IL( I
THE ECOLOGY OF WASTE STABILIZATION PONDS
by Bradley Duncan Mitchel1, B.Sc.(Hons. )
being a thesis submitted in fulfilnent of Ehe requlrernenËs for the Degree of Doctor of PhilosoPhY in the DepartmenÈ of ZooIogY' Uníversity of Adelaide
January 1980
A t à' e) i\\srül^ igB ¡ ^r "LÍnnoTogists can and shoufd plag a ptominent role ìn devising, testíng, and evaTuating methods for the treatment of organic wastes. As get theg have paid Tittie attention to t?rese probTems, but the basìc príncipTes that have been dÍscoveted can best be appTíed bg TinnoTogísts. If theg do not enter into applied reseatch and into the appTìcation of their ptínciples and findings, others not so we77 fitted bg training and experience wi77 da so."
C.M. Tarzwell (1966). SanitaÈional Limnol-ogy. In D. G. Frey (ed. ) t'Límnology in North Arnericarr. (Univ. ülisconsÍn Press) . CONTENTS Page Sumnary i Declaration .iv Acknowledgements v
Chapter 1 . General- Introduction 1
1.1 The Potential of tr{aste StabÍ1izatíon Ponds 1
r.2 Project Aims 3 1.3 trrlaste SËabilization Ponds - Advantages 4 r.4 Pond Usage in Aust.ralia 6
1.5 Probl-eurs in trrlaste Stabilízation Ponds 7 1.6 The Biology of Pond Function 10 L.6 .1 Algae-Bacteria Inte-ractions 10 1.6 .2 Protozoa 13 1.6 .3 Rotifera 13 r.6 .4 Crustacea 13 1.6 .5 Insecta 13 1.6 .6 Fish T4 1.6 .7 Macrophytes T4
Chapter 2. Study SiËe and Physico-Cheruical Characteristics L6 2.L Study Sire I6 2.2 Physico-Chemical CharacterisÈics t7 2.2.L Methods t7 2.2.2 Results 18
Retention Time 1B Temperature L9 Dissolved Oxygen 20 pH arrd Total Dissolved Solids 23 Bíochemical Oxyge.n Demand 23 Suspended Solids 24 Total Carborr and Total Organíc Carbon 25 Total Inorganic Carbon 2.6 Ammonia 27 Total Kjeldahl and Organic Nitrogen 27 Nitrate 2B Orthophosptrate 29 Phosphorus Retention Coefficients 32 2.2.3 Discussion 33 Page Chapter 3. Algae and Macrophytes 45 3.1 Introduction 4s 3.2 Methods 51 . 3,2.I Chlorophyll a 51 3.2.2 Algal CounËs 52 3.2.3 Fílamentous Algal Mats 52 3 .2.4 Suburerged Macrophytes 53 3.3 Results 55 3.3.1 Chlorophyll a 55 3.3.2 Conposition of Algal Cornmunities 5B 3.3.3 Algal Counts 60 3.3.4 Phytoplankton Productíon 60 3.3.5 Dynamics and Production of Cladophora 64 3.3.6 Dynamics and Productíon of Potanpgeton ochreatus 67 3.4 Discussion 73
Chapter 4. Zooplankton 90 4.I Introduction 90 4.2 Seasonality and Abundance of ZooplankÈon 95 4.2.L Methods 95 4.2,2 Results 100 4.2.2.I Composition of the ZooplankÈon Community 100 4.2.2.2 Zooplankton Dispersion 103 4.2.2.3 Seasonal Abundance 106 4.2.3 Discussion L22 4.3 Population Dynarnics and Production of. Daphnia carinata 134 4.3. I Methods r34 4.3.1.1 Size Distribution 134 4.3.I.2 Reproductíon 136 4. 3. 1. 3 Populatí.on Parameters 136 4.3.L.4 Calculation of Productíon: Populatíon Turnover-time Model frs 4.3.1.5 Egg Development Time 139 4 ,3,L.6 Length-Dry l^Ieight Relationship L4T 4.3.I.7 Calculation of Production: Biomass Turnover Model T4L 4. 3. 1. I Growth r43 4.3.1.9 Nitr:ogen and Phosphorus Content 144 Page 4.3.2 Results 144 4.3.2.I Size Distri-bution 144 4.3.2.2 Reproduction 148 4.3.2.3 Egg DeveloPment Time t52 4.3.2.4 PoPulation Parâmeters 1s3 4.3.2.5 Length-Dry l{eighÈ Relationship 155 4.3.2.6 Growth 1s6 4.3.2,7 Nitrogen and Phosphorus Conteqtt t57 4.3.2.8 Production 158 4.3.3 Discussion 165 4.4 Population Dynamics and Production of sj¡¡tocephaTus exspinosus L73 4.4.I Methods 173 4,4.2 Resul-ts L74 4.4.2.I Size DistríbuÈion 174 4.4.2.2 Reproduction L76 4.4.2.3 PoPulation Parameters 178 4.4,2.4 Length-Dry l^Ieíght Relationshíp 180 4.4.2.5 Production 181 4.4.3 Discussion 183 4.5 General Discussion 186
Chapter 5. Fish t92 5.1 Introduction L92 5.2 Methods 196 5.2.I Bnclosures and Experimental Design r96 ' 5 .2.2 Experimenffish r97 5.2.3 ExPerimental Procedure 198 5.3 Results 200 5.3.1 Physico-chemical characterísÈics in Enclosures 20L 5.3.2 Phytopl-ankton in Enclosures 202 5.3.3 ZooPlankton in Enclosures ?04 5.3.4 Físh Growth and Production ín Enclosures 205 5"4 Discussion 2r0
Chapter 6. Concludíng Discussion 215
Appendices 220 240 Bíbliography . l-
SUMMARY
Ecological interactions vrere sÈudíed in t\iro waste stabílization ponds aÈ Gumeracha, SouÈh AusÈralia, to relate the dynamlcs of the major
organisms present Èo effluent quality and, thereforer the efficiency of pond function. The roles of those organisms in algal control, the stabilization of organic material, and riutrient removal were evaluated to assess their usefulness as tools for the management of lüSPs. In this manner, biological prínciples for pond management ü/ere evaluated. The seasonal dynamícs of the phytoplankton were relaÈed to effluent quality. Phytoplankton blooms were tríggered by increasing
$raËer temperature and resulted Í-n a significant decrease in effluent quality. Effl-uent concentrations of BOD, SS, TOC, and organic nitrogen
exceeded influent values during phytoplankton blooms. Removal of solubl-e tO4-P and NO, was highest during phytoplankton blooms. Estírnated annual net producÈion of the phytopl-ankton in pond 2 represented a nutrient store equivalent to over 100% of Èotal nitrogen and toËa1 pO4- p retained annually. The dynamics of filamentous algae (Ctadophora) and the submerged macrophyte Potamogeton ochreaËus were related to phyÈoplankton abundance and effluent quality. F1-oating algal
mats and submerged macrophytes inhibited the development of phytoplankton
blooms and improved effluent quality. Estimated annual- net production
of. Cladophora in pond 1 represented a nutrient store equívalent to 477" of total tO4 - p and 12% of total níÈrogen retained in the pond annually. Anrrual net producËion of. p. ochreatus represented less than 3% of total
PO, - P and total nitrogen retained annually . t ¿+ The population dynamics of the major zooplankton \¡lere related to phytoplankton abundance and effluent quality. Although temperature was the najor faciuot determining Ëhe occurrence of zooplankton, competition and predation also appeared Ëo be irnportant in structuring the zooplankton community of the Gumeracha ponds. Phytoplankton bloons iÍ.
.ff.rrþ T
TÀrere Ëerminated by zooplankton grazing. The domínant herbivore, Daphnia cati¡tata, r¡ras a cold r¡/aËer form. High water temperatures inc.reased mortality and reduced the growth raÈe of D. carinata and prevented it from conËrolling phytoplankton durÍng the suÍìmer.r The dominant zooplankter during phytoplankton blooîìs hras the carnivore Mesocgclops
Teuckarti. D. catinata hras a ttfacultative browsertt and ingesËed the sedíments during períods of 1or^r phytoplankton abundance. D. carinata and Simocephalus exspinosus vrere both food 1iníted at high population densities. Total annual net product.ion of Ð. carinata in pond l dtrring
lg77 (345 g dry weigh t/^2), calculaÈed using the populatíon turnovel- tlme mode1, was the highest yet recorded for any planktonic cladoceran. Annual net production of o. carinata determined using the populatíon turnover-Ëime model- exceeded annual production determined using the bíomass turnover model by I00"/". Overestímation of daily produetion rate was highest during periods of high egg mortality. Total annual net production of D. carinata (biomass turnover nodel) represented a nutrient stoTe equivalent to less tlnan 5"/" of total P04 - P and total niÈrogen retained in Èhe ponds annual1y. A fish íntroduction experiment was conducted in enclosures withín the ponds. Calassius auratus had no signifj-cant effect upon phytoplankton and zooplankton populations or on effluent quality.
Growth of C. au¡atus increased after inÈroductíon to the pon v ACKNOI,üLEDGBMENTS I would like to thank the Engineering and tr{ater Suþpl-y Department of South Australia for allowing access to the Gumeracha ponds. Specíal thanks are due to the l,{asLewater Laboratory, Bolívar, for conducting the chemical analyses. In partícular, I thank Moss Sanders for his patience and assistance. Additionally, I would like to Èhank Arthur Haughey (Auckland Regional Authority) and Gavín l{ood and Ken IlarÈley (E&I,IS) for their conrnents. I am grateful to my supervisor, Professor Bill I^Iill-íams, for his support and encouragement throughout the course of Èhe project. Dr. KeiÈh trnlalker and Dr. Ríchard Marchant (ZooLogy Department, Universíty of Adelaíde) both gave freely of their tirue Èo make conrments and suggestions during the project. I thank them both" To Dr. Míke Geddes (Zoology Department, University of Adelaíde) who was ever willíng to l.isten to a neophyte, I can scarcely exPress my grati-tude. For your he1p, guídance, and friendship Mike, ttThankyou" hardly seens adequate. I would like to thank the following people for invaluable assistance in the erection of fish enclosures: Pat DeDeckker, Alice Iùells, Marg Brock, Phil Suter, Julie Harrís, Mike Geddes, Dave Papps' and Mike Thompson. I thank Roger Croome (River Murray Comrnission) for assistance with algaL identifications and the collectíon of fish from Millbrook Reservoir. I also thank Morris Ríchardson for permissíon to remove fish from his dam. Thanks are due to John Píllar (Fisheries Inspector, Loxton) for assistance in attempËs to capture fish. I thank Les Gray (South Australian Físheries); John Reynolds (New South Wales FÍsheries), and John Glover (South Australian Museum) for information \ and advice concerning fish ecology and collection. Special thanks are due to Victoï Theile for his eager assistance and continued good company in repeated, although somewhat fruítless, attempts to capture fish" vl_ I woul-d líke to thank the followíng persons for assistance in the idenËíficatíons of various ínvertebrates: Dr. Jon Martín (Genetics Department, Melbourne University), Dr. Nikolai Smírnov (Academy of Sciences, Moscow), Pat DeDeckker, Russell Shíel, and Dr. John Bishop (Zoology Department, University of Adelaide) . I would ljke to thank the following persons for supplyíng the ínforrnation used to compile Table 1.1: B.P. otconnell (DepartmenÈ of I{ater Supply and Sewerage, Brisbane), L. Henry (I,trater Quality Control CouncÍl of Queensland), A.D. Macqueen and A. tlaugh (l,trater Resources Branch, Department of Northern Territory), D.N. Keep (Rivers and trIater Supply Commission, Tasmania), T.J. Lewís (futtic !'Iorks Department, Perth), S.R. Smíth (Metropolitan lùater Sewerage and Draínage Board, Melbourne), G.T. Coulson (Latrobe Valley trrlater and Sewerage Board), C.!ü. Berkely (Department of Health, Melbourne), J.B. McPherson and. S. Hussainy (Melbourne and MetropoliÈan Board of Inlorks Farm, Vüerribee) . This study hras conducted while I received a Cor¡rnonwealth Postraduate Research Award; for this I am most grateful. Finally, to Jen and Amber, who too often had to put up with ny bad temper, sorry and Èhankyou. ChapEer 1. General Introduction t- I . 1 The Potential of tr^/aste SEabi lization Ponds Global food and fuel shortages and problems of pollution have revised attitudes to the management of non-renewable resources. Urban, industrialized societies have been forced to re-evaluate many widely accepted practices. The treaËnent and ultimate disposal of domesÈic sewage is one practice currently under review. Sewage, formerly regarded as lvaste) is a potentially valuable source of raw materials. Current mèans of sewage disposal, however, contribuÈe t.o eutrophication. Problems of wastage and environmental contanination can be partially offset by innovations and improvements in waste\^/ater treatment (Gutteridge Haskins and Davey , 1976; Tourbier and Pearson, 1976). Nutrient recycling from sewage could supplement global energy production. A city of 100,000 people produces sel¡rage containing 100 tonnes of total phosphorus and 400 tonnes of total niËrogen annually. This amount of nuErient has a combined current value of $57,000 as chemical fertilizer (Strom, l9l9). The potential of this resource has belatedly been acknorvledged in Australia (G, H & D, 1976) and its exploitation may take several forms: a) direct human consumption of sev/age-grown microalgae (Gross et aL., L97B; Kofranyi, 1978) ; b) indirect consumption of microalgae via aquaculture schemes incorporating se\,rage ef f luents (Meske and Pf ef fer, 1978; Sandbank and Hepher, 1978; Goldman and Rtryther, 1976; Reid, 1976; Heplier et a7., I975; Rhyther et a7.,1975, I9l2) or use as food for domestic livestock (Brune and \{aIz, I97B; Mokady et a7., 1978), c) direct culture of f ish in sewage ponds (white and l^lilliams , I97 8 ; Sclrroeder atrd Hepher, 1976; KrishnamoorLt- et a7., I9l 5; Noble, 1975; Slack , L974; ChatËerjee et a-L., 1967 ; Hey, 1953); 2 d) land irrigation of effluents for agriculture ot gtazíng (Strom, 1979; Searle and KirbY, 1973); e) use of se\,rage-gror¡rn macrophytes for stock food (I^lolverton and McDonald, 1978; Culley and Epps, I973; Seidel, 1971; Boyd, r968); f ) production of methane from se\^rage-grov/n macrophytes or micro-algae (Strom , I97 9; inlolverton and McDonald, 1978); S) derivation of liquid combustible fuel from lipid-producing microalgae cultured in sewage effluents (G. Gartride, CSIRO Division of Chemical Technology, pers. comm. , L979). Eutrophication may be alleviated by nutrient removal from se\4/age eff luents. Ciremical techniques f or the removal of nitiogen include denitrification, ammonia stripping, ion exchange, and demineraLtzation (electrolysis, reverse osmosis or distillation) (Rotrlictr and UtEormark, L972). Phosphorus may be removed by precipi¡¿tion of phosphates using lime, aluminium sulphate, sodir:rn aluminate or ferric salts, ion exchange, reverse osmosis and distillation (Rorrlict, and uttormark, 1972; Jenkins et a7., 1971). These Processes vary in cost but considerable expenditure is required for the production of effluents of consistent quality. In addition, coagulation techniques require the handling of large volumes of sludge. In any event, it has been shor"¡n that conversion of polyphosphaËes to orthophosphate during biological treatment is necessary for chemical phosphorus removal (nouolyi , r973). Biological alternatives for nutrient removal include land irrigation (Rohlich and Uttormark , Igl2), the culture and harvest of microalgae (Goldrnan, L979a ; Brar and Tollefson, I975; Van der Borgh and Ituyers, L974; Shelef, et a7., L972; Hemens and stander, 1969; Heme-ns and Nfason, 1968; Fitzgerald and Rotrlich , 1964; i,Jitt and Borchardt., 1960) and the culture of emergent or submerged macrophytes (Oinges , Lg78; hlolverton and llcDonald, L978; Corwell et a7., 1977; 3. Jong , I97 6; McNabb Jr . , 1,976; Seidel , 1976; Boyd, 1970) . The incorporation of nutrients inEo animal tissue (".g. zooplankton or fish) is an untested possibility. Obviously, biological techniques for nutrient removal and recycling are the same; removal is essential for re-use. Aerobic (maturation) waste stabitrization ponds (WSps) provide ideal sites for the types of schemes listed above. These ponds are already an integral part of many treaÈment plants, provide for easy access, have uniform shapes and depths, are corìtrollable in terms of water flow and depth, and have bottoms free from obstructions thus allowing convenient harvest of plant and animal biomass by conventional techniques. This thesis exarnines the effectiveness of aerobic I¡ISPs as a wasteh/ater Èreatment Eechnique, and investigates means of improving pond efficiency. In particular, biological alternatives for pond management, including nutrient removal, are studied. L.2 Pro.iect Aims Information abouÈ the biological characteristics of I^ISPs is fragmentary arrd clearly inadequate for effective managemerit to meet current effluent quality criteria. This project contribuÈes basie biological information on matlration ponds to aid in management and manipulation for nutrient recycling. The project design is outlined be low: 1) The current state of knowledge of VJSP ecology is reviewed and major problems highlighte 2), The efficiency of maturation ponds in stabilizing organic material and removing nutrients is examined at Gumeracha, South Australia. 3). The seasonal cycle of phytoplankton is described and population 4 f luctuations correlated \^/ith ef f luent qualiEy. Annual net production of phytoplankton is estimated' Ð. The i¡rfluence of submerged macrophyEes and filamentous algae upon rr-Inlanktonic lalgal abundance and effluent quality is determined. Annual net production of submerged macrophytes 1S determined. Annual net production of filamentous algae is es timated 5). The seasonal cycle of zooplankton is desc::ibed. The influence of zooplankton upon algal abundance and effluent quality is determined. 6). The population dynamics and annual net production of the dominant species of. zooplankton are studied intensively due Eo their importance for the stabilization of organic matter and the control of a1gae. 7). The effects of a higher order consumer (fish) upon algae and zooplankton, and the concomiËant influence upon effluent quality are examined. Annual net production of fish is determined. B). The relative nutrient "stores" represented by annual net productíon of pliytoplankton, filamentous algae, macroPhytes, zooplankton, and fish are calculated. These "stores" are comPared with annual pond nutrient rete¡tion and nutrient partitioning betrveen trophic levels is examined. Harvest of the annual net production of each group is examined as an alternative pathway of nutrient removal from the ponds. The current literature on the ecology of I,JSPs is reviewed below This review provided the basis for the investigations subsequently undertaken during the Project. 1 .3 i,laste Stabilization Ponds - Advantages The te.rm tlVaste Stabilization Pond' (tt/SP) describes any shallow, man-made basin utilizing natural biological. processes for the reduc tion of organic matter and the destruction of pathogenic organl-sms in waste- a 5 I.Iater(Marais,I97I;Gloyna,197l;Ì'fcKinneyeta7.,1971).Several different types of I,JSP are currently in use (Gloyna, I97l). A I'ùSP Aerobic ponds may be of three types: high rate aerobic, aerated, or maturation ponds' may be anaerobic, facultative or aerobic.f High rate aerobrc ponds are shallow (<0.5m), mechanically mixed, have short retention times and high algal p::oduction. Aerated ponds have virtually all oxygen supplied mechanically. Algae are thus replaced as a source of oxygen and algal growth is low. These t\,ro tyPes of aerobic pond have high energy inputs comPared to other Pond tYPes' (Ramani, and thus high operatiãnal costs(. Mãturation or polishing ponds Ig76) receive effluents treated to a secondary 1evel and provide high- quality effluents. By combining different pond types in series, tr{sP systems may be designed to meet a variety of ËreatmenÈ objectives ' The advantages of l,lSPs for waste-$/ater treatment result from their simplicity (Strelef , L976). Ponds require a relatively low initial capital investment and simple flow schemes require low energy inputs (desirable in view of current energy shortages). Simple operation and mainËenance mean reduced operating costs. I^lSPs cost substantially less per capita to construct and operate than other types of primary and secondary treatment (Shelef , Ig76; Gloyna, 1971). These features, plus the ability to markedly reduce waste-water biochemical oxygen demand (¡OO), suspended solids (SS) concenËrations, and bacteria and virus numbers, to smooth peak hydraulic loads and deal adequately wittr seasonal industrial and agricultural wastes, have made and I^lSPs attractive to less developed countries, small communities, certain stages of urban development (Boatright and Lawrence , 1977; via Gloyna , 1962). WSPs can also provide "ultimate" \n/aste disposal evaporation and seepage. WSPs have higher land requirements than oÈher methods of treatment, and are not without oPerational problems' These will be discussed below. 6 I.4 Pond Usage in Aust.ralia I¡laste stabilization ponds are used extensively by small communities throughout country areas of Australia. In addition, ponds are used at lüerribee, Victoria, to treat daily peak and wet weather flows from approximately 75% of Melbourne's population. At Bolivar, South Australia, domestic \^Iaste-I,raEer from a poPulation of 600,000 in Adelaide and trade v¡aste equivalent to a population of 700,000 is treated in ponds. A large pond system at Dutson Dov¡ns in the Latrobe Valley, Victoria, treats largely indusËrial waste, and smaller plants serve some metropolitan areas in Sydney. Current Australian ponding and effluent disposal practices are sunmarízed in Table 1.1. Ponds vary in size (approximate maximum 100 ha), alre characteristically 1.0-1.5 m deep (but rnay be up to 3m deep), and are subject to a wide range of loading conditions. Large cities usually ernploy aerated ponds for tertiary treatment, while ponds for secondary treatmenÈ are usually facultative. Anaerobic ponds are used widely for pretreatment prior to aerobic ponding (Parker et aJ., 1959, 1950; Hu.ssainy, 1978). Country tohrns use fully aerobic maturation ponds for tertiary treatment, facultative or aerobic ponds for secondary treatment, and anerobic ponds for primary treatment. Anerobic ponds are also used extensively for the treatment of farm wastes, esPecially from piggeries (Environmental Control Council and tr^later Quality Control Council of Queensland, 1975; Bryson, Ig72), and cannery \^/aste (Parker, 1966). Direct ocean discharge is the most coÍrnon method of effluent disposal in Australia; in many cases Ëhis occurs at the seconda¡y level of treatment. This practice, the result of population distribution throughout Australia, meant that euËrophication of inland rvaters lagged sornewhat behind other urban nat j.ons (Wif f iams, 1969). Many Australian lakes and reservoirs are nor¡I exhibiting signs of eutrophication (Har:t, Lg74) and discharge of incompletely treated seh7age effluents is a contributing factor. Table 1.1 l,laste stabilization pond use Èhroughout Australia. Compiled from information supplied by sewage treatment authorities and Gutteridge, Haskins & Davey, (1976). S tate Number of tov¡ns Surface area of Annual flow Type of treatment Disposal of pond effluent using ponds and ponds (tra) (ut) populaËion served South Australia Ade 1 aide 340 3r7 55 Secondary and tertiary. Irrigation and ocean + t5 (400-33000) 85 7206 Most tertiary, some secondary, d is charge . Several a few primary. irrigation, some river dis charge . New Souih iniaies Sydney 19 4501 Tertiary. Ocean discharge. + 106 (ZOO-tt3000) 3L2 5 6035 Most tertiary, secondary in Land disposal or river 2, primary in 1. d is charge . Victoria Me lbourne 1450 70000 Primary and secondary. Ocean discharge. Dutson Downs 283 12100 Primary and secondary. Ocean discharge. + 68 (r050-5700) 200 35920 Many tertiary, several Most irrigaËion, several primary. stream and ocean discharge Northern TerriËory 5 (220-25000) 52 3190 Primary and secondary. Ocean, river or creek discharge. Tasmania 25 (s00-8830) 44 5980 Most primary, some secondary. River or ocean discharge' Queens land Brisbane J 3285 Most secondary, several Ocean discharge. + 54 (120-25000) 40 9655 tertiary, some primary. Several land, several river Secondary (after septic tanks ) and creek, some seepage. lnlestern Australia 48 (100-208ó5) 64 6282 Most secondary, some tertiary, Most soakage, some a few primary. irrigation, several river, few ocean discharge. 7 1.5 Problems in l^las te Stabilization Ponds The advanEages of hISPs have been offset by a lack of theoretical data upon which to base pond management. The approach to pond design and operation has been largely empirical, often resultirrg in overloading and mismanagment of ponds. This has resulted in criticism of the usefulness of ponds for r¡raste\^rater treatment (Barsom and Ryckman, 1970). Although IJSPs have been in use in several countries for many years, only within Ëhe last two decades have specific design criteria in Ëerms of volumetric requirements, organic loading rates and detention times been developed (Goyna, 1971). Pond performance is largely clependent upon climatic conditions (temperature and solar radiation) b.tt until recently ponds had been constructed on the sole basis of the above criteria with little rational basis for varying design in areas of differing climate (nliss, 1976). The failure of pond effluents to meet current quality requirements is the result of mismanagement due t.o poor understanding of pond function, rather than limitations of ponds as a treatment Èechnique. The performance (eff iciency) of l,ISPs has been Èraditionally measured as the percentage removal of 5 day BOD (the relal-ive oxygen requirement of the effluent oç a measure of the degradabl.e load added to receiving rvaters), SS, viruses, and enteric coliform bacteria. Current effluent quality criteria extend beyond Ehese requirements. Nutrient and/or heavy metal removal is now recognised as an integral part of the ËreatmenË process. Conventional se\^tage treatment has centred upon mineralízatíon of organic compounds rather than remqval of nitrogen and phosphorus. The major operating problem of hISPs has been the presence of algae in effluents, their contribution to BOD and SS and, ltence, the effect of effluent quality on receiving water bodies. Fundamental processes in hlSPs convert unstable organics into algal cells. Much 8 higher standing crops of algae may be produced than are necessary to saÈisfy the oxygen requirement of the adcled se\ùage (Bartsch and Allum, 1957). During summer, filtered effluent BOD and SS may be negligible while total BOD and SS can exceed influent value (Mct 1976). In the past, I,JSPs have expor:ted their BOD and nutrienÈ load, albeit in a changed form, to rivers, lakes, and the ocean; it was assumed that algae in effluents would survive in receiving waters, thereby causing no harm (Fitzgerald and Rohlich, 1958). Algal-laden effluents, however, represent a Potential accumulated oxygen deficit and nutrient surplus. Chlorination of I{SP effluents for the destruction of pathogenic organisms is a widespread practice. Effective chlorination is a complex, exact process (Hom, 1970) and regrowth of coliforms occurs if doses are inadequate (Shuval et a7., 1973; Svore, 1968). Apart from the effects of residual chlorine on organisms in receiving lltaters (Bellanca and Bailey, 1977; Tsai, L973 and 1968),, potentially carcinogenic chlorinated hydrocarbons have been identified from chlorinated domestic se\^Iage effluents (Harris,1976). The most conrnon cause of dead algal cel1s in IISP effluents has been improper, excessive chlorination (Oswa1d, L976; Oswald and Ramani, 1976; Hom, 1970). Brief exposure to residual chlorine can produce a significant loss of chlorophyll a and permanently decrease rates of carbon uptake by phytoplankton (Broolcs and Liptack, Ig7Ð. The dif ference between chlorine concentrations resulting in nearly full ( The effects of tr^lSP eff luents upon receiving waters are complex and dependant upon effluent quality, dilution factor! and the ability of 9. algae to survive. Effects may be small in some cases (Oswald and Ramani, 1976; Patrick, L976), but oxygen depletion and elevated BoD can result (Athertou and King, I97I; Bain et aJ', 1970; King et al" f970). Bacterial degradation of algae in receiving waters r¿i11 release nutrients and contribute to eutrophication. MosË Ì,7aste\^Iater treatment plants currently in operation were primarily designed for BOD reducÈion and nutrient removal is generally less than 50% (nohlictr and Uttormark, Lg7Ð.AlthoughiEhasbeensuggestedthatrtlastevrâtersrePresenta small proportion of the total nutrient input to certain surface l¡aters (Boyd et aJ., 1976; Bachmann and Jones, L976), point sources can be significant contribuËors to euErophication (tr{urhmann, 1964)' Diversion of effluents or the introduction of tertiary treatment (nutrient removal) can significantly reduce the total annual nitrogen and phosphorus input to lakes and alleviate problems associated with eutropl'rication (nailey et aI., 1979; Forsberg et a7., L977; Larsen et a7', 1975; Sonzogni l^lilliams, and Lee , Ig74; Rohlich and uttormark , !972; Edmondson, 1970; 196e). lfhile llSP effluents currently satisfy BOD, ss, and coliform bacteria criteria, nutrient removal requires attention. Primarily, this involves the removal of algae. from effluents; a1gal biomass represents a large ,rstore" of rritrogen and phosphorus. The detrimental ef fects of algal-laden effluents and the possible value of algae as a byproduct have urged the development of chemical and mechanical alternatives for alga1 removal (John et a7., L916; Parker, 1976; Middlebrooks et a7" 1974; Oswald and Golueke, f968; Golueke and Oswald, 1965)' I'fost of Ëhese techniques require considerable capital investment and skilled supervision, detracting from the advantages of wsPs as a means of wastewater treaLment for small coürnunities. Chemical techniques may preclude furËher use of Ehe harvested algae (Rao , et a7. , 1975) . FurËhermore, techniques such as centrifugation or flocculation may 10 concentrate paÈhogenic bacteria and viruses (Cooper , 1962). In-pond techniques of algal control, such as biological harvesting via zooplankton and/or fish grazítg, have been discounted before their potential has been adequately researched (¡li¿¿lebrooks et a7., I974) 1.6 The Biolosy of Pond Function I'Iaste stabilization ponds evolved from the concept of naÈural purification, that is, the observation that organic contaminants could be stabilízed by naturally occurring organisms when waste-water r¿as discharged to rivers and streams. At some point downstream the river would regain its natural state, the organics having been assimilated by the aquatic community (e.g. Bayly and t'lilliams , 1973). This process is the function of a complex community consisÈing of many species and is largely achieved by trophic inEeractions between the community's constituents. The biology of l{SP conmunities has been neglected. Trophic interactions have been ignored in the design and operation of ponds as physical factors have been regarded as the major determinant of pond function. 1.6.1 Aleae-Bacteria InteracËions. The most intensely studied aspect of t{SP biology concerns the interaction of algae and bacteria and their role in the stabilization of organic matter. Algae utilize the stable, inorganic products of bacteriä1 metabolism (t'tct The biochemistry of this process is well understood (Ganapati, I975). Several fundamental problems await investigation. These include the identification of the bacteria involved in the stabilization of organic matter, Lhe agenèies of removal of pathogenic bacteria, and the precise relationship between algae and bacteria (uitctrell, in press).* The relationship has been assumed symbiotic. This may be the case for Senedesmus, Nostoc, and ÄuLosira, but for some species of Chfotel-l-a and OsciLLatoria Èhe relationship is antagonistic (Ganapati and Amin, Ig72). Algae produce antibacterial substances (ward and King, 1976; Fogg, 1962) and may compete with bacteria for phosphates (Ward and King, Ig76). BOD reduction in high-rate oxidation ponds may be primarily effected by algae adapted for heteroErophic nutrition (abeliovich and I'Ieismann, 1978). The interactions of algae and bacEeria are variable. However, the algae-bacteria model of IVSP function has so dominated design, procedures that a simplistic concept of pond communities has resulted. A typical model of the biology of an aerobic I,JSP is presented in Figure 1.1. This model implies Ehat algal numbers are regulated solely by the rr This paper is included in Appendix 3 Solar Radiation Non-b iodegradab 1e organfcs (suspended so1ld) Algae (reduction) (suspended co2+H2o+sf +roo -+o +c Il N O.P cells ]"t+uo' 2 ab cde soI]-d,l EffluenÈ Soluble Degradable Gr-N03 +P04= Material (C If N 0.P ) ,\*"odt.1Ð 2+ro 2+lI2 Influent 'abccle' * Cell-s Bacteria (oxidation) (suspended senescent ce11s Settleable soltd) Solids Sedíment FIGURE 1.1 Principal BiologJ-cal Reactions in a IISP (traditlonal sanltary engineering model, based on Bliss (1976) and Gloyna (1971)) 12. rate of bact,erial oxidation of organic rnaterial. This minimizes the importance of other biotic factors, particularly higher trophic levels, in regulating algal populaEions. The general practice has been to assume that nitrogen and phosphorus are abundant and readily usable (..g.Gloyna, I97I) and thaÈ algal activity is controlled by light, alkalinity, mixing and detention time (fing, I976; Gloyna,197L, 1968). The algae in InlSPs can become carbon or nitrogen limited under certain conditions (t The f ate of nutrients in I,tSPs has been neglect.ed. Nítrogen forms in facultative pond sediments have been identified by BrockeÈt í1977 ) and Le¡¿in (tgll) has shown that complex polyphosphates (frorn detergents) are rapidly hydrolysed to soluble orthophosphaÈe during biological sewage treatment. No information is available concerning nutrient cycling, storage in sediments, or parEitioning between trophic levels in IISPs In view of I,ISP operating problems the influences of other organisms, particularly from higher Ërophic levels, upon alga1 populations are imporEant and require attention. The importance of other members of the WSP biota in pond function will be briefly reviewed. In contrast to the algae, the study of other organisms, in l'/SPs has been neglected. This reflects the influence of the above model and the idea that organisms other than unicellular algae and bacteria serve no useful role in the stabilization process and are therefore unimportant or even detrimental. In addition to the influence upon algae, a more dj-rect involvement in r¡Iaste stabilization is implicated for many groups - plant and animal (Mitchell, in press). 13. I.6.2 Protozoa. The autotrophic Phytomastigophora and Èhe saprozoic Zoomastigophora may play an important role in the stabilization of organic maÈter (Pillai and Subrahmanian, 1944). The phagotrophic ciliates graze upon bacteria and may prevenË self-limiEation in that group. A high rate of assimilation of organic material by the bacterial connnunity would thus be maintained (Curds, 1975). Protozoa may also help in the clarification of effluents by reducing bacterial numbers via predation and/or flocculation. 