, Jtt. 1993. Relationship betweenvegetation and soil formation in a rapidlysubmerging coastal marsh. Marine Ecological ProgressSeries 96:269-279. primo, S., K. E, R 255 T. J. Hess et al. The areais considered"one of the most important Unit 14soils are classified as Bank an er series and wildlife areas in the United States" Soanen et consistof poorlydrained slowly, al. 1969!, therefore Louisiana Departmentof th t fo~ m flugclayey coastal alluvium and Wildlifeand Fisheries personnel developed a special orgarucsediments inbrackish ~h 1U permitto minimize environmentalimpacts Departmentof Agriculture1996! S tl k associatedwith the project. The seismic prospect which~m inthe tidg marsh south of Uinit14. a~ encompassed167 square miles andused a slanted sill totheBankmsenm,but~~~mlinelhan sourceline patternwith a 1980foot receiver line Banker'soils UnitedStates Department of spacing" to reach the survey's geological goal and Agriculture1996!. minimizemarsh traffic" Hulrne 1996!. INatenals and Methods Concernover the possibledeleterious effects of off-road vehiclesto wetlandecosystems in the Unit 14 and the Tidal Marsh south of Unit 14 RoridaEverglades began to developin the1970's. wereselected for thisstudy to comparethe effects Dueveret al. 981! documentedthe effectsof of vehicular traffic on marshsoil elevationswithin airboats,all-terrain cycles, and tracked vehicles on two differentmarsh types. The traffic routealong South Florida wetland habitats. Nidecker et al. receiver line number586, running north/south thru 993! developeda monitoring program to assess Unit 14 and the Tidal Marsh south of Unit 14. u as theimpacts of 3-D seismicact,ivity on wildlife and chosen for this study. Geco-Prak!a requested wetlands at Sabine National Wildlife Refuge, perinissionto conductan experimental equipment CameronParish, Louisiana. Nideckeret al. 993! test on the line after conventional3-D seismicdata foundthat soil compaction from marsh buggy travel was collected, and a comp!etetraffic historvof the varied from 0,3 inches to 2.0 inches at eight line was available. Two additionaltraflic routes. samplingstations. One damp marsharea in the running east/westwithin Unit 14and the Tidal projectarea experiencedsoil compaction of six Marsh were also establishedfor the study lFig 1!. inches;but "determining the impacton the soil Vehicles used during the seismicsurvey and matrixfrom seismicacti vity is a complexissue and experimentaltestincluded a 4.0 m by8.2 rn marsh onethat was beyondthe scopeof this study" buggyinounted with a vibra-ramandnumerous car Nideckeret al, 1993!. We designedthis study to enginepowered airboals. Marsh soil elevation data quantifythe effectsof airboatsand tnarsh buggies werecollected from February 21. 1997 o March 7, usedfor seismic exploration on marsh soil elevations !997 after all vehiculartraffic activity was within a semi-impoundedand tidal marshat completed.Thirteen, 30.5 m transectlines running RockefellerRefuge. perpendiculartotrafTic routes were established. Six lineswere located in Unit 14, while seven!ines were StudyLocation locatedin the Tidal Marsh Fig. 1!, Transectline 1 in Utut 14was not used for the study due to technic a I Weconducted this study at Rockefeller Refuge difficultiesencountered during data collection. in Unit 14 and a tidal marsh south of Unit 14 in Transectlines extended 15.2 m oneach side of a VermilionParish. Louisiana Fig. 1!. Unit 14is a perlrlanentcenter pole. Elevations atfifteen 9'72hectare semi-impoundment with bothforced samplingpoints with 30.5 cm spacings andfive drainageand gravity flow water control capabilities. samplingpoints with 305.0 cm spacings +ere The areais characterizedas intermediatemarsh with recordedon each side of the center pole iFig. 2i. majorvegetative species being wiregrass Sparti na Cross-sectionalvehicular traffic disturbance parens!,buHtongue Sagirraria lancifolia!, and dis~ceswere dete~ned visually oneach side of thecenter pole by exrending a tape measureasure fromro bullwhip Scirpus californicus! Chabreck and « ~enterpole along the transect lineto a point Linscombe 1988!. The area south of Unit 14 is e and undis- characterizedas a brackish tidal marsh with major wherecompressed vegetation endedand vegetativespecies being wiregrassand saltgrass turbedvegetation began. Distich!isspicara! Chabreckand Linscornbe 1988!. Effect of Vehicular Traffic on Soil Eluvations 2SI Fig- L Localioriof RockefellerRefuge, CanIeron and Verrn ~ lionParishes, Lou »8 > Locationattd cross-sectional viewpf transect Water level data was collected between the first Vehicular traffic activity was variable along and tenth of each month by Rockefeller Refuge traffic routes Table 1!. The width of disturbed areas personnel. Staffga.uges are locatedin Unit 14 and along eachtraffic route was variable Table 2! and the Tidal Marsh. Averagemarsh level mud line! ranged from 5.5 m at transect line 8 to 14.9 in at equalsa readingof 1,0 0.5 cm! on staff gauges, transectline 2. The average disturbedarea for all transect lines was 10.3 m. An EAGL-I electronic level mounted on a flatheadtripod and CR-16-I leveling rod equipped Waterlevels within Unit 14ranged from greater with a LS-4 detector was used to collect elevation than 30.5 cm below marsh level in June, 1996 to data at samplingpoints. The first readingon each 59.1 cm above marsh level in November, 1996. transect line was taken at the center pole. The Water levels within the Tidal Marsh varied from 4.9 levelingrod wasinserted through marsh grass to cm abovemarsh level in February,1997 to 64.6 cm the mud line. Grassand vegetativedebris was above marsh level in October, 1996 Table 3.!. cleared by hand, and the soil surfacewas also identifiedby hand. Care was taken to minimize There was no interaction between location and soil disturbanceat samplingpoints, The LS-4 disturbance F=Z.15, 1 ldf, P=0.1706!, Disturbed detector was moved along the leveling rod soil elevations were not different from undisturbed producingan audio signal and liquid crystal display soil elevations for all transects F=0.63, lldf, beam when the elevation value was reached on the P=0.4430!. There was no difference in soil leveling rod. elevations between Unit 14 and the Tidal Marsh F&.OL 1 ldf. P=0.9357!. Mean soil elevations were 1,18 crn, 0.61 cm, Differences in marsh soil elevatiotis between and 1.75 crn below the center pole soil elevation disturbedand undisturbed tnarsh subploteffects and readingfor disturbedsampling points and 0.66 cm, transect location whole-plot effect! Unit 14 and 1.05 cm, and 0.27 cm below the center pole soil Tidal Marshwere evaluated using a split-plot elevation reading for undisturbed sampling points analysisof variancemixed model in ProcMixed of for all transects. Unit 14, and the Tidal Marsh, SAS 990!. Leastsquares means were compared respectively Table 4!. at an alpha =0.05 level. Tabk 1. Numberof airboatand marsh buggy passes documented during the Geco-Prakla, 3-D seismicsurvey at RockefeHerRefuge, Camerot3 aad VermilionParishes, Louisiana, 1996-1997- Location Unit 14 Tidal 1VJarsh Line Year Airboat MarshBuggy Airboat Marsh Buggy Receiver 5S6 1996 5 3 12 1997 Total 13 East/West 1997 13 259 T. J. Hoss et al. Table 2. Disturbance widths of traffic routes Table3. WaterLevels frnan lJ+,.t y4 a~ d, recorded from transect lines established in Tidal Marshduring the Geko-Prakla 3-D lJrdt 14 rattdtbe Tidal Marsh following the seismicsurvey at RockefellerRefuge, Carneron Geko-Prakla3-D seismicsurvey at Rockefeller andVertttiTion Parishes, Louisiana, 1996-1997. Refuge,Cameron and Vermilion Parishes, Louiiaara, 1996-1997. Location Location. Transect Width m! Mean m! Month Year Unit14 TidalMarsh Water levels cml' Unit 14 14.94 12.80 »96 D~ 50.0 10.67 12.55 July 1996 Dry' 45.1 12.50 August 1996 Drv' 5 L8 12.19 September 1996 50.6 506 12.19 12 October 1996 69.5 95.1 Tidal Marsh 6 5.79 november 1996 89.6 62.8 13 12.19 December 1996 84.7 52.4 10.36 8.06 January 1997 68.3 39.e 6.10 5.49 February 1997 61.6 35.4 7,62 ' 30.5 cm = Marsh Level 10 8.84 '>30.5 cm = Be!ow Marsh Level Overall Mean = 10.3 Discussion Vehicular traffic on both sidesof the center pole may havecaused a slightlyelevated ridge at the Vehicular traffic activity varied along traf'fic centerpole, similar to ridgesformed by vehicular routesdiie to varied marsh water levels during the trafficalong test lanes in variousSouth Florida 3-D seisnucsurvey. Pry marsh conditionswithin marshtypes Dueveret al, l 981!. Unit 14caused marsh buggy use to increase,while warerlevels above average marsh level in the Tidal Thegreatest mean elevation value L75 crnl Marsh allowed increased airboat use. Louisiana occurredin thedisturbed area v ithinthe tidal marsh. Departmentof Wildlife and Fisheries 3-D seismic Althoughno significal diffidenc occurred between survevguidelines are flexibl. but encouragelimited disturbedand undisturbed soil elevati ons within the marshbuggy and airboat passes to minimize Tidal marshwe observed signs of visualvegetative environmentalimpacts. Seismiccompanies are damageindisturbed areas of transects13and 14. encouragedto limit marshbuggy passesto one and VegetativeC' damage assessment was outside the 15 airbMtpasses to 10on traffic routes, This goal was scopeof this study Chabreck ]994! ev al uated not achievableduring this seismic survey due to sitestraversed by marshbuggies and/or airboats sununerdrought conditions and the necessity to durinD~ the3-D seismic program conducted byPlains Performan additional equipmenttest after the Resources,Inc.at Sabine National%'ildlife Refuge. seismicsurvey was completed in thestudy area. Hacicberry,Louisiana andfound that four of 21 sites traversedby marshbuggies contained some Meansoil elevationreadings were lower than evidenceofrutting. Three sites contained oneinch centerpole soil elevationreadings for all transects. rutsand marsh damage was considered light. One Effect ot Vehicular Traffic on Soil Elevations 260 Table4. Leastsquares means of soil elevation etta! in disturbedand undisturbed marsh studied iu Unit14 and Tidal Marsh following the Geco-Prakla 3-D seismidsurvey at Rockei'ellerRefuge, Cameron and Vermilion Parishes, Lonisiataa, 1996-1997. Condition Sites Disturbed Undisturbed df Unit 14 -1.046 0,19 0.6772 Tidal Marsh -1.745 -0. 270 3.16 0. 1033 All Transects -1.177 -0.658 0.63 0,443 sitecontained four inch ruts and marsh datnage was Marshbuggy and airboattraffic did not appearto considered moderate. Chabreck 994! did not causesignificant marsh soil compactionduring this statisticallyevaluate differencesbetween soil study, elevations in disturbed versus undisturbed marsh, but stated"ruts thatare one inch deepshould not ACKNOWLEDGMENTS restrictplant growth." Chabreck 994! alsofound that threeof four ruttedsites showed signs of plant The authors wish to acknowledgeDr. Barry regrowth,The fourthsite had been burned and no Moser and Rebecca G. Frederick, Louisiana State plant regrowth wasnoted in the marshbuggy trail UniversityExperimental Statistics Department for or adjacentundisturbed site. their assistancewith statisticalanalysis, Geco- Prakla, Schlumbergerfor cooperation and data Marshbuggy and airboat traffic did notappear acquisitiori,and Fensterznaker and Associates for to causesignificant soil compactionduring this figure preparation.Special thanks go to Mr. Dermis study. Resultspresented by Duever et al. 981! Kropog. LouisianaDepartment of Wildlife and were similar, Airboars and track vehicles evaluated Fisheries. for his assistancewith developinent of in various South Florida wetland habitats did not laser level inethodsused during this study. This cause soil compaction. Rutting from vehicular project was funded by Louisiana Department of traffic wasconsidered the most severesoil impact. Wildlife andFisheries, Baton Rouge, Louisiana. but rutdepths decreased following the testsand were shallow or almost undetectable one year after LITERATVRE CITED treatments, CHABREcK,R. H. 1994. Damage assessmentof Summary Miami fee3D seismicprogram. Report to Plains Resources,Jnc. Geco-Prakla conducted a 3-D seismic survey CmarrEcx., R, H. ANDG. LrNscoMBF. 