1.6.3 Rotifera. The filer-feeding rotifers of the order Monogononta are corunon in IJSPs (Hussainl¡ ,I978; Goulden, I976; tr/hite, 1975; De Noyelles, L967). Although this group plays a secondary role in the removal of organic matter (Doohan, I975) it may significantly influence algal populations via grazítg, e.B, Btachionus (De Noyelles, Jr., 1967), I.6.4 Crustacea. Planktonic microcruscacea (suborder Cladocera and subclass Copepoda) are corTrnon in l^ISPs and effect BOD, SS, nutrient and bacterial removal (Andronikova, L978; Schroeder and Hepher, I976; Dinges, lg76; Kryutchkova, 1968; Loedolff, 1965). The influence of zooplankton grazíng upon a1gal populations lÀtarrants special attention in trISPs but has been studied ,rarely (hhite , L975). Until recently, zooplankton rìrere considered detrimental to pond function (see review by Dinges, 1973). Zooplankton may be useful for llsP management. 1.6.5 Insecta. The most significant group of insects in InlSPs is the Chironomidae, midge larvae, though composition of the insect community appears to be a function of organic loading and detent,ion time. Little attention has been accorded the functional role of Èhese communities in I^lSPs. Kimerle & Anderson (1971) have demonstrated that midge larvae are important in organic matter decompositional processes and that emergence and respiration may account for 7 per cent of the energy fixed in primary procluction. Midge larvae may also T4 contribute to the efficiency of waste stabilization by extending Èhe aerobic zone of decomposition further into the subsËratum' However, insects are usually associated with operational and public health problems (Peters , I975; Glover, Lg6g; Kimerle and Enns, 1968). 1.6.6 Fish. Fish have been cultured in ponds receiving sev¡age $rastes for many years (Hictting, 1968) but only recently have the effects of fish on \^lsP function been invesËigated' These studies suggest thaLplanktivorous and herbivorous fish effect apPreciable BOD' SS, nutrient and coliform bacteria removal (Carpentet et aI., 1976; Reid, Lg7O. Fish may act as a nutrient store and be valuable for nutrient recycling schemes (ritcrrell et a7., 1975; Hrbacek et aJ., 1961). l"Iany features of the complex effects of fish predation on aquatic cornmunities (Anderson et a7., 1978; De Bernardi and Guissani, I975; Hillbricht-Ilkor,¡ska and !'Ieglenska , 1973; Grygierek et aJ., Hrbacek et a7' 1966; Straskraba, 1965; Brooks and Dodson, 1965; ' 1961) have yet to be investigated in relation to VJSP function' l^/hile planktivorous fish may increase algal populations in tr{SPs (Wnite , 1975) the effects of omnivorous species remain to be tested' I.6.7 Macrophytes. Aquatic vascular plants have generally been regarded as detrimental to pond function due to Èheir association with insect problems (Ximerle and Enns, 1968). However, submerged and emergent macrophytes are able to effect considerable BOD, SS, nutrient and coliform bacteria removal when cultured in sevlage effluents or I'trSPs (Corwell et aI., L971; Wooten and Dodd , 1976; Inlolverton et al', L976; Spanglereta7.,1976;Seidel,1976;IfcNabb,Jr"l976;Jong''I976; Dinges, 1978, 1976; Culley and Epps, 1973; Boyd, 1970). MacroPhytes and algae interact in a complex manner (etritips et a7', 1978; Schindler and comita, 1972; Goulder , 1969) and macrophytes may inhibit the I977; development of algae (Crawforcl , Ig7g, Ig77; Kimball and Kimball' 1949)' Nicholls, L973; Fitzgera:!d, 1969; HasIer and Jones ' 15. Macrophyte harvest may remove significant anounts of nitrogen and phosphorus from lakes (Carpenter and Adams, I977; Wile, 1975; Boyd, 1971). Macrophytes may provide valuable methods for WSP management. Biological events in !ùSPs are more complex than Figure 1.1 suggests. A more realistic model of trophic interactions in a WSP is presented in Figure 1.2. In this model, partially suggested by Loedolff (1965), algae-bacteria interactions are part. of a much larger, more intricate food web. Such a model provides the conceptual basis for combined aquaculture-v/asEe treatment schemes incorporating organisms from several trophic levels (".g. Carpenter et a7., L976; Goldman and Ryther, 1976). Other components of the lrlSP conrnunity inf luence algal populations, in particular, zooplankton, fish, and macrophytes. The possible role of these groups in nutrient removal also makes their study in üfSPs important.. For these reasons, this study investigates the seasonal cycles of algae, zooplankton and macrophytes in WSPs, the effects of interactions between Èhese grouPs on effluent quality, the impacÈ of fish upon trlsP conmunities and funct.ion, and Ehe relative value of algae , zoopLankton, fish and macrophytes for nutrient removal from l{SPs . Solar Radlatl-on Fish gence EmerI I Rotifers Zooplankton Algae +O ,H6N"0¿P" 0) Influent Fl ø U EffluenÈ -o(d .rl .Ú (ú cd H Ò¡ òo }] q) Ê Pro to zoa Settleab 1e Solids Macre phytes SenescenÈ Sesescence, Senescence t cel-1s faeces faeces Gxazing enesceflc Benthos Sediment Insecta Mollusca (total pond communlÈy or trophic rnodel) FIGURE 1.2 Principal Biological Reactlons ín a WSP 16. Chapter 2. Study Site and Physico-Chemical Characteristics 2.1 Study Site Two ponds were studied at the small, rural town of Gr.¡rneracha (138o 5Z' 54,'E, 34o 49' 9" S; 330 m above sea level), 35 km north- east of Adelaide, south Australia (Figure 2.1,4). Pond effluent enters the Torrens River which is impounded by a sma1l weir 3 km downstream from the treatnent plant (figure 2.1,8). Water is diverted from this weir into Millbroolc Reservoir (surface area 178 ha, mean depth 9.3 m). Approximately 9 km downstream from the weir the Torrens River enters Kangaroo Creek Reservoir (surface area I2l ha, mean depth 20.2 m). During annual low flow periods in the river (January to March), pond ef f luent may contribute uP to 1.77" of mean daily river flow (calculated from Engineering and I'rlater Supply Department, 1978, p.2o) . The Gumeracha plant, shorn¡n in Figure 2.2, was conrnissioned in 1965. Raw sewage passes through an Imhoff tank (large suspended solids are removed Ëo sludge scrapes), a biological Ërickling filter, a humus tank and into pond 1. Pond 1 effluent flows into pond 2 (ín series) and pond 2 effluent is chlorinated before release into the river' The ponds rÀ/ere designed to provide tertiary treatment. Both ponds are 1.1 m deep; pond I has a surface area of L44Om2 and pond 2 a surface area of a I245m¿. The plant site is landscaped and well-drained; the ponds receive no surface runoff. The Ëotal design population equivalent for the Gumeraclra plant was 3,500 (dornestic population 400). Design flows and organic loads represented in Table 2.1 show the cornposition of the design populaËion. The bjological filters remove 907. of. the sewage BOD and the design load on the poncl system rùas 35.9 Kg BoD/ha/day' Neither the cheese factcrry nor the fruit works is in operation and the slaughter MURRAY MOUNT LOFTY RIVER RANGES GITLF ST. ,-: \: TORRENS VINCÐ{T RIVER I"ÍILLBROOK ADELAID RESERVOIR I ---s\ SET,TAGE D I,¡0RKS I @ Gt]MERACHA km FTGI-IRE 2. 1A I(ANGAROO CREEK RESERVOIR 01¡l kn FIGURE 2.18 TORRENS RIVER N I 2 Pond CHLORINATOR Pond I HUMUS SLI]DGE EN TANK SCRAPES ¡tr TRICKLING FILTERS 0 IMHOFF TANK m FIGURE 2.2 The Gumeracha treatment works' Table 2.1 Design flor¿s and organic loads for Gumeracha Èreatment works (calculated from Engineering and l{ater Supply Dept' information sheet). !üorking Flow (t/day) Organic Load (xg noo/day) 24.5 Domes tic 52,ggo (158,990 Peak flow) Cheese Factory 6,000 (popt equivalent 1070) 68 .0 Glace FruiÈ I'Iorks 3,Ooo( " '' 1780) 113.4 Slaughterhouse l,ooo(-" " 250) t5 .9 Total 90,840 (196,820) 222.7 t1 house contributes small, intermittent loads. The plant can be considered to treat solely domestic effluenÈs and average operat.ing characteristics for the ponds during 1977 are presented in Table 2.2. The Gumeracha ponds are currently operating at less than half design load (only one biological filter is in use). The Gumeracha ponds are fully aerobic maturation ponds which receive influents relatively low in BOD and SS. The function of such ponds is the polishing of effluents via the reduction of SS, nutrients, and coliform bacÈeria (Ramani , t976); BoD removal is not a primary requirement. 2.2 Physico-Chemical Characteristics 2.2.I Methods. Physico-cl-remical parameters r^rere measured forË- nighÈly (sampled near 1200 hours) from January 1977 to October 1978. rrvrr Discharge r^ras measured over a notched weir (Hynes, 1970). I^Iater temperatut. (oC) and dissolved oxygen (rg/1)v/ere measured at the surface and successive 10 cm depth intervals in the centre of each pond using a YSI Model 5IB oxygen meter and a YSI Model 5739 temperature-oxygen probe calibrated for altitude. Noncomposite \.rater samples \^/ere taken from the humus tank outflow (pond 1 influent), pond 1 outflow (pond 2 influent), and pond 2 outflow prior to chlorination. 1000 ml narrow-mouthed, glass- stoppered bottles were fi1led from a ladle taking care to avoid turbulence and entraining atmospheric oxygen; bottles \^rere overf lowed approximately 2 times their volume. Samples \,¡ere kept in the dark and stored ar 4oC within 2 hours. During suÍrner, samples were placed on ice inrnediately after collection. Prior to this study, pond 2 effluent quality had been monitored bimonthly. That progranune did not permit comparison of the relative treatment efficiencies of pond 1 and pond 2 nor the determination of nutrient removal . The following parameters \^rere determined during this study and all techniques followed APnA (1976): Eotal and filtered Table 2.2 Average operaÈing characteristics Lor L977, Pond I Pond 2 * Mean Daily Flow Rate (f/day) 90288 90288 ¡lrìk Retention f irne (days ) 17 .5 15.2 **-* Organic Loading . 10.9 5.5 (Kg soo/halday) * From discharge, see 2.2,L ,- ** Pond volume/mean daily flow raÈe *** (Mean influent BOD)x(mean daily flow rate)/Pond surface area. 18. (0.45 ptrl) 5-day biochemical oxygen demand (BoD); susPended solids (SS); pH (measured with an EIL Combination Electrode); total dissolved solicls (foS) (calculated from conductivity using VJilliams: (TIC) (measured 1966); total carbon (TC) an¿ total inorganic carbon (fOC) (calculated using a Beckman Carbon Analyser), total organic carbon (fXN); from the difference between TC and TIC); total Kjeldahl nitrogen acid after armnonia-nitrogen (nHr) (measured by titration with sulphuric (org-N), disÈillation into a solution of boric acid); organic nitrogen parÈiculate plus dissolved, (calculated from the difference between (t'tor') TKN and NH, after APHA, 1976, p. 437); nitrate-nitrogen (calculat.ed from the difference between nitrite nitrogen and total oxídized nitrogen measured using Devarda's al1oy reducEion method' Nitrite contributed less Ehan 27" total oxidized niÈrogen and will noÈ be considered.); total (filtrable pLús nonfiltrable) orChophosphate (total PO4-P) (measured colorimetrically after reaction with ammonium stannous molybdate to form molybdophosphoric acid and reduction by (filtrable) chloride to molybdenum blue); "soluble" orthophosphate Chemical (sol PO4-P) (measured as above after filtration (0'4s um))' analyseswereperformedbytheBolivarWastewaterLaboratoryofÈhe Engineering and l^later Supply 'Department of South Australia' 2.2.2 Results . instantaneous retention time R etention time. Seasonal variation of (volume/dai1y flow rate) for the Gumeracha pond system overall durrng Ig77 ís shown in Figure 2.3. Retention time varied considerably (ZB days) throughout the year being longest during the warmer months in pond 2 and shortest during mid-winter (5 days). Retention time wouldhavebeenslightlyshorterthanínpondlduetoÈhesmaller more value volume of pond 2. Annual mean daily flow rates were of rates when considering pond function than individual instantaneous ' BO 60 oà d E o .¡É ¡J 40 o 'r{ ¡J d o Ð úOJ z0 J D J r97 7 Tírne (Months) FIGURE 2.3 Overall retention time of the Gumeracha ponds. 19. Temperature. Surface r¡/ater temperatures (oC) an¿ mean weekly maximum and minimum air temperatures (calculated from daily records at Mount Crawford, 13.3 km north'-easÈ of Gumeracha, same elevation) are shov/n in Figure 2.4. Annual fluctuations of surface temPerature were similar in both ponds and closely followed air temperature. Surface temperature r,ras generally higher than the average of maximum- minimum air temperature. Surface maxima recorded were 24'5oC on 16 February I9l7 and 24.80ç on 15 March 1978 in pond 1' and 25'5oc on 16 February 1977 and Z5.3oC on 15 March 1978 in pond 2. Surface minima recorded I^7ere 9.0oC on 1 June 1977 and 7.3oC on 9 August 1978 in pond l, and 8.3oC on 15 June 1977 a¡d 8.0oc on 9 August 1978 in pond 2. TemperaÈure rdas recorded during mid-late morning and true surface maxima and minima would lie just outside the recorded range. Depth-tirne isotlrerms for pond I and pond 2 from February 1977 to October 1978 are shor^rn in Figure 2.5. For much of the study period both ponds \^/ere isothermal, or nearly so, and bottom h/ater temperature varied from surface temperature by less than loc. At certain times, both ponds exhibited temporary thermal stratification with temperature differences up to 4.6oC between surface and bottom \^/ater. In pond 1 stratification occured during May, August to September, and October to November ín 1977, and during January to February, Mayrand August to september in 1g78. pond 2 exhibited a similar pattern with additional periods of stratification during February and December in 1977, and June to July in 1978. Stratification in both ponds occurred during all seasons and at temperatures sPanning the annual range ' 1 TemperaËure Profiles Eaken in ponds 1 and 2 during periods of stratification are shown in Figure 2.6. On 15 March L978, Ëhe stratification pattern observed in pond I was typical of a much deeper water body during summer (i^letzel , Lg75; Hut.chinson, I9l5); the width of the thermal strata \^74s, of course, much narro\ÀIer. A thermally Pond 2 oì 1 I I I 15 è0 30 l-r a\ ì I d \ I , \ I É ,-'----s-rz:-7l 10 o 20 _\rr_\ I il - I Ð (ú þ O 5 {-J o 10 OJ U OJ 0 É lr 0 o U .¡J A (l Pond 1 d tl I I 15 a) U 30 òo a. >' /\ ";';, x F 20 ¿\ \ 10 € 0) F{ 10 ,i'-.... )*"-- 5 o .e""..."..,¡'....,....,.i'... (/) U' a ll 0 C J r977 r978 Time (rnonths) FIGI]RE 2 .4 Surface r^raÈer temperature (-¡, dissolved oxygen concentration (----) and mean !üeekly maximum-minimum air Èemperatuïe ('"""") for the Gumeracha Ponds (arrows indicate oxygen readings off the meter scale). Pond 2 0 20 25 t7l 1t 2 l0 8 12 2l l4 1S 20 t2 É 27 l0 4 9 l0 16 t7 14 I 17 lo 15 Ë. oo ZJ t0 1 0) t to !2 m 9 I H t2 l0 BO 18 20 100 Pond 1 0 I 2+ 17 2A t8.5 ll+ 15 I 18 l4 t4 L 16 12 9 l0 0 15 Ê 40 l2 l0 <) 20 L2 t2 l2 16 l6 t8 9 n Éoo s t Ê¡ 18 OJ 8.5 ts Ê 20 BO U+ I 100 J DJ r978 r97 7 Time (nonths) FIGLRE 2.5 Depth-tíme isotherms (oC) in the Gumeracha ponds. nd I rld 2 0 8.4.77 ,, :ts 8.1 t.77 | I A A ú. 10.n ^ 15.3 78 26.b ,rf l.5.3.78 I / I AA 20 ^ L.2.78 I /tA ^ I AAtt A 40 ^ (.) /t AI AA Ð I l Ê A tla c) 60 ^. ê I l / I AA/t A IA A A ^ I I I I I r/ 80 A A I ^ ^ I I I tl l / A A A .rA I ^ I I I 100 a-^- l-r A t5 2 0 25 30 ls z0 25 30 Temperature (oc) FIGIIRE 2.6 Temperature profiles in the Gumeracha ponds. 29. - uniform epilimnion extended to 10 cm, a narro\,I metalimnion from 10-15 cR¡ and the hypolimnion from 15 cm Êo the bottom. A srnall, secondary thermal discont.inuity occurred between 40 and 50 cm. "Diminutive" stratification (after lletzel, 1975) was observed in pond \ on 26 October and B November 1977; a poorly defined epilimnion (to 10 cm) vras not clearly separated from the metalimnion which lacked a steep temperature gradient. A secondary discontinuity layer from 20 to 30 cm was observed in pond 1 on 1 February L978. The epilimnion extended to 60 cm and the metalimnion from 60 to 70 cm. A typical deep-water summer straEification pattern was observed in pond 2 on 15 March 1978 with the epilimnion extending to 20 cm and the metalimnion from 20 Eo 36 cm. "Diminutive" stratification was observed in pond 2 on 26 October and 8 November 1977, and 1 February 1978, and secondary thermal discontinuities in the upper l0 cm of water on 26 October and B November 1977. Diurnal depth-time isotherms from hourly readings in pond 2 on 13 and 14 December 1977, are shown in Figure 2.7. Thermal stratification vtas pronounced from 1300 to 1900 hours. After 2000 hours stratificaÈion broke down and the pond became isothermal by 2400 hours. At 0300 hours slight inverse straLification was exhibited. Dissolved Oxygen. Surface ebsolute dissolved oxygen concentration (mg/f) is shown in Figure 2.4 (arrows indicate readings off the meter scale) and expressed as per cent saturation, calculated from Èhe nomogram of Mortimer in l,letzel (t925, p. 666), in Figure 2.8. Seasonal fluctuation in dissolved oxygen was similar in both ponds during 1978; event.s were dissimilar from January to Novembet 1977 Pond 2 \^ras supersaturated (,tlO7") from February to mid-March 1977, while pond I fluctuaÈed from 68-96"/. saturation. Dissolved oxygen in pond 2 fell sharply to 497. saturation on 27 April 1977, but the extent of saturation steadily increased thereafter and reached 1317" on 10 November 1977. After March 1977, saturation in pond 1 rose briefly to I43% on 0 27, ¿J 23,2 27 a.s 24 22.9 20 24 23,2 23.5 É o 40 25 24 JJ À q) â 60 23 a BO 24,2 100 24 120 0 I 600 2000 2400 0400 0800 Tirne (hours) FIGURE 2.7 Diurnal depth-time isotherms (oC) in ?ond 2, 13.L2.77-L4.L2.77 I iB0 I^ Lt I .l|I l,/ I I /t. , t , 160 I I I .1'-'l I I , ì I I \ I 140 t I , ì I I \ I o I 'rl ì , I ! 120 I , l¡ I có t I t-J I $-r I *J I .- 1 00 -''\ I rd rf- ¡/-4 1 (f) ,\/ I I I c) - I ò0 BO ì/ I I +J lr I H I I 0) I O 60 I $r I ! Êr 40 20 0 J DJ L978 r977 lime (rnonths) FIGI-IRE 2.8 Surface dissolved oxygen concentraËíon in Èhe Gumeracha ponds expressed as percentage saturation (arrows indicate oxygen readings off meter scale). Pond 1 (-), pond 2 (----) 2ï. 12 April, fell to 84% on 27 April, and gradually decreased to 487" on 12 July Ig17. Both ponds \^/ere suPersaturated during late 1977 a¡d early 1978. Dissolved oxygen declined drastically in pond I after 29 Ì{arch 1978 and reached 1.90 mg/l Q97" saturation) on 27 AptíL. In pond 2 dissolved oxygen declined after 27 Lpríl 1978, and reached 2.95 ng/L ß8% saturation) on 10 }fay. Saturation in both ponds increasecl steadily during lhe wirrter of. LglB and exceeded 168% on 10 November. Diurnal obserüaEions durj-ng a phytoplankton bloorn in December lglT , showed thar dissolved oxygen did not fall below 1307" satura¡i-on during the early morning oxygen sag, and exceeded 180% saturation for most of the night. Depth-time oxygen isopleths for ponds 1 and 2 during 1977 and 1978 arc sho\,m in Figure 2.9. Vertical dissolved oxygen distribution was homogeneous in boLh ponds for much of the study. Stratification of dissolved oxygen occurred in both ponds during periods of thermal stratification. Oxygen stratification r^/as most pronounce December , Ig77, and during'February to llarch and October, L978. In pond 2 stratif ication r¡Ias most pronounced during February to March, 1977 ar'd 1978, and during October, 1978. Dissolved oxygen profiles from ponds I and 2 during stratif ication are sho\,rn in Figure 2.I0. Within each pond profiles v,rere similar ot 26 Octoirer and 8 November L977, indicating that oxygen stratification persisted while thermal stratification l¡/as stable. Oxygen profiles were clinograde or: Wcakly positive heterograde on the above dates with rnarkecl hypolimnetic depleÈion. A fairly marked nret.alimnetic maxirnum \ùas observed in pond I on 26 October 1977, although waLer: wa$ supersaturated dornm to 70 cm. Oxygen profiles f roni pon dj-ssolved o>íygen increased wich depth as ternperature decreased. 0 9 20 1t 15 l0 l4 l0 l+ 15 12 t4 I 6 u 6 I 1l 6 t0 15 ^40É 9 o 9 ( l5 9 I2 60 5 ,d l3 l3 J.J lL3 È 15 aBoa.J t1 0 100 0 5.5 l3 20 15 9 r5 J 6 9 2 Iro l4 Ê 10 5 6 CJ I 7 12 13 4 -c 60 7 t lJ èq) êBo l+ 55 t+ r00 J DJ r978 L97 7 Time (rnonths) FTGIJRE 2.9 Depth-time oxygen isopleÈhs (mg/0) Ín the Gumeracha ponds. Pond I Pond 2 0 ^ ^ I .1 LN 26.L0.77 I8.11.77 1.2 :75 I \ \ \ A I A A r I \ A 20 A I ^ \ I \\ A A A ^ I \ I lt A 40 AA A ^ tr (.) \ I I A ^ ^ Ð I \ \ È A 3.78 AJ Att {ß ê 60 ^ ^ I \ \ I AAtt ^ I t,, 0 80 A L 7.2. 78 ^ I A I5.3. æ 100 5 10 15 0 5 ^ 10 15 0 Dissolved oxygen concentration (rng/l) Gumeracha ponds' FIGURE 2.10 Dlssolved oxygen concentration profíles Ín the 22. Profiles from pond 2 on 1 February and 15 l"larch 1978, ranged from weak to strong clinograde. Diurnal dissolved oxygen isopleths from hourly readings in pond 2 on 13 and 14 December 1977 , are shovrn in Figure 2.ll ' Dissolved oxygen v¡as inversely stratified from 1000 to 1600 hours. Readings were off the scale frorn 1800 hours until 0100 hours; at 0l0O hours dissolved oxygen r^/as homogeneous (15 mg/1). Slight stratification occurred from 0300 hours. Temperature, dissolved oxygen and per cent saturation profiles beneath floating atgal mats in ponds I and 2 on 19 July 1978, are compared with open I¡¡ater profiles in Figure 2.12. Algal mats consisting of an uPPer, dense layer of StigeocJonium sp. (10 cm thick) and a lor.rer layer of thin trailing filaments of ULothtix sp. encl-osures used in a fish introduction experiment (20 c¡n long), formed on the floating mesh covers of/{see chapter 5) ' Thermal stra¡ification rrras pronounced beneath algal mats and surface qtater \^ras up to 1 . 9oC wtt*.r than oPen water. VJater 10 to 20 cur beneath the maÈs was cooler than open !üater due to absorption of heat by the StigeocTonium. Porrd 2 exhibited a r^rell defined epilimnion (to 5 cm) and meLalimni_on Ctol5 ctrt) helolÀr the mat. In po dissolved oxygen concentration and per cent saturation decreased gradually with depth beneath the mat exceeding oPen l^¡ater values above 25 cm. In pond 2 the oxygen profile beneath the mat was clinograde; surface ü¡ater !,¡as supersaturated dorrm to 5 cm and dissolved oxygen concent.ration exceeded open \Iater by B mg/1. Saturation declined to 68|z at 10 cm beneath the mat in pond 2 and below this depth oxygen concentration was less than in open \^/ater. Oxygen depletion below 25 cm in pond 1 and 10 cm in pond 2 probably resulted from respiration of ULotl-trjx under low light conditions. Af ter 19 July 1978, enclosure covers were raised above the water surface and the algae died off 15 0 u.5 l1 11.5 1l+ 20 ) 15 14.5 t2 13 t4 ^40E 14.5 o 13.75 TJ o. 60 q) â BO I 100 0800 1 200 1 600 2000 2400 0400 Time (hours) FIGURE 2.11 Diurnal depth-tine oxygen isopleths (mg/l) Ín pond 2, 13'L2'77-I4'L2'77 Díssolved ocygen concentratlon (ng/Î,) 0 4 812048L2L6 0 A I ^ I Pond I Pond 2 I t I l ^ I A A I open under open t - I Í ma I water mat \"7ater tlt t A A I 1t I , I OPen IÀ7at,er I open water I I mat I l¡ I open I ll under I lwater under I I 4 ,¡ mat I I mat È1 l¡ I I o I I AA AA!t A A I .tJ lt ^I È I I q) l¡ I I â 6 l¡ l¡ t I ,t I i¡ I jr I rl I 8 ¡ jr I ll I I fr I I lr I , ,l I I 100 A rllllJ 5 0 15 5 10 15 0 40 80 L20 r60 Temperature (oC) Pereentage saturation Pond I (+ Pond 2 (-- --) FIGI]RE 2. 12 I^Iater temperature and dissolved oxygen (concentration and percentage saturation) profiles in open \rater and under floating algaL maËs in the Gumeracha ponds on 19 -7.78. 23 pH and Total Dissolved Solids. Seasonal fluctuaÈions in pH and TDS (mg/l) of pond l influent, effluent, and pond 2 effluent are shov¡n in' Figure 2.I3. Pond 1 influent pH fluctuated erratically between 6 and 7.5 throughout the study. Pond l. effluent and pond 2 effluent pH increased during the summer months (December to lufay) . Pond I ef f luent pH fluctuated between 7 and lO.5 and pond 2 effluent pH between 7 and IL.2. pll increases of pond 2 effluent were similar during the summer of. 1977 and 1978 while the increase of pond 1 effluent pH during the sunìmer of 1978 was 1.5 units higher than during L977. pH increased progressively through ponds I and 2. Pond 2 effluent pl{ exceeded pond 1 effluent pH by a maximum of 3.4 units during the summer of. L977 but by only a maximum of 2.1 units during the summer of 1978. pond I effluent and pond 2 effluent TDS were similar and both generally less than pond 1 influent except during March to May, L978. Pond 1 influent TDS increased markedly from l{ovember 1977. Pond I effluent and pond 2 effluent TDS increased accordingly during the summer of 1978; the increase during the suumer oÍ. 1977 was slight. Biochemical Oxyg en Demand. Seasonal fluctuations in BOD (rng/1) of pond 1 influent, effluent, and pond 2 effluent are shown in Figure 2.I4' pond 1 influen¡ BOD flucÈuaEed rvidely but was generally between 10 and 24 $g/L. Pond 1 effluent BOD was less than influent BOD during L977 (Z ro 5 ng/I) ¡ut increased during January 1978 (6 to 2I ne/l) and exceeded influent BOD on some occasions. Pond 2 effluent total BOD exceeded pond I effluent and influent from January to March ' 1977 ' vtas similar to pond I effluent from April to November of that year, dnd increased from November 1977 to Apri1, 1978, exceeding pond I effluent and influent on some occasions. Pond 2 effluent filtered BOD was equivalent to 20 Eo 3O'/" total BOD from January to March,Lg-l 7,and 1978, and to 60 to 100% rotal BOD from May to october , 1977. Pond 2 effluent filtere 10 \ .....- ,r."....' ËB * - --- -22¿ 6 0 I 20 0 èl ¿ Òo .-<.: E 800 -... - -'----4.------.-. tJ) ¿'ì â 600 ì.,--.*-¡.-*.l t{ ...; ..... 400 J D J r977 r978 Tíme (nonths) FIc'rlRE 2.13 pH and TDS in pond I influent (-), pond I effluent (----), and pond 2 effluent (..-..-'). 32 â24 Ò0 É t' t16 \j t Êrt I \ \ B (i "l-v' '-''.l.rì.-l:1?\t \- -l-l-t_r_ 0 J DJ L977 Tiue (¡oonths) t97B 300 t rì fr , HO I ^I I I g H2oo t ili oa) I ,l I I Êtr I t oo I ,l r ¡ ¡{ÉH I ,t I I 0) I I òo ,r I (ü I ¡ ,l I too I ¡ I ,tll Ëc) I o l ,1; t¡ I I tìr q G) Ê{ , I tI I\ I ' rr j \ 0 'r,,\-r, ^\- 1\ q) Ø (Ú q) \ ¡-{ r-A o \r 't -lì- q) Ê I 00 J DJ r97 7 I97 B Tiue (rnonths) FIGIIRE 2. 14 BOD in pond I influent (-) , pond I ef fluent (---) , and pond 2 effluent (tota1 ,"""i filteredr-t-l-), and mean monthly percentage removal of BOD in pond I (-), pond 2 (---), and the Gumeracha pond system over:all (total ,"""'i f iltered ,-t -tl . 24 v¡inter of. Ig77 (April to october). The eff iciency of a I,tsP in stabilizing organic matter is measured by the per cent reduction in wastewater characteristics as (increase) vrasteq¡ater passes through the pond' A negative reducÈion results if effluent values exceed influenÈ values. A reduction of and less than 30% will be considered "lo\nr", greater t|¿n 707" "high" between these limits "medium". MeanmonthlypercentreducËionsofBoDbypondsland2a¡d the pond systern overall are compared ín Figure 2'L4' Pond I reduced BoD by 60% until April , 1977, and by 80 to 90% from lfay to November, Ig77. Pond 1 effected only 2l% removal in late December, Ig77, and no removal in April , 1978. Pond 2 reduced BoD by less than 1977 arld 50% from April t.o November, 1977, and removal overall was due to the pejorative effecÈs of pond 2 ín L977 ' during and borh ponds in 1978. That is, pond 1 effected high removal 1978' Lg77 (summer and winter) brt removal was low during the sunrner of pond 2 increased BoD during the sunmers of L977 and 1978 and although removal improved during the winEer of 1977 ít ütas still low. (mg/l) pond I Sus Solids. Seasonal fluctuations in SS of 2.L5 influent, effluent, and pond 2 effluent are shown in Figure ' shown in ancl mean mont.hly Per cent recluction of SS by the ponds are (up Figure 2.L5. Pond I influent ss fluctuated randomly to 48 mg/l) during the study. Pond 1 effluent ss was less than influent during 1977 but increased in January 1978 and exceeded influent during March pond 1 and April (up ro 105 mg/l). Pond 2 effluent sS exceeded influent and effluent from January Ëo April , Ig7 7, was similar to pond pond 1 I effluenE SS from May Ëo October, 1977, and again exceeded I rì 100 l1 .'i lr .l BO r. ti. I oì I '..t f 'l Èo oo lL. t r ., fr 3 tro tì ll 20 \ -.J - --r 0 J r977 D J L97B Tine (rnonths) tlA t .l I I 600 I I I I -l(ú I >0)oo I Êd I CJ OJ 4 00 t{ lr I oÉ I ò0H I (Ú th Ð lr t"'1 q) ,, o t i ! 200 ¡l G) .,tl È it, .. I :l'. t-- o o i '.J d 0 OJ l't O a) 1 â J L977 D J r978 Tirue (months) (--- -), and pond 2 effluenË ("*"), and mean nonthly FIGURE 2.15 SS in pond I influent (-), pond I effluenÈ (""") p"r"".ttngs ¡srneval of SS in pond 1 (-), pond 2 (---), ånd the Gumeracha pond system overall- 25 influent SS from December, 1977, to April, 1978 (up to 88 me/l). Pond I effluent and pond 2 effluent SS both declined drarnatically after March-April, 1978. Pond 1 reduced SS by 90% from April Lo October, 1977 . Removal decreased steadily from December, 1977, and during March, 1978, pond I increased SS by 288"Å. Pond 2 increased SS by up to 800% from January to April , 1977, and effected no reduction of SS throughout Èhe remainder of that year. Pond 2 increased SS up to 3002 from NÒvember, L977 to March,1978. The pond system overall reduced SS by 70 to 9O% f.rom April Èo November, 1977. During the summer of. 1977 and 1978 SS rvas increased over 3007" by the system overall. 0vera11 increases were due Eo pond 2 during 1977 and both ponds during 1978. That is, pond 1 effected medium to high SS removal during 1977 (sunrner and winter) but increased SS during the summer of 1978. Pond 2 increased SS throughout the study, summer and winter. Total Carbon and Total Organic Carbon. Seasonal fluctuations in TC (*e/f) and TOC (mg/l) of pond I influenÈ, effluent, and pond 2 effluent are shown in Figure 2.16 - From January to March , 1977, pond I effluent TC was less than pond 2 effluenE TC and both exceeded pond I influent TC. Pond I effluent TC and pond 2 effluent TC were similar from April to December, 1977, and both r¡/ere less than pond I influent TC. Pond 1 influent TOC was generally between 20 and 40 ng/ 1 and pond 1 effluent TOC (13-22 mg/l) was less than influent throughout 1977. Pond I effluent TOC increased in January, 1978, and exceeded influent during March and April. Pond 2 effluent TOC exceeded pond. 1 influent and pond 1 effluent from January to March, L977 and 1978 and !,/as similar to pond 1 eff luent TOC from June to November, 1977. Mean monthly per: cent reduction of TC and TOC in ponds 1 and 2 are shown in Figure 2.I7 . Pond 1 increased TC up to 29% from January to }{arch, 1977, and by 2% duríng February, 1978. From Total organic carbon (ng/L) Tota1 carbon (nel[-) N)so\ N) N o\ o ooo o o O o rd H 6) C{ I d I F I I NJ I t ts ì Ol ) I I a¡å I lo t:i. ( l.t I lo, I I I I EÊ,o t OH t. 9ct F t O.O \o\¡ H I Ê!u. !o I i o5 H I Hlo, o ! HI t. I tsrl 5 Éo I ol-1 o ÞA, Þ I rTH rt i Ø 'j i 1" , ',,,, vûqlH uÞ) 5 I OJÞo P. it o. ir ':t o il -o g, :l o F.t ". ..t o.oÞd 5 t t.) :....r" H. U I oÉ t\L Ht Fd I H' t: tso q t: ÉÉ ..., ì'. oÈ t r+H I t I ¿r H' I i r-¡ F :lJ 9Ë \o{ .o 00 ¿ Ê Total organic carbon Total carbon percentage renoval percentage removal H 6) Decrease Increase Decrease Increase d æÞ sæ N) À. 1!tss ol\ w OO o oo o OOOOO o 14 l\) F ! q o< I Éo t Éo0t oFtÞ .::.''. Hæ oÞoÞ0iEl t ....:- --' :]. H.Þ ----3'' ÐOrt 1..' ¡dorJ ...'i, o Êr< ' rl lJH o- cr€ ts rl ,t oo H\o I ØþF1 H. \j lt qo Ë! Ø P.O o lr 11 ÞÞ lr ll lr Orr !l ÊJ l> EIEooa ; oÞo H -' <È rt oFl d Ho a I ÞEl I t-l April to November, 1977, pond I reduced TC by 20 to 407.. Pond 2 increased TC 20 to 30% from January to March, 1977 and 1978, and only effected rernoval during September and October, 1977. The system overall reduced TC by 5O% at best, and increased TC uP to 577" f.tom January to March, L977 and 1978. Both ponds contributed to sunrner increases in TC. Pond 1 reduced TOC 30 to 65% throughour 1977. Removal decreased steadily frorn January, 1978, and TQC increased 29% during March. Pond 2 increased TOC up to 113% from January to March, 1977 arrd 1978, and July to August, 1977. Rernoval was less than 40% from April to November, L977. The system overall reduced TOC up to 7I7" f.rom May to December, 1977, and increased TOC up to 602 from January to April , L97 7 and 1978. Overall summer increases were due to pond 2 in 1977 and, both ponds in 1978. That is, pond 1 effected medium to high removal during 1977 (summer and winter) but increased TOC during the summer of 1978. Pond 2 increased TOC during the sunrners of. 1977 and 1978; removal increased during the winter of 1977 buL rvas still low Mean annual per cent reduction in BOD, SS, TC, and TOC during L977 by ponds L and 2, and the pond system overall are compared in Tabl-e 2.3. Pond l effected high BOD and SS removal, medium TOC removal, and low TC removal. ' Pond 2 actually increased all parameters during 1977 , mosÈ notably SS. Overall BOD removal was medium but removal for other parameters \¡/as 1ol¡r; SS was increased overall. Low overall removal during L977 was Èhus due to the pejorative influence of pond 2 although pond 1 also contributed to decreased performance in 1978. That is, pond 1 performed efficiently during 1977 while pond 2 was inefficient, particularly during the summer. The efficiency of pond l decreased during the summer of 1978 and performance \^/as similar Èo pond 2. Total Inorganic Carbon Seasonal fluctuations in TIC (C02 + HCo3 '+ CO3=) (rng/1) of pond I influent, effluent, and pon Mean annual percentage ¡eduction of organic.parameters in the Gumeracha þonds during 1977. Pond I Pond 2 BOD 77.r '-40.1 70.0 - Filtered SS 82.I -27L.5 TC 21.7 -1 .3 TOC 46.4 -7 .9 27. sho\^rn in Figure 2.I8. Pond 1 effluent TIC exceeded inf luent throughout the study, excepÈ during ltfarch, L978. Pond 2 eff luent TIC was much lower than pond 1 effluent from January to February, 1977. During February and March, 1978, pond I effluent and pond 2 effluenL TIC were similar; in late May, 1978, pond 1 effluent and pond 2 effluent TIC were both very low (2 ng/L) and less than pond 1 influent TIC. 4g*""1g. Seasonal fluctuations in NH, (rng/f) of pond 1 influent, effluent, and pond 2 eff]uent are shovm in Figure 2.I9, and mean monthly per cent reduction by ponds 1 and 2 are shown in Figure 2.I9 ' Pond 1 influent NH, varied considerably (0.8 to 9.8 me/l). Pond 1 effluent NH3 (O.t to 1.2 mg/I) was much less than influent and pond NH3 (O.f to 3.9 was similar to pond I effluent excePt 2 effluenr ^e/1) during May, L977 and January, 1978. Pond 1 reduced NH, by 407" from January to March, L977, and by 80 to 907" f1om April until December, 1977. Removal decreased slightly during January , 1978. NH3 removal by pond 2 varied dramatically. Pond 2 reduced Ntl, by 787. duríng October, 1977, but increased NH3 250 to 300% from April to June, 1977, and during January, 1978. The system overall reduced NH, by 70 to 90% during L977 and 40"/" during January, L978. Overall removal decreased when pond 2 increased NHr. Total Kj eldahl and 0rg anic Nitrosen. Seasonal fluctuations in TKN (rne/l) and org-N (ne/L) of pond I inf luent, ef fluent, and pond 2 ef f luent are shor^rn in Figure 2.20. Pond 1 effluent TKN (1.94 to 14.10 mg/l) r^/as less than influenE TKN (1.98 to 61.50 me/l) throughout 1977 but increased markedly during February, 1978 and exceeded influent. Pond 2 effluent TKN was similar Ëo pond 1 effluent TKN during 1977, excePt on June 15th, and also increased during February, 1978 when it exceeded pond 1 inf luent TKÀ]. Org-N fol1o¡¿ect a simj. 1ar pattern to TKN, dif ferences resulting J I , I t êì t ò0 I I É I /r , /1 I o ¡\ , 20 ¿-' \ ,.olr / , (Ú I \ , O I r;... , o I t,' I , .rl ì- I , É I d :\ I ô0 I .t I lr I o I ,..\ t \ I .rl I I 0 I ..\ rl T I d \t- TJ I I o I 1 I H I I , 't , I , 0 J D J L97 7 Tine (nonths) L978 FIGIJRE 2. 18 Total inorganic carbon 1n pond I ínfluenÈ (-) , pond 1 eff luent (---) , and pond 2 ef fluent C-....) . Þl I 0 o0 É I Ë o ò0 o 6 ¡r +J 'r{ É 4 å rl çi o É 2 H '---<ì -..í.- 0 D J J r977 197 8 Time (months) 3 ì I I 1 I ll o ì Ë \ ri Þ Hzo l¡ o q) ì l¡ ¡{ 6 o I l¡ t{ Ê I H ¡ Ir a, t ft Ò0 (Ú I I ¡J I I É I I I 0, \ o I I tr .\ o \ I t Þr I I \ I \ I I I I 0 ì_ q) \ I I U' t \l I I (d I I \ ¡ kc) I t o v ol Ê 100 J DJ t97 7 r97 8 Tirne (nonths) FIGURE 2.19 () 60 ,l Þì I. ò0 ,r d ,l ,r,r É 40 Ir a) I ò0 o }] \ .¡IJ I 1 Fl 20 (d t "o ti -tq) :\ .rl ..\ ì v 'ìi'j.j I i¡.J zf"' 0 60 oì ¡ ò0 ,\ Ë \ 40 I I I OJ \ , I t ¡¡ \ .¡+J d 20 .¡U È (ú I t\-/\- ì òo /\/\ ,! oH t -- "ì 0 J DJ L978 r977 Time (rnonths) pond (-) I effluent (----), FIGURE 2.20 Total Kjeldahl nitrogen and organJ-c nÍtrogen in 1 lnfluent ' Pond and pond 2 eff luent ("."') . 28. from fluctuations in NH, concentrarion. Pond 2 effluent org-N was, however, consiclerably lorver than pond I effluent org-N from May to July, 1977. Mean monthly per cent reducËion of TKN and org-N by pond 1 and pond 2 are shov¡n in Figure 2.2L. Removal of TKN by pond l was less than 507" ftom January Ëo March, I9J7, and 75 Lo 857" from June to November, 1977. Pond 1 increased TKN over 100% during February and March, L978. TKN removal by pond 2 was low throughout the study except in October, 1977 03%). Pond 2 increased TKN during most of 1977. The sysËem overall increased TKN in April,1977, and during Februa::y and March, 1978. 0vera11 removal exceeded 707" only from AugusE to October, 1977. Low overall TKN removal \¡/as due mainly to pond 2 during 1977, and mainly to pond 1 during 1978. That is, removal by pond 1 was low during the summer of. L977 and high during winter; pond 1 increased TKN during the summer of 1978. Pond 2 generally increased TKN except during Èhe summer of 1978. Pond I reduced org-N by 77 to BB7" from June to October, 1977, but increased org-N during April Q607") and December, 1977, and February, 1978. Pond 2 reduced org-N over 707" in June and October, 1977, but increased org-N durÍng March, September, November, and December, 1977, and January, L978. The system overall reduced org-N by 65 to 981l from June Èo October,1977, but increased org-N over 2007. in April and December , 1977. Pond 1 and pond 2 both contributed to 1ow overall org-N removal duríng L977 and 1978. Nitrate. Seasonal fluctuations in NO, concentration (mg/l) pbnd I influent, effluent, and pond 2 effluent are shown in Figure 2.22, and mean rnonthly per cent removal by ponds I and 2 are shown in Figure 2.22. The relative concentrations of N0, and NH, in pond 1 influent indicated that nitrification reactions in the triclcling filter had proceeded to a considerable extent. Pond 1 influent NO3 Organic niÈrogen Kjeldahl nitrogen percentage removal percentage rsnoval '-) H Decrease Increase Decrease Increase H ts N l..J r o\ O o F o o o O O o o o trl O O O o O N) N) H L{ \ o ts.o É11Þ Ê, I Þ I øoq É ÊJ 60 oì ô0 40 I 0) òo I o \ t{ I .-l'LJ /-----' I iv I I \ q) Ð \ d 20 i tl ¡J I 'r{z 0 r977 DJ Time (months) I978 20 Fl cd I I I õor I !Ø 4 d I òoc) 0J \r do lr Ðq)Éâ 60 I a.) I ! \ I 0.) \/ O{ \/ B I J D J T978 Time (nonths) FIGURE 2.22 Nitrate-nitrogen ií pond 1 ínfluent (-), pond I effluent (---), and pond 2 effluent (...... ) , and mean monthry percentage removal of nítrate-nitrogen in pond 1 (-), pond 2 (---), and the Gumeracha pond system overall (...... ,). 29. varied from 19.5 to 64.6 ng/I. Pond 1 effluent NO, wa.s consistently lower than pond 1 influent and pond 2 effluent NO, consistently lower than pond I effluent. Pond 1 effluent and pond 2 effluent NO, minima occurred from January to April during 1977 (pond I effluent, 9.5 to 13.1 mg/l; pond 2 effluent,3.5 to 9.6 ne/l) and 1978 (Pond 1 effluent, 13.4 to 22.5 ng/I; pond 2 eff luent, 4.5 to 8.9 mg/l). Both ponds reduced NO, throughout the study period. Removal by pond 1 was highesÈ from February to March, 1977 (maximum 63%) arrd from January to February, 1978 (maxímun 68%). Removal was poor (4 to 537") from May Eo December, 1977. NO, removal by pond 2 was highest during February , Ig77 (maximum 60%) arrd 1978 (maximum 80%). Removal by pond 2 from April to November, 1977, was low and less than pond l. Overall NO^ removal was 80 to 90% during February and March, 1977, and January and February , 1978, but decreased from April to December, Lg77. That is, removal by pond 1 was medium during 1977 (except NoVember and December) and summer, 1978. Removal by pond 2 was medium during suûtrner, 1977, low during winter, and high during summer' 1978. Orth hos ate. Seasonal fluctuations in total (unfiltered) and soluble (filtered) fOO-e of pond 1 influent, effluent, and pond 2 effluent are shown in Figure 2.23. Pond I effluent total PO4-P exceeded influent from January to March, L977, decreased during March and April, and was less than influent until November. Pond I effluent total PO4-P exceeded influent briefly during November, 1977, and thereafter fe1l dramatically being less than influent (by a maximum of 8.47 rne/L) from December, 1977 urrtil ÙIarch,-I978, Pond 2 effluent Èotal po4-p was less than pond 1 influent and effluent from January to March , Lg77, but exceeded pond I effluent from April to July. From August, t977, pond 2 effluent total PO4-P decreased steadily and was considerably 1or.¡er than pond I effluent. Poncl 2 effluent total PO4-P 5 t ^1oì \ t,. ò0 d t;' t, OJ \ t' Ër 0 \ I \ \ I o. \ tt \ i o \ I :t È \ a :l o / \ ,7 Ð 5 \ t{ .'l \/ o \r r{ \/ d .u o H 0 15 I I, ol I I t; , ö0é I t' I a I ì r a) 10 , u I I d I I , t I È ì Ø t o I :t I À :t o I tt t Ð Ir 5 I .zr i o t¿l I t: q) / ,')""'; \ Fl \ ,.o ..\ .. l, Fl .t o an 0 1977 Tíme (months) D J Ig78 FTGURB 2.23 Total (unfiltered) and soluble (f iltrable) orthophosphate-phosPhorus ln pond I influen¡ (-) , effluent ( ---), and pond 2 ef fluent C""'). 30 remained lower than pond 1 effluent until March, 1978; Èhereafter pond 2 effluent total PO4-P increased and vtas similar to pond 1 effluent total PO4-P. Soluble PO4-P varied in a similar manner, aPart from minor variations; of course, concentrations \"Iere less than total PO4-P. Seasonal fluctuations in soluble PO4-P expressed as a Percentage of Eotal PO4-P for pond I influent, effluent, and pond 2 effluent are shorn¡n in Figure 2.24. Soluble POO-P was less than 407" ot total PO4-P in pond 1 influent and effluenE during January and February, Ig77, bur conrributed 80 to 95% or. total PO4-P from April Eo November, Ig77. Per cent soluble PO4-P in pond 1 effluent declined during December, Ig77 and fluctuated between 65 and 752 until February, 1978. Soluble pOO-p was less than 307. of. total PO4-P in pond 2 effluent until March , Ig77, contributed 75 Lo 90% of total PO4-P from April until November, and declined markedly from December, I977, until February, I1TB (147). percentage soluble PO4-P in pond 2 effluent increased Eo 95z by April, 1978. ParticulaËe PO4-P thus increased during the surmer months (January to March). Mean monthly percentage reductions of total and soluble PO4-P by pond I and pond 2 are show4 in Figure 2.25. Pond 1 increased total po4-p by 507" from January to March , lg77; removal increased thereafter, reaching 3I7" ín June, buÈ declined during the second half of 1977. Removal increased from December, 1977, and reached 7O% ín March, l97B' Pond 2 reduced total PO4-P by tP to 75"/" from January t.o l'Íarch , 1977, but removal declined thereafter and pond 2 increased total PO4-P by 1"37" during June, Lg77. Removal increased from September, 1977, and teadned 757. during November , I|TJ , and 787" during March , 1978. Removal declined after March ancl was only 87" during May, 1978. The pond system overall reduced total PO4-P by 65 to 897" from Janua'ry to Marctr, I97 7 and 1978, but by only 23-477" ftom April to September, 1911 ' 100 I \ I I \ I 80 I \ I \ I \ \, I \,/ \/ I \l o60 I ò0 cl ¡J c) l. O l. þ Þ40OJ I 20 0 J DJ r978 1977 Time (months) FIGIIRE 2.24 Soluble orthophosphate-phosphorus (expressed as a percentage of total orthophosphate) , in pond 1 influent (-), pond I ef fluent (---), and pond 2 ef fluent ("""). Soluble orthophosphate Total otthophosphate percentage removal percenÈage removal Decrease Increase P Decrease Increase H P t\)5 o\ O oo o\ N) t\)Þ o\ !J O Oo OrFN) O o o oo O d O O OOOO oo O o o o 14 l.J N) Ltr I Êro3 I ldrD I ÈñÊj ño -r:.. +H g -_Þ -. \\ o :l'o " ì.ì - \ 6)tr) rt I o5-i! Þ< ñ r-t È oE r> ooFl I t' :'.Ú B H. It 0r f o ã rJUJÞoo o t, r-t HOE +ôr É o,oga o Bo A chÉ, r-1 <(,l)HØou) i' rtp.B v o50 B< 2 'ú Ê) OOF.J <5o.o oHHì ÞF H11 .r:::_ lJaO ,*lo¡lrt :lH :v \iJ Ê .'do- \o{ Þoo-o H l-J É d aH l¡p I \,I 31, Removal of soluble POO-P followed a similar seasonal cycle to toÈal PO4-P. Pond 1 increased soluble POO-P during the sunnner of 1977; soluble PO4-P removal increased to 337" during the winÈer of 1977 and again to 66% during the su¡mner of 1978. Pond 2 reduced soluble PO4-P by 80 Eo 907 during the sununers of 1977 and 1978 but removal hras 1o$/ during Ëhe winter of. 1977. Pond 2 increased soluble PO4-P by 177" during June, 1977. The system overall reduced soluble PO4-P by 85 to 959l during the summers of 1977 and 1978, but by only 23 to 51% during the winter of 1977. Pond I increased total and soluble POO-P during summer, L977 , while removal by pond 2 was high. Removal by pond I increased (Iow to medium) during r^¡inter, 1977, but pond 2 increased total and soluble PO4-P during that period. by both ponds was medium to high -Removal during suflìrner , 1978. Mean annual percentage reductions of nitrogen and phosphorus compounds by ponds 1 and 2, and the pond system overall during I9l7 are shown in Table 2.4. Pond 2 removed a higher percentage of influent phosphorus than pond 1. Pond 1 removed a higher percentage of influent nitrogen than pond 2 and the latter increased NH' TKN, and org-N. Org-N removal by pond I was low. The system overall reduced total PO4-P, TKN, and NO, by over 5O%, and reduced NH, by over 80%. The system overall increased org-N by 297". Pond 1 reduced overall phosphorus removal, and pond 2 caused a deterioration in effluent quality, reducing nitrogen removal. PO4-P and NO, removal was highest during the sunrner months while NH3, TKN, and org-N removál was highest in winter. Nitrogen and Phosphorus Retention. Annual_ nitrogen and phosþttorus retention in pond 1 and pond 2 for L977 (ta¡1e 2.5) were calculated from the difference betr^¡een influent and effluent concentrations and daily flow rate. Annual retention of total POO-P was simiiar for TabLe 2.4 Mean annual percentage nitrogen and phosphorus- removal in the Gumeracha Ponds during L977, Pond 1 Pond 2 Overall Soluble POO-P 13.6 40.4 56.1 Total PO4-P 13 .5 38 .8 52.0 NO3-N 35.9 28.r 54.r NH3-N 82 .8 -16.5 86. I TKN 60.1 -35. I 52.O Organic-N 7.3 -11 .3 -29.r Table 2.5 Annual nutrient reEention in the Grrneracha ponds during L977. Pond I Pond 2 N03-N TKN ToÈa1 NO _N TKN Total 3 PO. -P PO, -P 4 4 Mean Daily 134.006 965.4L2 1432 .000 t43.359 422.7 02 -295.920 Loading (s/day) Annual Loading 48.9L2 352.375 522.728 52.326 r54.286 -I08.011 (re /vr ) AnnuaI Areal 33.967 244.7 05 363 .005 42.029 I23.925 -86.756 Loading Gl^'/yr) 32. pond 1 and pond 2. Removal by pond I was lor¿er than by pond 2 and similar retention resulted from higher influent concentrations Èo pond 1. pond 2 had higher areal retention due to its smaller surface area. Annual areal NO, retention in pond 1 was I.97 times thaÈ in pond 2 . . ponds rnras similar and the higher retention in pond NO^5' removal by both 1 reflected higher influenÈ concentrations. Pond 2 lnad a negative TKN retention; TKN increased on passage through pond 2. Pond 2 had a net as NO, \^ras numerically greater than TKN but posiÈive nitrogen retention J this pond, in effect, exported org-N. This contrasted \ntith pond 1 where org-N contribuËed the major nitrogen load. Phosphorus Retentiorr Coefficients Models for the determination of lake trophic status and critical phosphorus loading (u.g. Dil1on, I975; Dillon and Rigler, 1975, L974; Kirchner and Dillon, 1975:' Vollenweider, Lg75) provide equations for the calculation of a phosphorus retention coefficienE, R. These models regard phosphorus changes over time as the result of supply added per unit volume minus losses through sedimentation (retention) and outflow. R is thus a measure of annual phosphorus removal. If phosphorus removal in !ISPs is qualitatively the same process as in natural rvater bodies, R should be equivalent to mean annual per cent reduction. 'strictly speaking, R values refer to the retention of total phosphorus (organic and inorganic). However, most organic phosphorus compounds and polyphosphates are converted into soluble orthphosphate during the passage of wastewater through trickling filters (Nesbitt , 1973) . In maturation ponds, R will refer to the retention of total (soluble plus particulate) inorganic orthopho'sphate. R values for pond I and pond 2 are compared rsith mean PO4-P in Table 2.6. R2 annual per cent removal of toEal "ott""ponded well with per cent total PO4-P removal in pond 2 atð the system overall. R2 o.*r"t""timated removal by pond 1. R3.ott""ponded well witl-r per cent removal of total PO4-P by pond 1 buE considerably underestimated Table 2.6 Phosphorus retention coef ficients, R, for the Gumeracha þonds during 1977. 2 2 3 L (e'lm lyt )1 R R p (yt-r )4 Mean % Removal Total PO4-P Pond I 33.967 o.46 0.20 20.9 T4 Pond 2 42.029 0 .45 0. 17 24.0 39 overall 75.996 0.51 0.31 tt.2 52 (Pond 1 + Pond 2) 1 4t."1 retention of total Po4-P. 2 C"l",rlated using the model of Kirchner and Dillon (1975) 3 c"l",rlaÈed using the model of Vollenweider (rgZS). 4 Flushing rate (nr¡arber of times volume replaced per year). 33. removal by pond 2 and the system overall. Strnmarl. I,Ihile pond I and pond 2 functioned quite differently during 1977, performance \^/as similar during the sunrner of 1978. Pond t reduced BOD, SS, TOC, and NO, during sunmer' 1977, but increased TC, org-N, and PO4-P. During the same period, pond 2 reduced NO, and PO4-P buÈ increased BOD, SS, TOC, and org-N. VJhile pond I effecEed medium to high removal of BOD, SS, TC, TOC, and org-N during the winter of 1977, removal of al 1 parameters \^/as low in pond 2. During surtrner, 1978, both ponds reduced NO, and PO4-P b¡t increased BOD, SS, TOC, and org-N (as pond 2 had done during surtrner , L977). 2.2.3 Discussion Although it is ofÈen assumed thaE small , shallow \nlater bodies do not stratify (u.g.George, 1961), small are generally well-nixed "nà ponds may exhibit extreme Ëemperature stratification (Ruttner, 1963). The propensity of a small water body to stratify will depend upon many factors including morphometry, turbidity, and wind exposure. Stable stratification has been observed in wind-sheltered ponds 3-4 m deep (Happey, 1970; Moss, 1969; t'telch, 1968; Airl , 1966) but not in wind- exposed ponds of similar depth (Macan and Maudsley, 1966). Both ponds at Gumeracha were thermally stratified aË a variety of air temperatures during this study. This suggested that stratification arose in response to a peculiar set of climatic conditions. Solar radiation may be inportant in determirring \,¡ater temPerature even when air temperature is low (Macan and Maudsley, 1966) and it is, likely that stratification in the wind-exposed ponds at Gumeracha during winËer arose as a result of calm, cloudless days (high solar radiation). Stratification in shallow, turbid pools can arise as a result of lighE absorption by suspended material (Eriksson, 1966). Although stratification occurred in the Gumeracha ponds when the 3!+ standing crop of phytoplankton,'and therefore biogenic Ëurbidity, was high (the euphotic zone in hISPs during algal blooms may vary between 10 and 70 cm in depth (Bartsch and Allum, 1957; Towne et a,l-. 1957)), ponds were also stratified when light penetration was high (bottom visible). Thermal stratification was pronounced beneath floating algal mats. t'Diminutiverr stratification, exhibiLed in both ponds, is cofltrnon in shallow lakes or shallow, protected areas of large lakes (Vùetzel , 1975). This type of profile arises when water depÈh is insufficient to maintain a typical epi- and hypolimnion or when inflow causes turbulence (I\retzel , I975). The Gumeracha ponds have retention times of 15 to 17 days and influent volume is therefore large relative to epilimnetic volume. Turbulence may be responsible for the occurrence of "diminutive" profiles at Gr¡neracha. Thermal discontinuities, exhibited in both ponds, occur in larger rntater bodies when high temperatures alternate with periods of inÈensive mixing (I^fetzel , L975). This results in the formation of an epilimnetic thermocline, and if the epilimnion is thin the meEalímnion curve extends to the surface (Hutchinson, 1957). Such an effect may have been observed in pond 1 on -15 March, 1978, afËer a'period of isothermy in late February. The true metalimnion may have been between 40 and 50 cm, the discontinuity at 10 cm representing epilimnetic stratification at high air Èemperatures. Frorn Figure 2.6, stratif ication in the Gt¡rneracha ponds appeared to be stable for up to 6 weeks. It is more likely that the phenomenon r^ras short-1ived and that the apparent pattern reflectäd sampling interval. Thermal profiles with secondary discontinuities are characteristically short-1ived (tr'letzel , 1975). Diurnal events (Figures 2.9 and 2.I3) showed that stratification v¡as established on a daily basis. The meËalimniorÌ vùas broken down during the evening-earIy morrring and isothermy resulted from surface cooling (conditions r¡¡ere 35 calm during the 24 hour study and inverse stratification occurred during early morning). Daily patterns of stratification have been shown to be more important for shalloqt vlater bodies than seasonal events (Erikssen, L966; Young and Zimmerman, 1956; Vaas and Sachlan, 1953). StraEification of the Gumeracha ponds may have occurred diurnally but over an extended period while conditions \^'ere calm with high incident solar radiation. Diurnal stratification, following the same sequence of events as in natural shallow \^¡ater bodies, has been observed in many WSPs (Uhlmann, I979; Dodakundi et aI. , L97 3; Oswald, 1968; I^Iachs and Berend, I 968; Drews , L966; Marais, 1966; Bartsch and Allum, 1957). In deeper ponds, the thermocline may be stable for several weeks during summer (Hartley and lrleiss , L97O; Oswald, 1968; L{achs and Berend, 1968; Marais, 1966). Thermal stratification in facultative ponds may be self- rnaintaining; fundamentally different, biochemical processes above and below the thermocline result in the accumulation of dissolved substances (".g. HCO3 and NHr) in the arnerobic Trypolirnnion (Boksil and Agrawal, L977; Do Stratification in I,,lSPs has special implications for the stabilization process. During sunÌmer stratification, pond influent, generally with a lower temperature than epilimnetic r¿ater, will form a layer on the pond bottom. Sedjment deposition occurs below the thermocline ancl higher loadings may occur near the pond inlet (Oswald, f968). During winter, pond influent may have a higher temperature than pond surface htater resulting in streaming or sheet-spreading; settleable solids are distribr.rted over a wider area (Oswald, 1968; l"larais , 1966). tlhlmann (tglg) has demonstraÈed that low organic 36 in substrate removal efficiency can occur in ltrsPs due to variations flow patEern as a result of thermal st.ratificaEion. The polymictic behaviour of diurnatly stratifying t'lSPs, suclt as those at Gumeracha' and means oscillation between plug flow during isothermal conditions bypassing (vertical gradients) during stratification' Theconcentrationofdissolvedoxygeninabodyofwateris the result of the balance between gain from the atmosphere, photosynthetic production, animal and plant respiration, bacterial respiration during the decomposition of organic matter in the sediments, and chemical oxidation of dissolved organic matter (Hutchinson, :-g57). Photosynthesis by phytoplankton and macrophytes the was the most important influence uPon oxygen concentration in these Grmreracha ponds, The effects of population fluctuations of fully grouPs uPon the dissolved o*yg",' regime of the ponds will be more duríng discussed in chapter 3. While dissolved oxygen concenEration (1 >/ 30 pPm a phytoplankton bloom in facultative ponds may vary from to diurnally (Hussainy, 1978; King , L976, 1972; I^Iilliford and Middlebrooks,Ig6T;BartschandAllum,1957;TowneetaT''1951)' fluctuations of it was more const.anÈ in the Gumeracha ponds. Diurnal dissolved oxygen concentration are generally srnall in maturation ponds (Drews , 1966). InsÈratifiedfacultativepondsoxygenproductionisconfined to the euphotic zone above the thermocline; the epilimnion becomes (see in oswald, supersaturated and the hypolimnion oxygen depleted daÈa 1g6g; l.Iachs and Berend, 1968; Marais, 1966). Consequently, oxygen profiles in facultative ponds are characteristically clinograde or of posiEive heEerograde. The Gumeracha ponds displayed both types profile, although hypolimnetic \'/ater v/as not anaerobic' The over 24 reestablishment of stratification diurnally will mean that of hours oxygen profiles change fr,¡m uniform (with varying degrees 37 hypolimnetic depletion) to clinograde to positive heterograde (at the heighÈ of stratification) to clinograde and back to uniform as the pond is mixed (see data in Marais, 1966). Oxygen profile differences between the Gumeracha ponds on the same day may have resulted from ponds being at different Points in the daily cycle when sampled. Positive heterograde curves may have been the result of oxygen loss from a supersaturated epilimnion to the aÈmosphere or light inhibition and subsurface aggregation of phytoplankËon. Vertical stratification of algae has been observed in facultative ponds (Dodakundí et a7. , 1973; HarÈley and tr^Ieiss , 1964; Sless and Samsonov , L964; Bartsch and Allum, 1957). The pH of InISPs is mainly influenced by CO, uptake from the carbonate-bicarbonate alkalinity system by algae during photo- synÈlresis (fing , 1976, Ig72'). At Gumeracha, pH increased through pond 1 and pond 2 and maxima occurred during summer when retention time was longest. This is common in maturation ponds (Ramani, L976; Drer,rs, 1966). CO, produced by bacterial degradation may be insufficient to meet photosynthetic demand when alga1 standing croP is high. AdditionaL CO2 is exÈracted from the COr= - HCO3 system; pH rises due Èo the precipitation of Ca CO, and then the formation of OH ions as a resulÈ of the dissociation of CO, and HCO, (Cole , I975; trnletzel, Ig7Ð. COz is deplered during Ëhe day and recharged by nighttime respiratory release. During summer, pH increases Progressively as free CO, declines. Algae may become limited by CO, availabílity (fing, Lg76; 1972; Meron et a7.,1965 ' Bartsch, 1961). t During }larch, L977 and 1978, pond 2 effluent TIC was low and pH exceeded 10.2. Free CO, would have been absent and inorganic carbon would have been in the form of HCO3 q¡d CO, (I^letzel , 1975, p.163). Carbon limitation of algae might have occurred at those times. From pH and TIC variations it utas predicted that in pond 1 38. during the surmner of I 977 CO2 was abundanË and respiration exceeded phoÈosynthesis wtrile in pond 2 CO2 was reduced and photosynthesis predominated. In both ponds during the summer of 1978 C0, was low and photosynthesis predominated. It will be shornrn in chapter 3 ttrat phyLoplankton cycles matched these predictions. Quality criteria for domestic wastel^tater effluents aftet Lg77 (in the United States) are: PH, uPper limit 9; 5 day BoD, upper limir 30 me/l; ss, upper limit 30 mg/l (Boatwright and Lawrence , Ig77). Porrd 2 effluent pH exceeded'the uPper limit from January Èo April, 1977, and from October, 1977 to April, 1978. Pond 1 effluent pH exceeded the upper limit after December , 1977. Pond 2 effluent BOD meE quality requirements throughouË the study. BOD removal by the overall system was only 52.51( during 1977. If the ponds were fully loaded, pond 2 effluenE BoD would exceed Èhe upper limit during suflrner. The Gumeracha ponds are maturation ponds and advanced \^/aste\¡/ater treatment BOD requirements may be as low as 5 ng/L (Anon. , 1978). Pond 2 effluent met this requirement only from August to OcÈober, Ig77. During low flow periods in the Torrens River, the Gumeracha plant contributed up to 0. 54 W BOD to each litre of river water. Flowing \daËers are of susPect quality if BOD exceeds 5 ng/I (Hart , Ig74). [,Iaste\n/ater treatment plants exPort varying proportions of their organic load and effluent quality criteria may need to vary between plants taking into consideration the assimilative capacities of the receiving water bodies. Pond 2 effluent ss exceeded the uPper limit for domesqic wastewaters from January to March,1977, and from December, 1977 to May, 1978. Pond I effluent ss exceeded the uPPer limit during March and April, Lg78. Advanced treatment crit.eria for SS may be as 1ow as 5 mg/l (Anon. , 1973). Pond 2 effluenL ss met this requirement from May to October, 1977. The pejorative effects of pond 2 upon 39 effluent SS make it unlikely that the Gumeracha plant would meet the domestic was¡ewater SS criteria if subjected to full design load' Despite the extensive use of maturation ponds for tertiary treatment, boÈh in Australia and in other countries, very little operational data documenting the treatment capabilities of this type of IJSP have been published. The relative performance of the Gumeracha maturation ponds is, therefore, difficult to assess. BOD removal varies generally from 13 Eo 357" and SS removal from B to 507" (Carpenter et a7., 1976; Ramani, L976). Dinges (1978, L916) reported 80 to 90% BOD removal and 90-957" SS removal in ponds culturing EichhornÍa crassipes. Loadings in these studies were sirnilar Èo Èhose at Gumeracha. Overall BOD removal at Gumeracha was reasonable but SS were increased. Pond I performed noticeably better than most maturation ponds almost reaching the extremely high removals reported by Dinges (1978, 1976). Pond 2 increased BOD and SS. BOD removal in facultative ponds ranges from 58 to 97"/. (most in the range 75-85Ð v¡hile SS removal ranges from 857. in winÈer to 550% increase during summer (carpenËer et aJ-., I976; Goulden, L976; Rodgi and Kanabur, IgTL; Bopardikar, 1969; Williford and Middlebrooks, L967; Meron et a1., 1965; Nemerow.and Bryson, 1963; Neel et aJ.., 1961; FíEzgerald and Rohlich, 1958; Bartsch and Allum, 1957; Merz et a7., L95l; Towne et aL., 1957; Malchow-Móller et a7.,1955). BOD and SS removal by pond I was similar to that in facultative secondary ponds ' Removal of NO, and POO-P at Gumeracha tdas highest during the suÍtmer when org-N, BOD, SS, and TOC hTere increased during the p4ssage of r¿astewater through the ponds. It will be shown in chapter 3 thaÈ changes in chernistry during summer I^/ere correlated with high standing crops of phytoplankton. This was reflected by an increase in particulaÈe POO-P in effluents during suilmer (fig. 2.24). Particulate PO4-P also increased in the trickling filter effluent (pond 1 influent) 40. during suntrner probably due to sloughing off or washout of the zoogleal growth (algae and photosyneEic Protozoa) from the surfaces of stones in the filter (McKinney, I97I; Bartsch, 1961; Usinger and Kellen, 1955). Turnover of these populations would be higher during summer. pond 1 and pond 2 effluent TKN exceeded advanced \n/astewater treatment requirements (3 mg/1: Anon., 1978) during most of the study. pond 1 effluent NO3 exceeded safe drinking levels (10 mg/l, 1 mg/1 for infants: Hart, 1974) Ehroughout the study but pond 2 effluent met this requírement during suflrmer. During periods of 1ow flow in the Torrens River, the plant contributed up to 0.15 mg NO, to each litre of river r,rater. This ís 507. of the critical load for eutrophicarion (0.3 mg/l: Stewart and Rohlich, 1967). The lability of nitrogenous compourrds *akes the total nitrogen pool a more important measure of pollution load than any one form of nitrogen. The Gumeracha plant contributed up to 0.14 mg TKN to each litre of river hrater during low flow. The toËal nitrogen contribution from the planE t.o the river \¡/as as high as 0.29 ng/l during summer' Pond 1 and pond 2 effluenË total Po4-P alone exceeded advanced \À/astevrater treatmenË requirements for total phosphorus (1 mg/t: Anon., 1978) Ëhroughout the study. Pond 1 and pond 2 effluent soluble PO4-P exceecled the safe drinking level (0.2 mg/l: Hart, Lg7Ð throughout the study. During 1ow flow the plant contribuËed up to 0.019 rng of soluble PO4-P per litre of water in the Torrens River. This exceeded the critical level for eutrophication (0.015 mg/l: stewart and Rohlich, 1967). Phosphorus loading is the most significant factor deËermining lake trophic state (Oi11on and Rigler , lg75; shannon and Brezonik, 1972; Schindler et a7., 1971) and it has been demonstraEed that phosphorus control is an effective primary step in preventing eutrophication (Schindler and Fee, I9l4; 4I Vallentyne et aJ.., 1970). Overall PO4-P removal by the ponds was 527., removal by pond 2 being 3 times that of pond 1. The latter effected higher removal of nitrogenous compounds; overall mean removal of all nitrogenous comPounds was 41%. Nitrogen and phosphorus removal is a fundamental requirement of maturat.ion pond function, and ponds are used widely throughout Australia and other countries ostensibly for this purpose. Yet, remarkably, fery studies actually reporÈ nutrient removal efficiencies for fu¡ctional maturation ponds. The following removal efficiencies have been directly reported or calculated from primary data: TKN, 2 to 66l (Carpenter et a7., 1976; Drews, 1966); org-N, 0 to 72% (Oinges,1978, Ig76; Drews, t966); NH3' 29 ta 7I% (Oinges' 1978, 1976; Ramani, 1976); PO4-P, 3I7. (oinges , 1978, t976); Ëota1 phosphorus, 257" (Carpenter et a7., I97O. Overall removal of nitrogen and phosphorus by the Gumeracha plant was high, excePÈ for the production of org-N. Rernoval of NO, , NH3, and TKN by pond 1 was high but org-N and POO-P removal was poór. PO4-P removal by pond 2 was above average but this pond increased NH3, TKN, and org-N. Nutrient removal by facultative secondary ponds varies considerably. Phosphorus removal ranges from o to 96% (Meron et aI., L965; Neel et aJ., 1961; Fitzgerald and Rohlich, 1958), and total nitrogen removal from 9 to 93Z. (Hussainy, 1978; Meron et aI.' L965; Wuhrmann,1964; Neel et a7', f961); org-N and NH, removal has been reported at less tlnan 607. (Fitzgerald and Rohlich, 1958; Malchow-MóIIer et a7.,1955) and 80 to 95% (Neel et a7., 1961). In high rate oxidation ponds, .nitrogen removal,from 44 to 947" :nas been reporËed (snelef et a7., 1978; Caldwell-Connel1, 1976; Wuhrmann , 1964) while phosphorus removal has been reported at 202 (Shelef et a7., Ig7Ð. Under current operational practices, nutrient removal by maturation ponds aPPears not to be superior to that effected by other pond types. The polishing of effluents in maturation 42 ponds depends upon lower influent nitrogen and phosphorus concentraEions. Dillon (1975) has shown thar vollenweider's Q975) model of phosphorus retention is inapplicable to lakes wittr trigtr flushing rates (i.e. low retention times). The Gumeracha ponds obviouslly fall into Èhis category. This explains why phosphorus retention coefficients calculated using Vollenweider's model do not correspond with measured phosphorus removal. Kirchner and Dillon's (1975) model predicted phosphorus removal by pond 2 and lhe overall system well but over- estimated removal- by pond I. It r¿ill be shown in chapÈer 3 that this resulted from fundamental biological differences between pond I and pond 2 during Lg77. During 1978, r¿hen biological conditions vrere sirnilar in both ponds, mean monthly removal of total PO4-P from January to May was 487" for pond 1 and 457" fot pond 2 ' The applicability of Kirchner and Dillon's (1975) model to the Gumeracha ponds suggested that phosphorus removal was influenced great,ly by f lushing rate. Drews o966) has also suggested that No, removal in maturation ponds is a function of retention time' Nutrient removal in maturaËion ponds thus aPPears to be qualitatively the same as in natural water bodies. R values for lakes with low flushing rates (p = 0.001 to 0.96) vaqy from 0.95 to 0.53 while lakes wittr trigtr f lushing rates (p = 1.75 to 18.5) have R values from 0'49 to 0.01 (tillon, Lgl5; Dillon and Rigler, Ig74). R decreases as flushing rate increases. PO4-P removal by pond 2 (p = 24.0) and the pond sysËem overall (p = 11.2) v¡as very high compared to natural lakes ¡¡ith similar flushing rates (and vastly reduced load-ings). The relqEionship of R to flushing rate suggests Ëhat nutrient removal in hISPs could be increased by increasing retention times. This relationship had, in the past, only been guessed at by pond designers based upon the role of algae in nutrient removal and the observation that high algal standing crops developed at increased retention times' 43 Increasing retention time in maturation ponds may, hov/ever, generate operational problems. Excessive retention time can lead to carbon li¡nitation of green algae and the dominance of blue-green algae (xing , :Ig76). Blue-greens form floating mats which block light penetration resulting in anaerobic conditions (McKinney, L976)' Long retention Èimes result in increases of the algal fraction of SS (Meron et aJ., 1965). The oxygen required for algal respiration may exceed Èhe BoD óf incoming sewage (Bartsch, 1961). LlaËer loss by seepage and evaporation will raise TDS causing problems if water reclamation is involved (Ramani , Ig76). Increased retention time also increases aieal requirements and Èherefore plant cost. This sÈudy has shown that nutrient removal in the Gumeracha ponds is not compatib]e with other aspects of pond function, parÈicularly SS, BOD, TOC, and org-N reduction. Manipulation of retention time to increase nutrient refnoval is finely tuned to algal requirements and has limits if effluent quality in other areas is to be maintained. Alternative approaches to improving nutrient removal in maturation ponds are important and information concerning nutrient Partitioning within pond ecosystems is vita1. TheaquaticphosphoruscycleisadynamicSyStem;phosphorus j-s constantly incorporaÈed into organisms and simultaneously released via excretion and deeay. Exchange beEween \¡/ater and the sediments is a major component of the phosphorus cycle in natural r^raters, and in most lakes there is a net movement of phosphorus into the sediments (Schindler et af . , 1975: inletzel , L975; Hesse, 1973) ' The sedimentation 'of suspended organic matter and the precipitation of phosphates at high pH in l^/SPs (Ramani, Lg76; Lewin, I97 3) would suggesË that phosphorus loss to the sediments is also important in these ponds. Phosphorus exchange across the sediment interface is regulated by oxygen concentraLion at the sediment surface (wetzel, Ig75; Kramer et al'., L972) and 44 phosphorus release from the sediments is líke1y to be low in fully aerobic VISPs. This suggests that the sediments are Èhe major phosphorus pool in I,tSPs. Nutrient removal schemes incorporating algal harvest from I'ISPs assume that the incorporation of soluble inorganic phosphorus into algal cells is the most important avenue of phosphorus removal. The implicaÈion is thaË events in maturation ponds resemble the epilimnion of lakes where phosphorus is incorporated rapidly into the seston (Rigler, 1973; l,letzel , 1975). The nitrogen cycle is also highly dynamic. The major nitrogen transformations in natural waters are the removal of NH, by nitrifying bacteria which produce NO, (the major nitrogen source for algae and macrophytes: Inletzel , 1975) , and NH, release via Ehe decomposition of organic material and zooplankton excretion. The sediments are a major ,ritrog.n store (print< , 1967) and the presence of an oxidized surface layer prevent.s NHO+ release (Barica, I974; Breponick , 1972). However, the major avenue of niÈrogen removal in maturation ponds is (as for phosphorus) assumed to be incorporation into the seston. Nitrogen, unlíke phosphorus, can become limiting in IJSPs as a result of NH, Ioss to the atmosphere at high pH (t r97 6) The model presented in Figure 1.2 indicates alternative avenues of nutrient uptake in maturation ponds. A1gal ,tondi"ff;ay not be high in some maturation ponds (Ramani , I976) suggesting that organisms other than algae are responsible for nuÈrient removal. The most significanË groups are 1ikely to be macrophytes, zooplankton, and fish. No account of nutrient partitioning in any type of l^lSP has, as yet, been published and the importance of these grouPs for nuËrient removal from the Gumeracha ponds is subsequently investigated in this s tudy . 