1988. Louisiana on RockefellerRefuge from June18, 1996to July coastalmarsh vegetative type map. Louisiana 1, 1997. We evaluated the effect of vehicular traffic, Departmentof Wildlifeand Fisheries,Baton which includedairboats and tnarshbuggies, on Rouge.Louisiana. ntarsh soil elevations. Vehicular disturbance was DEpartmxm OF Wn DLm ~r D FrSHZrueS. 1946. First evaluatedalong 13, 30.5 m transectlines running biennial report, 1945-1946. Department of perpendicularto traffic routes, An electroniclevel Wildlife and Fisheries. New Orleans, Louisiana. andleveling rod equipped with a.detector were used Dt.'EVER,M., J. C~~, mo L. Rro~. 198 1. Off- to collect elevatio~ data. Disturbed soil elevations road vehicies and their impacts in the Big were not different from undisturbed soil elevations Cypress National Preserve. South Florida for all transects, Unit 14, and the Tidal Marsh. ResearchCenter Report T-614, Homestead. Florida, 261 T. J. Hess eI al. HLt.Sts,C., Executive Editor. 1996.Int.O the tranSi- tionzone. Signals. Geco-Prakla, Schlurnberger Producedby TechnicalEditing Services, Ltd Chester.England. JOANEN,T., L. McNEAsE, AI'o H. DL'PUIE. 1969. Vegetationsurvey of RockefellerRefuge im- poundments. Annual Progress Report. Louisiana Wildlife and Fisheries Commission. Ne w Orleans. NIDEcIcER,w., R. RAIblcoL'RT,M. WILMO4T,AND D. ZwtLLo. 1993, Plains Resources Inc., 3-D seismic project: environmental program. Interim Report November 9, 1993. Sabine National Wildlife Refuge. Hackberry. Louisiana. SAS I~sTITuTE.II C. 1990, SAS PrOCedureSGuide. Version6. 3rd. Edition.Cary, North Carolina. Vh'ITEDSTATEs DEPARTME."I1 OFAGRICULTL'RE. 1996. Soil survey of Vermilion Parish, Louisiana. Natural Resources Conservation Service. Abbeville, Louisiana. B. C. Wilson et al. deposits Ensminger etal. 1997!. Incoastal rnarshes StudyAres h Methods thisrequires considerable vehicular traffic by airboatsandmarsh buggies inareas that normally RockefellerSWR consistsof approximatciy experiencelittleor nosuch traffic. Previous 3O,400hectares of coastal marsh in Cameron and accountsofsimilar activities have met with rrnxed VermilionParishes of Louisiana four lines - 2 north-southrecei ver lines and 2 east- seismicactivity or control!, line -4!, tutte befo~ west shot lines - were chosenbecause they were one year after, or two years after!, andall approximatelyequaHy distributed ]attitudinally and interactions.The treatinent-by-time BACI! longitudinallywithin the unit. interactionindicates the effect of an impact meansare reportedas least-squaresmeans, We We sampledvegetation with thefine-intercept performedpairwise comparisons using Tukey's methoddescribed by Chabrecket al. 960!. Two procedure Steel et al. 1997!. Means are hundredtwenty satnplingstations were evenly detransformedforreporting. An alphaof 0,05was spacedalong receiverand shot lines at 76.2-m usedto determine significance, intervalswith the followingexceptions: ]! half- mile line sectionswhich crossedSuperior Canal WhenP-values for the BACI interactionwere were not sampledbecause visibility prohibited marg}na] ,05 - 0.10!, we a]soevaluated those data determiningline location,and 2! stationswhich with a logistic analysisin PROC GENMOD in occurredtotal]y in openwater were moved to the which the responseis a binomial count with 50 nearestpoint along the line with emergent possiblevalues .1-5.0 in incrementsof 0.1!, Wa]ti vegetation,from whichthe next 76,2-m intervalwas statisticsand associated pmbabilitics were then used measured,Live vegetationby speciesand open to determinesignificance. waterwas estimated to thenearest O. I-ft .0 cm!at each station. We inade visual estimates of the Aspart of routinerefuge management activities, portionof a 5-foot .52-m! linecomprised of live thestudy area was prescribe burned in thefall of vegetationby speciesand open water, with the 1994. Most of the studyarea was burned20-28 remaindercomprised of dead stems, bare ground, November1994, after annual vegetati ve satnpling, andspace. Open water was defined as an area void A sinai]southeast portion of the studyarea was of emergentvegetation, but can include SAV. For burned14 October 1994, five weeks prior to annual eachsampling station on a rem:iveror shot line, a vegetativesampling correspondingcontrol station was estab]ished approximate!y 30 m fmmthe line in a similarhabitat type.Wooden stake markers em*5 em*3 m! were placed3.66 in duesouth source lines! or west Seventy-ninepairs of samplingstations were receiver lines! from sampling stations. usedin analyses The remainderwere discarded forone or more of the following reasons: I! seismic Initia]data were co]]ected 10-18 November, activitydid not actually impact thc treatment sample 1994,6-7 ~eeks prior to the seismic activity. station,2! we were unableto relocatemarkers after Thereafter,data were collected bythe same observer prescribedburns, or 3! they wereunintentiona]]y annuallyfor two years 13-21 Noveinber. All data impactedby subsequentseismic activities, werecollected and analyzed in Englishunits, so resultsare reported as such, Fortotal einergent ve.getation TEV!, the BACI interactionwas non-significant F = 1 07.df = Datawere logratio transformed Aitchison 520,P =0,3243! Table 1!. Treatment,tnne 1986!to better accoinodate ana]ysis asa continuousthetime-by-line interaction were significan«ff~+ proportion.Values of 0 or5.0 were perturbed Table1!. Thetrend of higher control values, b h s]ight]yto0.01 and 4.99, respectively, toaccomodate thetransformation. Values for total emergent beforeand after the treatment, isevident inthe ]east vegetation,marshhay cordgrass, Cyperus oderatus, squaresmeans Tab]c 2!. andopen water were each analyzed asa response variableina separateBefore/After/Control/Im pact Forinarshhay cordgrass, the BACI interac ' " BACI!model Green 1979, Stewart-Oaten etal. was non-significant F = 1.90, df = 2 52 ' ] 986!using PROC MIXED in SAS SAS institute, 0.1510!gage 3!. Treatmentand the time-by-line Inc.1997!, Models included effects of neatment interactionwere sigruficant effects Table 3! withTEV, the trend of highercontrol values f« yearsis evident Table 4!, B C. Wdsonetal. TableL Resultsof BACI model for effect of 3-D seismic activity on total eme~nt v~eb ho Utut6 pf RockefellerState Wildlife Ref'nge, Cameron ~ Source NDF DDF Proh! F Treatment 520 13.73 Tune 520 5.17 0,0060 Treatment*Time BACI! 520 1,07 0.3428 Line 236 23104 0.32 0,8097 Treatment*Linc 520 1.82 0.1433 Time~Line 520 4,29 G. 003 Treatment*Time*Line 520 0.49 0,8195 ForCypencs oderahcs, theB AC I interactionwas Table2. Least-squarestneans' of total significant F= 4.69,df = 2,520, P =G.0096! Table emergentvegetation values' by treatment' and 5!. CyperusoderarMs values were higher at treat- thne'in Unit6 ofRockefeller State Wildlife mentstations the first year following the treatment Refuge,Camcron Parish, Louisiana. thanat any other combination oftime and treatment Table6!. Treatment,time, linc, and the titne-by- Tlnle Treatment Control lmeinteraction were also significant P&,0216!. For openwater, the BACI interactionwas Before 1.7881AB 1.9990A marginallysignificant F = 2.76,df = 2,416, P = 1.7097AB 2.3357 A 0.0647! Table 7!. Logisticanalysis indicated a non- After 1 year significant%'aid statistic for the BACI interaction After 2 years 1.2795B 1.8302AH X'=3.3454, df = 2,P =0.1877!. Tukey's pairwise comparisonsofthe least-squares meansrevealed the 'Meanswith the same letter are not statisticai ly valuefor the treatment stations the first year after different Tukey 'sprocedure! thetreatment was higher than the value for the 'Kxptessedinfeet, out of a 5foot sampling line controlstations that year, but values the ~nd year followingthetreatment didnot differ Table 8!. The 'Su b'ected jec to3-D seismic traffic or control treatmenteffect and the time-by-lineinteraction 'Before,one year after, oi 'twovears .ere alsosignificant Table 7!. after3-D seisinic activity Theeast and west receiver lines were subjected Discitssion 8 and114 airboat passes, respectively. ervicingrecorders accounted for80 8 1 if,ofpasses Lackofsignificant BAC1 interactions indicates eivcrlines. The north and south source Bnes thatthe seismic activity had n «e subjectedto 45 and30 airboatpasses, tnarshhaycordgrass,or open water Tables l. 3,and p «ly, ui additionto a marshbuggv pass.ass. A 7!.Although tracks were evident immimmediate! y after nd~h buggypass occurred ona short 0%! theseismic operation, thhe first post-seismic non of the north shot line, 3-D Seismic in a Coastal Marsh 286 Table3. Resultsof BACI modelfor effectof 3-D sefstmcactivity on tnarshhaycnrdgrass Spurfina paterrs!in Unit 6 of RockefellerState Wildlife Refuge,Cameron Parish, Louisiana. Source DDF Prob > F Treatment 520 21.43 O.N]0] Tlnle 520 1.32 0.2674 Treatment~Ti tne 8ACI! 520 1.90 0.1510 Line ]04 0.60 0.6] 45 Treatment*Line 520 1.19 0.3111 TimeLine 520 5.32 0.0001 Treatment~Time'Line 520 0,78 0.5883 Table4. Least~naresmeans' of marshhay area, Any vegetation that could have been cordgrass Spartirns patents! values' by compactedtoprevent recovery was removed by the treatment' and time' in Unit 6 of Rockefei]er fire. StateWI]d]]fe Refuge, Cameron Parish, Louisiana. Thesignificant BACI interaction inthe Cyperns oderarustnode] indicates that the seismicactivity Time Treatment Control didchange the relative occurrence of that species Table5]. Wechose a posteriorito evaluatethis speciesbecause. it typical! y respondstodisturbance, Before ].2385AB 1.4502A andappeared toperfectly delineate the survey lines in someareas the first yearafter the survey. The After1 year 0.9236AB 1.5786A datareflects that it didincrease oii treatment plots After2 years 0.8673B 1.4457AB 190times over pre-seismic conditions, while the increaseon controiplots was only about2-fo]d 'Meanswith the same letter are not statistically Table6!. The effect was oniy short-term, ascontrol different Tukey's procedure! andtrmtttent values were not different the fo]]owing year Table6!, 'Expressedinfeet, out of a 5 footsampling line 'Subjectedto 3-D seisnuc traffic or control Thesignificant time-by-line interaction inevery 'Before,one year after, or two years modelindicates that the natural vegerative changes after3-D seismic activity thatoccured did not change the same way for every line Tables1, 3, 5, and7!. Partof thereason we chosethe 4 linesis becausewe expected natural samp]ingperiod occured after a fu]] growing season. variationeven within the same management unit. Chabreck 994! foundevidence of regrowthof Tosome extent, each line represents a different sproutsafter marsh buggy tracks from ] 5 October- nucro-habitatof subtle elevation, hydro]ogic, and 9 3anuarywithin the same year. The management edaphicdifferences withtn theUnit 6 mterrnediate burnafter the first post-seismic sampling period marsh.It istherefore not surprising that a time-by- couldalso have influenced recovery of the study lineinteraction i» significant for each model. 