45 Chapter 3. Algae and Macrophytes 3.1 Introduction The role of algae in facultative and maturation WSPs includes Ehe uptake of stabilized nitrogen and phosphorus compounds and the production of oxygen during photosynthesis. The detrimental effects of algae upon effluent quality mean that the use of algae for effluent polishing is dependant upon removal prior to discharge. A conflict arises between the need to maximize algal standing crop for nutrienÈ removal and Ëhe need to prevent aLgae from entering the receiving hrater body. The high financial and energet.ic ínvestments required for mechanical algal harvest offset the advantages of !ùSPs for waste treatment. This problem may be overcome by the utilization of in-pond methods of algal control. Ponds with differing treatment requirements may be connected in series, the final pond performing an algal removal function. Understanding Ëhe factors controlling a1gal numbers in maturation ponds is thus important for effective pond management. The seasonal cycle of chlorophyll a concentration in maturation onlY ponds has,(been described in the studies of Shillinglaw and Pieterse and V,Ihite ( 19 75 ) . (1977)l Generally, 1ittle attempt has been made to correlate seasonal fluctuations in algal abundance with pond performance, or to examine the factors controlling population fluctuations under operational conditions. Algal studies in I^lSPs to date have been restricËed to: a) extensive species lists (Goulden, I976; Benson-Evans and Williarns, 19753 Ahmed,1974; Singh and Saxena, 1969; Malchow-MóLLer et a7., 19s5), b) descriptions of succession during blooms (Patit et a7., 1975; King, 1972; Haughey, 1965; Singh and Saxena, 19691, De Noyelles, 1967; Fitzgerald, 1964; Neel et aJ., 1961), 46 c) the examination of short-term yields in mass-culLure situations where conditions for a1gal growth are optimized (Goldrnan, I979a, b; shelef et a7., Ig7B, L973; Uhlmann, 1978; McGarry et a7., L973; Oswald and Golueke, f968), and, d) nutrient removal experimenEs in laboratory-simulated I'{SPs (Fitzgerald and Rohlich , L964) or on a short-term field scale (paelínck and Maeseneerr 1978; Hemens and Stander, L969; Hemens and Mason, 1968). A1gal productivity may be limited by factors which supPress reproductive rate (nutrients, light, temPerature), or which remove individuals from the population (predaÈion, flushing, sedimentation, and disease). IÈ has been suggested that Èhe factors responsible for the seasonal variation of a1gal numbers in tr{SPs are those operating in natural vraters, in particular, light, temPerature' and grazing (Vtrhite, Ig75; Rodgi and Paril , l97I; De Noyelles, 1967). Additionally, phytoplanktonproductivityinlnlsPsmaybelimitedbycarbonavailability (ring, 1976, t972); rhis is unlikely in naÈural lakes (schindler, L9lla). High flushing rate can also reduce phytoplankton productivity (O'Conne11 and Andrews, 1977; Dickman , Lg6g) and may be important in VISPs during perio The influence of biotic factors, such as zooplanltton and fish, uPPn algal populations is examined in subsequent chapters ' Phytoplankton is generally regarded as the major contributor Èo primary production in natural lakes. A greater proport.ion of the nitrogen and phosphorus retained in such a lake would be íncorporated into phytoplankton biomass than into other comPonen¡s of the autotrophic 47. corurunity. In some lakes, however, a high proportion of the total carbon fixed annually may be contributed by macrophytes and periphyton (Huntsinger and Maslin, 1976; Gak et a7', 1972; Rich et aJ" I97I; Davies, lgTO; WeEzeL, 1964). Standing crops of aquatic vascular plants may thus represenL significant nuÈrient stores. Macrophyte harvest could possibly provide a useful pathway for nutrient removal from maturation ponds. Unlike unicellular a1gae, which must be removed from effluents continuously, nutrient removal using macrophytes could be achieved in a single, annual harvest provided this occurred prior to plant senescence. In this regard, the rnraste\^Iater treatment capabilities of the floating vascular plant Eiclthornia ctassipes have been extensively studied (wolverton and McDonald , lg7g; i^lolverton et aJ.-, I976; Anon', l97B; Dinges, l97B , 1976; òott"tl et a7., 1977; llooten and Dodd, Ig76; Boyd, 1970). Although niErogen and phosphorus removal during growth of E. crassipes may be above B0%, sËudies have generally been of shorÈ duration and have computed nutrient removal by comparison of influent and effluent concentrations. The effectiveness of macrophyte harvest as a pathway for nutrient removal is more properly deEermined by a comparison of the nutrien't pool represented by annual plant production with the total amount of nutrient retained annually in the hrater body (carpenter and Adams , Lg77). Although values for the production of floating plants generally exceed those of submerged species (Uitctrell , L978; Davies , I}TO) ttte use of E. crassipes for effluent polishing is restricted to the warmer Part of the year in temPerate areas (Wolverton and McDonald , lgTg). Evaporation and transpiration by the plant may increase the TDS of pond rvatel and nitrogen may become limiting before Èhe desired reducËion of orthophosphate has been achieved (l.looten and Dodcl , Lg76). Additionally, E' ctassipes Prevents light penetration resulting in anaerobic effluents (t{olverton and 48. McDonald, 1979; Corv¡ell et a7., 1977; Culley and Epps, 1973) which may have higtr BoD (BoYd, 1971). oÈher aquatic vascular Plants studied include the emergents scìrpus arld Phragm.ites which can reduce BoD, ss, and coliforms in effluents(oeJong,|976;Seidel,|976).BoDandbacterialremoval (De appears to be effected largely by attached microorganisms Jong, L976; Spangler et a7., lg7Ð. De Jong Qg76) has shown that the phosphorus contained in scirpus and Phragmites production may be equivalent to 50% of annual pond 1oad. However, nitrogen and phosphorus removal ceases (De when the nutrient uptake capaciEy of the plant is exceeded Jong, Ig7Ð and Scirpus may release orthophosphate at certain times of the year (Spangler et a7., 1976; trnlhigharn and Simpson, 1976). Generally, only smal1 quantities of orthophosphate are removed by harvest of emergerits, the remainder accumulating in the sedimenËs with the unharvestable root-rhizome and microflora-substrate complexes. The phosphorus content of the sediments in reed or rush ponds may increase until equilibrium levels in effluents reach excessive amounts (Boyd, 1971). Rooted emergent plants obtain most mineral nutrient from the sediments (t"titctretl, 1978; Hutchinson' 1975) and may thus mine nitrogen and phosphorus from the substraËe. Nutrient budgets for these plants (".g. De Jong, Ig76) are susPect, parÈicularly as underground' unharvestable parts may represent a higher areal mass of nitrogen and phosphorus than aboveground parts. Provision must be made to control algae in reed or rush ponds (Sei¿et, 1976; Spanglet et a7.,1976) and the use of emergents for effluent polishing is likely to be accompanied by insect problems. Despite considerable research effort, the value of floating demonstrated and emergent macrophytes for effluent polishing remains to be convincingly. Neither grouP is without its attendanË problems' Study of the usefulness of submetged macrophytes for wastewater treatment has 49 been neglected. In naÈural ponds and lakes' low phytoplankton density is often associaÈed with high standing crops of submerged macrophytes; macrophyte removal or decline is often followed by an (crawford, increase in phytoplankton density, biomass, and productivity Ig7g, |977; McCord and Loyacano, 1978 Kimball and Kimball, 1977; Brooker and Edwards, 1973; Nichols , lg73; Fítzgerald, 1969; Goulder, (..g. Ig69; Hasler and Jones , Ig4g), Filamentous algae CTadophora) (Cra¡¿ford 1977; may also have an inhibitory effect upon phytoplankton , Boyd, L973; Fitzgerald, 1969; Goulder , 1969) ' This type of inter- action has not been described in wSPs but subrnerged macrophytes ar.d/ot filamentous algae could provide a simple, convenient, and inexpensive means of controlling alga1 levels in effluents ' Althoughsubmergedmacrophytesarelessproductivethan from emergent species (i,Jetzel , I975; I^Iestlake, 1963), their harvest natural lakes may remove significant ProPortions 06-377") of annual total nitrogen and phosphorus retention (Carpenter and Adams , 1977; lrlile, L975). Submerged macrophytes may be more ef fective for the removal of dissolved nitrogen and phosphorus than"- rooted emergents ' the Although many submerged aquatic plants obtain nutrients from sediments, vittate plants (wittr long stems, thin trailing leaves' and small underground parts), characÈeristic of eutrophic 1akes, obtain (Hutchinson, 1975) most of their required nutrients f rom the \'rater ' This is advantageous for effluent polishing. within the gen'us potamogeton dependence upon root absorption ranges from high in the thick-cuticled P. thun'bergij (wittr thick, coriaceous f loating leaves) (Bristow to low ín the submerged, ribbon-leafed P. schweinfurthii and l^Ihitcombe, 1971) . Naturally occurring populations of subrnerged macrophytes (including a thin-leafed Potamogeton) in maturation ponds have been species studied by McNabb og76). tlis study showed that submerged 50 could concentraËe nitrogen and phosphorus above the leve1s in wasËev/ater and it was calculated that harvest could remove 20-257" of the Eotal nitrogen load and 50-70% of the total phosphorus load during the growing season. Hor,rever, the actual nutrient store of harvestable biomass was not compared directly with annual nutrient retention' maturation submerged macrophytes may also contribute to sS removal in rates ponds as they reduce turbulence thereby increasing sedimentation ' (Schiemer and Prosser, 1976). Monospecific stands of Potamogeton ochreatus Raoul occurred in both the Gumeracha ponds during the present study. This submerged plant is vittate, hyphydate, and tereÈe-branched in form with 1ong, thin leaves and slender rhizomes. Leaf fc¡rn and cuticle thickness in this (c'f' species suggest that nutrients are obtained mainly from the water at Bristow and l,lhitcombe, 1971). No emergent vascular plants occurred Gumeracha. Dense mats of the filamentous aLga cTadoplnta KueËzing formed in both the Gumeracha ponds at various times during the present study' (in This genus exhibirs extreme morphological variability branching pattern, chloroplast form, and relative development of intercalary and (Whitton, apical growth) in response to.environmental conditions 1970; Prescott, 1968). Specific identification l^tas noË attempted but species most frequently encountered in eutrophic waters ate c. gLomerata' C. rivularis, and c. ftacta (Whitton, 1970)' standing The effects of p. ocltÍeatus and Cfadophora upon a1gal production crops and effluent quality at Gumeracha ,¿ere monitored' The of p. ocltreatus in the Gumeracha ponds r¡/as measured and the producËion The oÍ, cTadophora and PhytoPlankton in the Gumeracha ponds estimated. p' nutrient stores represented by annual net production of ochteatus' nitrogen and cTadophora, anld phytoplankton were compared with annual the phosphorus retention in the Gumeracha ponds' In this manner' 51. poEential of submerged macrophytes and filamentous algae as tools for the managernent of maturation ponds \^/as investigated' 3.2 Methods 3.2.L Chloro 11 a. Surface r¡¡ater samples (600 mt) from the centre of each pond were taken fortnightly from January 1977 to OcÈober, 1978. During \¡/armer months samples were also taken from depths of 50 and 100 cm with a "Chimp" hand pump. ülaËer was filtered through 150 Urn mesh to exclude herbivorous zooplankton. Samples rÀrere stored on ice in darkness. On each sampling date live material was examined in the laboratory and ttre algae identified using Fott (1971), Prescott (1970, 1968, 1951)! Haughey (1969, 1968, 1965), Tiffany and Britton (1952), Smith (1950), and Chodat (1909). Chlorophyll a and phaeophytin were determined after Strickland and parsons (1968). Samples from different depths were pooled prior to filtration. Depending on algal density, a 50, 200 or 500 ml subsampl-e was filtered using Gelman filtration flasks and a vacuum Pump. Until March 1977 samples were filtered through 0.45 Urn Millipore filter discs. Chlorophyll was extracted ín 90% acetone and absorbance measured on a Perkin-Elmer 124 double beam spectrophotomeler using 5 cm cells ' The use of Millipore filters resulted in incomplete chlorophyll extraction at high cell densities due to poor cell disintegration' Chlorophyll a concentrat-ions in pond 2 from January to March 1977 were therefore underestimated. After llarch 1977 samples were filtered through Whatman GF/C glass fibre filter discs (particle size retention of 1'2 Um: !,/hatman f ilter selection guide). Holm-Hansen and Riemann (1978)'htt'e shown that concentrations of chlorophyll a recovered from Whatman GF/C filter discs and 0.45 Um membrane filters are equivalent' Chlorophyll \,/as extracted in 90% acetone after disintegration of filter discs in a ground glass tissue grinder. Absorbance of pigment extracts l^tas measured on a Varian SuÞerscan 3 spectrophotometer at 750r 663r 645, 52 and 630 nm using I cm cells. Absorbance was also measured at 665 nm before and after acidification with 502 hydrochloric acid. Chlorophyll a concentration (*g/*3) was calculated using the SCOR/UNESCO tri- chromaÈic equation (Strickland and Parsons, 1968, p. 189) and active chlorophyll a and phaeophytin concentration calculated using Lorenzenrs equation (Strickland and Parsons, 1968, p. 194). Autot.rophic sulphur bacteria may be present in large concentrations in oxidaLion ponds (Hussainy , I972). The contribution of this group to chlorophyll concentration can be determined from absorbance of pigment extracts aË 720 nrn (blant at 850 nm) (Hussainy' IgTZ). Sulphur bacteria did not contribute to chlorophyll conceritraÈions in the Gumeracha ponds. 3.2.2 A1gal Counts. Cell density in each pond was deÈermined from the peak of the phyÈoplankton bloom in March 1978 until algae were virÈually absent from the rtrater column. 1 ml of fresh, agitated sample was placed into a Thomas C20 counting cell (no. 9851) and examined under 200 times magnification. Five random fields vlere exaníned, the algae identified and counted. Cell number per ml was calculated from the Tir-Ls technique marl have failed to c]-etect verv relative area of the ocular field.srnalf algae (less than 61-tm) and- tl-rerefore underestimated totaf a1ga1 croÐ. 3.2 .3 Filamentous A1 al Mats. On each sampling date frorn July 1976 until October , Ig78 percentage coverage of the v/ater surface in each pond by floating CTadophora mats was estimated visua1ly. Coverage l¡/as recorded as O% (if mats were absent), less than 5% (plotted as 2.5%) if any maËs vüere present , less than lOZ (plotted as 57.), I0"/., and multiples of 10 thereafter. This technique is subjecË to error arising from observer inaccuracy and variation in wind force and direction. 0bserver error could have been overcome by the acEual measurement of mat dimensions. However, variation in the speed and direction of the wind was considered a more significant source of error. It was felt that the extra effort involved in measuring mats would have been largely wasted 53. in Ëhe absence of daily measurements of wind speed and direction abundance 3.2.4 Submer Macr tes . Visual observaËions on the and shoot heighE of Potamogeton ochteatus were made throughout the study period. P. ochveatus beds r¿ere mapped on 15 June, 19 October, and 13 December 1977 arrd on 30 August 1978 from boat änd bank observations ' Per cent bottom coverage was estimated from these maPs using a graphical square counting method. Due to time and labour constraints, an aPProximate method was used to measure net production (excluding losses due to respiration) of P. oc|veatus in both ponds during L977. Biomass l^/as measured in both ponds on 15 June 1977 when areal standing croP \¡Ias judged (by observation) to be maximal . It is stressed that biomass r.Ias not sampled regularly throughouE the growing season. Production was Ëhen calculated from published production to biomass ratios ' Areal standing crop hTas sampled from a boat using a dredge- rake sampler (Figure 3.1). One end of a 2.5 m steel pipe (2.5 cm diameËer) was angled at 4Oo and welded to a steel frame (¡g x 18 cm) ' The lower long side of the frame bore teeth with a 2 cm side length' A large bag of 1 cm plastic mesh was attached to the back of the steel frame. The sampling Eechnique \^las similar Èo that of Swindale and Curtis Og57). The Eoothed-edge of the frame r¡/as Pressed into the sediment and then dragged towards the boat (anchored to the shore) for a distance of approximately 0.5 m. This gave a quadrat size of 0'19 m2' Samples included underground parts; that is, standing croP r^Ias equivalent to biomass. six representative samples within the area under plant coverage hlere Ëaken from each pond. Sedirnent I^/as washed from samples before return to the laboratory. Excess water v/as removed from each sample by spin dryíng and wet weight measurecl. Samples hlere then dried to constant weight in an oven at 60oC and sLored in desiccators over silica ge1. 220 c¡D FIGURX 3.1 Dredge-rake macrophyte sanpler 54. showÍng Cr itioue of Produc tion Estimate. In macrophyte PoPulations losses during the a marked annuar fluctuation in biomass, and in which growingseasonduetomortalityar.ð'grazíngaresrnall'theincreasein biomassuptoitsmaxinrumisameasureofnetproduction(I^Iestlake, I974a', 1965, 1963; Sculthorpe, :967). In a harvest situation, Such than gross as for nutrient removal, net production is of more interest production.IfÈheinitialbiomassisnegligibleorlostbeforethe biomass is alone seasonal maximum is attained, a determination of maximum T'hat is, if suff icient to determine net production (I^lestlake , 1963). of maximum biomass none of the previous year's growth remains by the time initial biomass need not be determined (I,testlake , I974a). L977' P. ocltÍeatus was absenL from pond 2 at Gumeracha in early ThatisrsuÍlmerdie-offofabovegroundpartshadbeencomplete' a single season's Maximum biomass in late 1977 rhetefore represented (l'Jestlake, 1965) in pond gro\^rth; p. ochreatus behaved as a true annual (L976) present 2. In pond I, plants from the previous season were growth) but had during early L977 (at the start of the current season's of estirnating disappeared by the Eime of maximum biomass. The method productíonfrommaximumbiomasswasapplicabletothepopulationsof P. ochreatus in both ponds at Çumeracha' by cooEs ducks grebes Species of Potamogeton are Srazed ' ' ' tyPes of birds herons, and plovers (Sculthorpe, 1967). Although these 1oI^7 Grazing losses were recorded at Gumeracha, their numbers \^tere ' ' (Jupp I977b), usually involving the removal of uPPer leaves and Spence, graztrrg intensity' r^rere not obvious and no attempt was made to estimate Noestimatewasmadeofmortalí.ty.Inthemorphologically similarP.pectinatus,shootsabsorbwacerandcollapseuPondeath (Howard-I^lilliams, 1978). Shoots in this condiËion vter:e not obvious IE must be at Gumeracha prior to the period of maxj-mum biomass' sampling interval rememberecl that the time of maxirnum biomass reflects 55. and may have occurred just prior to or later than the actual sample date. Losses over short periods may usually be neglected (ülesÈlake, Ig74a). Ideally, maximum bíomass should be determined by frequent, regular sampling throughout the growing season. In the absence of mo1.e complete data, a single measurement of biomass (when judged to be maximal) might be expected to yield a reasonable, although approximate, esÈimate of net Production. The dredge-rake sampler used to measure biomass gave only an approximate quadrat síze. This may have been the most significant source of error in the meÈhod of production estimaEion. Ilowever, Swindale and CurËis QgSl) have shown that with practice this technique can aPProximate a quadrat of similar síze with reasonable accuracy. The sampler used in this study hras not tested against a quadrat of known síze. Nitroeen Contenl of Potamogeton ochteatus.- -. Stem, leaf , and rhizome tissue of p. ochreatus collected on 15 June, L977 was ground and homogenized. Total particulate nitrogen \¡/as determined using a Kjeldahl digestion technique after Major et af . Q972). Organic matter l^7as digested in a mixture of potassium sulphate and sulphuric acid (mercuric chloride catalyst). Nitrogen \¡/as converted to ammonia and determined specËrophotometrically (absorbance at 640 nm) after reaction with phenol and hypochlorite under alkaline conditions (sodium nitroprusside caÈalyst) to produce indophenol blue (Stainton et a7., 1974), No analyses of tissue phosphorus content were conducted. 3.3 Results 3.3 .1 Chloro 11 a. Chlorophyll a concentrations calculated using the SCOR/UNESCO equation included phaeopigments and exceeded values for active chlorophyll a calculated using Lorenzen's equation. Seasonal trends in chlorophyll concentrations calculated using both equations rnrere identical. The tri-chromatic equation is no more accurate Ehan that based upon a single reading at 665 nm (Vollenweider, I974) and allowance 56 must be made for inacÈive chlorophyll in shallow, well-mixed waÈer bodies where zooplankton grazing might be high. Seasonal variation of active chlorophyll a and phaeophytin (*g/*3) in rhe Gumeracha Ponds, calculated using Lorenzenrs equation, is shown in Figure 3.2. Field observations cornmenced in July 1976 and pond 1 remained very clear until the end of Decemb er 1976. Active chlorophyll a concentration increased frorn mid January to mid February 1977 (62 mg/m3) although the transparency of pond l- remained high (could see sul:strate). Chlorophyll a concentration varied between 0 .) and 10 *g/*J from March until early November L977 arld the pond bottom was usually visible during this period. chlorophyll a concentration increased steadily during December L977 arld early 1978 reaching a maximum of 988 ,ng/*3 on 29 March, lg77. Thereafter, chlorophyll a concentration declined rapidly and was 13 mg/m3 on 27 April Lg78. Chlorophyll a concentration was less than 10 *g/*3 until October 1978 when it again increased rapidly. The concenLration of phaeophytin in pond I r¡¡as generally less than 10 *g/*3 but increased to 35 ,r,g/*3 i., March and April Ig7l. Phaeophytin increased during the phytoplankton bloom in ? LaEe 1977 - early 1978 and reached 115 mg/m' in April 1978 as active chlorophyll a was decreasing. Pond 2 \^/as very clear until 8 November 1976 r¿hen it became turbid and appeared quite green. Turbidity and the intensity of green colouration both increased during December L976. Chlorophyll a' concenËrations in pond 2 ftom January until March lr977 wete underestimated due to incomplete pigment extraction. The intensity of water colouration during this period suggested that chlorophyll concentrations during tl-re peak of the phytoplankton bloom \¡/ere similar: to those from February to March Ig78. Chlorophyll concentration decreased rapidly in Pond I I 80 60 400 200 (f) I Ê 0 ò¡) É l! r{ r{ h .dÈ o t{ o r{ Pond 2 o (¡) 1200 rl +J o 1000 800 600 400 200 A t I I I 0 J DJ L977 Time (months) T97 B FIGURE 3.2 Active chlorophyll a concentration (-) and phaeophytin C--) in Èhe Gurueracha Ponds. 57. late March Lg77 ancl remained low (<10 mg/m3) until November' Chlorophyll a increased steadily during December 1977 and early 1978 reaching 1185 mg/m3 on 15 March. ïhereafter chlorophyll a concentraËion 1, declined rapidly and was 5 mg/m' on 10 May 1978. Chlorophyll concentration remained low unEil October. Phaeophytin concentration in pond 2 l^tas lovl in January L977 (t5 *g/*3) but increased in March as the phytoplankton bloom declined. A secondary peak in phaeophytin concentration occurred o¡ 27 April after the bloom had declined. Phaeophytin concentration remained low until January 1978 when it reached 180 mg/*3 just after a decrease in active chlorophyll a. Phaeophytin decreased in February but reached 60-70 *g/*3 during March and April as the phytoplankton bloom declined. PhaeophyÈin concentration remained low until October when it increased slightly as active chlorophyll a concentration increased' In sunrnary, a phytoplankton bloom developed and continued in pond 2 from early November L976 until March 1977. A bloom did not develop in pond l during this period and \¡rater remained very clear until November Ig77. Phytoplankton blooms occurred in both ponds from early r¡/ere November 1977 until March 1978. Chlorophyll a concentration maxima similar in both ponds. Maximum chlorophyll concenËration in pond 2 occurred 2 weeks earlier than .in pond 1, although chlorophyll concentration declined to very low levels in pond 1 earlier than pond 2. Phytoplankton blooms developed in both ponds in Octobet L97B ' A plot of chlorophyll a concentration (*g/*3) versus mean \'later temperature in both ponds on each sampling date from September 1977 until the peak in chlorophyll concentration (mid March 1978) is shown in Figure 3.3,4. The curve (fitte¿ by eye) showed a rapid increase ín chlorophyll a concenttation at \,rater temperatures above about 18oC' Phytoplankton blooms occurred during late 1976 and late 1978 when water temperature exceeded 17-1BoC. However, rvhile maximum chlorophyll a concent.rafion in pond 2 (1186 tg/.3) occurred at a mean l\rater temperature 1000 A / ^ A L20 a. A A A ê A ^ c1 (')  A Ê't É \\I A 00 òf) Ò0 ^ É d A A É É o .¿ A .¡ A +J 100 A {J d (Ú 800 l] l¡ +J É É OJ a) o U o O 600 ^ r$ rõ F.{ Fl ^ Fl Fl X >. ,c ^ A  À o ^ tr ! A o 10 ^ 4 00 Fl ¡A -l o A o A/\ A q) c, A .rl 'rl ^ ¡J ¡J I o 2 00 ^ A I ^^ ^¡t ^ /t ^ 0 I L2 L4 16 18 20 22 24 (oc) Temperature (oc) Tenperature AcÈlve chlorophyll a concentration FIGURE 3.34 Active chlorophyll a concentration FIGURE 3.38 water temPeÌature' versus depth-averaged \,Iater temPerature' versus depth-averaged (r), 2 (¡). Pond I (r), Pond 2 (a). Pond 1 Pond 58 of.22.5oC, maximum concentration in pond I (988 mg/m3) oc.curred at 16.6oC. A semilog plot of chlorophyll a concentration versus mean rn/ater temperature in both ponds on each sampling date from September 1977 until late May 1978 is shov¡n in Figure 3.3,8. This graph includes all data presented in Figure 3.3,4. A linear regression of log chlorophyll a on temperature yielded a relationship of the form log chlorophyll a = -1.50 + 0.20 (temperature), 12 = 0.42. That is, vêriation in temperature accounted for only 42% of the variance in chlorophyll a concentration. Ihe regression line intercepted 100 *g/r3 chlorophyll a (concentrations above this constitute a "bloom") at l7.7oC, although chlorophyll concentrations above this also occurred at r^7ater temperatures as low as 13.ZoC. Most of these values occurred during the decline of the phytoplankton bloom. Seasonal variation of phaeophytin, exPressed as percentage of the total chlorophyll a pool, in ponds I and 2 is shown in Figure 3.4. phaeophytin was low (<302 total chlorophyll) in the early stages of phytoplankton blooms as the number of actively growing cells increased' As blooms progressed, the proportion of inactive chlorophyll in the total chlorophyll a pool increased. Phaeophytin constituted over 9O"/" of total chlorophyll a as phytoplankton blooms declined and senescent cel1s predominated. From May until November 1977 phaeophytin fluctuated markedly but was generally less than 507" of. total chlorophyll. Total chlorophyll a concentrations \ÁIere very low during this period. During Lhe same period in 1978 phaeophytin constituEed more than 60% of the toLal chlorophyll a Poo1. ' 3.3.2 Compo sition of Aleal communities. Phytoplankton blooms in both ponds at Gumeracha were dominated by species of,scenedesmus Meyen' (Schroeder), S. quad.ricauda (Turpin), S . opoliensis (Richter), S. acutiformis S. dimorphus (turpin), S. pannonicus (Hortobagyi), S. acuminatus (Lagerheim), and S. abunclans (Kirchner) were recorded. Species of this 100 lì l\ \ I l 80 I .¡ I ¡J >' I ,r È I o \ I CJ 60 d I ll \ I tl \ I I \ À OJ l ò0 40 d \ I Ð \ \ I It /'\_ CJ I U --J \ , 20 I l \ o \ Þ{ lt tl \i \ Í \, 0 J DJ L978 L977 Tirne (months) FIGURE 3.4 Concentratíon of phaeophyËin, expressed as a percentage of total chlorophyll a, 1n pond 1 C-) and pond 2 (----) 59. genus have generally been described on the basis of cell shape and size, the number and position of spines on coenobia, and the presence of lateral rídges or teeth on ce11 walls (Chodat, 1909). Several species exhibit extreme phenotypic plasticity with resPect to spine distribution and wal1 ornament.ation, and both coenobe formation and spine lengths are affected by the nature of the culture medium (particularly Èhe Presence of organic material and bacteria) (Trainor and Roskosky, 1967; Trainor, Lg66, 1964, 1963; Trainor and Hilton, 1963). These species, including S. dimorphus and 5. acuminatus (Trainor, 1964), can mimic several different coenobial types and pure culture studies are necessary for identification. Other species, including S. quadticaucla, S' acutifotmis' In and S. abundans, are morphologically sEable (Trainor, 1966, 1964)' the absence of pure culture studies, the identification of S' opoliensis' s. acuminatus, S. dimotphus, and S. pannonicus from the Gumeracha ponds must remain tentative. From November 1977 until mid-February I978, the phytoplankton of both ponds was dominated by a small (Z-ro ¡rm long, approximately 2pm across), crescent-shaped, unicellular green alga most like Outococcus or pers' Sel-enastn¡m (Dr. G. Ganf, Botany DeparÈment, University of Adelaide' although cornm., 1978). Scenedesmus beeame dominant by 22 February L978, several species had been present in low numbers prior to this ' During were the summer blooms of scenedesmus several other species of algae (Schrank)' present. These included Attl<ístrodesmus sp., CJosterium acenosum (Schröder) ? ctgptomonas sP'' c. moniJ-iferum (nory), schroederia setigera ' ? Microspo-ra sp., Characiochlotis sp. (epiphytoic'on filamentous algae), Micractinrum sp., and one or more species of the diatoms Navicufa, CephaTomonast Cocconeis, and Nitzschia' Several genera \¡7ere recorded from surface \nlater samples during winter periods of low chlorophyll a concentration (t"tay to October L977 included and May to september 1978). Diatoms were most abundant and 60. species of CgcTotefLa, Surirel.-Za, Navic.uTa, Nitzschia, Cgmbe77a, ? DenticuTa, 1. Amphora, ? FtagiTaria, ? FrustuTía, Sgnedra¡ âûd Diatoma. Green algae, generally less abundant, included Scenedesmus, Allçistrodesmus, Chlamgdomonas, Cl-osterium, ? Ctgptomonas. ? RacibotskieTl-a, paLmeTLa ? mucosa (Kuetzing) (epiphytic on filamentous algae), and Ggrosigma. Active chlorophyll a generally constituted more than 50% of total chlorophyll a during these winter and spring periods. That is, most algal cells present in the r¡7ater column were live. periphytic growths formed on the concrete aProns of both ponds during most of the year. These growths consisted mainly of Scenedesmus and diatoms on filaments of the blue-green alga, Phormidium sp. short- trichome blue-green algae \^rere recorded rarely from Gumeracha pond water. 