267 B. C. Wilson et ai. Table 5. Resultsof BACI modelfor effectof 3-D seisrnkactivity on Cyperas4irieraras in Unit 6 of RockefellerState Wildlife Refuge, C,ameron Parish, Louisiana. Source DDF F Prob ! F Treatinent 520 5.31 0,0216 0.0001 Time 520 51.90 Treatment~Time 8 ACI! 520 4.69 0.0096 3.63 0.0154 Linc 104 ],84 0.1394 Treatment*Line 520 3.61 0.0016 Time*Line 520 0.0654 Treatment*Tirne4'Line 520 1,99 Table6. Leastsquares means' of Cypersrs seismicactivity. These facts, though unrelated to arferarrrsvalues' by treatment' and time' in thcprimary objective ofthis study, point out the needfor analysesthat control for bothnatural Unit 6 of Rockefeller State Wildlife Refuge, temporalchanges in marshvegetation and Cameron Parish, Louisiana researchers'inadequaie attempts tosubjectively identifypaired control s. Time Treatment Control Thisseismic operation represents botha worst- caseand best-case scenario relative toother coastal Before 0.0099AB 0.0103A 3-Dseismic surveys. Technological advances have farsurpassed whatwas ava.ilable atthe time of this After1 year 1.87glAB 0.0187A survey.Recent 3-D surveys have employed radio After2 years 0.0112B 0,0107 AB teleinetryfortransmitting seisinic signals and inonitoringreceiving equipment, i.hus greatly 'Meanswith the saine letter are not statistically decreasingtheneed for airboat maintenance of signalrecording equiptnent Ensminger etal. 1997!, different Tukey'sprocedure! Otherrecent iinprovernents include enhanced 'Expressedinfeet, out of a 5 foot sampling line coinmunications,increased useof helicopters, and 'Subjectedto3-D seismic traffic or control slantgeometry linepatterns thatminiinire theneed 4Before,one year after, or two years fordamaging right-angle turnsby marsh buggies after 3-D seismic activity Knsmingeret al,. 1997!. Conversely,thisseismic survey atRockefeller Thesignificant treatment effect in all inodels SWRprobably represents a best-case scenarioin indicatesthat there was a differcnce, regardless of termsofmonitoring andcommunications. Seismic seismicactivity, hetw een ~nt andcontrol sites. activitieswere carefully planned and closely Thoughwe attempted tomatch vegetation types monitoredhySeismic Section andFur & Refuge withineach pair,weunintentionally andconsistently Divisionstaffof the Louisiana Department of chosecontrol sites with moredense vegetation %'iidlifeandFisheries. Twopre-planning meetings. {Tables2 and 4!, The significant timeeffect inthe weeklyoperations meetings, anda post-cleanup TEVand Cypenrs oderara models alsoindicates that meetingofall involved parties refuge staff.Se isinic thesevariables changed over time, regardless of 3-0 Seismic in a Coastal Marsh 268 Table7. Resultsof BACl modelfor effectof 3-D seismicactivity on openwater in Unit 6 of RockefellerState WMlffe Refuge,Cameron Parish, Louisiana. Source NDF DDF Prob! F Treatment 6.55 0.0120 Time 520 0.84 0.43] 4 Treatment'Time BACl! 520 2.76 0,0647 Line 0.14 0,9367 Treatment*Line 520 0.57 0.6368 Time 'Line 520 4.30 0.0003 Treatment~Time~Line 520 1,32 0.2489 'Logisticanalysis resulted innon-significant Wald's statiscis X2 = 3,3454,2 df, P =0.1877!. TableL Least-squaresmeans' af openwater Accessto the projectarea via SuperiorCanal values'by treatment'and time' in Unit ti of alsocontributed to the successof the project. RockefellerState Wile}liYe Refuge, Cameren SuperiorCanal provided an extensiveand centra! Parish, Louisiana. accessroute to virtualiythe entire study area, thus minimizingthe need for excessive buggy and airboat Time Treatment Control traffic on the vegetatedwetlands. We emphasizethat these resulls,though Before 0.0306AB 0.0316 A encouragingrelative to vegetation,do not reprcscnt otherpotential effects on the ecosystem. For After 1 year 0.0592AB 0,0260A exarnp!e,Knott et al. 997! foundthat despite good After2years 0.0448B 0.0289AB vegetativerecovery at a coastalmarsh study site in SouthCarolina, pipeline construction virtually 'Meanswith the same letter are not statistically eliminatedseveral invertebrate species. We suggest different Tukey's procedure! furtherstudy on seismic impacts not evaluated by this study, such as impacts of disturbance on 'Expressedinfeet, out of a 5foot sampling line migratory and resident wildlife. iSvbjcctedto 3-D seismictraffic or contml 'Before,one year after, or two years AC KNOWLKDGMENTS after3-D seismicactivity We thankMobil Explorationand Producing U.S., Inc. for their cooperationthroughout the Sectionstaff, Mobil operations managers, and field project,including replanning someof their line foremen!greatly enhanced conununications and routesto accomodate our sarrrplestauons. Rebecca avoidedor quickly resolvedany problems. Frederick,LSU Exp.Stat. Dept provided data Chabreck 994! attributedthe successof the managementand statisticalhelp. Eric Richard. seismicsurvey on Sabine NWR to careful planning LDWFRockefeller Refuge, assisted with sample ofaccess routes and use of the tnost en vimnmentally sitepreparation and data collection. Larry LeBlanc, sensitiveequipment available, LDWF SeismicSection, provided detailed technical informationregarding the survey. 2M B. C. Wilson et al. LITERATURE CITED AtTcHtsox, J. 1986. The statistical analysis of compositional data Chapmanand Hall, New York, 416pp. CttAaREcx,R. H. 1960. Coastalmarsh impound- ments for ducks in Louisiana. Southeastern Associariortof Came arrd Fish Commissioners 14:24, CHAattzcx,R. H. 1994. Damageassessment of Miami fee 3D siesrnicprogram. Reportto Plains Resources,Inc. 18pp. ~, R, H. 1979. Sampling designand statistical methodsfor environmentalbiologists. John Wileyand Sons, New York,68-71. EYSMtvGFtt,A., R. FOSSIER,M, H. GAGLtANtj,S, M. GAGL1ANO,E. MOUTox, Avn M. WtNuHAM.1997, Lake Sand:A reduction of environtnental itnpactsduring a 3-D seismicsurvey in the Louisiana Coastal Wetlands. Gulf Coast Associationof Geological Societies,New Orleans, Louisiana, October 15-17. Kvuvr, D. M., E. L. WavvER,AvD P. H, WENnr. 1997. Effectsof pipelineconstruction onthe vegetationand macrofauna of twoSouth Carolina,USA salt marshcs. Wetlands 17:65- 81. PoLAsax,L, G. 1997,Assessment of wetland habitat alterationsresulting from construction of a pipelinethrough coastal marshes in Orange County,Texas. TexasParks and Wildlife DepartmentFinal Report,40pp, SASINsttTL~, Iwc. I 991. SAS/STATsoftware: changesand enhancements through release 6.12, SASInstitute, Inc., Cary, North Carolina, 571-701. STEEL,R. G. D., J. H. Toatttr.,Avo D. A. DtcxEv. 1997.Principles and procedures of statistics: a biometricalapproach, third edition. McGraw- Hill BookCo., New York,666pp. STEwAzr-OArFw,A W. W. MuttnncH,ANn K. R. PARKER,1986. EnvirOnmental asSessment: "pseudoreplication"intime? Ecology 67:929- 940. Taxation of Private Marshland: The Use Value Method Applied to Louisiana's Coast KEMvETHJ. Roe eRTs LouisianaCooperative Extension Service, PO. Box 25l00, BatonRouge, LA 708ft4-5 0;email: krobertstiltagctr lsu.erlit PAVLA. CORHL LouisianaCooperative Extension Service, P.O. Box 25/00. BatonRouge, Ltt 70894-5100;emat'l: pcoreil@'agctr. su,edu ALeERTJ. ORTEGA~,JR. louisianaCooperative Extension Service, PO. Box 25l00, BatonRouge, LA 70894-5100;email: aortego@agc tr.lsu,edit ABSTRACT:Public benchts, many of them olfsitc, of'privately owned end managed mars«nds «rewell documentecL Onectatt of ownership, property taxes, was high enough inthe view of some privatemarshland owners toprompt a legal challenge ofthe basis of Louisiana marshland taxation Thestakes werc high rcgsnHng impacts tostewardship ofthc 80 percent ofLouisiana's 1.4nutIion haof ~ marsh privatelyo wnctL Knresponse tothe landowners' pending legal proceedings, the l995Louisiana Leghtiaturc ~ Act230. Thc Louisiana TaxCotnmission LTC!was directed to determinetmifortn marshland usevalues, forad valorem taxation purposes. Usevalue's basis lsnet incomeFrom surface use, not tnarkct value. To develop a use value table lnaccordance withAct 230, a surveyresearch study design was implemented. Average usevalue was obtained bydividing thc averagenet income from surface uses by the appropriate capitalization rate.The usc values obtahted frotnthc 9Al percent capitalization ratewerc: $9.67 hs' freshwater!,$3.72 ha' brackish!and SI89ha ' saltwater!.LTCprocedure provkies thataverage ass++ed valuebe obtained hymultiptyhtg theuse value by l0 percent.The study's rendtlug assessed valueper acre was far below levels inuse byLTC. Thc research nvealcd a dubious future for the uac value approach totaxing Losusiaaa marshland.Landowners appear headed toward tax reductkms. County prxtpcrty taxrevenues, whichhelp support many vital ktcai services, willdcc~ significantlyasa result.This could affect therelationship between htndo|vncra andcommunitics strlviag tomaintain andrestore publk benefits of marshland. Introrduction functionsand valuesof marshlandas well as mineral revenue cannot be tncluded in tax estimation. Seventy-five percent of marshland in Louisiana is privatelyowned McBride1992!. The The Louisiana Tax Commissionestablishes marshlandis subjectto propertytaxation. The marshlandtax guidelinesfor assessors.From l 97< Louisiana constitution directs assessorsto uti!ize to 1995the marshlandguidelines were set without one method of determining the value on which to the rigor affordedto usevalue calculationsfor farm apply millage. This method is use value. Market land and timber. Two marshland owners filed value, potential value and other alterttatives are separatelawsuits claiming the lack of rigorresulted excluded, Thus, the constitution restricts taxation in higher taxes. In these cases landowners to incotne from surface uses. Well known off-site documentedthat average per acre surface revenues werebelow the ratestraditionally usedfor Frorrtthe Syrnpositttn ResentRrserrrrh in Cnastoi Lrrtritt'irtra: marshlandbythe Louisiana Tax Commission LTC!. iVatrrratSystem F rrn cttitrr atrd Respr>trrr ro 0 rrrrrznIrrflrrrttcc'. Rozas,L.P., J.A Hymen,C.E. Protfitt, 'X.N.Rabalais, D J. Reed, Inresponse theLouisiana Legislature in 1995 passed andR.E. Tirrner editors!. lrt99 PubbshedbyLotttsittntt Sea Act 230dtrecting LTC to preparea usevalue tsx Grant College Program. table for freshwater, brackish and saltwater 270 271 K.J. Roberts et al. marshland.LTC contractedwith theLouisiana State in thequestionnaire: ! Presh~~h marsheswith UniversityAgricultural Center, the same organiza- nosalinity, dominated bytypical freshwater plants tiondoing the use value estimates for agriculture. suchas waterhyacinth, alligator weed and bull History of UseValue bya mixtureof fresh and salt water, dominated by plantssuch as wiregrass, three-corner grass and to Usevalue for propertytax assessmentof land a limiteddegree, bullwhip; t3! ~Smarsh - tidally originatedfrom encroachingurban and suburban influencedmarsh subject to high salinity levels with propertyuses in traditionalagricultural and forestry dominantplants being $y ~a orsmoothcord grass, areas.Assessment of farmlandnear urban areas, wiregrass,black rush and saltgrass. The seven on the basisof its marketvalue resulted in taxes selectedsurface uses were alligator egg sales, abovethat which could be supported byagricultural commercialalligator harvest,aquaculture, fur uses. As a result,strong incentives were created to trapping,hunting enterprises, recreational fishing shift the landto residentialor industrialuses. Not andcattle grazing. allland influenced byurban sprawl could be quickly transferredto thesehigher valueduses. Further, Coreil 995! found44 percentof marshland many landownerswanted to continueto use their ownerswith tracts of less than 200 ha derived no landfor agriculturalproduction, revenuefrom surfaceuse. Another27 percent receivedrevenue less that $25ha '. TheMUVAC Usevalue was conceptualized, developed and comprisedof assessorsand agency personnel implementedforagriculture and forestry property recommendedthe datacollection process include owners being impacted by assessmentsbased on marshlandowners with holdingsof 400ha or more. highmarket value and to allow ownersto continue Eachparish's respective assessor's once provided agriculturaluse of land, Usevalue is normally the namesand mailing addressesof landowners determinedon the basis of theestimated net income meeting the criterion. peracre for thespecific class of land.Uniformly applieduse value tables are then developed for each Contentvalidity of thesurvey was pre-tested land class. througha focusgroup consisting of membersof the MUVAC and LouisianaCooperative Extension SurveyDesign and Methodology Servicepersonnel with experiencein survey methodologyand design. Mail survey and personal Mail questionnairesand personal interview interviewsproduced data on 0.5 million ha. techniqueswere used to collectthe data necessary to calculateuse value as delineated in Act 230. The Respondentswere asked to classifyland sameprocedure used by LTC to obtain use value holdingsinto the threemarshland classifications forfarmland and timberland was used in this survey. outlinedpreviously. Distribution ofmarshland types included25 freshwatermarsh respondents, 22 Louisiana's 1.4 million ha of coastal brackishmarsh respondents and 18 saltwater marsh marshlandsare usually separated into fourwetland respondents. Twenty-four percent of the categories,freshwater, intermediate, brackish and respondentsowned more than one marshland type. saltwater,Act 230 mandatesthat only three marshlandclassifications beidentified: freshwater, Saltwatermarsh recorded the highesttotal saltwaterand brackishmarsh. After consultation acreage approximately 253 thousand ha! followed withthe Marshland Use Value Advisory Committee by freshwatermarsh 65 thousandha!. Brackish MUVAC!, it was decidedby consensusthat marshrecorded the smallest acreage at 106thousand intermediatemarsh be placedwithin the brackish ha. Saltwatermarsh accounted for nearlyhalf of marshcategory. thereported marsh area in thesurvey 8%!. Toassist study participants identify these three Survey responsesaccounted for 37% of the marshtypes the following descriptors were included totalmarshland in Louisiana, Eliminating publicly Use Value Method for Marshland Taxation 272 held lands results in total private holdings of Range of Income approximately1 rniHionha. The study,therefore included 50 percent of the privately owned Freshwater marshland owners recorded the marshland in Louisiana. highestpercent area with a positiveincome 1%! followedby brackish 1%! andsaltwater 8%!. The Alligator huntingwas the most prevalent positive-incotnearea for the brackish and saltwater revenue-earningsurface use reported,accounting tnarshcategories was roughly equivalent with 22 for one thirdof all surveyresponses 2%! followed thousand ha of brackish marsh and 20 thousand ha by hunting enterprises 6%!. When salesof of saltwatermarsh reporting a positive return. alligator eggs are included, alligator related enterprisesaccount for nearlyone half 5%! of the Grossrevenue pcr ha are caJculatedby sutn- revenueearning surface uses reported. In total, tningthe marsh categoryrevenues and dividing by alhgatorand hunting enterprises account for nearly the total marsharea. The average gross revenue three-quarters 1%! of thc revenuesderived frotn per ha for freshwatermarshland $5.51! waseight marshland surface uses. times higher than for saltwater $0,69!. Alligator huntingis thc pritnary surfaceuse Therange of grossrevenue per acre by tnarsh identified in freshwatermarsh accounting for type is shownin Table 1. Grrxssrevenue per ha approximately one third, 31%, of the revenue ranges were cakulated by dividing individual earningsurface uses, Other important freshwater propertyincome by the respondent'sreported area marshsurface uses inc/uded hunting enterprises and for eachspecific marsh type. alligatoregg sales. In totalthese three surface uses accounted for 69% of the revenue source~ in the Table 1. Rangeof grossrevenue per hectare by freshwatermarsh with alligator enterprises alone marsh type. accountingfor 48% of the total. low high avg. income In brackishmarsh, alligator enterprises were ha' even more important in revenue generation. Alligatorhunting and egg collecting accountedfor FreshwaterMarsh $0.32 $1g.g2 $5,51 3S%and 14%,respectively. Revenue from hunting enterprises comprised another 27% of surface Brackish Marsh $0.12 $16.75 $4.17 revenue. In total these three uses accounted for 79% of the revenue sourcesfor 6rackishmarsh. Saltwater Marsh $0,35 $6.42 $0,69 Saltwatermarsh was the only category to not Net incomeper ha wascalculated by summing recordalligator hunting as theprimary revenue the positivenet income profn! and dividingby the earning source. Huntingenterprises reported the total marshlandacreage. Fresh water marshhad the highestsurface use 0%! with alligatorenterprises highestaverage net incomeat $0.91 ha '. Brackish eggsand hunting combined! accounting for 31% marshaveraged $0.35 ha ' with saltwatermarsh of the revenue. reportingthe lowestnet income at $0.15 ha'. One of the pritnaryreasons for the low per ha estimate Three conclusions can be drawn from the is thefact thatmany marshland owners report either surfaceuse data: ! the importanceof alligator noincome or lossesfrom surface uses. In thisstudy, enterprisesamong marshland owners. particularly 40% of the freshwatermarsh respondents, 64% of for those owning freshwaterand/or brackish marsh; the brackishrespondents and 67% of the saltwater ! the importanceof huntingenterprises in revenue marshrespondents reported losses. Since the total generation;and ! the apparentdifferences in use marsharea is usedin the cajculationof thc avcragc characteristicsfor saltwatermarshes, i.e alligator net incomeper ha, the averagenet income per ha is enterprises. considerablyreduced by the largeamount of area K J, Roberts et al. ~ttingno net income. This is the procedure set uses,3! increasedfederal and state od andgas hythe use value procedures of LTC, not the reveiluesharing opportunities in coastal pari»he» and researchers, 4! reviewingthe constitutional prohibition on a marketvalue approach, ~~tion of UseValue LITERATURE CITED Theaverage use value per ha was obtained by d;vidingthe average net incotne by the appropriate CoaEn.,P. D. 1995, Landowners'perceptions ~i~zationrate, This rate used as a divisoris a relatedto wetlandregulatory policy in coastal keycomponent tothe usc value. The lower the r», Louisiana. Ph.D. Dissertation, Louisiana d ehigher the use value. The rate is comprisedof StateUniversity, Baton Rouge, Louisiana . ~idson U.s. government securities. Thetefore, McBRIDE,D. J. 1992. Wetlandsregulation: a 0 M~l~onof thee%l~ion~rsnotsubJ~ landowner'sperspective. Paper presented at tomanipulation. The rate prevailing atthe time of Louisiana Wetland's Conference, Ncw thestudy as9.41 percent. Orleans,Louisiana, March 5-6, 1992. Thefreshwater marsh net incoine level of $0.91ha ' dividedby the capitalization rate,094 i.e, 9.41percent! results in a usevalue of $9,67 ha', Thebrackish and saltwater marsh use values are $3.72and $1.59 ha', respectively.Millage for determiningthetax due is applied to10 percent of theLTC use value. The term applicable to these estimatesis assessed value. The assessed value estimatesare $0.967 ha' freshmarsh, $0.327 ha' brackishmarsh and $0.159 ha' saltmarsh, Theresearch revealed a dubious future for the usevalue approach totaxing Louisiana's marshland, Thereis toomuch disparity between the LTC's undocuinentedassesaed values and the study's fmdingsoflower values for there to be rapid ntovementto lower assessed values. The LTC has sincereceiving thereport acted to reduce the assessedvalues. This must be a slowprocess so thatparish tax collections canbe cushioned from thetrend toward lower tax revenue from marshlands, Forexample, Louisiana voter»in November 1991998 passedbya wide margin a constitutional amendment ~tting parishestoretain 50percent tnoreoil and gasseverance taxescollected intheir jurisdictions. Thereare other alternatives notrelate atcd to ~acemarshland usevalues that counties andd the Lou'stanalegislature »villhave to evaluate, e, These 'elude-'1!setting a minimum assessed valu,value, 2! e blishingfinancial budgets forkey marshland COASTALFLORA AND FAUNA 4178 W. B. Stickle, Jr. sa]initiesand limit thoseprey to low salinitiesin changesin thesize of the ferna]ecapsu]e-albumin estuaries Brown and Richardson ]987}. Stnall g]and complex and the gonad-digestivegland oysterdrills can only prey on srna]l oysters Garton complex Bc]isle and Stickle 1978!.The capsule- 1986;Brown 1997!, At waveexposed sites, 10 to a]butning]and comp]ex peaks in sizein April and 39% of the oysterdriHs are on]y capableof Ju.ly,the testis-digestive gland in April and consumingoysters less than 50 g wetweight, the September,while the ovary-digestive g]and reaches mediansize oyster in theintertidal reef, because of maximum size in April. Copulation has been their smaller size Brown 1997!, observedfrom April until June. Egg capsule depositionoccurs from six hoursuntil sixty days Distribution,Taxononuc Status, and Life History aftercopulation Roller and Stick]e1988!. Egg capsulestructure of S. h. canaliculata Roller and The systematicstatus of Thaididmolluscs has Stickle1988! and S. h. floridana O' Asaro1966! is beenrecently revised. The soothemoyster drill has similar. Each egg capsuleof S. h. canaliculara been placed in the genus Srramonirabased on contains3246 X 21 SE! embryosembedded in a anatomicaldata Kool ]987, 1989!.Clench 947! viscousalbuminous f]uid, Developtncntalpatterns andothers Abbott 1974; Andrews 1971! considered havebeen followed to hatchingfor S, h. floridana S. haemasromacanalictdata Gray 1839! and S. O'Asaro 1966! andS. h. canaliculara Rol]er and haernastomafloridana to be two subspeciesof the Stickle 1988!, Teleplanicveliger larvae emerge type S. h, haemasromaLinne whichoccurs in the from theegg capsule, spend morc than 90 daysin MediterraneanSea and along the westAfrican coast. the planktonand can be dispersedover a large Two genetically-differentiatedgroups of southern geographica]range before settling and undergoing oysterdril]s were identifiedby allozymevariation metamorphosisto snails Schel terna 1978!. The life at ]8 electrophoretical]y-detectedloci fmm nine cycleof S. haemasromais depictedin Fig. I, collections in the southeastern United States and northernGulf of Mexico at a geneticlevel thatis BiaenergetieConsiderations characteristicof congenericspecies in other taxa Liu et al. 1991!, Srramonira haemasroma Researchon the bioenergeticsof the southern canalictrlara ]ike snails were collected at six oysterdri]1 has yielded several important principles locations in the northern Gulf of Mexico; S. h. thatare also operative along intensity gradients of floridana like snail~ were co]]ectedat South Padre environmentalfactors in other speciesof marine ]stand,Texas and Marine]and and Ponce Inlet, invertebratecarnivores. The primary component of Florida. Neither shell nor radu]ar characters were scopefor growthto vary as a function of environ- useful in differentiatingthe two groups.The mentalfactor gradients is energyconsumption