3.3.3 Algal Çounlq. some counts of algal cell density were made during the presenÈ study. Counts I^/ere undertaken during Èhe course of a fish introduction experiment (chapter 5) over a short time interval. In the absence of more complete records the most useful information gained concerned the succession of Scenedesmus species. The density (number of cells/ml) of Scenedesmus species in both ponds during the decline phase of phytoplankton blooms (March to June 1978) is shown in Figure 3.5. In both ponds S. opoliensis ri/as nt-rmerically dominant at maximum chlorophyll a concentra¡ions. s. acuminatus r¡ras recorded in pond 2 on 15 March 1978 but was not present when counts commenced on 29 March. The order of disappearance in both ponds \^/as therefore S. aciminatus, S. acutiformis, s. opoTiensis, and finally s. quad.ticauda. s. quadricauda reached maximum density on 13 April in pond I and 27 AptíI in pond 2. s'. quadricauda increased in density as ,9. opoliensis declined; maximum density of s. quadricauda was much lower than for s. opoliensis- Scenedesmus declined to very low density in pond 1 about 4 weeks earlier than in pond 2. 3.3.4 Phytop lankton Ptoduction. The production of phytoplankton in Pond I Pond 2 100000 10000 ¿ I f I èì I \ I Ê I t I t I I I o I t É I I I I t h I {J I ì 'r{o 1000 I t É \ t c) \ I I "d t ^I F-{ r{ \ t t q) I t I I C) / t t tr, t I I I I I I t -.t I I I I t I 100 ¡. I ì T I I I I I t I t I I I I I I I I t I I t I I I t I t I I 10 A M A ì4 J Tine (months) FIGURE 3.5 Succession of .9cenedesnu.s species in the Gumeracha ponds S. otrnTiensis S. quadricauda (---) S. acutiformis ("""") S. acuminatus (-l-t-) 61. the Gumeracha ponds l^/as measured indirectly. Estirnates of producÈion were calculated on the basis of the correlation between chlorophyll a concentraËion and gross phytoplankton productivity (Brylinsky and lulann, L973; Anderson and Banse, 1965; RyÈher, 1956). Obviously, in situ productivity is dependant upon many factors (".g. nutrients, light, temperature, and physiological stat.e), not simply chlorophyll content, and Èhere is not. always close corresPondence of chlorophyll a concentration and producËivity (Hickman, 1919, 1973). Ideally, the degree of correlation should be established individually for each water body. chlorophyll a concenÈrations in pond 2 during early 1977 were underesËimated due to incomplete pigment extraction' Chlorophyll a concentraËions during early 1978 were considered more rePresentative of algal events in pond 2 arrd have been used in the following calculations. Two methods were u'sed to approximate net phytoplankton production. The first was based upon the relationship of average chlorophyll a concentration (*g/*3) and gross phytoplankton production (X.aL/*2) during the growing season presented by Brylinsky and Mann (L973, p.10, graph B). Mean chlorophyll a concentration in pond 1 during the 37.4 mg/m3 (t error equal to 36 .0% of 1977 growing season v/as "a"ndard the mean) and gross production during the growing season r¿as estimated to be 8750 Xcal/^2. Mean chlorophyll a concentratj-on in poncl 2 during the equivalent growth period (late 1977 a¡d early 1978) was 359'0 mg/*3 (! 26.3%) and gross production during the growing season \^7as estimated to be 84,000 Kcal/m2 To calculate gross annual productior, (ec/^2 /Year), production during the growing season I¡/as assumed to be 857" of annual production and 19 Carbon assumed to be equivalent to 9.4 Kcal (Brylinsky gross and Mann , lg73). Net annual production was taken as 50% of production af rer l,lestlake (:Ig74b) and Likens (1971). It was assumed that Scenedesmus was responsible for total phytoplankton production' The carbon con¡ent of Scenedesl¡¡us v/as taken as 46% of dry weight 62. (Strickland, 1960). Net annual production or yield was calculated as 1,190 g dry weight/m2 /year (+ sÈandard error equal to 36.0% of the mean) in pond 1 and 1L,427 g dry rveight /^2/y"ut G 26.37") in pond 2. From these values average daily net production rate In¡as 3.26 g dry weighE/*2/ day in pond I and 31.31 g dry weightl*2/a^y in pond 2' The second method used to calculate production \^¡as based on the relationship of chlorophyll to hourly production rate. Strickland (1960) reported an average figure of 4 rng of carbon synthesized per hour per mg of chlorophyll at optimum light (ca. 2OoC). Manning and Juday (in Ryther,1956) reported that 1 mg of chlorophyll corresponded to a mean gross production of 6.7 mg 0, per hour at the depth of maxinn:m phorosynÈhesis. This is equivalent to 2.09 rrtec/hour/mg chlorophyll (assuming a photosynthetic quotient of l'2; that is, lg}2 x 0'312 = lgC : Westlake, Ig74b). A rate of 3mgc/hour/mg chlorophyll was chosen for the following calculations. This represented production under optimal light conditions. Although diurnal variation in photosynthetic rate may be unimportant for the calculation of integral daily production in lakes (Fee, lg7Ð, allowance must be made for the increased inf luence of diurnal changes in physico-chemical conditions upon photosynthesis in shallow ponds (stengel and soeder, 1975; Anderson, L974). Light period was probably about 14 hours during the growing season at Gumeracha' A t hour period has been chosen to compute daily production to al1ow for sub-optimal conditions and surface inhibition at high light intensities ' This gave a correction factor of 0.64 times optimal daily rate which corresponded with the ratio of mean photosynthesis in the euphotic zone (1956) to rate under opËimum light conditions of 0.65 reported by Verduin Gross production \^/as converted to net production as above. Chlorophyll a concentrations (*g/*3) in both ponds were converted to mg per square meEre of pond surface and daily net production rates (g dry weight/m2 /daÐ calculatecl for each sampling date' Results 63. are presenÈed in Table 3.1. Average daily production rates \^Iere 1.904 g dry weígnt/m2lday (+ standard error equal Eo 37.17" of. t:ne mean) in pond 1 and 11 .589 g dry weight/m2 /day G 26.37) in pond 2. Daily production rates were plotted against time for each pond and the area under the curves (total net Production or total yield) determined using an Ott compensaEing polar planimeter, type 30 115. Total annual production hras 288 g dry weight/^2/yerr in pond I and 2r5I3 g , dry weightlmz/year in pond 2 during an equivalenÈ growth period. Maximum daily yields of outdoor mass cultures of Scenedesmus may exceed 30 g dry weight/n2/¿ay for short periods (1ess than 30 days) (60-90 during summer (Goldman , Ig7 9a, b). Average long term yields days) range from 10-25 g dry weígt-rt/mz/ðay (Goldman , 1979a; Becker, 1978; Heuss:Ier et a7., I97B Payer et a7.,1978; Shelef et a7.' 1978; SÈengel and Soeder, Ig75). These culture systems generally employ artificial nutrient media, mechanical mixing, and the addition of COr' yield is considerably reduced in cultures without COZ enrichment (Becker, 1g7B; De pauw et aL.,1978). The average daily yield from pond 2 calculated using the first method (31.31 g dry weight/m2 /d,ay) appeared much too high for a pond lacking CO, enrichment. Heussler et aL.(1978) reported average summer yields of 25 g dry weight/m2 /ðay at chlorophyll The second method of production concentrations of 400-70 O ^g/^2. calculation afforded more realistic results f.or a pond dependent upon natural CO, replenishment. Daily raËes were similar to those reported from a WSP v/ith similar organic loading under operational conditions (Bartsch and Allum, 1957). The nitrogen content of Scenedesmus gro\^,rl in sewage ranges Shelef from 7 .7-g.07. dry weight (Becker, 1978; Payer et a7., 1978; et a¡.,1978) and the phosphorus content from 2-3.I7" dty weight (Becker, L978; Shelef et aL.,1978). Strickland (1960) reported a phosphorus content of 1.o-2.\i¿ dry weight for natural populations. In the following TABLE 3.1 Chlorophyll a concentration (*g/*2) and calculated daily net production rate (g dry weight/m2 /aay) in ponds 1 and 2 at Gumeracha. Pond 1 Pond 2 Date Chlorophy 1 1 NeÈ Prodn Date Ch lorophyl 1 Net Prodn (g r (rg /*2 ) (g dry wr/ u (*g/*2) dry wt/ | ¿^y) o',2 ¡a^y) ^2 5.r.77 0 0 4.r.78 239.4 7 .025 19.L.77 36.0 1.057 18.1 .78 440 .0 L2,9T3 2.2.77 29.4 0.863 t.2.18 506 .0 14. 850 16.2.77 68.3 2.004 22.2.78 9r3.4 26.807 2.3.77 0 0 15.3.78 1304.0 38;271 29.3.78 610.9 17.930 L3.4.78 381.8 I I .205 2r.9.77 0 0 27.4.78 114. 5 3. 360 5.to .77 tr.2 0.329 10.5.78 5.8 0 .171 26.rO .77 5.8 0.170 8.rr .77 14.7 0.431 8.tr.77 6.5 0.196 23.rL.77 98 .3 2.885 23 .rr.77 162 .5 4.7 68 7 .12.77 154.0 4.520 7 .L2.77 276.r I .103 22.12.77 23r.0 6.779 22 .L2.tl L72.3 5 .055 11.589 " 1. 904 S t and ard Error !37 .t% !26.3 as %; 64. calculations the nitrogen content or scenedesmus has been taken as 8.0% and phosphorus as 2.0% ðtY weighE ' Total annual phytoplankton neË production (yie1d), calculated using the second method abover lfas 4I.472 kg in pond 1 and 3,128'062 kg in pond 2 during Ig77. In pond I during 1977 total phytoplankton producEion represented a nutrient store equivalent to 0.63% of TKN retained in the pond annually, 0.38% of total nitrogen (tfN + NO3-) retained annually, and 1.697. oÍ. total PO4-P retained annually. In pond 2 toÈal phytoplankton production represented a nutrient store pond during 1977 equivalent to 540 .B% of. total nitrogen retained in the ' and 119.6% of total PO4-P retained annually' It must be sLressed thaË the above phytoplankton production estimates are highly speculative; conclusions based upon them must be guarded. Calculated production rates are likely to be overestimates as the relationship betrnreen chlorophyll concentration and production was assumed to be linear. This will not hold at very high phyÈoplankton densities where self-shading reduces net prodtrction (Jewson and Taylor' 1978; Bindloss , 1976; Talling et a7. , Ig7Ð. Temperature variation during the growing season (tl-ZSoC) has not been taken into account' In view of the assumpÈions intolved in the method it was felt that this Theaccumu]-atederrorsinthemethodsuseda.bovecouldbefarqe. would be false;;";;;;t/ It may be concluded that harvest of total net phytoplankton production in pond 1 during 1977 would probably have removed less than 2% of Ëotal nitrogen and POO-P retained in the pond ' In pond 2 during 1g77, harvest of total net phytoplankton productíon could, perhaps, have removed a significant percent.age of toÈal nitrogen and POO-P (possibl.y 50-1002) retained in the pond' 3.3.5 Dynamics and Pro duction of Cfadophora. Seasonal fluctuation in percentage surface coverage of ponds 1 and 2 by floating Cladophota mats is shown in Figure 3.6. Cladophora r^7as present in large amounts on the bottom of pond 1 from July to October 1916. Surface coverage 80 q) 60 ò0 d H o) Þ o o o d t+] l¡ 40 (/) OJ ò0 çd +J ç I o l¡ tr 0) ll Fr 20 I > 0 DJ DJ L97 6 L977 I978 Time (months) EIGIJRE 3.6 Percentage pond surface coverage by Cladophora mats. Pond 1 (-), pond 2 C--). 65. rìras less than I0% during Ehis period. Coverage increased rapidly in November and reached 7O7" by 22 December. Mats were discoloured at this time. coverage declined to 10% on 19 January 1977, and although CTadophota r¡ras fairly dense on the bottom of pond l unti1- May, surface coverage r{as less than 102. cTadophora disappeared from pond I during June and July 1977. A small amount reappeared in August 1977, buË surface coverage \¡ras less than 10%. Abundance increased during November declined to less t]nan 57' L977 i coverage reached 407" on 23 November, but in late December Lg77. CTadophora vtas absent from, pond 1 by mid-January 1978 and did not reaPPear until October I978' ctadophora \^/as less abundant in pond 2 than in pond I from July to November I976 and coverage reached 30% briefly during late December 1976. cTadophora \^/as absent from pond 2 by 5 January 1977, and reappeared in small amounts in April Ig77. Coverage htas less t]nat 57" during April and from August to late September 1977. cTadophota l¡/as absent from pond 2 in early october Ig77, and did not reaPPear in that pond during the remainder of the present study' In summary, high surface coverage occurred in pond 1 from November L976 to January L977 arrd a phytoplankton bloom \^7as not observed in that pond. Moderate coverage occurred only briefly in pond 2 during pond. December and a dense phytoplankton bloom developed in Èhat Moderate coverage occurred only briefly in pond 1 in late November 1977 and a phytoplankton bloom developed in Èhat pond' No floating mats occurred in pond 2 during laLe I9l7 and a phytoplankton bloom developed' The biomass of cTad.ophora at Gumeracha !'Ias not sampled,directly Tentative estimates of mean biomass during ]I977 were calculated from the relationship of mean annual total inorganic phosphorus concentration (mg/1) and mean annual dry weigh t (g/^2) of. CJ-adophota presented by Pitcairn and Ilawkes (1973) ' This relationship is based upon stream samples taken above and below points of sewage input. Mean annual total 66. PO4-P concentration during 1977 was 7.99 nel1- (t standard error equal to 13.I% of mean) in pond 1, and 4.78 ne/l (1 10.92) in pond 2. Mean annual biomass was calculateð, as 362.5 g dry weight/*2 in pond I and ZO2.O g dry weight/m2 in pond 2. Estimated biomass values fell r¿ithin the range recorded from fast flowing streams of lower nutrient staEus (whirron, 1970). The ratio of production to biomass (p/s) is a measure of the exËent to which production exceeds biomass or sÈanding crop. P/B ratios for CTadop.hora during the vegetation period vary from 15-16.5/I (nohr and Luéciiska, 1975; Gak et aJ., 1972). Total production of CTadophota for the year occurs during the growing season and may be approximated by rnultiplying mean annual biomass by P/8. Annual net production of Cladophora h/as calculated as 5.709 kg dry weight/^2/y"^t in pond I and 3.L82 kg dry weight/*2 /year in pond 2, using a PIB ratio of 15 .75/I. Maximum growth of CTadophora ín temperate localities occurs during two short periods in late spring and autumn (May-June and September -october in the northern hemisphere) (Mantai , I97B; trrlong eü a]', L978; wong and clark , 1976; Whitton, l97o; HerbsÈ, 1969; Bellis and Mclarty, Lg67). Crops usually decrease during midsummer and growth rate is highest at intermediate temperatures (approximately tg-ZOOC) (Wong et a7-, L97B; Mantai , 1974; !'Ihitton, I97O; Herbs t, L969; Mason, 1965) ' Maximum growth at Gumeracha during 197 7 would thus have occurred during March and OcLober-November (figure 2.4) . This coincided with northern hemisphere periodicities . Floating maLs of Cladophora during suûEner are the result of thal1i deteriorating and breaking loose from the substrate (Mantai, 1978). Trapped oxygen bubbles then lift mats to the surface (Vtrhitton, 1970). The extent of floati-ng mats preserit during a given surtrner r^¡ill therefore reflect bottom coverage during the two prior growth periods as mats overwinter (between growth periods) on the bottom (Mason , 1965). Total 67. annual net production is equivalent to maximum area of surface coverage (*2) *.rttiplied by areal net production (Ug/^2/year). Surface coverage in pond 1 was 40% duríng late November 1977. Coverage in pond 2 was less Ehan 5% during September 1977 (CTadopnora l¡/as absent after that time). Total net production during I977 was calculated as 3,288.600 kg dry weight/year in pond 1 and 198.048 kg dry weight/year in pond 2. Mean phosphorus content of cTadopåora tissue is 0.77" of dty weight (Kwei Lin, 1977; l^lhitton, 1970). During the course of the growing season tissue nitrogen content may vary from approximately 1.4 to 5.7% oÍ. dry weight with a mean value of 3.27" (c.f . .Mantai, 1978), Total estimated annual net production of Cladophora in pond I during 1977 represented a nutríent store equivalent to 47.L7" of total PO4-P retained in the pond annually, 20.17" TKN retained, and 12.0"/. of total nitrogen -of (lfN +. NO3-) retained. Total esÈimated annual net production in pond 2 represented a nutrient, store equivalent to I.37. of total PO4-P retained in the pond annually and 6.97" of total nitrogen (tfN + NO3-) retained. The above calculations are speculative and, like those fbt the estimation of phytoplankton production, involve many assumptions. The results must, therefore, be interpreted with caution. It appeared that total annual net producËion of Cladophora írt pond 2 during 1977 represented a minor nutrient store (probably less than 27" of. total PO4-P and less g¡an 77" of total nitrogen retained annually) and that harvest of CTadophora from that pond would not have provided a significant pathway for nutrient removal. Ilarvest of total annual net producÈion of Cladophora from pond 1 during 1977 couLd, perhaps, have removed a significant percentage of the nutrients retained (possibly 407" of. total PO4-P anð. IO% of total nitrogen) in that pond. 3.3.6 Dynam ics and Production of Poúamogeton oclveatus- Maps of P. och3eatus beds in the Gumeracha ponds on 15 June, 10 October, and 13 December L977, and 30 August 1978 are shown in Figure 3.7, A-D. Area o 0 0 o" 0 00 0 :0 o 0 0 .ô q'd 0 0 0'. 0 5 D ooBå 0, 0 0o to r 0 ô 0 ho $ ú 0o I B q D o A B t 0 o o 0 0 b ß ó 0 ,Å 0 0 0 0 6oo o o ,0 d b 0 0 0 ô a Þ 0 ô 0 t o Pond I C Pond 2 Pond 1 D Pond 2 in the FIGURE 3.7 Bottom coverage- ( ) by Potamogeton ochreatus Gumeracha Ponds orr A f 5.6 . 7J , ß: 26 .lO -77 , C: 13 "I2.11 , and D: 30.8.78. 68 of coverage by P. ochreatus (*2 an.l as. Percentage of bottom area) on these daËes is presented in Table 3.2. P. ochreatus was abundant in both ponds from July to late September 1976. In pond 2 plants lost colouration and became overgrowrl by Cladophora duríng October and November. P. ochreatus was not Present in pond 2 by December and did not reappear in that pond until l"lay L977. P. ochreaÈus remained in pond 1- throughout laEe 1976 and early 1977 and although shoots r^lere overgror¡7n by cTadophora, bottom coverage was high. shoot height and bottom coverage in pond 1 increased from March until June 1977' Growth from the previous season disappeared during this period' Bottom coverage reached a maximum in June ß7 JÐ (fig' 3'7, A) and remained fairly constant until flowering occurred in late October (inflorescence spikes on peduncles reached the surface). In pond 2 shoot height increased during Nlay I977; botËom coverage reached a maximum during ocEober ß6.8"/") (rig. 3.7., A and B). Flowering occurred during early october in pond 2. P. ochreatus may flower from August to March although this generally occurs in November and December (Jessop, 1978; Aston, 1973)' p. ochteatus beds in boËh ponds \dere overgro\n by cTadophora during November and December 1977. Plants collapsed and lost their colouration (fig' (assuming a brornrnish appearance), and bottom coverage decreased 3.7, C). A rapid decline in bottom coverage occurred in both ponds during late December and P. oclveatus was absent from both ponds by 4 January 1978. P. ochreatus did not reappear in either pond until August 1978 when very small stands) consisting of only a few plants, became established (fig. 3.7, D) ' P.oclweatusthusbehavedasaperennialinpondlfromJuly 1976 until October L977; in pond 2, P. ochreatus behaved as an annual with regrowth from May to November 1977. In pond 1 plants from the 1976 season had disappeared by the tirne t]ne 1977 crop had reached maximum biomass. Bottom coverage in pond I during Late 1976 and early Table 3.2 Area (m2) and percentage of bottom covered by P. ochreatus in the Gumeracha ponds. , Pond I (Bottom area = tttZ m2) Pond 2 (Bottom area = 1006 m') 2 2 Date Area (m ) Z boÈtom coverage Area (m % boËtom coverage L5.6.77 978.9 87 .7 100.0 9.9 26 .LO .7 7 370.2 36 .8 13.L2.77 804.2 72.O 109.7 10.9 30. 8.78 6.7 0.6 8.0 0.8 69. 1977 was high (although plants hrere noË growing actively) and a phytoplankton bloom did not develop in that Pond ' P' ochteatus was about from pond 2 during the same period and a dense phytoplankton bloom developed. P. ochzeatus was absent from both ponds during laEe each' 1977 and, early 1978 and phytoplankton blooms $/ere observed in Mean wet and dry biomass (g/quadraf) (1 standard error (g/*2) expressed as percentage of the mean) and biomass Per uniÈ area of. p. ochreatus in ponds I and 2 on 15 June 1977 are Presented in Table 3.3. Biomass was sampled during maximum bottom coverage in pond 1 but prior to maximum coverage in pond 2. The determinants of areal biomass (shoot density and height) appeared not to change afEer June 1977 in pond 2, although in the absence of regular biomass samples this observation is subjective. The similarity of dry areal biomass in both ponds during June suggested thaÈ maximum areal biomass was achieved at the the same Èime in both ponds. A standard error equivalenl Eo IO7" of biomass mean is acceptable in this type of study (Davies, 1970) and samples from pond 2 met this requirement despite the approximate nature of the sampling method. The variability of biomass samples in pond 1, therefore, appeared to reflect inherent variation in the distribution of biomass within that Pond. DryweightofP.ochteatuswasequivalenttoT.9%of.wet weight (+ standard error equal to 2.8% of the mean)' No encrustations of Ca CO, occurred on the stems oÍ P' oclteatus plants from the Gumeracha ponds. PlanÈ weight was not, therefore, subject to over- esEimation from this source. organic compounds in sewage apparently prevent the formation of marl encrustations even at high pH (Sculthorpe, 1967). Net production of a true annual macrophyte is defined as the amount of material produced over a year and is equivalent to maximum biomass if losses, other than respiration, are small. Losses aË (see but Gumeracha, prior to maximum biomass, v/ere not obvious above) Table 3.3 Mean biomass of' P. ochteatus per quadrat (g), t sÈandard error expressed as Percentage of the mean, and biomass Per unit area , (glt2) ir, the Gumeracha ponds on 15 June 1977' Pond 1 Pond 2 lJeE Dry lùet Dry Biomass 115.9 GZZ.i7.) 9.6G33.9"/.> r2B .9 (!10 .9%) 9.6(110.S%) (g/quadrat ) Areal biomass 609.9 50:4 677 .9 50.5 G/*2) 70. are likely to have occurred Èo some extent. Losses that are not obvious may also occur. These include leaf fall, stem damage, and invertebrate grazíng (I^festlake , Lg75, 1965). In additiorr, po"itive neE photo- synthesis nlay occur after maximum biomass has been reached (Dawson, Lg76). Production estimaÈes must be corrected for these losses' This (p/n). can be done using the ratio of production to maximum biomass This ratio is a measure of the amounE by which annual production exceeds maximum biomass. i,lestlake {ogl5) has estimatecl the production of aquatic vascular plants with pronounCed seasonal growth (annuals or perennials in r,ihich loss of the previous year's growth occurs before maxirm'rm biomass is reached) by adding 20-25% to the seasonal maximum biomass (giving, in effecr, P/B ratios of 1.2-1'.25/I). P/B ratios for submerged (Howard-tr'li1liams, macrophytes, including Potamogeton, range from 1.1-1.5/1 of 1978; Kver and Husák, 1978; Darnrson , 1976; Gak et a7.I972). Ratios I.5ll, or higher, occur only in populations r¿ith long growing seasons and in v¡trich mortality of the current yearts croP is high prior to maximum biomass(KvetandHusák,|g7B;AdamsandMcCracken,IgT4;Matthewsand study I,lestlake, 1969). L P /B ratio of 1 .2/I was used in this ' Annual production (net) is equivalent to the biomass increase (regardless of the length of the growing season) multiplied by the P/B ratio. Daily production must, of course, be related to the actual period of growÈh. Annual areal production (g dry weight/m2 /year) (! standard error as percentage of the mean) and total annual production per pond (tg dry weight/year) of P' ocbreatus in the Gumeracha pgnds during 1977 axe presented in Table 3.4. Annual areal production of p. ochteatus was similar in both ponds during 1977. Total annual production in pond I was 2.64 tímes that in pond 2 due to higher boÈtom coverage and larger bottom area in pond 1 ' Table 3.4 Annual areal producEion (g dry weight/m2 lyear), t standard error expressed as percenÈage of the mean, and total annual production per pond (kg ary weight/year) of P. ochreatus at Gumeracha during L977. Pond 1 Pond 2 n Annual areal prod 60. 5 (1 33 .e%) 60.6 (1 10.82) (el^2 /ye"t) ToÈal annual prodn 59.240 22.423 (tglyear ) 7L. Mean kjeldahl niErogen content of P. ochteatus tissue at maximum biomass in the Gumeracha ponds was equivalent to 1.927' of' dty weight (+ standard error equal to 20 .I7" of the mean). A tissue niËrogen content of 1.8-2.5i¿ of dry weight has been reported for p. oclu:eatus from fertile New Zealand lakes (Rawlence and tr{hitton, Ig77). AlEhough tissue nitrogen and phosphorus conLent of submerged macrophytes varies seasonally (Carpent.er and Adams , I97 5; t{ile , I97 5; Adams and Mccracken, 1974; Cowgill, Lg74; Boyd, 1970; Gerloff and (maximum is Krombholz , 1966) content at the tine of harvest biomass) of most importance for nutrient removal. The total annual production of p. oclteatus in pond I during !977 teptesenled a nitrogen store 0 of equivalent to 0 .227" of TKN retained in the pond annually and '137" the total niËrogen (rrN + NO3 )retained. In pond 2 total annual production represenÈed a .rit.og.t store equivalenC to 0'91% of the total nitrogen retained annually' The nutrient contenÈ of submerged macrophytes at maxinrtrm biomass in natural lakes generally lies in Ëhe middle of the annual range (carpenter and Adams , Lg77; Nichols and Keeney, 1976; I'lile, L975; Adams and McCracken, I97Ð. A reasonable value for tissue phosphorus contenÈ in P. oclreatus would aPpear to be about 0.25% ot dry weight (Rawlence and !trhitton, Ig77). However, intra-specific variation of niErogen and phosphorus content in submerged macrophytes (Ho, is apparently correlated with habitat nutrient status 1979i Trhe only Rawlence and Whitton, 1977; Hutchinson, 1975; Boyd,1970)' study reporting nutrient content of Potamogeton from the hypereutrophic condiÈions of aerobic I,JSPs is that by McNabb (1976). McNabb reported a significant linear relationship between plant tissue phosphorus content and ambient soluble phosphorus. This relaÈionship yielded tissue phosphorus values of 2.IL% of dry weight for P. ochreatus in pond I and 1.44% of dry weight for P. sçþreatus in pond 2. These apPear extremely 72. high compared to literature values for Potamogeton species (including P. ochreatus) from natural lakes (Rawlence and Inlhitton, 1977; I^IiIe, L975; Cowgill, L974 Boyd, 1970; Gerloff and Kromb]no]-z, 1966). However , Spirod.eTTa oTigothiza may have a tissue phosphorus content equivalent Lo 2.847. of dry weight when cultured in swine wasÈe (Culley and Epps, 1973). In lake hrater, nitrogen and phosphorus concentrations are generally highest prior to the period of plant growth and decline as planÈ growth becomes heavier (Gerloff and Krombholz, 1966). This may explain why Èissue nitrogen and phosphorus of submerged macrophytes from lakes is lower at maximum biomass than early in the season. In WSPs, nutrient inpuÈ is continual and plants have access to water of high nutrient concentration_while growing most vigorously. This could explain why McNabb (1916) found híghest tissue nutrient content at maximum biomass and an extremely high phosphorus coritent. Using tissue phosphorus content calculated from McNabb (I976), total annual net producÈion of P. ochleatus in pond 1 at Gumeracha during 1977 would have represented a phosphorus store equivalent to 2.567" of the total PO4-P retained in the pond. In pond 2, the phosphorus store represented by total anàrral net production of p. ochreatus would have been equivalenÈ to O .627" of the total PO4-P retained in the pond ' ToÈal annual producËion of P. ochreatus was higher in pond 1 than in pond 2 but represented a higher percentage of total nitrogen reÈained in pond 2 due to a negative TKN retention. As toËal PO4-P retention v/as similar in both ponds the higher production of P. ochreatus in pond 1 reiresented a higher percentage of toËal PO4-P retained. The use of a harvesEing strategy which removed half the standing crop at certain critical times during the period of maximum biomass couId, theoretically, increase total yield by IBO'/" (t"tcNabb, L976), Even if this could be accomplished aE Gumeracha wllen bottom coverage was 73. P. ochreatus IOO7., theoretical upper limits to nutrient removal by harvestwouldbelessthan5%oftotalnit'rogenandtotalPo4-P retained annually in the ponds. Thar these yields could be achieved did not in reality is extremely doubtful. Production of P. ochteatus rePresentasignificantnuErientstoreintheGumerachapondsand pathway for harvesË of this macrophyÈe would not have provided a useful nutrient removal. production (kg/yeat) Pr Produc Ëion - Summa ToËa1 annual net 2 during of p. ocltreatus, cTadophota, and phytoplankton in ponds 1 and rePresented Lg77, together with the percentage of Lotal primary production byeachgroupispresentedinTable3.5.Despitetheapproximatenature and phyto- of the methods used to estimate the production of Cladop]rora plankton, total net primary production in both ponds showed a close correspondence. Production of p. ochreatus rePresented a minor proportionoftotalprimaryproductioninbothponds.C]'adophota wasthemajorprimaryproducerinpondlduringlgTTandphytoplankton the major contributor to primary production in pond 2 ' 3 .4 Dis cus s ion Thealgaethatoccurin}JsPsmustobviouslybecapableof Although 4 adaptation to high concentrations of organic compounds ' Euglenophyta, phyra are represented in the flora of wsPs (the chlorophyËa, Chrysophyta,andCyanophyta),relativelyfewgenerahavebeenrecorded irrespectiveofgeographicallocation,climate'se\^/agecomposition'or Fitzgerald and degree and type of pretreatmenË (I^lard ancl King , Lg76; Anabaena' Anaé¡stis' Rohlich , Lg64, 1958). The most comlnon gener:a are sCenedesmus' At.tkist.rodesnus/ chTamgdomonas, chLorel-J-a, EugTena, ar'd (Goulden, I976; This holds for northern and southern North America 1967) Central America Palmer , Lgl4, Lg6g; Gloyna, 1968; De Noyelles ' ' (Melchow-Mó];Let et a7' 1955) and the ltlest Indies (Palmer , Lg74), Europe ' ' rhe united Kingdom (vnrite, lg75), India (Patil et a7" 1975; Ahmed' Table 3.5 Total annual net production (kg/year) of P. ochreatus, CTadophora, and phytoplankton in the Gumeracha ponds during L977. Pond 1. Pond 2 n ol Total net prodn 7! Total net prod (kg/year) (kglyear) 59 L.7 22 0.7 3288 97 .O 198 5.9 4L 1.3 312 I 93.4 x 3388 100 3348 100 74 Ig74; Singh and saxena, 1969), New Zealand (Haughey, 1969, 1965), and Australia (ttris study; Hussainy, 1978). No local or regional floras develop and attempts to influence species composition via inoculations 1964; Bartsch' are ineffective (Goldman, 1979b; Fitzgerald and Rohlich ' 1961). Apart from cursory references to the periods of peak algal abundance (..g. De Noyelles, 1967; Neel and Hopkins' 1956)' little attempt has been made to describe the seasonal dynamics of algal populations in I^lSPs. In the Gumeracha ponds a single, annual algal population increase occurred from November to March (summer) ' Maxímum chlorophyll concenËrations occurred from mid to late March' This type of algal cycle has been described in maturation ponds in the united Kingdom (Potten, Ig72) and is similar Ëo seasonal events in highly eutrophic, temperate lakes where the spring and autumn phytoplankton (Mathieson, 1971; maxima are obliterated by an extended mid-summer peak Round, IITI). A fundamentally different situation has been reported for maturation ponds in southern Africa (stiitringlaw and Pieterse , 1977) ' Although organic loads and chlorophyll a maxima in the African ponds resulted rirere similar to Èhose at Gumeracha, higher ambient temperatures in the occurrence of dense phytoplankton populations during all seasons ' (less than The algae underwent a series of rapid, although short-lived one month), population increases throughout the year' Lightandtemperatureinfluencetheseasonaloccurrenceof (Stengel algae (Jones , lg77; Lund , 1965) and population growth rates and Soeder, 1975; Moss, Ig73b), No data were collected on thq light seasonal variation of incident light intensity or the underwater the climate at Gumeracha and it is, therefore, difficult to separate effects of temperature and photoperiod. It has been shown that although the onset of phytoplankton blooms apparently occurred when temperatures of the exceeded 17-18oC, temperature variation accounted for only 422 75. variance of chlorophyll a concentraËion. Furthermore, chlorophyll a concentration rvas maximal in pond I at 16.6oC. That is, temPerature appeared to be imporÈant for triggering the onset of phytoplankton blooms but was not a major factor terminating blooms ' self-shading at high algal densities can reduce net productivity by decreasing the depth of the euphotic zone(making the lake "optically deep" by reducing the relative fraction of water volume !,tithin the euphotic zone) and increasing respiration relative to photosynthesis (Jewson and Taylor, 1978; Bindloss, 1976; Ta11ing, 1971). Talling et aJ. (1973) reported severe self-shading by phyto- plankton in African lakes with chlorophyll a concentrations of 900-2000 ? mg/mJ and euphotic zones less than 30 cm deep. At maximum chlorophyll a concentrations in the Gumeracha ponds (March 197S) the depth of the euphotic zone would have been less than 50 cm in pond 1 and less than 25 cm in pond 2 (c.f . I,Ietze1, 1975, p. 337). LighE inhibition at the pond surface may have further restricted the optimal- zone for photo- synthesis. Self-shading may have reduced net phytoplankton production in the Gumeracha Ponds. The irnportance of niLrogen and phosphorus for a1gal growth has been repeatedly demonstraÊed and, generally, phosphorus is dominant as the nut::ient most frequently controlling production (Weldn et a7', 1978; Schindler and Fee, Ig74; Schindler et aJ., I97I; Fogg, 1973; Jordan and Bender, LglÐ. *O3- and soluble POO-P concentrations in borh ponds at Gumeracha exceeded limiting values (300 pg/1 and 25 ve/I respectively : Hart , Lg74; Stewart and Rohlich, 1967) throughorlt the study. carbon may become limiting in llsPs (ring, 1976, 1972) although this is rare in natural lakes unless nutrient inputs are extremely high (Steeman-Neilsen, 1955). Carbon limitation may occur diurnally in facultative ponds due to the rapid depletion oÍ CO, accumulated during Èhe night (Barrsch, 1961). Talling et aJ. (1973) reported algal crops 76. of over 2000 mg/m3 chlorophyll a in tl-re Bishfotu soda lakes ' These authors pointed out that lvhile the soda lakes were similar to se\¡Iage lagoons in that they exhibited high phytoplankEon concentrations and high rates of oxygen producËion, they differed fundamentally in their CO, reserves and pH buffering capacity' It was calculated from prosser et a7. (1968) ttrat the total alkalinity (HCO3- + CO, ) in the soda lakes at the time of Tallingrs study would have been 2866-3062 mg/l of which 2282-2605 mg/l was in the form of HCO3 That is, the carbon supply for species able to use IICO3 would have been adequate even at high cell densities. The TIC concentration in the Gumeracha (March ponds during the latter stages of phytoplankton blooms 1977 a".d 1g7B) was less than 5 mg/|. AË the pH values attained during these tímes (10.5-10.8) no free CO, woul that the algal benthos rnras les.s well developed ' The algae of facultative I,ISPs undergo a characteristic succession high' usually' of dominance during \¡Tarmer months when standing croPs are an initial mixed population of flagellated greens is followed by blue-greens (Patil EugTena, then scenedesmus, chforelTa, and finally rnixed eta7.,1975;King,1972;Haughey,1965;SinghandSaxena'L96'9;De Noyelles, 1967; fíLzgerald, 1964; Neel et al'' 1961)' Succession was the small, less obvious in the Gumeracha ponds, although during early 1978 ,unicellulargreerrwasreplacedbyScenedesmus.CellcounEdatawas limited but indj-cated a shift in scenedesmus species comPosition culminating is in the dorninance of 5. quadricauda. Little ecological information available for species of sceneclesmus although s. quadricauda has been 78. rated the most pollution tolerant member of the genus (Palmer, 1969). Succession in InlSPs generally favours species less tolerant of high organic concentrations (fing , lg72). BOD and TOC increased in Ehe Gumeracha pbnds as algal blooms progressed. The liberation of otgtti" acids, polysaccharides, and nitrogenous comPounds during photosynthesis and cell decomposirion (ttobbie , Lg76; VJard and King, L97 6) may mean that algae themselves apPreciably increase the organic contenL of their m.edium. Succession also generally favours species able to use low concentrations of free CO, (Xing , I972). TIC concentrations were low during March 1978 (fig. 2.18) when S. quadricauda was dominant and this species is able to use HCO, directly as a carbon source (Moss, 1973a' Osterlind , 1949). It has been shown that a phytoplankton bloom did not develop in pond I when it was dominated by a Potamogeton - CTadophora association. A bl oom did develop when P. ochTeatus r,/as absent and surface coverage by cladophora r^/as brief . As in natural ponds and lakes, the presence of submerged macrophytes and/or filamentous algae can apparenÈly inhibit phytoplankËon development in lJSPs. This is reflected in the similarity of net productior- of cTadophora in pond I (3288 kg) and phytoplankton in pond 2 (3128 kg) during L977 -' It has been suggested that macrophytes and filamentous algae (McCord compete directly with phytoplankton for phosphorus and nitrogen and Loyacano, L978; Fítzgerald, L969; Ilutchinson and Bowen, 1941). It is extremely doubtful that nitrogen and phosphorus ever constituted a lirnited resource in the Gumeracha ponds. Neith": n. och'teatus rror cladophora \Árere in an active growth phase in þond I during early L977 ' ThaE is, nutrient uptake by these species would have ceased. In fact, it is 1ike1y that both were undergoing bacterial decomposition and that nutrients were released A morè likely explanatiori for the effect uPon phytoplankton is that the Potamogeton - CJ-adophora association resËricted light penetration into the lrater column thereby inhibiting photosynthesis ' Floating a19al maËs can re-duce illumination drastically (Goulder , L969) and phytoplankton producÈivity beneaÈh mats may be reduced (Boyd, L973) or suppressed entirely (Goulder, 1969). Light penetration and phytoplankton productivity are both higher amongst submerged macrophytes than beneath algal mats (Boya, lg73; Goulder, 1969). Shoot density of p. ocllîeatus at Gumeracha v¡as 1ow (c. f . Howard-l{illiams , 1978 ) and light penetration would have been greater Èhan beneath algal mats. It is unlikely Lhat P. ochreatus stands at Gumeracha would have reduced phytoplankton productivity completely. It appears that phytoplankton development vtas prevented in pond 1 by the presence of floating CTadophota mats. Hartley and l^leiss (1970) reported that algae l¡/ere absent beneath a floatin g OscilTatoria mat but Present in the adjacent mat-free portion of a small oxidation Pond ' Surface coverage by cTad.ophora in poncl l during late 1977 and in pond 2 during late L97 6 was. insufficient to prevent the development of phytoplankton blooms. Apparently, surface coverage must exceed 507' for approximately 2 months during the period of phytoplankton growth onset to inhibit blooms. Surface mats in pond I sank to the bottom during late December L977 and a small increase in chlorophyll a occurred during January and Februaty 1978. However, the presence of P. ochfeatus !,¡as apparently suf f icienE Èo PfevenE the development of high phytoplankton standing crops. It has been postulated that submerged macrophytes may excrete an antibiotic substance which inhibiËs phytoplankton (e'g' Philips et aI.,1978); the existence of such a substance has not, as yet, been experimentally verified' 80. Poncl chemistry and performance at Gumeracha may be interpreted in the light of macrophyte and phyroplankEon population cycles ' Dissolved oxygen concentration and Percentage saturation were highest in both ponds during phytoplankEon blooms but decreased abruptly as blooms declined. oxygen concentrati<¡n and saturation in pond 1 were much lor.¡er than in pond 2 during the period (from November I91 6 Eo March Ig77) that a phytoplankton bloom developed in pond 2 but not in pond I. Oxygenation of both ponds \,^7as greater during the winter of 1977 than the winter of 1978 due Ëo the presence of actively growing p. ocþteatus stands. Respiration of submerged macrophytes only contributes to deoxygenation ¡,ihen areal biomass is much higher than encountered at Gumeracha (Jorga and i'Jeise , lg77; Buscøni'' 1958) ' Lower oxygen concentrations in pond 1 during the winter of 1977 may have resulted from higher zooplankton respiration (see chapter 4)' Oxygen depletion near the bottom of pond 1 during November-December Ig77(rig.2.g)Ílayhaveresultedfrombacterialdecompositionof senescent P. ochteatus and CTadophota' This would have been more severe than in pond 2 due to higher standing crops of both' Bacterial decomposition in pond I may also have contributed to clinograde oxygen profiles (nig. 2.10) The effect of photosynthesis on pH has already been discussed' pH was highest in both ponds during phytoplankton blooms and decreased abruptly as blooms decliued. The pH of pond 2 was much higher than pond I during the summer of 1977 when a bloom developed in the former but not in the latter. Pond effluent pH exceeded influent duri¡g the winter of 1917, probably as a result of phoÈosynthesis of the P' ochteatus below influenE - CJadophora association. The pH of pond 2 effluent fell during ltfay 1977 (rig. 2.I3); this corresPonded to the period between the decline of the phytoplankton bloom (April) and the reesEablishment of moderate P. ochreatus stands ' 81. Effluent BoD and ss exceeded influenÈ values during phyËoplankton blooms. That is, the Presence of alga1 cells contribul-ed to the BOD and increased SS. Reduction of BOD and SS was highest in pond I from autumn to spring 1977 and was probably effected by actively growing P. ochteatus and CTadophota- Removal r¡ras lower during early L977 as the P. oclteatus population was in a senescent phase. Removal during Ehe winter of 1977 was lower in pond 2 than in pond I due to a lower total sËanding crop of P. ocizreatus in the former. Mean annual percentage reduction of BOD and SS during l-977 was higher in the macrophyte-dominated pond 1 (table 2.3) . That is, submerged macrophytes and filamenËous algae appeared Lo contribute substantially to BOD and sS reduction. ReducEion of BoD and ss during the growiflg season of P. ochteatus and Cl-adophora at Gumeracha approached (Dinges, thaÈ recorded in ponds supp<ìrting gro\^¡th of Eíchltornia crassípes Lg78, 1976; Cornwell et a7., 1976; ülolverton et aI.' 1976) and, on some occasions, \¡ras equivalent to that effected by the emergents Scirpus arrd pltragmites (De Jong, 1976; Seidel, 1976; Spangler et al., 1976)' Effluent TOC also exceeded influent values during phytoplankton bloonrs. Removal in pond 1 during the winËer of 1977 was much higher than in pond 2! as was mean annual removal. Submerged macrophytes apparently contributed to TOC removal although this was substantially lower than BOD and SS removal. poor performance of the Gumeracha ponds, individually and overall, wiËh respect to BoD, ss; and Toc reduction occurred during phytoplankton blooms and was the direct result of algae in effluents ' Perfonnance overall was highest during periods of rnacrophyte growth, although other factors (".g. zooplankton) may have been involved during those times. Even allowing for lower temperatures, oxygen saturation during winter generally exceeded 60%. In fact' severe deoxygenation only occurred during the decline of phytoplankton blooms. It may, B2 therefore, be asked whether unicellular algae are necessary for oxygenation or the s tabíIízation of organic matter in the Gumeracha ponds. The theory of IJSP function based upon the algae-bacteria modelaPPearstobeinappropriateforpondsoftheGumerachatyPe. NH,removalinpondlwaslessthan50%duringthesummerof Lgl7, increased as P. ochreatus 6rrð Cladophota) growfh Progressed and remained high (> S0%) throughout the rest of 1977 arld early 1978' (from Apparently, P. oclÙ eatus, Cladophota, and algae November I977) contributed to NH, removal. In pond 2, NH3 reduction was high during the phytoplankton bloom of early 1978 but decreased markedly as the bloon declined. Removal of NH3 did not improve in pond 2 until peak to biomass of p. ochreatus was achieved in october. NH3 may be lost Stander, the atmosphere when pH exceeds 9.0 (t TKN and organic-N removal in both ponds was highest when p. ochreatus and cJadophora r^rere well established. Removal in pond 1 j.s crops in was higher than in pond 2 as consistent with higher standing the former. Effluent TKN exceeded influent values during phytoplankton blooms. NO¡- reducËion, however' \^7as generally highest during the phytoplanlcton blooms, although removal was high in pond I during sufltrner of. L977 . Reduction of total and soluble PO4-P in both ponds was highest during phytoplankton blooms. PO4-P increased. in pond 1 during the P' ocltreatus summer of L977, probably due to decomposition of senescent ponds elsewhere arld cLad.opl-tota. This has been observed in maturation (Stritlinglaw and Pieterse, IgTl). PO4-P removal dicl, however, increase markedly in pond 1 as P. ochreatus stands developecl during mid 1977 ' 83 Removal during periods of macrophyte growth was highest in pond 1; Èhis was consistent with higher standing croPs. In pond 2, removal of Poo-P in the absence of phytoplankton only toolc place in spring 1977 when P. ochieatus had achieved maximum biomass. In Ëhis pond, phytoplankton rapidly assumed the function of PO4-P rernoval in late 1977 ' In pond 1, PO4-P removal decreased completely as P. ochteatus and CTadophora declined and did not increase again until Ëhe phytoplankton standing crop had become rve1l established' ' Nutrient removal during periods of P' ocitreatus - CladoPhota dominance and during periods of phytoplankEon dominance is summarised in Table 3.6. Removal of nitrogenous compounds (except NOr-) was highest in pond I during periods of p. ochreatus - cJ-adophora dominance' NH3, TKN, and organic-N generally increased during phytoplankton blooms' However, NO3I and POO-P removal was highest in pond 2 during the sununer periods of phytoplankÈon dominance. In ponds, or lakes, of similar morphometry and flushing rate, nutrient retention must be greatly influenced by ecosysÈem structure. The predominance of phytoplankton in pond 2 a¡d P. ochreatus - cJadophora in pond 1 during 1977 accounted for the overestimaËion of the phosphorus retention coefficient in the latter ín 1977 (f ab1e 2.6) . 'Nitrogen and phosphorus removal in pond I when standing crops of P. oclreatus - Cladopho-ra were high was equivalenE to that reported lot Eicltltotnia crassipes cultures (Oinges , L978, L976; Cornwell et al ., Lg7û. Nutrient removal during this period was lower (Ue Ëhan that reported in trials using emergent macrophyËes Jong, L976; Spangler et aI ., Ig7O. Nutrient removal in the Gumeracha ponds' during phytoplankton blooms r^/as equivalent to that f oi mechanically mixed, sha1low, outdoor cultures of Scenedesmus in climates of high incident light inrensity (De Pauw et a7., I97B; Shelef et a7.,1978)' A1Èhouglrnitrogerrremovalduringperíodsofmacrophyte dominance was high, inf luent-eff luent compar;'-sons do not give a true Table 3.6 Percentage nitrogen and phosphorus removal in Èhe Gumeracha ponds during macrophyte dominance in pond 1 and phyEoplankton dominance in pond 1 and pond 2. Macrophyte Phytoplankton 200% increase NH3 80-907" 60, but uP t.o rr tr rI TKN 75-85 30, " 407" 0rg-N 75-90 up to 5002 increase Nog' 20-50 60-80 Toral PO4-P 20-30 40-70 Soluble PO4-P 20-30 60-90 84. indication of the nutrient removal capacity of a particular group' This type of experiment fails to talce inÈo account nutrient removal role by oÈher organisms Present in the pond at the sarne time' The of a given ecosystem comPonent in nutrienË removal can be more accurately determinedbycornparingthenutrientpoolrePresentedbyitsannual that production with total annual pond nutrient retention' It appeared nutrient annual production of P. ochÎeatus during I977 reptesented a store probably equivalent to less than 2 .5% o1 total PO4-P and 27" or' of Èotal niÈrogen retained annually in t.he Gumeracha ponds. Harvest pathway for this submerged macrophyËe would not have provided a useful nutrient removal. Production estimates lot Cl-adophota are aPproximate pond 1 but suggested that harvest of the total annual production in côuldpossiblyhaveremovedupto4OT"oftotalPO4-Pandl0Zoftotal nitrogen retained in the pond during 1977. Production of this species represented an insignificant nutrient store in pond 2. cTadophora removal appeared to be resPonsible for a major part of the nutrient contrary to the observed during the period of macroPhyte clominance and figuresinTable3.5wasmoreeffectiveinphosphorusremoval' during the Zooplankton may also have contributed to nutrient removal effluent period of macrophyte dorninancê. comparison of influenÈ and concentrations can present a misleading picture of nutrient removal solely to pathways. The tendency is to ascribe the effects observed the organism, or grouP, of most interest to the researcher' .Thephytoplanktonproductionestimatesalsorepresentgross nitrogen ãnd approximations buL suggested that the incorporation of pathway in pond 2 phosphorus into algal ce1ls was the major rem'oval probably during Ig7l. In pond 1 during 1977 phytoplanlcton production retained in represented less than 17. of. total PO4-P and total nitrogen the pond. Although net pr:oducti-on of cladophora in pond 1 and phytoplanktoninponcl2appearedtobeverysimilar,unicellulara|gae 85. have a higher nitrogen and phosphorus content Èhan filamentous algae. The harvest of unicellular algae appeared to be the most effective pathway of nutrient removal aÈ Gumeracha. However, the problerns of a1gal harvest have been discussed. Phytoplankton production in pond 2 appeared to remove a much higher proportion of the total nitrogen retained than of total PO4-P. Percentage removal based on influent - effluent comparisons (table 3.5) suggested Èhat the reverse was the case. As stated above, this type of comparison can be misleading and poor nitro!"r r"*oval during phytoplankton bloorns reflected Èhe inclusion of algal cells in TKN analyses. That is, tl-re niÈrogen in pond 2 effluent r¿ould have been bound in algal biomass. Phytoplankton production in pond 2 may have accounted for more than 100% of the total nitrogen retained during 1977 sttggèsting that considerable recycling had occurred. A much lower proportion of the annual PO4-P was incorporated into algal cells. This situation might be expected as nitrogen exists in a wider range of chemical forms' is subject Èo a wider range of biological transformations, and is, therefore, more labile than phosphorus (V¡alker and HilIman, l9l7)' A greater proportion of the total phosphorus pool may be bound in the organic state at a given time. and, therefore, be unavailable to algae. Nevertheless, phosphorus recycling may have occurred in pond 2 as a consíderable amount of influent PO4-P could have been lost via precipitation at pH above 9.0 (Hemens and Stander, 1969; Fítzgerald and Rohlich, :-96Ð. This would have occurred in the Gumeracha ponds during periods of phytoplankEon growth but not during macrophyte, growth' Although significant proportions of'the nitrogen and phosphorus retained annually in natural lakes may be removed by the harvest of submergeclmacrophytes(CarpenterandAdarns,LTTT;llile'1975)'the productíon of P. ochreatus did not represent a significant nutrienE store in the Gumeracha ponds. Production of p' ochreatus at Gumeracha 86 of Èhe genus was firrch lorver than has been recorded for other members (1978) from unpolluted sites. For example, Howard-l^Ii1liams recorded pectinatus írt an annual product,ion of 2506 g dry weight/m2 /year for P. an African coastal lake. Annual production of submerged macrophytes g dry from fertile, temperate sites is generally in the range 500-800 t 1967) Production of wer'-ght/mz fyear (ltrestlake, I975; Sculthorpe, ' 20-307" of rhle this magniLude at Gumeracha could have accounted for total nitrogen and Poo-P retained in the ponds annually. However, sites is low maximum biomass of submerged macroPhytes at polluted p' pectinatus in a se\¡Iage conpared to clean sites; maximum biomass of effluent channel has been reported at 120 g/*2 (s",rlthorpe , 1967) ' from suspended Lower biomass may be due to light limitation resulting solids (including algae) (ucNa¡¡ , lg76) ' The growing season of Although p. ochteatus aE Gumeracha extended from autumn until spring' temPerature and \^7ater clarity was high during Ëhis algal-free period, incidentlightintensitywerelow.Predictedyieldsofupto400g a (t'tctlab¡ 1976) would dry weigh t/mz for submerged macrophytes in l'ISPs , aPPeartobeextremelydifficulttoachieveonapracticalbasis.Due from to their low productivity, the harvest of submerged macrophytes maturation ponds is of limited value as a nutrient removal pathway' algal IncorporaËion of nitrogen and phosphorus into unicellular nutrient removal at biomass appeared to be the most effective pathway of load (albeit Gumeracha. Ilowever, unicellular algae carry their nutrient biologically bound) into effluenËs and must be harvested continuously' of InlSPs' The The cost of this process offsets the fundamental advantages of hours turnover time of algae at optimum temPeratureS is a matter The (stengel and soeder, LglÐ and nuErient recycling is considerable' productionofCladophoraappearedtobeamajorpathwayofnutrient' this filamentous removal in pond 1 during Ig77. Increased production of possibly have alga (e.g. to the level in pond I during late 1916) could 87. removed over 507" of the total niËrogen and PO4-P retained in Ehe pond annually. In submerged vascular plants, individuals are relatively long-lived and store nutrients over a period of time. The accumulated pond by single nitrogen and phosphorus can be removed from the a ".t,r"l harvest. The turnover time of CTadophora ranges from approximately 7-16 days (¡ohr and Luscinska, Ig75) and for effective nutrient removal from the pond, biomass rvould have to be harvested every 1-2 weeks. Harvest of cTadopltora would probably be labour intensive rather than a high technology process. As such it would be cheaper than the harvest of unicellular algae , Cl-adophora harvest could possibly be simplified if the alga could be induced to grohT on floating, mesh- covered frames. This was observed to take place on the netting covers of fish enclosures (see chapter 5). High phytoplankton density was incompatible with other asPects of pond function, particularly BOD, SS, and Toc removal. Although the removal of organic maEter and ss is not a primary requirement of maturaÈion ponds, the presence of algae can have a detrimental effect upon effluents previously treated to a reasonablá d"g.". of purity' These problems can be overcome by removal of algae from effluents prior to discharge. Although the.production of submerged macrophytes did not constitute a significant nutrient removal pathway in the Gumeracha poncls, both submerged vascular plants and filamenEous algae may play a role in the con¡rol of phyËoplankton, the stabíLízation of organic matter, and the reduction of SS. A systemmay be envisaged in which the effluent from a phytoplankton culture pond (for nutrient reryoval) passes through a submerged macrophyte and fitramentous alga culture pond' Tl-re lat,ter pond would inhibit phytoplankton and theoretically yield an algal-free effluent low in dissolved nitrogen and phosphorus. The inhibition of phytoplankton takes p1,ace when filamentous algae from mats which float to the surface. This occurs in natural situations when the 88. alga is senescent, and thalli are deteriorating. A floating culture system, as suggested above, would exÈend the desired effect over a much longer period. This could reduce light penetration to such an extent as to inhibit the development of rooted macrophytes. However, submerged vascular plants would probably be unnecessary in a system dominated by a high standing crop of Cladophota. The proposed system for effluent polishing is simply the reverse of the Pond sequence at Gumeracha,; that i", pond 2 should precede Pond 1. The use of phytoplankton, macrophytes, and filamentous algae for effluent polishing suffers a major drawback in temperate localities. The growing seasons of the various groups are restricted and high standing crops are only maintained for part of the year. Periods of maximum growth of phytoplankton (late spring - suÍrmer - early autumn) and macrophytes - filamentous algae (autumn - winter - spring) appeared to be out of phase at Gumeracha. Due to the inhibitory effect.s of macrophytes and filamenËous algae on phytoplankton and vice versa (J.tpp and,,Spence, 1977a; Boyd, 1973) ttris is not surprising. However, it does suggest that a \¡raste treatment system incorporating Èhe three grouPs would need careful management and could, therefore, be difficult to maintain in an efficient state. The time lag between macrophyte- - filamentous algae harvest and the reestablishment of standing croPs sufficient to provide an effluent of acceptable quality could result in operational problems. The amounE of CJ-adophora harvested is 1ike1y to be critical if over cropping is to be avoided. These tyPes of problems may mean that a system, such as that suggested above, is not workable on a Practical bas is . Alternative methods of phytoplankton control and pathways for nutrient removal require attention. Herbivorous zooplankton incorporate the nitrogen and phosphorus bound into the algal cells upon which they gxaze. Zooplankton grazíag pressure may reduce Ehe phytoplankton 89 sËanding crop completely, or could, conveivably, maintain the phytoplankton population in an active growÈh phase resulting in high productivity from a low standing crop. The population dynamics of the dominant species of zooplankton and their influence upon phytoplankton abundance and effluent quality in the Gurneracha ponds are examined in the follo\^/ing chaPter' 90. Chapter 4 Zooplankton 4.1 Int.roduction Thealgae-bacteriamodelofl,IsPfunction(rig.1.1)minimizes the importance of organisms from higher trophic Ïevel-s, and has promoted overall the,assumption that such organisms cannot contribute Eo the (fig' l'2) suggests treatmenE process. A more realistic trophic model pond that organisms of higher trophic status may Prove useful for management. The detrimental effects of algae uPon maturation pond algal effluent quality emphasize the need for research into methods of contro1. However, the harvest of unicellular algae is a major pathway for nutrient removal from maturation ponds. Therefore, if algae are excluded from ponds (as opposed Èo harvest from effluents), an alternative nutrient removal pathway must be provided' Filamentous inhibited algae and submerged macrophyEes reduced organic maÈter and of phytoplankton development in the Gumeracha ponds ' I^Ihile the role Gumeracha ponds was, submerged macrophytes in nutrient removal from Ehe limited, harvest of filamentous algae may have removed a reasonable proportionofannualnutrientretention.Howeverrproblemsassociated that with the use of filamentous algae for pond management require This alternative biological methodå of algal control be investigaÈed' conËrol chapter examines t.he role of planktonic microcrustacea in a1gal grouP as a Eool for and nutrient removal to assess the usefulness of the managing maturation Ponds ' Learner (Gg75) reported rhat crustaceans \¡/ere found only tt" occasionally in se\¡,age works and concluded that the group "ttiiktly variety of to prove important in the purification process' In fact' a over entomostraca, often in large numbers, has been recorded from I¡lSPs of I'JSPs a wide geographic range (table 4.1). The entomostracan fauna includes littoral and limnetic species but is generally dominated by to be poorly Daphnia and cyclopoid copepods. Calanoid copepods appear Table 4.1 Species of entomostraca recorded from waste stabilization Ponds' Species Recorded from North South Ameríca England Europe Africa Australia Cladocera Daphniidae x ÐaPlnia magna x x x x x D. PuLex x D. simil.is x D. catawba x D. TongisPina x D. catinata x CerÍdaPIutia rigaudi x x C. quadranguTa x SimocePhalu s exsP inosus Macrothr icid ae- Mactothrix sPinosa x Bosminidae Bosmina Tongirosttìs x x Sid id ae DiaPhanosoma sP. x Moinidae Moina dubia x X x M. macroPa x l,I . btacltiata x I"I . micrura x x M. tectitosttis x M. tenuicotrtis x x I'Ioina sP. Species Recorded from North South America England Europe Africa Aus tralia Chydoridae x Chgdorus sPhaericus x x x ALona diaPhona x Pleutoxus inermis Os tracoda Cyprid id ae X Candonocg Pt ís ass imi Ii s x CgPrídoPsis sP. Copepoda Cyclopoida Cyclopidae x MesocgcToPs Teuckarti x MicrocgcToPs minutus x AcanthocgcloPs gigas CgcToPs vernalis x x C. vicinus x EucgcToPs speratus x Calanoid a Temorid ae Eutgtemora affinis x Diaptomidae DiaPtomus graciTis x CentroPagidae x BoeckeTTa sP ' ('1977)' Goulden compiled from Hussainy (1978), Shillinglaw and Pieterse (1968) (rg76), Intrhite ij-g75), Teoh Og7Ð, Dinges (1973) ' Kryutchkova (1965) and De Noye1l.es (1967), Jolly and Chapman (1966), Loectolf f Elster (1965). 91. ostracods represented. More intens:-ve study may reveal that benthic are abundant in !JSPs. Duetothevaryingfunctionalrequirementsofdifferentpond types(primary,secondary,andtertiary)thepresenceofzooplankton inponds,parEicularlyDaphnia,hasbeenvariouslyregardedasbotlr of l^lsPs dealt with beneficial and detrimental. l-fuch of the early study primaryandsecondarypondsinwhichoxygenation,andthereforeahigh that a algal standing crop, I¡/as desirable' The frequent observaEion declineinalgalstandingcroP\^Iasoftenaccompaniedbyanincreasein oxygen concentration) the abundance of Daplnia (and a reduction of dissolved to pond function resulted in the view that zooplankton r^rere detrimental (G978) suggested that (see review by Dinges, 1973). Daborn et a7. have a major influence upon the abundance of Daphnia in aerated \^ISPs can exert rate at which oxygen the efficiency of the stabilization process and the mustbesupplied.ThedevelopmentofpondsfortertiarytreatmenËand of maturation ponds (a1gae Èhe appreciaEion of the major operating problem role of zooplankton in effluents) has brought about a reevaluation of the grazítg uPon algal in pond function. The effects of zooplankÈor- (e'g'Porter' L977)' populaÈions in natural lakes and ponds can be profound production Zooplankton may crop over LOO7.. of the daily net Phytoplankton (Haney,Ig73)andrapidlyeliminateEheentirealgalstandingcrop (pennington, 1941). The aPparent ability of filter-feeding cladocerans (oinges lg73; Uhlmann, I97I to produce a "klare\^rasserstadium" in ülsPs , ' 1967)isnowregardedaSonepotentialsoluËiontotheproblemofalgal removalfrommaturationpondeffluents("'g'Dinges'1973;McKin¡ey a relatively et a7., I97I; Ehrlich, Lg66)' This approach offers inexpensivealternativetochemicalandmechanicalmethodsofalgal harvest. solely The role of zooplankton in WSPs may not be restricted occur in ponds to algal control. significant BOD and ss recluction can 92 during cladoceran blooms (oinges , L973; McKinney et aI., I97l; Loedolff, L965; Elster, 1965). That is, pond purification capacity does not diminish during a "klarewasserstadium" even though algae are excluded. It has been suggested that BOD and SS reduction by zooplankton is effected via filtration and flocculation of organic and inorganic suspended material (Uhlmann, 1967; Loedolff, 1965). However, few of the above studies have monitored zooplankton standing crop quantitatively or correlated seasonal flucEuations in zooplankton population density with effluent quality and algal standing crop. In some cases (e'g' Dinges , Lg73), observed fluctuations in effluent quality could not definitely be ascribed Èo the effects of zooplankton' A primary mechanism of wastevrater purificatíon may be the incorporation of unstable organic material into living tissue' Thus, zooplankton production and metabolism (assimilation) can be considered as a means of waste stabilization (Andronikova, L978; Krlrutchkova, 1968). The major operating problem of maturation ponds arises because a significant proportion of the influent organic maEerial is converted into algal biomass (Goulden , Ig76; Bartsch, 1961). The current inability to remove this biomass from effluents economically means that organic matter, albeit in a changed form, is exported from ponds into receiving l^tater bodies. The possibility of converting algal biomass into a trophically higher, more easily harvesËable forrn (i.e. zooplankton) ther{ï;arrants investigation. The efficiency of assimilation by zooplankton varies with temperature, food type and density, body síze, and reproductive condition (schindler, 197lb, 1968; Riclman, -1958). For populations of Daphnia in natural waters, assimilation is generally about 407' of gross annual phytoplankton production (culati, I975; Gak- et al-.' 1972; Korinek, Lg72; lJright, 1965). Kryutchkova (1968) has shown that daily production and respiration of cladocerans (including Daphnia) in I^lSPs may be energetically equivalent to almos t IOO7" of fhe daily influent organic 93. load. Such a value suggests that the zooplankton rvere feeding directly upon suspended organic material rather than on phytoplankton. In any event, it is likely thaË a significant proportion of the influent organic load could be converted into zooplankton biomass in I^lSPs, whether algae r¡rere Present or not. At the same time, the stabilization of organic material is noË the only requirement of tertiary treaËment; nutrient removal is also important. The function of zooplankËon in the assimilation of organic material, and hence in energy transfer, need noË reflect the relative importance of this grouP as a nutrient store. Although the study of nutrient cycling within aquatic ecosystems is as yet incomplete ("'g' schindler et a7., 1975; Keeney, lg73), it is aPParent that nitrogen and phosphorus are both continuously and rapidly uEilized and regenerated by rhe plankron (Keeney, L97i; Rigler, Ig73, 1964, 1956). Uptake of inorganic phosphorus by mí-crocrustacea may be rapid (Rigler, 1961; Whittaker, 1961) but, due to high rates of food consumption and metabolism, zooplankton consurne and release back into the water an amount of nutrients many times greater than their body content. Recent research upon aquaÈic nutrienË cycles has focussed upon the rates of transfer beEween ecosystem compar,tments. However, in Lhe context of nutrient removal from l'lSPs, nutrient partitioning beÈween comPartments at the time of harvest ís of more interest than rates of transfer. Emphasis is placed upon the nuErient store represented by the annual production of a species (or trophic group) rather than its role in nutrient regeneraLion. This is not a return to a static model of nutrient cycling but, instead, focusses uPon a d'ynamic system at one Pornt rn tame. Although 60-807" of the total phosphorus Present in natural waters may be bound in the seston aL any given time (Rigler , 1964), nutrienË partitioning between sestonic compartments has been little studied. Kitchell et al.. QgTg) calculated that 36-68% of the total 94 phosphorus pool (dissolved + algal-P + zooPlanlcton-P) may be bound into zooplankton biomass. In the present study, the nutrient store represented by the annual producEion of the dominant herbivorous zooplankton in the Gumeracha ponds \¡7as measured to deËermine the usefulness of zooplankton harvest for nutrient removal. In a sense this is an artificial situation as it assumes that IOOT' of annual production can be removed from ponds. For organisms such as zooplankton, with high turnover rates, removal would require periodic cropping rather than a single aDnual harvest. obviously, cropping would substanÈia1ly alter subsequent production rates. The concept of utilizing natural phytoplankton grazers to clarify !üSP effluents has helped promote the trophic model of pond function, This has prompted the design of wastel^later treatment schemes unicellular irutrient removal) and organisms from incorporating "tgr.