C! collectionfrom CaminadaPass, Louisiana contained or absorption Ab! Stickle 1985!. The ratio of 96% S. h. canalicularalike, 2% S. h.floridana like, energy consumption or absorption to energy and 2% putativehybrid snails. The PonceInlet and expendituredue to respiration R! andexcretion U! Marineland, Florida collections also had wasfound to be 5.1:I for salinityand temperature representativesof both genetic groups and hybrid gradients Stickle 1985! and 3.1:1 for a hypoxia snails Liu ct al. 199]!. gradient Das and Stickle,1993!. Stickle ]985! reportedsimilar C or Ab: R + U! ratios for the Srrarnonira haemasroma,like prosobranchsin gastropodsThais lapillus acrosssalinity and genera],has a life spanthat ranges from 1-20years temperaturegradients Stickle and Bayne 1987! and But]er1985!. In thenorthern Gulf of Mexico, oyster Thaislima exposedto the watersoluble fraction drills attain scxua]maturity at 8-12 monthsafter PVSF!of Cookin]et crude oi] Stickleet al. 1984!. metamorphosisfrom the veliger larval stage Hoese BothT. Iapillusand T. limaprey on bivalvesby et al. 1972!. Growth rate appearsto be a direct boringa holein the she]]and using an everstb]e response to food consumption and ambient probosciswith a radulato ingestprey tissue. ]n temperature Butter 1985!. Seasonalchange in contrast, Srramonira h. canali culata secrete' a to»n biochemicalcontent is predominantlydue to from thehypobranchial gland which paralyzes the EcologicalRole of theSouthern Oyster Drill 279 Life cycle of Stramonita haemastoma Fig. l. Life history of Stramnnirahaemastoma canahculata. Snails deposit egg capsules on hard substrata. Teleplanicveliger larvae emerge in uthe water culumn and can spend over 90 daysin theplankton before settlement andmetamorphosis to juvenile snails, adductormuscle and allows individual or groupsof oysterdrills ceasedfeeding below 7%cS and13'C. oyster drills to ingest tissue through the gaping IsolatedS, Aaemastomawere used in the salinity- valves Roller et al, 1995! with thc proboscis- temperaturematrix study reported in Stickle 985!. radularcomplex Roller et al. 1984!. Smalloyster Likewise, more than 90% of T. lapi llus ceased drHlscannot feed efficiently on largeoysters Garton feeding durmg the three week experiment at l 986!,perhaps because'they cannot produce a salinitiesbelow 25%a S and8.3'C. Groupfeeding sufficient amount of toxin. did not occur in groupsof T, lapillsts,probably becausethe snails fed through the bore hole. Like other marine invertebrate carnivores, a higherpercentage of S. h, cattalicstlata cease feeding The first study to document a positive altogether,rather than exhibiting a reducedfeeding relationstupbetween scope for growth ananimal's rate at the extremes of the zone of capacity energybudget! and the number of heterozygous adaptationalong environmentalfactor gradients loci heterozygosity!infeeding marine invertebrates Stickle1985!. This phenomenonwas also found wasconducted on S. h, canaliculata Garton 1984!. to existin the seastar Leptasterias hexactis and the Sixof 25 enzymeloci assayedwere fou.nd to hc gastropodThais larrtellosa along a salinity gradient polymorphicanda significantpositive relationship andin Thaislima along a WSFof CookInletcrude existedbetween total heterozygosityand scopefor oil gradient Stickle 1985!. Multiple regression growthof snailsadapted to all threeexperimental equationswere generated for feedingdata in an salinities; 7.5, 20, and 35%r S at 21'C. The experimentalsalinity-temperature matrix for both increasedscope for growth of heterozygoteswas ~tramonitah. canaliculata and for Thaislapillus correlatedwith significantlygreater feeding rates Stickle1985!. More than55% of the southern onjuvenile Crassostrea virgin'ica. The number of 2tto W. B. Stickle, Jr. heterozygouslociper snail explained 16% of the in salinityat Barataria Pass only varied from 17.5%< varianceof scopefor growthat 7.5%~ S, 14%at S in May-Juneto 26.5%rS in November Barrett 20%~S, and 15% at 35%o S. In contrast,only two of 1971!. Average monthly water temperatureat 12enzyme loci assayed in Thais lamellosa, which BaratariaPass varied between 12,8 "C in Decembcr- producescrawl away juveniles, were found to be Januaryand 30.4"C in August Barrett 1971!. polymorphic Garton and Stickle 1985!. Evidence Monthlymean salinity and water temperature was of heterozygotesuperiority in scope for growth of obtainedfrom only threeto five discretedeter- T. lamellosawas present; however, there was tninationsper month. insufficientgenetic variability for correlationof scopefor growth wi h heterozygosity, Theobjective of thisreview is to summarize our knowledgeof theeffects of variationin dis- Thepriinary energy source, from a bio- solvedoxygen, salinity and watertemperature on chemicalperspective, of a numberof speciesof the southernoyster drill S, haemasroma. carnivorous marine invertebratesexposed to environmentalfactor gradients is protein Stickle Effectsof DissolvedOxygen on Srramonita 1985!.0: N ratioswere determined in orderto assess haernastoma whetherprotein or carbohydrate/lipidwas thc primarysubstrate catabolized. 0:N ratios in the 2-8 Thesouthern oyster drill istolerant of hypoxia rangeindicate that proteinis the substrate with28-day LC valuesranging from 8-29 Torr 0, catabolizedbut 0;N ratios as high as 200-300 - 19%oxygen saturation! Kapper and Stickle indicatethat carbohydrate and/or lipid is the primary 1987;Stickle et al. 1989!.In contrast,the 28-day catabolicsubstrate. Within the zone of capacity LC~of juvenile Callinecres similis is 43 Torr0, adaptation,0:N ratiosranged from 3.1-28.5 in the 8% saturation!and that of C. sapidrrsis 106Ton five speciesof marineinvertebrate carnivores 0, 68%saturation! Das and Stickle 1993!. studiedindicating that proteinwas the primary Oxyregulatoryability of S. h. carialicu aravaried substratecatabolized Stickle 1985!, inverselywith ternpcrature and did not exhibh acclimationafter 28-dayexposure to 53 Torr 0, Variation in Dissolved Oxygen, Salinity and 4% saturation'}.Activity ratiosof the four pyruvate Tetnperature oxidoreductascenzymes identified in Srramortitah. cartalicalara,alanopine dehydrogenase, lactate Variabilityof dissolvedoxygen, salinity and dehydrogenase,strombine dehydrogenase, and watertemperature has been well documented in octopinedehydrogenase were not induced in foot coastalLouisiana. Seasonal development of hypoxic tissueafter 28-day exposure to 15-100 Torr 0, 100 watermasses offshore has been well characterized Torr= 64%oxygen saturation Kapper and Stickle andis relatedto freshwater and nutrient input from 1987!.Adenylatc energy charge AEC = the molar the MississippiRiver Rabalaiset al, 1986a,b!. concentrationof ATP 6 I/2 the molar concentration Averagediurnal variation in dissolvedoxygen at of ADP divided by the sum of the molar PortFourchon and Caminada Pass, Louisiana over concentrationof ATP+ ADP+ AMP! and arginine a 14-drecording period in June1992 ranged from phosphateconcentrations, theprimary muscle high 25-175 Torr or 16-122% oxygensaturation un- energysource of phosphatebond energy, were published!.Likewise, tidal variation insalinity has reducedat 10- 32% saturationcompared to snails beendocumented by a salinometerprobe placed tnaintainedat 64 - 100'Fcsaturation Kapper and 0.33 m off the bottom for 791 daysat a location Stickle1987!. Metabolicheat producuon, a measure 14.5 km north of Barataria Pass Hewatt 1951!. of total metabolic rate, declined linearly with Dailyamplitude of salinityvariation varied as severityof hypoxiaas did energy consumed and follows:0-5%o S perday = 41%;5-10%~ S perday absorbedfrom predation onthe bivalve Ischadium = 35%; 10-15%rS perday = 15%;15-20%r S per recarvrrm Das and Stickle 1993!. In contrast, day= 7 k; 20-25%rS perday =2%; and 25-30%o S energyconsumption andabsorption rate of juvenile perday = 1%of thedays. Average monthly change Calliriecres sapidus did not decline at hypoxic levels EcologicalRole af the Southern Oyster Dnll 281 down to 47% oxygensaturatiort, but was saturatton Stickle et al 1989! Ad 1 significantlylower at 32%saturation Das and chargedeclined from 0,79 to 0.58atter one day Stickle1993!. Consequently, Scope for Growth of exposure to anoxia, and argininc p h,osp h ate thesouthern oyster drill varied directly with oxygen concentrationdeclined by 95% Kapperand Stickle partialprcssure down to 16%oxygen saturation, 1987!.Adenylate energy charge cycled at the whilesurviving juvenile blue crabs did not exhibtt expenseofarginine phosphate with cyclic exposure a significantdecline in Scope for Growth atreduced to anOXia frOm nOrmoxia oxygentension. S.h. carralicrriara is very tolerant ofexposure toconstant hypoxia 8 dayLC of 5- Effectsof Salinityr¹t Strvu¹arritak carmlierrlata 19%oxygen saturation between 10 and 30%0 S at 10-30xC!. Depression of heat production to9% of The effects of salinity on the tolerance and the normoxicrate occurs within hours,S. h. capacityadaptations of snails and the intracapsular carraticalaratolerates diurnal variation in percent developmentof Stramorrirah, carralicrglarahas oxygensaturation from 100% to 25% over 28 days receivedconsiderable attention, The low saliruty Dasand Stickle 1993!. Ingestion of foodrequires 28-dayLC of Srnunonirah. carrahcrrlaracollected moretime in the southernoyster driH thanin the at four sites was 3.5-7.1%o S while that of one blue crab. populationof Srranumira h. floridarrawas 7.3~x 70 BO o 40 O 10 3 5 7 g it q3 t5 17 lg 21 23 Day Fig.2.The upper andlower 28-day LC ofSrrarrroru'ra haemasroma corralicgglaro andS,h. Jloridapro asa function o salinity.S.h. floridana wascollected atMarineland, Floridaand S. h. canahcggiar Neitherthe rate of predationnor theScope for Southern oyster drills preying on oysters as Growth of S. h. canaliculata preying on small individualsenter cold torpor below 12.5'Cat 20%a Crassostrea virginica varied significantly with S Garton and Stickle 1980!, cease feeding on salinity between 10 and 35%o S at 10, 20, 25 or juvenile oysters Garton and Stickle 1980! or exhibit 3PC but there was a direct relationship between minimal feeding on juvenile oysters Stickle 1985! Scope for Growth or feeding rate and salinity at and enter the sediment over the winter months 15'C. Feedingrate and Scope for Growth of the unpublished!.Snails can actively uptake &ee amino southernoyster dril1 was significantly lower at 7.5%a acidsfrom pore water under anoxia at relatively high S at all teinperatures than occurred between 20 and primary amine concentrations 16 364 ItM! 35%aS Stickle 1985!. Benthic S, h, canalieulata during the winter months. are extreinely euryhaline with respect to exposure EcologicalRale of theSouthern Oyster Qrill Oysterdrills exhibit evidence ofheat stress oystersiftcreased directly with temperature from 1 q whenthey are maintained and individually fed to 25 C andwas lower al 15 and 3PC. Attractionlo juvenileoysters -5 cmlength! at25 and 3PC preywas positively correlated wnh salinity p t throughoutthesalinity range except at20%o S and 25%pS. Crawlingvelocity was minimal at 15"Cural 30~! Stickle1985!. A muchhigher percentage of was affected by ambient salinity at 20, 25, and 3 rg variationin Scope for Growth was accounted for Meancrawling velocities ranged from 0.07 cm min byvariation inseawater temperature 5.4%!than ' at 15'C and 10%oS to 18.0 cm min ' at 25< and insalinity 2.7%! inthe experimental matrix of 20%p S, 10 3 y anti7 5-35%p S Stickle1985!. Groupfeeding on large oysters is maximum Attractionof thesouthern oyster drill to oysters at3 yCbut the feeding rate of individualsnails on ina Y-maZe is setsSitive tOtemperature andSalinity largeOyaterS aSa functiOnOfWater tetnperature ts Fig.3!, The percentage ofoyster drills attracted to unknown.There is.no differencein thefeeding rate of individualsand groups of oysterdrills on large oystersat 2' and20%v S Gartonand Stickle 1980!.Both prey size and the nutnber of snails 100 preyingon large oysters influence the temperature at whichthe highestfeeding rate occurs.. Group foragingoccurs frequently inthe estuary but snai Is ra feedingin groupson small and large oyster prey exhibitedreduced per capita feeding rates Brown Vl andAlexander 1994!. However, the fraction ol oysterflesh consumed was 21% higher in snails z 30 feedingingroups resulting in similar per capita z 20 oystertissue consumption andsnail growth rate» 10 forsolitary and group predators. ~ 0 la Is za SALINITYrs } Eggcapsule deposition occursduring the late spri~g April-May! andceases aswater ternpcraturc reaches30'C unpublished!,Capsules were depositedonlyat 20 and 28+ in southern oyster drillsthat were acclimated to20, 22, 28, and 3ly'C andsalinities from l~ S RollerandStickle e 0 1989!,Optimal intracapsular survival and E r developmenttohatching occurred at20 and 25%< S 0 at22 and 28'C, Survival tohatching washigher and developmentfasterat28< than at22% for all Salinities Q1pvalues forhatching = 1.60-2.64!. Weightspecific oxygen Consumption andam moniumexcretion rates and the 0:N ratios were hiher inpost-hatching veligersat28'C than at22"C forg all salinities tested Roller and Stickle, 198 ! Kl ls zo ss Thebenthi~ stage ofSrrarnorala !Lcanalicnlara 1s SaLal1rV ~ veryeuryOxic withreapecl, toConStant andd1odiurnal moattractionOf SrramOr1irahaemasrama exposuretohypoxic waterthroughout itsseaso sona1 3< cm Crassasrreavirginica as a temperaturerange.Snailsof both subspec iesarc a!s" mperatureand salinity ina Y-maze. A!The euryhaline LC, range = 3,5-54-8% compositionofthe southern oyster drill, Thais wat r colu~ rnth MlssrsslpplRiver D,tta haemastorna.Biologi'cal Bulletin 159: Bight, June 19g5 to Decemh r 1985 Rep < No. 2, LouisianaI.lniverstriev ' iiq 148-161. HoEsn,H.D., W, R. Nr-r soN, avn H. BEcrcErtr, 1972, sortrurn, Chauvin, Seasonaland spatial setting of fouling Reacts, N. N., R, E, Triat r~, W. J. Wrsr:.M~s,Ja, organismsin Mobile Bay and Mississippi AND D. F, Boascrt, 1986h. Hydrographic, Sound,Alabama. Alahama Marine Resource biological,and nutrient characteristis. t 1'the water column on the Louisiana Shell; July and Bulletin 8:9-17. Kitprid, M. A. AvDW. B. SrrcKLE, 1987. Metabolic September1985. Data Repon No. 3, Louisiana responsesofthe estuarine gastropod Thais Universities Consortium. Chauvin. haernastornato hypoxia,Physiological RoLLatR. , A., D. W, G~arou,ant> W. B. Srr ST,Ast 288 6, E. Fleury et al. colonialwate*irds arc at the topof theaquatic food Furthermore,BBS data suggested that these chain,and even share similar tastesin prey specie~. populationchanges arepart of abroader pattern of This historicconflict has becomemore important changesinpopulations of Gulf Coast wading birds in the past twenty years as aquaculture has inresponse tohuman-induced changes in thenatural developedinto a majorglobal industry Huner 1994, landscape Fleury 1996, Frederick ct al. 1996!, Priceand lslickum 1995!.Many speciesof birdsprey on aquaculturecrops. The USDA's Southern Louisianahas «n abundance ol healthywetland RegionalAquaculture Center has identified several habitats Williatns and Chabrck 1986!. and the "proble in species" on aquaculture farms in southern wetlandsites surveyed by Flcury 996! hada states Stickley 1990!: Double-crestedCormorant diverseprey base and high !cvels nf wadingbird Phalacracoraxauritus!, Anhinga Anhinga foragingsuccess. Crayfish ponds, howcvcr, provide anhinga!,American White Pelican Pefecanus a foragingenvironment thatis equivalent toor hetter cryrhrorhync Jros!, Hooded Merganser Lop Jtodvtes thannatural foraging habitats Fleury 1996!. cucuffatus!,Great Blue Heron Ardea herrrdias!, Becauseindividual farmers tend to rnanagctheir GreatEgret Castnerodiiaxalbu,r!, Snowy Egret cmpsin the same way from year to year. farm pond Egrettathuia!, Tricolored Heron Egrettcr tricotar!. hydrologyisalso more predictable in space and Green-hackedHeron Burriridesstriatux!, Black- trine. crownedNight Heron Xycticoraxnvctirorax!, Ye! low-crowned Night-Heron Nycti rorax Farmpond management follows the natural vinlaceus!,White Ibis Eudocimusa!bus!. Belted annualhydrological pattern inswamp~, except that Kingfisher Cery Je alcynn!, Osprey Pandian farmponds are out of phase with the natural cycle. haliaetus!,and various species of gullsand terns Thewild crayfish harvest depends on the drainage Laridae!.Wading birds are problem species atboth ofspring rains into southern wetland habitats. High crayfishand catfish fartns, sprtngwater levels of the right temperature bring crayfishout of their burrows.Crayfish farms, WadingBirds and Crayfhsh Farms however,are ref!ooded in Fall, which brings farm crayfish out of their burrows several months before Coionialwading birds regularly forage in thewild harvest begins. Here we describe a ricefield- Louisiana'scrayfish farm ponds.These new crayfishpond management planthat is typical of foraginghabitats have significantly contributed to about60% of crayfishfarms Huner 1990, 1994, therapid increase of wading bird populations in 1995!. southernLouisiana Huner 1994, 1995. Reury 1994, Reuryand Sherry 1995, F]eury 1996!. Crayfish are Wadingbirds are first attracted topond~ m the animportant fooditem for several species ofwading Fall,when ref!ooding drives numerous terrestrial birds.Winter populations ofthese species correlate arthropodsonto emergent vegetation. Flocks significantlywiththe annual harvest ofswamp dispersewhen this resource hasbeen exploited. and crayfish,and these same species populations reassemblein4-8 weeks when young crayfish reach correlatemore significantly withannual changes in about5 cmin length,and the bioinass of insects, landarea devoted tocrayfish aquaculture Fleuiy tadpolesand other aquatic prey increases Huner andSherry 1995!, These correlations arebased on pers.obs.!, Harvesting begins asearly as November, annualChristmas Bird Count data CBC!. which andcontinues into May. Annual pond production estimatewinter bird populations, butBreeding Bird averages600-700 lbs/acre, with good ponds Survey BBS! data, gathered in Suinmer. have producingupto 1,500 lbsjacre Huner un pub. data!. corroboratedthesetrends. Methodological problems Rice-crayfishpondsare usuagy drained inApn1 and withsuch data are beyond the scope ofthis paper, May,and permanent crayfish ponds are drained m butHenry and Sherry 995! review some ofthe Mayand June. Ponds may then be seeded forrice majorconcerns. Fleury 996! suggests thatCBC or othercrops. By the end of thecrayfish season dataare especially appropriate forcolonial species mostunharvested mature crayfish have already thatregularly and predictably aggregate. burrowedto await the Fall reflooding. AgriculturalWetlands and WadingBirds in Louisiana 288 Drawdown i.e., draining ponds! marks the end The measurementof damageto aquaculturefarms of the crayfishharvest, and the periodof major from avianpredation was recently highlighted as influx of wadingbirds into farm ponds Martin 1979, an importantgoal of wading bird research Price Fleury 1994!, Pond drawdowns strand high and Nickum 1995!. This is especially true in densities of prey in shallow pools. Drawdowns Louisiana,where the commercialcrayfish crop is usually fall within the annual breedingseason of currently estimatedat $35 million per year. The wading birds, and supply a rich diet for both adult potentialproblem may havebecome more serious andjuvenile birds Fleuryand Sherry 1995, Fleury in the last severalyears, as winterpopulations of 1996!. The coincidence of maximum prey the mostiinportant predatory species on crayfish availability during drawdownand wadingbird farins Fleury 1996,Huner 1994!, have continued nestingcycles may be a primaryfactor linking the to increase Fig. 1!. expansionof crayfishfarm ponds with wadingbird reproductivesuccess Fleury 1996!. Non-lethal control methods such as audio and visual frightening techniques,overstocking, Control of Waterblrd Predation distractionponds, relocating birds, and covering ponds with nets have met with limited success Crayfishfarmers have increasinglyvoiced Draulans1987, Littauer 1990a, 1990b, Boyd 1991, concern about the rapidly growing flocks of Cezilly 1992!. Furthermore, these non-lethal predatorybirds in their farm ponds Fleury 1994!. techniquesare expensive, with annualcosts of more R ~0.57 ' a~0% a I Year : '.Ri G.46 4O!! , ~' o$~ ~w ~~ +~ ~ * ~~ ~~ -!O00I ! NO !!!!! '!f% IW0 !'!70 le '!t% I!!I Year Year Fig.1. Linear regression models of winterwading bird populations, 1950-1997, for selectedspecies recorded in LouisianaChristmas Bird Counts, number observed per count. Note: Plegadis sp, includes two species of darkibis, theGlossy Ibis [Plegadisfalcinellus ] andthe White-faced Ibis [Plegadisehihi]!. 290 B.E, Flaury et at than$13,000 per five-month season Littauer 1990b, Glahnand Stickley 1995!, The simultaneous Draulans 1987!, Audio frightening methods include increaseof catfishpond acreage and cormorant pyrotechnicssuch as screamer shells and "bird populationssuggests a cause-eff ectrelationship that bangers"fired from a,22 caliberblank pistol, parallelsthe growthof Louisiana'swading bird waterprooffirecrackers, butane cannons, electronic populations Weseloh et al. 1995,Jackson and noisegenerators, playback ofrecorded distress calls, Jackson1995!. Great Egrets and Great Blue Herons andthe firing of live ammunition, theuse of which alsoforage along the edges of catfishponds, and is obviously limitedby the farmer'siminediate aregenerally viewed as serious agricultural pests. environment.Visual frightening techniques include Severalhundred wading birds have been killed each theusc of scarecrows,regular vehicle patrols, hawk yearon catfish farms, under U,S. Fish and Wildlife silhouette kites, helium balloons, and radio- Servicepermits Stickley 199 l,Price and Nickum controlledminiature aircraft Littauer1990b!. Such 1995,Littauer 1990a!. Permits were issued to catfish frighteningtechniques are only effective for a short farmersin Louisianain 1990/91, for example,for time before birds acclimate to the disturbance. 