(for. successive trophic 1evels (for algal consumption) (Oinges , 1976; Goldman and Ryther, 1976; Trieff et aI.,1976; Ryther et a7., L975' 1972; McShan et a7., Lg74). Many of these schemes require complex, expensive equipment to maintain constant, artificial culture conditio¡rs ' Such schemes depart from the fundamental concePt of WSPs as a simple h/aste\¡rater treatment techniquen To be successfully and ef f iciently utilized as a lrlSP management technique, zooplankton grazíng and harvest must be incorporated into existing treatment plants under normal, operational conditions. The basic assumption is that optimal standing crops of a desired species can be maintained throughout the year' It vras shol^rn in chapter 3 that the inability to maintain standing crpps of submerged macropl'rytes in temperate maturation ponds repr:esents a major problem in their use for pond management ' Obviously, tl're dlmamics of the zooplankton communities in maturation ponds must be stuctied in¡ensively before schemes utilizing zooplankton for pond nanagement can be contemplated. In particular, 95. the factors determining the seasonal abundance of the dominant herbivores must be elucidated. In natural waters, herbivorous zooplankton populations are regulated by food leve1' predation' and temperature (Golterman, 1975). The relative importance of these factors in maturation ponds requires investigation. Although Daborn et af. (1978) studied the population dynamics of Daphnía puTex ín aerated oxidation ponds in Canada, this study did noÈ relate population fluctuations to environmental conditions ' seasonal cycles of the major planktonic entomostracans in the to Gumeracha ponds were sÈudied quantitatively and abundance related various physico-chemical parameters, interspecific interactions, algaI the sËanding crop, and effluent qualiry. Annual neE production of dominant herbivores v/as measured and Ehe nutrient store represented therein compared with the amount of nitrogen and phosphorus retained in the ponds annually. In this manner, the potential of zooplankton as a managementment tool for maturation ponds was investigated' 4.2 SeasonalitY and abundance of. zoopLankton 4.2.I Methods samplilåZooplanktondensity(numberperlitre)wasmeasured fortnightly from July 1976 until October 1978 ín pond 1 and from December (between 1100 and 1976 until October 1978 in pond 2. Samples \¡¡ere taken 5 cm 1300 hours) using a clear persPex tube sampler' 1'4 m long' of internal diameter, and graduated in 0.10 litre. The Eube was pushed vertically into the pond until it reached the bottom, thereby sampling the entire water column, and a large rubber bung inserted in the top' another bung The tube, plus v¡ater contained Èherein, \n/as then raised and inserted in the bottom of the tube prior to removal from the pond ' The (150 cloth) sample volume was noË.ed, ancl a \^tater filter um mesh bolting (Fig.4.1) inserted in one end of the tube. The sample was filtered and permit preserved ín 47. (v/v) formalin. Mesh size was too large to 21 co 1 5 Tube sampler J: Threaded internallY to take 130 m.Q, pornade FIGIIRE 4.1 ZooPlankton filter <+ oo N r I eo eo 1__T m <+ FIGURE4.2Samplingstations(C)inbothpondsatGumeracha. 96 quantitative study of planktonic rotifers' prior to field use of the sampler, water loss from the tube due to turbulence and drag - during raising was examined using coloured dye' Over the same water depth as encountered in the Gumeracha ponds, dye escaped from the lower 5% of Ëhe tube. Loss from Ehis source \nlas not significant in the field as the bottom of the Eube was invariably sealed with a "plug,' of sediment when lifted to the surface. During preliminary sampling, the density of Ðaphnia carinata in tube samples 1¡as comPared r¿ith density estimated from samples taken by vertical haul of a zooplankton net at the same sarnpling station' the The net (25 cm mouth diameLer, 150 pm mesh) was allowed to rest upon qt/ bottom for 3-5 minutes and then raised aE a rate of approximately 25 second. Volume filtered was taken as cross sectional area of net opening multiplied by distance hauled. DensiEy esLimated from net hauls was on average only 1 3% (range 3-577") of densiÈy in tube samples. Volume samplers characteristically yield higher densities than nets and difference factors of 2.5-8 times have been reported (Bottrell et aL" Ig76).AlthoughactivelyswimrningzooplanktersmayavoidboÈhtube samplers and neEs (Prepas and Rigler , 1978 ; Edmondson and l^linberg , 1971) it was concluded that, aÈ. leasË for D. catínata, avoidance of the net was greaEer. An additional disadvantage of net use is that the actual volume of water filtered is not known precisely; calculated volume overestimates filtered volume due to net resistance (Edmondson and l,Iinberg, 1971). It was concluded that for a shallow water body, such as clear the Gumeracha ponds, in which light penetration htas often high, the tube sanpler was more effective in capturing larger zooplankters than vertícal hauls rvith a zooplankton riet' submerged stands of Potarpgeton ochreatus occurred in both ponds at Gumeracha during the study (chapter 3) ' Pennak Q962) has demonstratecl that a tube sampler (6.4 cm diameter) can be used for 97. effective quantitative sampling of free-swinrning zooplankters amongst littoral vegeEation. samples were taken from a boat at 9 fixed sampling stations in each pond (¡'ig. 4.Ð. Steel pegs \^/ere driven inEo the ground on either side of the ponds and a nylon rope drawn taught between them' along The boat was atËached to this rope and could be pulled across or the ponds in a sËraight line; sarnpling staÈions \^Iere f ixed accurately and boat position could be maintained even during windy conditions ' HorizonËal and vert,ical heterogeneity musÈ be accounted for in studies of zooplankton population dynamics and production (Prepas and Rigler, 1978; Bottrell et al., :rg76). Vertical heterogeneity was overcome in this study by sampling the entire water column' Preliminary sampling of zooplankton density was conducted at 12 stations in each pond during July and Augus t Lg76. The numerically dominant zooplankter atthattíme,D.catinata,I^/ascontagiouslydistributed.Itwas calculated (after ElliotÈ, 1971, p. 12Ð that a sample síze of 9 would that have yielded a standard error equivalen:- to 407" of mean density at time. Over 30 samples per pond would have been required to reduce the sampling standard error to 20"/" of the mean. Fixed, regularly spaced staËions were employed during the present study' Samples were thus representative but not independent. of position in the pond' This would have been a problem had the population being sampled displayed a not consistent horizontal heterogeneous distribution pattern' This was the case in the Gumeracha ponds. Most statistical methods assume a from regular random distribution of sampling units. However', the data number samples may, in practice, be treated as if obt¿rined from the same coincide of random points provided the spacing of sampling units does not (George I974) with any repetitive pattern in Èhe population ' ' sampling Sample treatnent. Inclividual samples taken on each occasion were treated separately' l"licrocrustacea were identified and 98 total number per species counted; Ehe number of ovigerous and ephippial females per species $7as also noted. Mean density values included juvenile and adult cladocerans, and adult. copepods plus copepodite stages. Nar.rpliar stages r^7ere not included ín copepod counts. s",npr"" containing more than about 1O0O individuals were subsarnpled volumetrically' using sarnples were made up to a known volume, homogenízed, and subsampled a 10 ml bulb pipette (8 mm inËernal diarneter). The error of the sub- sampling technique in estimating actual sample number averaged from -11'52 to +L4.57.. No particular size class appeared to be favoured by Lhe technique . The arithmetic mean is the best unbiassed estimate of'a finite (Marchant population even if the data indicate a contagious distribution has been and I¡¡illiams , lg77; Elliotc, 1971). Zooplankton density (n expressed as the arithmetic mean number of individuals per liÈre = 9) on each sampling occasion. The data vlere converted to logarithms for (1971) the calculation of. 957" confidence limits as suggested by Elliott for contagiously distributed populations. The logarithmic confidence limits t¡ere converted to the arithmetic scale and combined with the arithmetic mean. SËrictly speaking, the log transformation provides confidence limits for the geometric mean. The method employed in rhis study is thus a compromíze (after Marchant and !'lilliams , 1977) ' major ZooÞ lanlcton dispersion. The spaÈial distribution of the of zooplankters in the Gumeracha ponds f/as investigated using an index (see clispersion. Numerous indices of dispersion have been devised detect review by Elliott, 1971) and differ widely in their ability to indices and quantify trends in dispersion (George , Lg74). T\^to tyPes of of exist: measures of contagion applied to a single sample and measures dispersion based on a series of samples. The former include chi squared tests of the variance to mean ratio for agreement with a Poisson series (the per (¡llíott , lgTL), the ratio of "mean crowding" mean number 99. individual of other individuals in the same quadrat: Lloyd, 1967) to (Iwao 1971)' mean density, and MorisiÈa's index of aggregation and Kuno, Indices based on a series of samples include the regression coefficient of the pov/er lar¿ relaÈion of mean and variance (Taylor, 1961) and the (twao regression of "mèan crowding" on mean density and Kuno, 1971)' In a discussion of the spatial distribution of a population, distinction must be drawn between v¡trether the basic comPonent of the distribution is an índividual or group of individuals, and how such uPon a components are distributed in habitat units. Indices based (deParture single sample provide information on the degree of aggregation from randomness) but do not distinguish between the tv/o asPects of spatial distribution (Iwao and Kuno , lgTI) ' Ihese measures are not satisfactory for describing the aggregation patterns of a species, and are, in any event, based upon the't"ti"tà" to mean ratio and therefore essentially identical (Irvao and Kuno , L}TI; Stiteler and Patil ' L97I; Lloyd ' 1967) ' The variance to mean ratio is largely dependent uPon sample size, sample number, and plankton density (Dumont , 1967) ' A more comprehensive means of describing the spatial distribution of a population is based on the relationship of Lloyd's Q967) "mean 2 crowding" (x.") to mean density' (f), wtrers ¡ç:k = x + 1!- - 1)' "Mean x density crowding,, is linearly related to mearr density over a wide range of values. That is, x* = ¿ * b. i, where a is an index of basic contagion (a = 0 when a single individual is the basic component of the distribuÈion; is a > I or a < I when a positive or negative association of individuals density the basic component of the distribution) and b is the coefficient' of contagiousness (b = 1, < 1 or > 1 when the basic comPonents are distributed randomly, uniformly or contagiously) (Iwao and Kuno, l97L)' Ihus, a linear regression of "mean crowding" on mean density most successfully provides information on both aspects of Ehe spatial distribution of a population; this measure is essentially independant of population densiÈy 100 . (George , 1974). lrlhen sampling units are widely spaced, Èhe slope coefficienÈ,.b, will include an elemenL of variance due to habitat heterogeneity. 4.2.2 Results 4.2.2.r Composition of the Zoop lankt on Communitv. Entomos traca recorded from the Gumeracha ponds during the present study are listed in TabLe 4.2. The generic composition of the enLomostracan fauna of the Gumeracha ponds was similar to InISPs elsewhere (see Table 4.1). Ihe Gumeracha assemblage, typical of natural ponds or the littoral zone of lakes, included the following groups: limnetic, littoral, and benthic cladocerans; limnetic carnivorous and littoral herbivorous cyclopoid copepods; a limnetic herbivorous calanoid copepod; benthic and planktonic ostracods. These groupings were derived from P. De Deckker (Zoology Dept., University or Adelaide, pers. comn., Ig79), Sheil (1976), Quade (1969), Fryer (1968, Lg57), Geddes (1968), Armitage and Davis (1967), Timms Qg67), Elgmork (1966), Byars (1960), and Smyly Q957, 1952). AlÈhough macrophytes may control the distribution of liÈtoral crustacea in lakes (Quade, 1969), the disÈinction between oPen Ttater and the macrophyte dominated marginal zone in ponds is not necessarily clear cut (.Smyly, 1952). For example, Ahgdorus ,sphaeticus is often reported as common in both weed beds and open r^¡ater (Sheil', L976; Tim¡ns , 1967; Smyly , 1957, L952) but this species is not adapred for a planktonic mode of existence (Fryer, 1968). Although chydorids occurred frequently in samples from the Gumeracha ponds this grouP must be regarded as "pseudoplankters" (Pennak, L962) in that their adaptations are not those of planktonic organisms (Fryer, 1968). The presence of chydorids in the tube sampler probably resulted from their being dislodged from positions of a¡tachment to vegetation. The tube did not sample the microhabitat of this group adequately ancl chance probably greatly affected their Presence in samples. Table 4.2 EnÈomosÈraca recorded from the Gumeracha ponds during Èhe period July 1976 to October 1978. Branchiopoda Cladocera Daphniidae Daplnia carinata King SimocephaTus exsPinosus Koch Cer íodaplnia quadrangula I'Iu1 ler Lfacrothric idae Mactothrix hitsutícornis Norman et Brady Chydoridae Chgdorus sPhaeticus Mul1er Iegdigia ciTiata GauÈhier L. Tegdigi Schoedler PTeuroxus aduncus Jurine Biapertura affinis LeYdig AToneTJa sP. Copepoda Cyc lopoida Cyc lopidae MesocgcTops TeuckarËi Clals EucAcloPs agiJis Koch PatacgcToPs sP. Calanoida, Centropagid ae Boeckelfa triatticu-Zata Thomson Os tracoda Podacopa Cyprididae CanðlonocAPris assimiLis Sars SatscgPridoPsis acuTeata Costa CgpridoPsis sP 101 Althoughmacrothricidsaregenerallybottomdwellers.Ëheycan means of the antennae swim persistenÈly if necessary; propulsion is by trunk limbs or and not, as f,or Èhe chydorids, by crawling using the M' hirsuticornis post-abdomen (Fryer, LglÐ. At times, large nunbers 9f Guneracha ponds were observed near the surface in oPen \^Iater in the ' and the tube This species may spend considerable time in the htaler column of seasonal population samples rnay be adequate for a quantitative analysis cycles. EucgcTopsagíTisandParacgcTopssp.h/ererecordedonlyrarely These species from the Gumeracha ponds as r^ras ceriodaphnia quadrangura. and will not be considered r¡¡ere not an important comPonent of the pond fauna further ' MesocgcTopsTeuckarti,Boecl;e]TatriarticuTata,andÐaplnia habitats in carinata have been recorded from a wide variety of aquaEic free-swinnning' limnetic A¡sEral ia. These species are, ho\^Tevert true 1963)' plankrers (rinrns, 1970; Geddes, 1968; Elgmork, L966; Jolly, Ëo the substrate AlEhough simocephaTus exspinosus can attach dorsally be considered (Cannon in Horton et aI.,1,g7g) this species can probably as a 1itt.ora1 free-swinmer' are, Ïhe zooplankton of major interest in Èhe Present study (including therefore, those species adequately sampled by Èhe tube particularly the larger herbivores I,I . Ieuckartj and M. hirsutìcotnis), Ð.carinata,B.ttiatticuTata,andS.exspinosus. ThetaxonomyofDaplniainsouth-easterrrAustraliahasbeen in ths D' revised by Hebert |Gg77) who has erected eight new species Hebert has carinata complex. on the basis of electrophoretic studies elevatedwhatwerepreviouslythoughttobecyclomorphicformsofn. 1967 to species status ' carinata (Bayly and I'Jilliams, 1973; Jolly ' ) interpretations However, the assumptioris upon v¡hich Hebertts electrophoretic (Professor c' Manrvell' are based may not be valid in all situations IO2 ZooLogy Department, University of Adelaide, Pers. cofltrn.' I977). OtBrien and Vinyard (1978) do not support such an extensive reclassification. Morphologically, many of Hebertts species are difficult to distinguish on the basis of characters other than gross body shape. Many animals were encountered in the Gumeracha collections Èl-rat could not be satisf actorily identified using Hebert's key. Hebert has stated that individuals can be most readily identified on the basis of species-specific differences in the protein banding patterns of two enzymes. However, his electrophoretic evidence for species recognition remained unpublished aË the time of completion of this study' Therefore, even had attemPts been made to identify material from Gtrmeracha electrophoretically (beyond the scope and resources of the presenÈ sÈudy), in the absence of Hebertts elecËrophoretic data a particular banding pattern, could not. have been referred to any of his rnorphological tyPes ' In effect, Hebert's species are unidentifiable' Hebert(1978b)hasgonefurtherandsuggestedthatwhatwas assumed to be cyclomorphosis in D. carinata is, in reality, a seasonal change in the relative frequency of several cohabiting species ' This phenotypic cycle mimics true cyclomorphosis. The situation is made more complex by the occurrence of true cyclomorphosis in some "species" of the D. cazinata complex (Hebert , L978a; Daly , I974). Seasonal morphological changes (as evidenced by caraPace width to body length ratios) ín Daplnia from the Gumeracha ponds !/ere studied frornMay 1976 until October 1977 (Uitctrell, 1978'å). It was concluded Ëhat the and Gumeracha population oÍ Dapiùja exhibited both polymorphism t cyclomorphosis. Juvenile and primiparous adult instars maintained coristant carapace width to body length ratios throughouL the year; carapace expansion occurred only in adults larger than 2 mm in body length This paper is includecl in Appendix 3 103. Juvenile instars l¡Iere morPhologically uniform throughouÈ'the year despite changes in adult morphology. Although Hebert (1978b) does not accePt the predation hypothesis (".g. Dodson, 1974) to account for cyclomorphosis, OtBrien and Vinyard (1978) have demonstrated that caraPace expansion in D. catìnata affords protection from notonectíd predation. It.appears that some of Hebert's Q977 ) "species" may be true bíological species; introgression does not occur between D. carinata, D. cephalata, or D. magniceps in ponds in which t\to or more sPecies are present during periods of sexual reproduction (laly, 1974). The status of the remaining "species" in the D. carinata complex awaits verification. D. ceplzalata \^/as not recorded f rom the Gumeracha ponds r nor was any f orm that could be confidently identified as D. magniceps. Practicality demanded that a conservative approach be adopted during the present study; the population of Oaphnia at Gumeracha r¡ras regarded as consisting of a single species, designated as D. carinata sensu Tato' 4.2.2.2 Zoop lankton DisÞerson. "Mean crowding" was calculated on each sampling occasion for the 5 major species of zooplankton' "Mean crowding'r was then plotted against mean density for each species in both ponds during 1977 and 1978. These plots are Presented in Appendix 1. In each case, except fot B. tiiarticuTata in pond 1 during L977, the relation of "mean crowding" on mean density could be fitted to a linear regression accounting for a high proportion of the ,variance. The regression parameters for each species are summatízed in Table 4'3 ' The significance of the difference of the intercept a (an indicator of clumping on a scale defined by rhe limits of the sanípling unit) from zero, and the difference of the slope coeffj.cient b (an indicator of clumping in gross environmental terms) from 1, hlas determined at the 57" Level af ter Bailey (1959). l,lith the exception of B- triarticul-a,ta ín pond l, b was significantly greater than I and a significantly less than zeto fot all species populaÈions in both the Table 4.3 (x) Regression coef ficients for mean crowding (x'*) on mean density ' plus rt' values (proportionnronortion of tlthe varrance accorunted for bY the regression) for major species of zooplankton in the Gumeracha ponds during 1977 and 1978. Pond I Pond 2 197 7 2 2 Species b a t b a 1 Daplnia carinata r.77 -22.82 0.95 5.13 -239.25 0.73 0.89 Simoce phalus exsPinosus 6.26 -131 .63 0.96 r.77 2.81 0 .66 MesocgcloPs Teuckatti 2.72 -30.10 0.91 1 .63 7 .47 2.28 B0 0. 9I Boeck.eT l- a tri art iculata r.24 2.70 0.30 -3. ILacrothrix hitsuticotnis 6.08 -67 .12 0.90 t.99 5.64 0. 78 L97 B D. carÍnata r.66 -63.04 0 .90 I.I2 4.33 I .00 S. exspinosus 3.67 -L.69 0.97 M. Teuckatti 1.11 3.76 1 .00 I .05 0.75 I .00 B. triarticulata M. hirsuticotnís 104. G-rmeracha ponds during Lg77 . For B . ttiarticul-ata in po.nd I during Ig77,.b was not significantly different from 1 and a l¡/as significantly greater Èhan zero. In pond 2 during L977, a \¡¡as significantly less, than zero for D. carinata and B. triarticuJ.ata but significantly greater than zero for s. exspinosus, M. Teuckartil and i4. hirsuticotnis' In pond I during Ig7B,.b was significantly greater than 1 and a.h¡as significantly less than zero f.or D. catinata and S. exspi¡?osus. greater -b was not significantly different from 1 and a was significantly than zero for M. feuckarti in both ponds and D. carinata in pond 2 during Lg78. a and b for a given species thus varied between ponds and over time within a pond. The dispersion patterns for each species, in terms of the relative magnitude of a and b, could be described as follows: D. carinata. In pond 1 during 1977 and 1978 and pond 2 during 1977 this species \^/as contagiously dístributed on a gross scale (over the pond) but negaEive a intercepts suggested repulsive interactions between individuals ' In pond 2 during 1978 this species \^/as contagiously distributed on a small sca1e, or formed clumps, and the clumps hrere randomly distributed over Èhe pond. s. exspinosus. In pond 1 during 1977 and 1978 this species was conÈagiously distributed over the pond and negative a íntercepts suggested repulsive interactions between individuals. In pond 2 during Ig77 this species exhibited small scale and gross aggregaEion' That is, animals formed clumps v¡hich htere contagiously distributed over the pond' M. l-euckarti. In pond 1 during 1977 this species rvas contagious'ly disCributed over the pond and a negative a intercePt suggested repulsive interaction bet\^reen individuals. In pond 1 during 1978 and pond 2 during 1977 this species formed cl.umps which \¡Iere contagiously distributed In pond 2 during 1978 this species formed clumps which were distributed randomly. 105 B. triarticulata. In pond 1 during 1977 this species forrned clumps v¡hich ¡¡ere distributed randomly. In pond 2 during 1977 this species was contagiously distribuÈed over the pond and a negative a intercePÈ suggested a repulsive interaction between individuals. M. hìrsuticornis. In pond 1 during 1977 this species was contagiously distributed over the pond and a negative a intercePt suggested a repulsive interaction between individuaÍ.s. In pond 2 during 1977 this species formed clumps v¡hich \^lere contagiously distributed' That is, species \^rere generally contagiously distributed on a gross scale; a random dístribution over the pond was rare. Individuals rtrere never randomly distributed on a small scale (i.e. a = 0) for any species. oî 2l october 1976, during very calm conditions, dense aggregations of D. catinata were observed in clear water between stands of p. oclveatus in pond 1. These clumps, roughly cylindrical in shape, hrere approximately 0.5-0.75 m in diameter and extended from the surface to the pond bottom. The clumps lrere discrete with well-defined limirs, although the outer boundaries r¡rere continually changing shape. Ani¡nals were relatively rare in the water between clumps ' Species differences in overall patchiness v¡ere summarized by a comparison of the slope coefficient b for each species in both the Gumeracha ponds during 1977 artd I978 (l'ig. 4.3). Overall patchiness was generally more Pronounced in pond 1 than in pond 2 during 1977 ' In pond 1 during 1977 the littoral cladocerans 5. exspinosus and M. hirsutico-rnjs exhibited the highest leve1 of overall patchiness (fig. 4.3r4). The true limnetic species D. catinata and B- triatticuLata exhibited the lowesË level of overall patchiness in pond 1 during 1977 ' In pond 1 during 1978 s. exspinosus exhibited the hjghest level of overall patchiness while ¡. carinata exhibited a low 1eve1 similar to that for Lg77. M. Ieuckarti exhibited a lower level of overall patchiness in 7 Pond 1 Pond 2 ^ 6 I o 5 4 a A 3 I c 2 t o o ^ I o o tr_ I tr Random e:rpectatlon FIGI]RE 4 .3 Comparison of the slope coefficient .b (overall patchiness) for major zooplankËers fn the Gumeracha ponds \977 I 1978 O Daphnia carìnata 1977 a, 19780 MesocgcTops Teuckarti ' exspinosus 1977 L 1978 BoeckelTa triarticulata L977 O SiracephaTus ' ^ Macrothrix åirsuti cornìs L977 I 106. pond 1 during 1978 than during L977. In pond 2 during I.977 D. carinata exhibited the highest level of overall patchiness while all other species exhibited sirnilar, low levels (rig. 4.3,8). In pond 2 during 1978. D. carinata and M. J-euclcarti both exhibited similar, very low levels of over:al I patchiness. D. carinata exhibited another type of distributional heterogeneity in the Gumeracha ponds. On most sampling occasions this species was observed to be aggregated in the lor¿er 10-20 cm of Èhe sampling tube' This was not invariably true; on some occasions aggregation htas observed in samples from one pond while animals were distributed throughout the tube in samples from the other pond' 4.2 .2 .3 Seasonal Abundance. Seasonal variation in toEal zooplankton standing crop and percentage occurrence of the major zooplankters in pond 1 are shown in Figure 4.4,A'. Zooplankton blooms (>zoo individuals/1itre) occurred during october L976, from mid January until late ApriL Ig77, and from November 1977 until early September I97B' Large fluctuations in total zooplankton density occurred during the latEer period. A succession of species was apparenL during blooms. Initially (mid-sunrner) blooms consisted of U. Teuckarti and S. exspinosus, although the former r¡/as dominant . D. carinata replaced M' Teuckarûi as the dominant. during autumn or autumn-winter. This species dominated the zooplankton during the laEter part of 1976 and lg79. AlLhough M' l-euckatti exhibited a secondary increase in dominance during June 1977 total zooplankton density \¡ras very low. During Ëhe latter half oÍ 1977 ' D. catinata was absenE from pond I and the zooplankton \^/as dorninated fairly equally by M. l-euckarti, s. exspinosus, and M. hitsuticorni-s. B' triarticufata was a minor component of the pond I zooplankton conrnunity. seasonal variation in total zooplankton standing crop and percenËage occurrence of the major zooplankters in pond 2 are sl-tov¡n in Figure 4.4,8. Zooplankton blooms (>200 individuals/litre) occurred Tfme (nonths) Tirne (nonths) L97 6 L977 197 I r976 t977 t978 1200 a1 20 0 o 800 h 80 0 ! 'rl Ø É 400 AJ 400 F{ d }J 0 o F 0 50 50 I 7.L 0 1 7"1 0 Lt- OJ I 2 -^Al c) ^ór a-v -Y CJ t¡ 2 V w t¡ o o 3 o Þ - AJ ¡l-, èo 3 ^-.-. ^^ ! w 4 --v-v ^l q) -Y O ) ¡¡ OJ 4 F4 A B occurrence of major species in pond I (A) and FIGIJRE 4.4 Total zooplankton density and percentage pond 2 (B) B. triatticulata, 5 D. catínata, 1 S. exspinosus, .3 hir:suticorñis , 4 l"l . TeuckarEt , 2 M. 107 . during April Ig7l, from August until the end of October L977, and during May 1978. Fluctuations in zooplankton standing crop in pond 2 were less erratic than in pond 1. In contrast to pond 1, D. carinata was dominant throughout zooplankton blooms in pond 2 (except for a brief period in early September 1977). Although M. J-euckarti was dominant during mid-summer total zooplankton standing croP was very low. As in pond 1 Ð. carinata was dominant during autumn-winter. In contrast to pond 1 D. carinata \^ras present in pond 2 Ehroughout the latter half of Ig77 . Accordingly, It. feuckatti and M. hirsuticornis did not contribute grea¡ly to the zooplankton standing crop during that period. S. ex.spinosus r^ras a minor component of the pond 2 zooplankton conrnunity. B. triarticul.ata contributed a higher percentage of the total zooplankton standing crop in pond 2 than in pond 1 but during periods when total numbers were low Average zooplankt.on standing crops were fairly similar in each pond during 1977 and 1978. However, maximum standing croPs were much higher in pond 1 than in pond 2. The major difference betv¡een the zooplank¡on cycles of the Gumeracha ponds r¡ras the absence of a marked midsununer bloom in pond 2. AlÈhough 14. leuckartj was dominant in both ponds aE these times total zooplankton numbers \^/ere much lower in pond 2- I¡terpond differences in the relative importance of the major zooplankton species suggested Ëhat species populations in each pond were, to some extent, independent. Seasonal variation in mean population density (pLus 957" confidence limits) of D. catinata in the Gumeracha ponds is showq in Figures 4.5 and 4.6. D. carinata \¡/as present in pond 1 from the commence- nenr of sampling (fig. 4.5) and although mean density peaked at 380/l in late October 1976 confi in mean density occurred in early November 1976 f.ollowed by a small, secondary peak in late December 1976. D. carinata Ì^Ias not recorded in 1000 o o T o¿ a o Ê I 00 h o .tJ rl o Ê c) 'o É d I 0, O 10 o 1 DJ DJ r97 6 L9t7 T97 B Tine (months) FIGURE 4.5 Mean population densíty of n. carinata (plus 952 confidence lirnits) in Pond 1" 1000 o èl ì o Ê i h +J .rl I 00 o Ê OJ 'ú É (Ú tc) T oI t0 o T I DJ DJ r976 L97 7 r978 Time (months) FIGURE 4.6 Mean population densíty of D. carinata (plus 952 confidence liurits) in Pond 2- 108. samples from mid-January to mid-February 1977. A rapid increase in mean density occurred during late February and early March 1977; population peaks (>1000/1) occurred in mid-March and again in late April Ig77. Mean population density declined rapidly during May Lg77. D. carinata was not recorded from June 1977 until late March 1978. Mean population density increased during early April 1978 and peaked in late April and again in early June 1978. Although mean density declined from June to August confidence limits lJere wide and overlapped. A secondary peak in mean density occurred in late August 1978; this was followed by a rapid decline and D. carinata I¡Ias not recorded in mid October. D. carinata \./as not recorded in pond 2 until May 1977 (rig. 4.Ð. Mean density increased rapidly during April 1977, and peaked briefly (333/1) in lare April. A significant decline occurred during May and June 1977. Thereafter mean density gradually increased, reaching a second peak (590/1) in late October 1977. Mean density declined rapidly during November. D- carinata r¡ras not recorded from early December 1g77, until late April 1978. Mean density increased rapidly during April and May 1978 and peaked (M7/L) in early June. Mean density declined during J'uly and although a secondary, smaller peak occurred in late August confidence limits overlapPed. Mean density declined rapidly thereafter and D. carinata was not recorded in mid October. Although population cycles lvere similar in both ponds during Lglg, events differed during 1977. Onset of the 1977 D. carinata bloom occurred in pond I earlier than in pond 2 but the species \^las pre'sent for several months longer in pond 2. Maximum densities were higher in pond 1 than in pond 2. Highest mean densities occurred in both ponds in autumn and early spring and D. carinata !Ías generally present throughout Èhe winter. Seasonal variation in mean population density (plus 952 109. confidence limits) of S. exspinosus in the Gumeracha pond.s is shown in Figures 4.7 and 4.8. 5. exspinosus \^tas first recorded in pond 1in lare August 1g76 (rig. 4.7). Mean density increased steadily during November and December 1976 a¡¡d peaked (52IlL) in mid-January 1977' A significanË decline occurred during early March I977 and mean density remained low ( vras rare in pond 2 and constituted a minor comPonent of the zooplankton cornrnunity in that Pond. Seasonal variation in mean population density (p1us 95% confidence limits) of. u. hirsuticornjs in the Gumeracha ponds is shown in Figures 4.9 and 4.10. M. hirsuticornis vJas recorded only rarely in pond 1 (fig. 4.9) until July 1977. From July until December 1977 this species underwent a series of marked density fluctuations with maxima in September, November, and December L977. Confidence lirnits l¡Iere extremely wide but significant decreases occurred in early October and earl! December 1977 . Mean density declined during January L978 and I't. hirsutico.rnis was not recorded in pond 1 after that tirne. M. hirsuticornis r¡/as present in pond 2 at Ëhe conmencement of sampling (fig. 4.f0) but mean density declined during January L977' The species r^/as not recorded in pond 2 ftom February Eo May 1977. Mean 1000 t o oì 100 o Ðà .rl o É o T o É d tc.) o l0 T o o T o I D J Lg77 1977 r9it I L976 I97 6 (rnonths) Time (months) Tlme population density of S' exspinosus FIGURE 4.8 Mean population density of FT.GURE 4.7 Mean (plus 95% confidence limlts) (pltrs 9-5% conf íãeñc. 1i¡nits) ín pond 1' s. exspinosus írr pon oì o 100 H o X I Ð a Ø AJ I 'Ú É d o OJ 10 o 1 t976 D J D L976 D J 7 D Tirue (months) Time (months) u. hitsuticotnis I'IGURE 4.9 Mean population density of FIGIIRE 4.10 Mean population denslty of M. hirsuticornjs (plus 957. conf-ídence (plus 957" confídence lirnits) in pond 2. limits) in pond 1. 110. density increased during July and August 1977 artd reached a peak (85/1) in early September 1g77. A significant decrease in mean density occurred in early October and although mean densi-ty increased through November and Decembet 1977 confidence limits \^/ere very wide and over- lapped. Mean density declined during January I978 and M. hitsutícornis $/as not recorded in pond 2 after that t.ime. Mean density was generally higher in pond I than in pond 2; population cycles in both ponds during the latÈer half of 1977 appeared to be synchronized. wide confidence limits for all mean density values may indicate that the tube sampler was not adeguate for a quantiÈative study of this species ' VariaEion in the percentage of ovigerous and ephippial females in sample s of M.hítsuticornis from the Gumeracha ponds is shown in Figure 4.11. The percentage of ovigerous females fluctuated widely (5-802) in both ponds. An inverse relaËionship appeared to exist beËween population densiËy and the Percentage of ovigerous females in both ponds; percentage of ovigerous females was highest when population density was low and declined as density increased. Thus peaks in percentage of ovigerous females occurred prior to population increases ' Ephippial females \,rere rare in both ponds; in pond l the percentage of ephippial females reached a'maximum of l0% just prior to the decline of the population. seasonal variation in mean population density (plus 95% confidence limits) of ¡1. Teuckartì in the Gumeracha ponds is shov¡n in Figure 4.I2 anð. 4.I3. M. Teuckatti v/as Present in pond 1 throughout the study (rig. 4.IÐ. Mean population density increased from November 1976 until January 1977 and peaked from January unÈil February L9l7 ' Confidence limits overlapped during the latter period' A significant decline in mean density occurred during March 1977. Although mean density increased gradually from March until December L977 confide'nce limits overlapped during that period. Mean density reached a peak I 80 ll l¡ l¡ tt tt tl f\ 60 ¡l t\ o tr ò0 l¡ rú , +J fi I I ,t ç¡ I Q) fr I U tl t ¡{ tt a I fl40 I I ¡l I I I t ,41 t ¡ , ¡l t t I 20 I I I I I , I , I I I I I I ( I 0 DJ D J r977 Time (nonths) FIGURE 4.11 Percentage of the total number of female M. hitsuticornis carrying eggs in pond I (-) and pond 2 (---)' and carrying ephippia in pond I (""")' I 000 o i\-r Io Þì I 00 o Ê h +J O T{ o d c o c) O -o o E, Ë ftl o o t c t0 T o e o I r976 L97 7 L97 B Time (months) FIGURE 4. ] 2 Mean population density of M - feuckarti (p1us 95% confidence limits) in Pond 1. 