1,023kills howeveronly 751 kills were reported; USFWS 1990191unpubl. data!, Netting pondsmay be effective,although manybirds quickly learn to gothrough or under the EconomicImpact on Crayflsd Farnts largemesh nets. But covering farm ponds with large- rneshnets requires a largeinitial in vestment and high Theimpact of wadingbird predation falls most maintenancecosts. The only scientific study of the heavilyduring the drawdown period Martin 1979, effectivenessof pondexclosure failed to exclude Fleury1996!. None of the crayfish or fish available birdsfrom the testponds. Martin's 979! attempts to wadingbirds during drawdown, however, have toexclude birds fmm test ponds were not successful, anysignificant commercial value. Most of the and further research is needed to establish the crayfishthat carry the broodstock for nextyear' s effectivenessof such techniques, cropmay have already burrowed before drawdown begins Huner 1994!. Bird predation could hurt Thepressure by somefarmers for lethal control farmersduring drawdown, however, if mostof the continuesio mountwith increasing bird populations, remainingcrayfish at drawdown were females that highlightingthe need for furtherresearch on the hadnot yet bred and burrowed, but might still do ecologicaland econoinicimpacts of thesebirds so. If there were significantlyinore males than Huner 1993!. Althoughdepredation permits for femalesremaining at drawdown,the economic wadingbirds have been issued to Louisiana's catfish impactof birdpredation during drawdown would farmers,no USFWS permitsfor wadingbirds have be negligible. been issuedfor crayfish farmers.U.S. Fish and Wildlife Servicepermits are only issuedwith the To test the hypothesisthat mostcrayfish concurrenceof stateand local wildlife officials, and remainingat drawdownwere male, we sexed onlyafter non-lethal control techniques have proven crayfishsampled atwild and farm sites with a half- ineffecti ve. squaremeter drop trap, and comparedobserved frequencieswith those expected from a I:1sex ratio. Lethal controls are already used against Farmpond samples taken before drawdown had wading birds and cormorantson catfishfarms, significantlymore females than males P<0.003, wherethe annualdamage from water bird predation n=38traps!. Crayfish in trap samplesfrom farm may exceed$2 million Stickleyet al. 1992,Glahn pondsat drawdown n=65 traps!and wild sites and Stickley 1995!. Between1965 and 1991,the n=78traps!, however, showed a balancedscx ratio, Mississippi Delta catfish industrygrew to over althoughwild samples contained a greaterrelative 50,NN ha of farm ponds. Along with this rapid frequency of female crayfish. There was a increase in catfish farm acreagecarne a rapid significantshift in farm pondsex ratios between increase in the numbers of cormorants, which floodedand drawdown stages, with 71%fernale flockedinto catfish pondsby the tensof thousands crayfishprior to drawdown,and 54% femalesat AgnculturalWetlands and Wading Birds in Louis,ana 29t drawdown,Thc missing females probably burrowed reachmarketable size Avauii ct ai. 1974Huncr during the two to threeweeks that typically andBarr 1991!, An LSU farmpond with this separatedpre-drawdown anddrawdown samples, probleinyielded crayfish 2 cmor less at drawdown These.crayfish are inaccessible toforaging birds. Fleuryl996!. Night-Herons andLittle Egrets Furtherstudies arc needed on crayfish sex ratios in feedingon israeli fish farm» improved commercial farmponds, the tinung of femaleburrowing, and stocksbyfeeding onpredatory species, culling weak theoverlap of thecrayfish life cyclewith the annual orinjured fish, and reducing dense populations of cycleof thewading birds that use farm-ponds, These fish fry Ashkenaziand Yom-Tov1996!. Thc resultssuggest that depredationefforts should be problemwith relying on birri predation asa strategy focused on the period just prior to harvest to forthinning crops, however. islike regulating acoal ameliorateany economicimpact, furnace,Once it gainsmomentum, it is difficult io controland nearly impossible io stop. The effectsof wadingbirds on the crayfish populationduririg floodedstages, however, has not WadingBird Predationand CrayfishFarm beenas thoroughlyexamined. Martin 979! found Management that flocks fed primarily on fish and otherprey during floodedstages, and switchedto eating Theannual pattern of wadingbird foraging. priinarily crayfishduring drawdown. Only 9% of coupledwith the crayfishlife cycle, suggeststhat crayfish consumed by wading birds were of there are two periodswhen bird controlefforts marketable size .5-12,5 cm iong!. Overall, less shouldbe focused:when crayfish start to reach than 2% of the total commercial harvest was taken harvestablesize after the Fall reflooding,and again by wading birds Martin and Hamilton 1985!. in the weeksjust beforedrawdown. If farmers Althoughsome wading birds take large nuinbers of concentratedtheir effort during these tw FAsoLA. M., ANn X, Rt.tz. 1996. The value of rice ManagementConference. Conservation Tech- fields as substitutes for natural wetlands for no!ogylnforrnation Service. West Lafayene. waterbird»in theMeditcrrancan region, Colo- La. nial Waterbirds 19 SpecialPubl, 1!:122-128. HuNEst,J. V., ANtrJ. L. BARR.1991 Redswamp FASOLA,M., L. CANovA,ANU N. ShtNo. 1996, Rice crayfish,biology andexploitatinn. 3d cdiuon. fields supporta largeportion of heronsbreed- LouisianaSea Grant College Pnigrarn. enter ing in thc Mediterraneanregion. Colonial for Wetlands Rcscarch. Louisiana State Waterbirds19 SpecialPubl. 1!:129-134. University.Baton Rouge. FLEt;Rv,B. 1994, Crisis in the crawfishponds, JAcksoN, J. A., AND B. J. s. JhcxsoN, 1995. Thc I.iving Bird ]3 !:28-34, Double-crested cormorant in the south-central Ft Et.ttv,B. E. 1996. Populationtrends of colonial UnitedStates: habitat and population changes wading birds in the southern United States: ol a feathered pariah. pp. I lg-130. In Thc foodlimitation andthe responseof Louisiana Double-crestedCormorant: Biology, Conscr. populationsto crayfish aquaculture,Disser- vation,and Managernenl..Crrk>nial Warerbinli tation, Tulane Univ., New Orleans. 18 SpecialPubl. 1! FLEURY,B. F.. ANDT. W. SHERRY.1995, LOng-tenn LtrTAttEtt.G. A. 1990a. Avian predators: populationtrends of colonialwading birds in Frightening techniques for reducing bird the southernUnited States:The impact of damage at aquaculture facilities. Southern crayfishaquaculture on Louisiana populations. Regional Aquaculture Center, S RAC Auk 112:613-632, Publication No, 401, FRFrnERICK,P. C K. BlLDSTEtN,B, FLEURY,ANU J, LrrrhuER,G, A. 1990b. Controlof bird predation OGDEN.1996. Conservation of large,nomadic at aquaculturefacilities: Strategiesand cost populationsof WhiteIbis Eudocimusalbus! estimates.Southern Regional Aquaculture in the United States. Conservatiorr Biology Center, SRAC PublicationNo, 402. 10: 203-216. MARttN,R. P. 1979, Ecologyof foragingwading GLAHr', J. F.,AND A, R. SrtcXt.EVJR, 1995,Wintering birds'atcrayfish ponds and the impactof bird Double-crestedcormorants in theDelta region predationon commercialcrayfish harvest of Mississippi:population levels and their M.S. thesis,Louisiana State University, Baton impacton thc catfish industry.Colonial Rouge. Waterbirds18 Spec.Pubn. I!:] 37-142. MARttN,R, P.,AND R. B. HrcsttLtriN.1985, Wading HUNER,J. V. 1990. Biology, fisheries, and bird predationin crayfishponds. Lriuisianv cultivation of freshwatercrayfishes in theU.S. Agrr'culture28 !;3-5, AquaticScience 2:229-254. Nhssha,J. R., P.J. ZwANK,D. c. HAYDN,AND J. v. HttNER,J. V, ed,! 1993,Management of fish-eating HUNFR.1991, Multiple.-useimpoundments birdson fish farms;a symposium.National forattracting waterfowl and producing cray- AquacultureAssoc. and National Audubon fish.U. S. Fish & Wildlife Service,National Society,5-6 January1993, New Orleans Wetlands ResearchCenter, Slidell, Louisiana. National AudubonSociety, Shepardstown, ParCE,I., ANO J. G. Ntcxtrvt, 1995, AquaCuhure and WestVirginia. birds;the context for controversy.C TtNn~,R- W., JR 1984. Wetlandsof the United States: Current status and recent trends. National Wetlands inventory,Washington, DC. +rrousnK,P. M MooNsv, H. A,, Lt.'tKHENco,J.,8r, MELi~, J. M. 1997.Human domination of Earth'secosystems. Science 277: 494-499. WEsEtoH,D, V., P. J. Ewms,J. StttuoER,P, 1VIoaAU, C. A. BlsHop,S, PosrLp~ K Y,aMo J. P.Lt>wta. 1995. Doub! e-crestedcormorants of the Great Lakes:changes in populationsize, breeding distribtjtionand reproductive output between 1913artd 1991,p, 48-59.In The Double- crestedCortnorant: Biology, Conservation, andManagement. Colonial Warerbirds 18 Special Publ. 1!, WtLuiAMs,S O. III, m'o R. H. CHAsRrav.1986. Quantityand quality of waterfowlhabitat in Louisiana.School of Forestry,Wildlife, and Fisheries,Research Report No. 8,.Louisiana State Univ., Baton Rouge. 296 J,M. Visser et a!. INTRODUCTION METHODS HurricaneAndrew made landfall in coastal Naturttl Colonization Louisianaon August 24, 1992. Thehurricane had sustainedwinds of 54 m sec ' and created a storm We selectedtwo scour~ on thc central surgeof 1-2m. Thestorm was especially damaging Louisianacoast identified during an aerialsurvey to oligohalinemarshes Jackson et al, 1995!. of hurricaneimpacts gasser ctal. 1994!.One site Guntcnspergenet al. 995! described.six types of was locatedon a canaleast of LocustBayou and disturbancethat occurredduring the storm; ! theother south of CreoleBayou Figure 1!. Both compressionofthe marsh surface, ! deposition of scourswere surrounded by aligohalinewiregrass thick sediment, ! depositionof wrack, ! marsh Visserct al, 1996!, a vegetation type depositionof thin sediment, ! scour, and ! salt dominatedbySparri rta paterts Ait.! Muhl. At each burn.In this paperwe describe the recovery of areas of thesesites 3 replicateexclosures x 2 tn!were of scourby HurricaneAndrew. randomlyestablished atthe edge of thescour area. Eachexclosure ungrazed treatrncnt! was paired In thesescour areas, unconsolidated or weakly withan area adjacent to theexdosure which was rootedmarsh was washed away by the storm. With unprotectedfrom grazing grazedtreatment!. thevegetation and root tnat removed, bane substrate Speciescotnposition andpercent cover Braun- severalcentimeters lower than theoriginal marsh Blanquetscale; see Kent and Coker 1992! were elevationremained and becameshallow ponds. recordedfor all plots on February 2, 1995 at Creole Surveysshortly after the hurricane showed that there Bayou,and on February 22, 1995 at Locust Bayou was little or no recovery in the scour areas andafter one growing season October 9, 1995!. Guntenspergenetal. 1995!. Colonization of these However,no emergent plants had colonized bythis shallowponds was very slow, probably because the time, Speciescomposition and cover in this seedbank was retnoved with the vegetationand root experimentwere also recorded 6 times during 1996 mat,Guntenspergen etal. 995! predictedlittle or and 1997at the sametimes that the transplant norecovery inthe scour areas, because elevations experimentwasvisited July 1996, 8 August1996, aretoo lowfor emergent plant establishment. 1 October1996, 27 March1997, 20 June1997, and 15 September1997!, Thereare severalherbivores in the coastal marshesof Louisiana,including waterfowl, deer, rabbits,muskrats and nutria. Grazinghas been shownto reverseor haltsuccession Bakker, 1985; Girouxand Bedard 1987; Shaffer et al. 1992!and cooMtherefore be an additionalfactor in the lack ofrecovery inthe scour areas, Previous studies have beenshown that grazing can have a greatereffect inthe presence ofan additional stress such as fire or salinity Smithand Kadlec 1985, Taylor et al. 1994,Grace and Ford 1996!. We hypothesized that the lackof recoveryin scoursis causedby the combinedstresses ofgrazing and increased flooding an seedlingestablishment. Asa managementoption, we evaluatedif plantscould be established inthe scour through plantingsandthe effect ofgrazing onthe success of plantings. Figure1. Locationof thestudy sites in southwestern Terrebonne Parish LA G z'n9 E"ttctson RtKovery atty Plantings account for possible difference in visihilitv of aninialsamoiig sites, we alsoperformed ground In 1996,we implementedan additional surveys.Ground surveys consisted ol four random} experimentwhich consisted of 2 levelsof grazing selectedsites surrounding each scour and consi. tcd grazed,ungrazcd! and five plantings Distich is of sixplots I x 1 m! persite lbr a totalof 24plots. spicara L.! Greene,Paspafttm vagirtaturrt Sw., these plots, scat was counted and presence/ Sparrirtaalrerrtiflora Loisel., Spartina parerts, and absenceof grazingeither above ground clipped notplanted! with two replicates at the sametwo stems!or below ground digs! wasreconled, scoursites. Species were chosen to represent a large rangeof flooding and salinity tolerance. InJune of Statistical Methods 1996we constructed10 additional exclosures x 2 m!in eacharea. These exclosures and adjacent Paired 1-tests were, used to test for difference» controlareas were planted with nursery grown plants in survival of transp!ants due to grazing. Plots were on July 1and 2, 1996.Ten sods diarncter 10 crn! pairedwithin site such that the grazed and ungrazed of therandomly assigned species were planted in treatment in each pair had similar elevaiions eachreplicate, Survival of the transplantedsods floodingfrequencies!. Onlythe end-of-growing wasdetermined on August 8 andOctober 1, 1996, seasonsurvival percentages October 1, 1996!were ln additionplant species which naturally colonized used in the analysisof surviva1.Due to the small in eitherthe grazed or ungrazedtreatments were samplesize replicatesper treatment pcr site! identified.Vegetation cover of transplantsand normalityof thesurvival data was not detcrnuned. colonizerswas estimated to the nearestfive percent However,the t-test is robust to departuresfrom onthe same dates as the survival estimates. During normality Gilbert 19g9!. thesecond year of the study, indi v iduaI transplanted sodscould not be separatedand coveronly was Analysisof variancewas used to deiermtne detertninedon March 27, June20, andSeptember the sigruficanceof differencesin transplantcover. The designwas a two-wayfactorial treatment 15, 1997, grazingwith 2 level~and treatment planted species Environmental Measurements with 4 levels!blocked by site lcvcls!and split on date levels!. Thedistribution of coverwas noi To account for differences in flooding stres.s significantJydifferent from nortnality Shapiro-Wilk andgrazing pressure at the two scoursites we statistic= 0,73,P WW,0001!.Separate analyses measuredthese two variablesat bothsites. of variancewere performed on the ungrazed treatmentsonly to determine differences among sites Floodingstress was estimated by determining andtransplanted species inend-of-season coverin thepercentage of time each planting was flooded. 1996 and 1997 Therefore,a water-levelgauge was operated inside eachscour from July 19, 1996to September15, RESULTS 1997 andthe elevationof the scourrelative to the gaugewas measured on October1, 1996. andFlooding lJjfferences AmongStudy Sites Grazingpressure was determined by esti- matingherbivore density and grazing frequency in LocustBayou has a muchhigher number of theproximity of theexperitnental treatments. Four grazerspresent thanCreole Bayou Table 1!,This transectsof 1 km surroundingthe studyarea were ismostly due to the high number ofmuskrat ob- flown by helicopteron May 13, 1997 0 meter servedin LocustBayou. Deer and rabbits are abovethe marshat an approximatespeed of 50 relativelyrare,and were only observed nearCreole km~h'!. AII herbivoreswithin 25 meters of the Bayou.The relative densitv ofgrazers isalso transect were countedon both sidesof the helicopter. reflectedinthe grazing pressure atboth sites 1 Table To avoid counting the same animals twice, the 2!.Locust Bayou hasa highergrazing pressure both transects were not connected with each other. To abovean d belowpound than Creole Bayou. 298 J.M. Visser et al. Tablel. Averageherbivore andscat densities atCreole Bayou and Locust Bayou tstutiq sttec. Densityof anima!»' Density of scat number~ ktn'l tturnher ~ m ! Creole Bayou IatcustBayou Species Creo!eBayou LocustBayou .6+ 7.7 0 0 Nutria 3.8 % 4.9 'tg8 % 23 5 0 !.6 + 2.5 Corntnon Muskrat 0 White-tailed Deer 0,6 X 1 7 0 0 SwatnpRabbit 1,9 + 3.5 0.0 X0.2 '!vtuskratttcnsittcs «re in numhcr of houses.Densitics are provided Xone standard error. Table2. Estimateof grazingpressure at the in thcspring of 1996,and at LocustBayou in the summerof !996 Figure4!. However.the exclosurc two sites. with the lowest elevationwas never colonizedat GrazingPressure-' both sites. Colonizationby Scirpu. Grazed biomass Creole Locust Pers. previously S. olneyiGray! and Amtnvrtiu Bayou Bayou coccirteaRottb. was observed in thegrazed scour atCreole Bayou in 1996 Table 3!, AtCreole Bayou. Aboveground ,5 58,3 thcmost abundant co!onizers of un graze! treatments wereAmarvrtthas austrafis C3ray! Sauer, Scirptrs Belowground 0,4 62.5 vafidtts Vaht., Sagittarialartcifriiia L, Scirptrs arttrrt'cartttsandEchirtr>ch svvlteri rta Pursh! Helter ' Percentageof 1m' p!ots at which evidence ofgrazing Figurc4!. A totalof t! differentspecies were was!trcscnt. Satnplc size was 24. observedin he ungrazcdtreatments at Crciilc Bayou,However, Spartina prztrtt.s, thedominant in thcsurrounding marsh. was absent. At Locust Bothsites show similar ranges of waterlevel Bayou,only three species colonized thcungrazed f!uctuationsof approximately 1 rn Figures2 and treatments:Scirptrs arnericvrttrs, Spartirtv parens, 3!. However,thc tidal amplitude atLocust Bayou andAster tett ttifofi trs L. Figure4!. isapproxitrtate!y 20cm, white at Creole Bayou it is onty cm.The larger water-level f!uctuations at Survivaland Coverof Tratxsplants LocustBayou arc due to winddriven setup and dischargefrom thcAtchafa!aya River. Due to the Afterone growing gleason, survival tn the relativeelevation of thescour surface, the substrate ungrazedtreatments wassignificantly higherthan atLocust Bayou is almost never drained % of the inthe grazed treatments forall species ti'igure 5}. time!and has an average water level of 15cm above At theend of thefirst growing season, a few thescour. ln conuastthe Creole Bayou scour is transplantsofeach. species survived inthe grazed drained15% of the time andhas an averagewater treattnentsof Creole Bayou. while only Sparttrta !eve!of 11ctn abovethe scour surface. patenssurvived inthese treatments atLocust Bayou. However,notransp!ants survi ved inthe grazed areas Natural Colonization of Scours afterthe w interandno resproutittg occurred during thenext growing season. Natural co!onizationof ungrazedplots t insta!led in February, 1995! started atCreole Bayou Grazing Effectson Recovery '30 '2 - 19 l m 150 2 ! 70 IY160 130 97 Oc 1. 96 ~ 1, 96 Feb pr Figure2. Hourlywater level at CreoleBayou. 210 190 180 E 170 C II160 'Q 150 rs.'140 t3 12 110 Oct . 96 Dec l. 96 Peb1. 97 Apr 1, 9> aa »gure 3. Hourlywater level at LocustBayou. 300 J.M. Viaaer et 4!l n 0 !anApr Ja, rkI JanAIir Jni Orr Jan Api !n! CkrJan 199> I99A I997 0- JanApr 'n I!ri JanArn !nI OCIInn *pr !ril Or.rJ air 199i i 99i; I O'O Figure4. Natural colonization ofungrazed scours. Data from exclosures established inFebruary l 995within each scour, I 00 40 20 200 JulA Scprag 0 !ut Ang SCp kq ~ pic!crL! SperCswc!!crt~ 0 100 h 20 20 0 0 Jn!Avg Scp Ocr Jn! Arrg Scp Month in 19' Figure5.Survival oftransplar!ts ingrazed and ungrazed treatments duringthe first year 996!.l Data presented is theaverage survival fOr both sites. Grazing Effects eri Recovery Mt Table3. Natural colonizersof the plotsplanted with nurserystock at Cook Bayou.Numbers represent the numberof plotsthat were colottized out of a totalof tett4 m'plots. 1996 1997 Grazed Ungrazed Grazed Vngrazed Plots Plots Plots Plots Scirpus ainericanus Sagittaria lancifolia Ammania cocci nea 0 Amaranthus australis Paspalumvagi natum Unknown dicot Polygonum punctatum Vigna luteola Spartina patens One monthafter planting, there wasa signifi- Hurricane Andrew. Therefore,the lackof coloniza- cant difference between grazed and ungrazed tion of scourareas is not on!ydue to decreased treattnentsin plant coverfor all speciesat all sites, elevation,as postulated by Guntenspergenet al, Mostspecies showed an increasein coverin the l995!, Althoughthe secdbankwas removed during ungrazedtreatments during the study, which slowed thc hurricanein 1992,regeneration of theseedbank duringthe winter months Figures 6 and7!. The has occurredfrom adjacentmarsh seed sources. exceptionwas Distichlisspi cata «t LocustBayou, Throughthe exclusion of grazers,we haveshown whichretnained constant in coversince the planting. thatthe parts of the scourwith sufficientelevation At LocustBayou, both exclosuresplanted with will becolonized by severalspecies {Figurc 4 and Spartinaalterniflora failed to protectthe transplants Table 3! that arecoimnon m oligohalinewiregrass from grazing during the winter, due to muskrat tnarshes Visser et al. 1996!,The most frequently tunnelingunder the fence. Therefore,no datawere floodedscour at Locust Bayou had fewer colotuzing obtainedfor this speciesduring the secondyear of species three! than the lessfrequently flooded the study. CreoleBayou scour { 1l species!, Long-term monitoringof these exclosures will benecessary to At CreoleBayou, nine otherspecies colonized determineif spccics compositioit will changeaver the ungrazed-plantedtreatments. Of theseSci rpus time to resetnblethe surrounding Spartina parens- americanusand Sagi ttaria lancifoliacolonized the dominatedmarsh, Spartina parens was on}v found mostplots Table 3!, Only one of the ungrazed- in oneexclosure at LocustBayou and is a species planted treatments was invaded by Scirpus with low seedproduction. This speciesalso americanus at LocustBayou. performedpoorly when transplanted into the scour, probablybecause ofthe high frequency andduration DISCUSSiON of floodingin thescours. At bothsites, Srirpus arnericanu.sw asan abundant natural colonizer, This Ourresults show that grazing is a significant speciesalso increased in cover when grazers were factorin thc reduced recovery of areasscoured by excludedfrom oligohaline rnarshes dotninated by Spartinapatens Taylor et al. 1994}. GrazingEffects on Rrieovery Some colonization of the scour area at Creole would like to thankGreg Linscomhcand Niicl Bayouoccurred in the presenceof grazing. This Kinlerof theLDWF Fur andRefuge Dis is«in f»r mightbe dueto the lowergrazing pressure aswell theirinput in the designof thecxpcnmcnt. 1 l!WF asthe lower fretluency of flooding tn thisarea. ln personnelfrom the New iberia From the increasein coverof the transplants BAKER,3. P. 1985.The impact ol' grazing on plant aftertwo growing seasons, it appears that Parpaltrrrr communitics,plant populatitinsand s»il vaginatrzzrrperforms the best in bo hlocations. conditionson sah marshes ti'grnitiri 62: 39 t Spartirtaalterztiflora was the best performer at 398. LocustBayou, but the exclosures protecting these Cowoamv,R, P. Krstt,J. Vtsstzt,J. Gosstt «x. D plantsfailed to keepout muskrat during the next Ltt~'vsrtarr,E. Mt~wxit',3rt G. Pr nit~is, ssti winter.This species also performed well at Creole B. TnoMvsoi',1995. Characterization Coastal Research 2 l: 324-339, of Barataria and Terrebonne estuaries 1968- JActrsoe,L, L A. L Form:, L. S, Be rsmraru.1995, present. BTNEP publication 29. Barataria- Hydrological,geornorphological and chemi- Tcrrcbonnc National Estuary Program, cal effects of Hurricane Andrew on coastal Thibod aux, Louisiana. marshesof Louisiana. Jottenalof Coastal Research 21: 306-323. KENT,M. ANDP CotcErt. 1994, Vegetation descriptionand analysis: a practical approach, JohnWiley &. Sons, Chichester, England, IAwvERY,G. H. JR. 1974. The rnarnrrutisof Louisiana and its adjacent waters. LouisianaState UruversityPress, Baton Rouge Louisiana. McQrvzrs, T. E IL 1997. Shorelrnemovement and soil strengthin a Louisiana coastal marsh. M.S. Thesis,Univ. of SouthwesternLouisiana, Lafayette,Louisiana. O'Nrem. T. 1949. The muskratin Louisianacoastal rnarshes.Department of Wildlife andFish- eries,Baton Rouge, Louisiana. P~LMrsAhlo,A, W. 1972. The distribution and abundanceof muskrats Ondatrazibeth