1000 T êl 100 a; É h il+J o o É o) 'o É o qt c) 10 o a T I o o o T I D J r97 6 Lg77 I97B Tine (months) FIGI]RE 4. 13 Mean population densíty of M. leuckartì (p1us 95% confidence limits) ín poncl 2. 111 during mid-January 1978 GI6/L) but this was followed by a rapid, significant decline at the end of thaÈ month. A significant increase occurred again during mid-February l91S ($53/L). ThereafLer, mean density declined during March and April I978. Despite considerable fluctuation mean density remained lor¿ ( Mean density of M. Leuckartj fluctuated widely and somernrhat erratically in pond 2 (fig. 4.13). As in pond 1 a peak in mean densiÈy (109/1) occurred during January 1977. This was followed by a significant decline ín February and early March. A small increase in mean density occurred in late March-Apr iL 1977. Mean density again declined during late llay. Thereafter, significant increases in mean density occurred during late July, early September (peak at ILZ/L), and early December Lg77. A peak in mean density occurred in late January 1978 (137/l). This was followed by a significant decline in laEe February and a significant, but small, increase in March 1978. Mean density fluctuated at very low levels (<10/1) unti-l early June 1978. M- feuckarti was not recorded in pond 2 after that t.ime. Density of I'I . Teuckarti was lower in pond 2 than in pond 1; although peaks occurred during summer in pond 2 a LaEe winter peak also occurred in that pond. Variation in the percentage of ovigerous females in samples of M. l-euckarti from the Gumeracha ponds is shown in Figure 4.I4. Ovigerous females \ôrere present in pond 1 from Deeember 1976 until the end of January Ig78. Four peaks occurred in the percentage of ovigerous females during that period: late Decenrber 1976 ß87"), early June 1977 Q9%), mid July G67.), and mid-December Q3Ð. The peaks in Decembet 1976 and 1977 preceded a population increase by about one month. The mid-year peaks 80 , ll tl il I I 60 I I I I I 0) I ò0 d I Ð É I q) 40 O I tr 1 I ÈCJ ll ¡l lì rltl ll l¡ ,t Ir 20 ,l l¡ fl l¡ I l, ì I t ,i I I f' I I ì I I I ¡\ It \ I I^ ^a--l I lt I 0 DJ D J L976 L977 r978 Time (months) tI2. in 1977 r^/ere not followed by an increase in mean density. Ovigerous females appeared briefly in March and late April I978. The peak in early Augus E Ig78 G27.) may be an artifact as mean density was very low. A minor increase in mean density, probably not significant, followed the August peak. A series of peaks in the Percentage of ovigerous females occurred in pond 2 during 1977. Peaks in late l"Iay Q57"), early August OI7), early october Q37), and early November (I27") were followed by increases in mean density. The peak in late May 1978 (35%) was probably an artifacÈ resulting frorn very low sample numbers. Seasonal variation in mean population density (plus 957" confidence lirnits of B. ttiarticulata ín the Gumeracha ponds is shown in Figure 4.15 and 4.16. B. ttiatticuLata occurred in pond 1 from January until the end of March 1977 arrd then briefly in Septernber 1977 (f ig. 4.15). Mean density was very low (maximum of 5/I) and B. triarticu-Z.ata was a minor component of the pond I zooplankton community' B. triarticui.ata was present in pond 2 throughout 1977 except for June of that year (Fig. 4.16). Peaks in mean density occurred in April (7.6/l) and November (50/f) Ig77. Mean density declined rapidly during December 1977 anð, B. triatticufata was noÈ recorded from pond 2 after that time. Mean density of 8.. triatticuLaËa in pond 2 was similar to pond 1 except for the peak in November L977 ' Variation in the Percentage of ovigerous females in samples of B. triarticul.ata from the Gumeracha ponds is shown in Figure 4.17 ' In both ponds peaks in the percentage of ovigerous females coincided with peaks in mean density. Only in pond 2 during late October 1977 was an increase in percentage of ovigerous fernales followed by an increase in mean density. In sunrnar:y, D. carinata attained the highest mean popularion densities in the Gumeracha ponds, although .f4. I'euckatti \¡/as Present f or longer periods of Eime . D. carinata and S. exspinosus viere the dominanE 100 10 ôì ï T X ]J .rl ct) L É €0) Ê d a G) 1 o o OO \/ 0.1 DJ D DJ 1.97 6 L977 L976 L977 Tine (ruonths) Tl-rne (months) FIGURE 4.15 Mean population densiÈy of FIGIIRE 4.16 Mean population densíty of B. triarticul-ata (plus 95"/" confidence límits) B. triarticuTata (p1us 95"1 confldence l1miËs) ín pond 2. in pond 1. 80 60 o (lè0 +J 640 U I'l a) È I fl 20 ,1 ,l l\ ,l ,1 ¡rr----l ¡l lq ¿l ,t rl /'\. ¡l /r I I I t I \ l\ I I \ ,ì t I t 0 D D J L977 Time (nonths) eggs in pond 1 (-) and FIGURE 4.17 percenËage of the total number of n. triarticufata carrying pond 2 G-Ð. 113 herbivores in pond I and D. carínata and B. triarticulata were the dominant herbivores in pond 2. In the latter case' mean density of B. tríarticu-z,aÈa was very low. Population cycles of a particular species $rere not necessarily synchronous in boEh ponds. Although pond 2 received the effluenÈ from pond 1, zooplankton populations in each pond were independant to some measure ' In fact, observations made during a bloom of D. carinata in pond 1 suggested that animals avoided the area inrnediately surrounding the outflow pipe' Environmental factors. Ttre entomostracans that occur in IÙSPs are obviously capable of adaptation to extremely high nutrient and organic levels. It seemed unlikely, therefore, that seasonal abundance would be affecEed by influent nitrogen, phosphorus, or BOD levels. Physico- chemical parameters that underwent the most pronounced seasonal variations in the Gumeracha ponds, and which might be expected to affect zooplankton populations, \^rere s/ater temperature, dissolved oxygen concentration, and pH. The influence of variation in these parameters upon the zooplankton cycles observed in the Gumeracha ponds was investigated via individual linear regressions of log mean zooplankton density on each parameter. Semilog plots of mean density on !üater temPerature, dissolved oxygen, and pll for the major zooplankters in the Gumeracha ponds during 1977 and I978 are presented in Appendíx 2. Regression lines accounting The for over 407. of Èhe variance in mean density are also included' regression coefficients for each of these ploÈs are sunmarízed in Table 4'4' The relative imporEance of variation in \'later temperature, dissolved oxygen concentration, and pH in accounting for variation in mean density of the major zooplankters v/as as follows: D. carinata. Best fit for the regression of 1og mean density on l¡ater temperature for this species was obtained if the points above and below 12oC in pond l and 13oC in pond 2 \^Iere Lreated independently' t2'0"1u"" for the pooled data were 0.14 in pond 1, L978 (alL 1977 values were above tZoc), 0.00 in pond 2, 1977, and 0.01 in pond 2, 1978' HighesÈ mean TabLe 4.4 Regression of log population density (no./1) of major zooplankton species in the Gumeracha ponds during 1977 ar.d l97B on water t"*pãrãt.rt" ("c)T dissolved oxygen concentration (mg/l)* and pH?k*. a, intercept i b, slope of regression line; r¿, goodness of fit (or amount of variance accounled for by variation in temperature, dissolved oxygen, and pH). (tt.p. = noE present). Pond 1 Pond 2 r97 7 L97 B r97 7 1 978 2 2 2 2 a b r a b r a b t a b r Temperature: I Dissolved Oxygen: D. carinata 1.10 0.11 o.27 3.16 -0.15 0. 70 4.02 -0.22 0.28 2.93 -0.11 0. 82 S. exspinosus L.76 -0 .05 0 .02 2.14 -0.12 0.49 3 .38 -0.33 0 .66 n. p. M. l-euckarti 1.61 -0 .01 0 .00 0 .02 0.15 0.46 1.14 -0 .04 0.02 0.96 -0 .02 0.02 B. triarticuLata I .60 -0.19 0.44 n. P. -0.44 0 .05 o.02 n. P. M. hirsuticornis 0. 70 0 .02 0.00 n. P. -2.06 0.22 0.29 n. p. PH: D- carinata 2.80 -0 .05 0.L2 6.45 -0 .56 0.70 1 .68 0 .01 0.00 -5.79 r .06 0 .57 S. exspinosus 4.43 -0 .4r 0.30 -4.65 0 .55 0.74 n. P. 14. feuckarti 1.30 0 .03 0.01 -4 t7 o.67 0.70 1.33 -0.06 0.01 1 .01 -0 .04 0 .01 B. triarticul-ata 6.01 0.73 0.66 n. P. -0 .30 0 .05 0.00 n. P. 0 .28 0 .12 n. IUI . hirsuticornis 3.70 -0.37 0. 14 n. P. -2.02 P. Averaged over depth pH of pond taken as equivalent to pH of effluent. I 14. densities occurred in the range 11-15oC. A positive relationship between Iog mean density and water temPerature I^Ias found below 12-I3oC while a negative relationship was found above 12-13oC. Temperature variation accounted for the highest anount of variance in log mean density in both ponds during 1977. In both ponds during 1978, variaÈion in temperature, dissolved oxygen conceritration, and pH all accounted for l'righ amounÈs of variance in 1og mean density. Negative relationships were found between log mean density and both dissolved oxygen concentration and pH. Although Ð. cazinata vras recorded up to pH 10.5 at Gumeracha, only one record occurred above pH 9.5. Significant positive correlaËions occurred between \^7ater ternperature and dissolved oxygen concentration in pond 1 (p = 0.68, p < .01) and pond 2 (p = 0.50, p < .05) and between !'rater temPerature and pH in pond 1 (p = 0.83, P < '05) and pond 2 (p = 0.85, p < .01) during 1978. These correlaÈions explained the importance of dissolved oxygen and pH during 1978. Temperature appeared to be the most imporLant parameter affecting D. carìnata; this species generally occurred at lower temPeratures' dissolved oxygen concenÈration, and PH. S. exspinosus. Variation in temperaËure and dissolved oxygen concentration vrere unimportant in accounting for variance in log mean density of this species in pond 1 during 1977. Variation in pH accounted for a low amount of Ehe variance in 1og mean densiry in pond 1 during 1g77. Variation in dissolved oxygen concentration accounted for the highest amount of variance in 1og mean density in pond 1 during 1978' However, the number of data points was low (3) and they felI over, a restricted range of dissolved oxygen concentrations. Variation in temperature, dissolved oxygen concentration and pH all accounted for high amounts of variance in log mean density in pond 2 during L977, Temperature and pH were significantly correlated (p = 0.59, P < .01) in pond 2 during 1977. Although S. exspinosus occurred over a wide 115 . Èemperature range, highest densities occurred in sunrner around temperatures of 22oC. M. hirsuticotnis. Variation in Ëemperature and dissolved oxygen concefitration accounted for none of the variance in 1og mean density in pond 1 during Lg77. Variation in pll accounted for a very low amount of the variance in log mean density. M. hitsuticotnis hlas recorded up to pH LI.Z at Gumeracha, with several records above pH 9.5. VariaÈion in temperaËure and dissolved oxygen accounted for similar, low amounts of variance in log mean density in pond 2 during L977 - I'{eak positive relationships were found betrveen log mean density and both temPerature and dissolved oxygen concentration. 14. hitsuticornis occurred over a wide ternperature' oxygen, and pH range' M. Ieuckarti. Variation in temperature accounted for the highest anount of the variance in log mean density in pond 1 during 1977 ' A positive relationship was found between temPerature and log mean density' Highest mean densities occurred over the range IB-24oC, although iU' Teuckatti $ras present throughout the year. variaËion in t-emperature, dissolved oxygen and pH all accounted for high anounts of the variance in 1og mean density in pond 1 during Lg78. It has been shown above that dissolved oxygen and pH were significantly correlaLed with temperaLure during 1978' lI. LeuckarÈj occurred up to pH 11.1 at Gumeracha with several records above pH 9.5. Temperature, dissolved oxygen, and pH were all unimporEant in accounting for the variance in log mean density in pond 2 during L977 ' Variation in temperature accounEed for the highest anount of variance in log mean density in pond 2 during L978. 14. Teuckarti occurred oyer a wide temperaEure, dissolved oxygen, and pH range although blooms occurred in summer, B. triarticufata. Variation in pH accounted for the highest amount of variance in 1og mean density in pond I during 1977 ' A negative relationship was found between pH and log mean density' Although 116 . B. tríarticuJ.ata was recorded uP Ëo pH 11.1 at Gumeracha, few records occurred a.bove pH 9.5. Temperature, dissolved oxygen concentration, and pH were all unimportant in accounting for variance in log mean density in pond 2 during Ig77. B. triatticu-7.aÈa occurred over a wide temPerature range but appeared to occur at lower pH' Other factors vrhich may be important in regulating zooplankton populations are food level and inÈeractions w'ith oÈher organisms (predation and ccrnPetition). S. exspinosus, although a littoral dweller, is not a sediment feeder but typically attaches dorsally to the substra¡e and filters suspended maËeríal from the water (Cannon in Horton et a7., Ig7Ð. It is highly probable that 14. hirsutìcornjs is detritivorous (c.f. Fryer, lg74), No dataars available on the diet of B. triarticulata but it is likely thaÈ this calanoid copepod is an obligate filter feeder (c.f. McNaught, lg75). While the nauplii and early copepodite stages of M. Leuckartj are herbivorous (Gophen, L977), Iate copepodids and adults are carnivorous and include cladocerans, rotifers, and the young of other copepods in Èheir dieÈ (Gophen, L977; McQueen, 1969; Fryer, 1957)' The diet of o. carinata in the Gumeracha ponds r¿as investigated during this study. D. carinata was collected from the ponds and individuals (plus washed with distilled h¡ater. The distal half of the intestine postabdomen) was dissected out and gut contents ejected onto a microscope slide. Animals were collected from pond 1 on 30 March 1977 (chlorophyll a concentration fO mg/*3) and pond 2 on 10 August 1977 (chloroPhyll a concen¡raEíon 24 tg/*3). On both occasions gut contents includq'd Scenedesmus cel1 fragments, diatoms, and large amounts of detritus ' Gut contents of animals collected from pond 2 on 29 March 1978 (chlorophyll a concentration 555 *g/*3) included mainly fragments of S. opoliensis, although some cells were still intact, but very low proportions of diatoms (Navicufa and Nitzschia) and detritus. It thus appeared thaE D' carinata 117 . hras a filter feeder during phytoplankton blooms buL ingested sediment when phytoplankton v¡ere not abundant ' Live animals plus hrater from pond 2 collected on 29 l"larch 1978 were placed in a laboratory tank. On 26 April 1978 water in tfre tant< r¡ras observed Èo be quiËe clear. l"licroscopic examination of waÈer samples from the tank revealed the presence of a small number of ciliate and flagellated Protozoa but no Scenedesmus. Surface sediment from the tank bottom consisted of both intacL and fragmenEed Scenedesmus cells diatoms, and detritus. Gut contents of. Ð. carÍnata in the tank at ËhaÈ ti¡ne (the second generation that had developed since Èhe tank had been set up) consisted of sedimented material as present on the tank boEtom' Animals in the tank were observed to periodically sink to the bottom, ro11 over until horizontal, and then place their ventral caraPace margin onÈo the sediment surface. Animals either remained in the one position (wittr trunk appendages beating) for uP to 2 seconds or moved horizontally across the sediment surface. This behaviour was consistent with gut contents of animals collected from the field during periods of low phytoplankton abundance. D. catinata thus appeared to be a "facultative brohrser" (Horton et a7-, lg7Ð. That is, D. carinata is capable of switching from suspension feedíng to foraging on the bottom and ingesting the sedirnents when the suspended food concentration is 1ow. Based upon dietary considerations, the following interspecific interactions may have occurred in the Gumeracha ponds. Ð. catinata, s. exspinosus, a]r¡d B. triarticuJata may have cornpeted for food during periods of phytoplankton Presence, After the decline of phytoplankton to blooms , D. carinata (a facultative browser) míght have been expected be aÈ a competitive advantage over the oblígate filter feeders S' exspinosus and B. triarticuLata. In this context, D. catinata, S. exspinosus and B. triarticLZata could be expected to exert consíderable grazing Pressure upon phytoplankton populations at Gumeracha. It was also thought that 118 H. feuckarti could have preyed upon the juvenile instars of D' catinata and S. exsPinosus. The nature of interspecific interactions and the effect of zooplankton upon phytoplankton abundance in the Gumeracha ponds was investigated via deÈermination of the correlation between species densities, and between species density and chlorophyll a concentration' Regression analysis vras noÈ applicable in studying these relationships as iÈ could not be assumed that the independant variable (mean density) $ras normally distributed; measurement of mean density also involveC a (p) considerable error comPonenË. The non-Parametric Spearman's rho rank correlation coefficient v/as used. In some cases mean density data íncluded a large number of. zero values (that is, a particular organism was absent) . These values were retained and treated as tied values ' Due to the large number of tied zero values p was calculated by applying the formula for Pearsonrs product moment correlation coefficient to ranked data after Conover (1971). Chloroph yll a concentration versus zoop lankton densiËy Values of P, plus significance level, between chlorophyll a concentration (*g/*3) and mean population density (number/litre) of the major herbivores in the Gr¡meracha ponds are PresenEed .in Table 4 ' 5 ' Significant negative correlations were found between mean density of D. carinata and chlorophyll a in both ponds during 1977 arld Lg7B. Chlorophyll a concentration declined in pond I during March-Aprí1 LglB, and in pond 2 during March-Apri'L L977 and April-May 1978 as mean density of. p. carinata increased. During early 1978 D. catinata, appeared in pond 2 approximately one month aft.er it was first recorded in pond l' Chlorophyll a concentration in pond 2 remained higher than in pond 1 during thaE period. That is, temperature did not appear to be the major factor terminating phytoplankton blooms in the Gumeracha ponds ' Phytoplankton blooms developed in both ponds during November 1977 and Table 4.5 Spearman's p (plus level of significance) between chlorophyll a concentration and population density of herbivorous zooplankton and between percentage phaeopigmenEs and density of D. carinata in the Gumeracha ponds during 1977 atd 1978' Pond 1 Pond 2 197 8 197 7 L97 B r97 7 s1g. sig. sag. slg' p p p p 1eve1 1eve1 1evel leve 1 chlor. & p<.r7" D. catìnata -0. 50 5'/.>p>I% -0.57 I"/.>p>.I% -0.75 P<.17" -0.82 p>57. S. exspinosus o.42 P>5%' 0 .33 P>5i( -0.41 B. triarticuLata -0 .04 p>57" 0.07 P>57" % phaeo. & 0.88 p<.r7" D. carinata 0. 59 I%>p>.L7" 0.70 IY">p>.17" 0. 36 p,57" 119. October 1978 after .p. carinata standing croPs had declined. However, if the absence of grazíng pressure had been the najor factor triggering phytoplankton blooms the onset of the bloom in pond 1 in late 1977 w.ould have occurred earlier than in pond 2. This was not the case. It has been shown (Chapter 3) that phytoplankton blooms developed above temperaÈures of 18oC. Although temperature effects may have explained the negative correlation betr,¡een Ð. carinata density and chlorophyll a, high chlorophyll a values did occur at temperatures below 18oC and D. catinata was present at temPeratures above l8oc. No significant correlation r{as found between chlorophyll a concentration and the mean density of s. exspinosus or B. triatticuLata in pond 1 during 1977 and 1978 or in pond 2 during 1977. Although 3. triarticul-ata was present during periods of phytoplankton abundance mean density was very low. fhe ìegative p for S. exspinosus in pond 2 was probably an artifact due to a low number of data values. This species declined soon after sampling comnenced and r,ras rare in pond 2 thereafter. The non-significant positive p values for S. exspinosus in pond 1 may have resulted from temperature effects. Although S. exspinosus and B. ttiarticu-Z.ata would have consumed Scenedesmus during phytoplankton blooms, neiÈher species appeared to be.very important in reducing phytoplanÈton standing crop. Tfhe digestion of algal cells by zooplankton results in the formation of phaeopigmenÈs. The correlation between mean density of D. carinata and the percentage of phaeopigments in the total chlorophyll a pool in the Gumeracha ponds has also been presented in Table 4.5. Significant positive correlations were found between mean density of D. carinata and the percentage of phaeopigments in pond t during 1977 and 1978 and in pond 2 during 1978. A non-significant posiEive correlation was r20. found in pond 2 during L977. However, chlorophyll degradation rs influenced by temperature; phaeopigments are mosË abundant when hrater temperaËure is highest (Glooschenka et aJ., 1972). The importance of temperaÈure in the Gumeracha ponds was investigated via a linear regression of the Percentage of phaeopigments in the total chlorophyll a pool on average r^rater temperature. Variatio¡l of water temperature accounted for none of the variance in the Percettage of phaeopignents in both ponds during lg77 . Variation in water temPerature accounted for 787. of. the variance in the percentage of phaeopigments in pond 1 during 1978 and 52% of. the variance in pond 2 during 1978. Hor¿ever, in both ponds during L978 a negative relationship between temPerature and percentage phaeopigments was found (fig. 4'18, A^ and B)' Although this may have resulted from resu"p.rr"iot of senescent cells from the sediments, it has been shown thaÈ D. carinata l¡/as a predominantly cold r¡Iater form ánd highest mean densiEies occurred at lower water temPerature' D. carinata appeared to be the major herbivore in the Gumeracha ponds . Grazíng by D. carínata reduced phytoplankton standing crops during early auLumn, thereby terminating phytoplankton blooms. However, temperature, and not the release from grazírtg Pressure, was the major factor triggering the onset of phytoplankton blooms during laEe spring' D. ce; inata \"/as a cold water species and, therefore! Prevented from lirniting phytoplankton on an annual basis by high temperatures ' Inters ecific interacÈions Values of p, plus significance level, betr¿een nrean density of A. cazinata and mean densify of S. exspinosus, B. ttiatticuTata, and 14. l-euckatti, and beEween rnean density of S' exspinosus and mean density of M. Teuckartj in the Gumeracha ponds are presented in Table 4.6. A significant negative correlation was found between mean density of O. carinata and mean density of S. exspinosus in pond I A B I 100 o\o I a tr tr l6 I I \ ID 80 o ¡-, tr 0) o É \ b0 o .Fl o I tr q) 60 I d o Ê ¡ l+{ o o I lt I 9oao (d +J t t É ¡ OJ (.) I tr E GJ Ê.t I I ¡ 20 Io I B I I tr rtr ?D I tr t I I I r 1l- I 0 I -o -trtr t6 20 24 8 L2 T6 20 248 T2 Temperature (oC) phaeopigments, expressed as percentage of total chlorophyll a, versus depth-averaged FTGURE 4.lg (r) 1978 (o) plus _ hrarer remperarure'in pond f ie) and fond 2 (B) durtng 1977 and ' regression lines Table 4.6 Spearman's p (plus level of significance) between population density of p. carínata and major zooplankters and between density of S. exspinosus and ¡4. l-euckarti in the Gumeracha ponds during 1977 artd 197B. POND 1 POND 2 r977 r978 L977 197 8 s19. slg. sig. p sig' p p p leveI level leve 1 1eve1 D.carinata & -0.79 -0.68 17.>p>.1% o.34 P>57" S.exspinosus P<.17. D.carinata 6 B. triarticul-ata 0 .09 p>57" 0 .13 p>57" D.carínata ù M. Teuckartí 0.01 p>57" -0.57 5%>p>LI" 0 .06 P>5% -0.57 P>5"/" S.exspinosus & 0.33 P'51l 0.54 57">p>l% 0 .39 5%>p>L7" M. Teuckarti \ T2T, during L977 and.1978. During February-l{arch 1977 mean density of S' exspinosus decreased as mean density of D. catinata increased; a secondary increase in mean density of S. exspinosus occurred in pond 1 during June 1977 after the decline of D. catinata. Mean density of S. exspinosus decreased in late March 1978 as mean density of O' carinata increased. Although highest mean densities of S' exspinosus occurred during summer the species v/as Present in pond I fhroughout the year. Variation in temperature accounted for a small amount of the variance in mean density of S. exspinosus. The non-significant posiEive correlation between mean density of O. carinata and mean density of S' exspinosus in pond 2 during 1977 was an artifact due to 1ow number of data points. Mean dens íty of. o. carinata and mean density of B. triarticuLata trere not significantly correlated at Gumeracha. Although B. triarticufata r¿as present ÈhroughouE L977, mean density !'/as aPParently too 1or¿ for serious competitive interactions to occur. Mean density of S. exspinosus and mean density of M. Teuckarti nere not significantly correlated in pond I during L977. Mean densiEy of the two species v/as positively correlated in pond 1 during 1978 and pond 2 1977, Positive correlation r^ras probably due to temperature effects (both species exhibited highest mean densities in sunrner) raËher than a positive interaction beEr¡Ieen species ' Mean densities of D. carinata and ¡4. Teuckatti \^Iere not significantly correlated in the Gumeracha ponds during I977 ' Despite a reduction in mean densíty, M. Leuckarti was still present in l4rge numbers during the period of D. carinata density increase in pond 1 during February-Marcl:- !97'/. Mean densit.y of both species increased concurrently in pond 2 during late August-early September 1977 - A significant negative correlation raras found between mean density of D. carinata and mean density of. M. leuckarti in pond I during 1978. llean density of o. carinata increased as mean density of tl' L22. Teuckarti decreased in March-April 1978. However, temperature accounted for a high arnount of the variance in mean density of both species in 1978. The negative correlaEion may have resulted from temperature effects; M. Teuckartj bloomed during suflmer while D' carinata vlas a cold wa|er form. The same negative p u/as found between mean densities of the two species in pond 2 during 1978' A lower sample size made this p non-significant. Although temPerature accounted for a high amount. of Èhe variance in mean density of D' carinata in pond 2 during 1978, temPerature \¡/as not particularly important in accounting for the variance in mean density of M' l-eucl:arti during that year. The effects of predation will be discussed further in subsequent sections of this chapter' In summaryr EemPerature aPPeared to be the major factor influencing the seasonal occurrence of D. carinata in the Gt¡meracha ponds ' This species attained highest mean densities during autumn-winter' The effects of food and predation upon the population dynamics of' O' carinata are discussed in the subsequent secÈion of this chapter. Temperature also appeared to be a major factor affecting the abundance of M' Teuckarti' Although present throughout the yearr this species attained highest mean densities during sulûner. A1Èhough S. exspinosus attained highest mean densities during summer, a comPetitive interaction with Ð. carinata may have influenced the abundance of this species; the population dynarnics of S. exspinosus is discussed more fu1ly in section 4.4. B' ttiarticulata and M. Itirsutico.rnjs both constituted minor components of the zooplankton communities in the Gumeracha ponds' ' 4.2.3 Discussion. The zooplankton conununity of the Gumeracha ponds resembled that of other lJSps in that. it was dominated by cladocerans and cyclopoid copepods; calanoid copepods were rare. The composition of lnlSP zoo- plankton conrnunities is consistent with Èhe observation made in natural L23. lakes, thaE the relative imporÈance of calanoids diminishes as the degree of eutrophicaÈion increases (Gannon and Stemberger, L978; Godenau, 1978; Patalas , lg72). This siEuation may reflect differing evolutionary responses to variable food conditions. Calanoids aPPear to be successful in oligotrophic lakes as they are adapted to a dilute food source; calanoids exhibit high ingestion rates at low cell densities and high ingestion efficiency at smal1 ce1l sizes (McNaught, Ig75). Cladocerans tend to be generalist feeders, exhibiting equally high ingestion efficiencies on nanno- and net plankton, and maintaining high filtering rates at high ce1l densities (Bogdan and McNaught, 1975)' of cladocerans are, therefore, adapted to the higher food concentrations eutrophic r{aters . ïhe occurrence of calanoid copepods in wsPs is likely, Èherefore, found in to be determined by organic loading. calanoids have not been (Hussainy, 1978) ponds at !,lerribee or in other parts of Victoria ' Although influent BoD to Ehe llerribee ponds is much higher than at connected in Gumeracha (initial ponds are anaerobic), several ponds are series and final effluent BOD compares with effluent from pond 2 at Gumeracha. Thus, in some ponds aE !trerribee, organic loading must be similar to loads at Gumeracha. B. ttiarticuJata might be expected to occur in such ponds. Effluent NH3 concentrations at Lferribee are much (see higher than aË Gumeracha and may explain the absence of calanoids belor¿). It remains somewhat surprising, however' that calanoids have not been recorded from other Victorian l'lSPs ' ThedominantzooplanktersintheGumerachapondswerel contagiously distributed on both a small and gross scale' Confidence limits for mean density estimaEes r.¡ere of ten wide. Ihis reflected orders of the extreme nature of contagion. Density varied by tP Èo 3 be argued magnitude between samples on some sampling dates. It might that, due to the small tube diameter' the sampling technique itself L24. generared contagion. However, the tube sampler $ras more effective at capturing Ð. carinata than vertical hauls with a zooplankton net of uruch larger mouth diameter. Due to the vertical distribution of Ð' catinata in the Gumeracha ponds, closure of the bottom door of pttt'ttot' traps enclosing a large volume of water (".g. schindler,1969) could have excluded animals. The best method óf improving the reliability of mean density estimates would have been to increase the number of samples taken. However, over 30 samples per pond would have been required Eo reduce the standard error to 207. of the mean. Lingeman (1978) reported Ehat 34 samples (tZ cm diameter tube sampler) were required from an artificial, rectangular pond 5 x 3 x 1 rn deep to provide reliable population estimates for D. magna. Time and labour constraints precluded such an intensive sampling progranme during the present study' overall patchiness or' M. hirsuticornis, S. exspinosus, and M. leuckarti was more pronounced in pond I than in pond 2 during L977. This coincided wiEh greater bottcrn coverage by P. ochteatus in pond I during that year. Contagious distributions of trtactothrix spinosa, S' exspinosus, artd M. Leucl:arti, apparently related to weedbed variation, have been reported from a billabong v¡ith extensive littoral macrophyte development (streit , Ig76) . .The límnetic species, D. catinata and B. trÍarticuTata, displayed low overall paÈchiness in pond I during I977' overall patchiness of D. carinata and ¡4. Teuckatti \^Ias similar for both ponds during 1978 and lower than during 1977. P. ochreatus was absent from both ponds during Lg7B. Thus, patchiness of littoral microcrusËacea in the Gumeracha ponds may have been determined by the degree of, macrophyte development. This did not explain the patchiness observed in the distribution of D. carínata in pond 2 during 1977. Stratification in smal1, shallow water bodies has been discussecl in chapter 2. It cannot be assumed that limnetic plankters in such waters are homogeneously distributed by wind action. Planktonic t25. organisms are generally non-randomly distributed over a wide range of spatial seales and many facÈors have been implicated in producing patchiness ' A dominant factor influencing gross heterogeneity may be the wind-induced circulation pattern (George and Edwards, L976; Schröder, 1961)' This can result in the development of upwind surface aggregations or dovmwind deeper aggregations of plankters ' D' catinata did not display aggregations of this type in the Gumeracha ponds ' D' hgaTina has been observed Eo clump in regions of upwelling midway between foamlines of Langmuir circulations (George and Edwards, 1973). Langmuir foamlines rúere never observed at Gumeracha duri.ng the present study. A minimum fetch (and therefore surface area) is probably required for the develoPment of Langmuir circulations and they may noÈ occur in small water bodies (f . Watlis, Caldwell-Conne11 Engineers, pers. coIIIrn. , 1979). HeterogeneiÈy in the dístribution of D. catinata in the Gumeracha ponds was aPParently not due to effects induced bY wind ' Patchinessofaplanktonicspeciescouldalsoariseduetoan inherent aggtega:ion lendency, environmental heterogeneity, or reProductive activity (Tonolli and Tonolli, 1958). That Ð- catinata did not exhibit inherent aggregation behaviour is suggested by the occurrence of negative a intercepts in plots of mean. crowding on mean density. Although not invesEigated in the present study, some degree of chemical variation would catinata have been expected frcrn inlet to outlet in the Gumeracha ponds ' Ð' did not display any consistenÈ horizontal distribution Pattern with respect to this gradient. Aggregations of ephippial fernales have been observed (Young I97 B) and in D. carinata (Santharam et a7., lg77), Daptnia magna ' ceriodaplvtia affinis (Brandl and Fernando , lgTI), and may be caused by sexual activity. The dense clumps of O. carinata that occurred in pond 1 on 21 october 1976 were not sampled directly. Hovrever, the Percentage of adult females carrying ephippia was high on that occasion and sexual not activity may have been pronounced' These types of clumps \^Iere L26. observed ofÈen and cannoÈ account for the patchiness observed on a long term basis. It may simply be that, as Roughharden 0977) has suggested, zooplankton patchiness is an inevitable consequence of dispersal in a randomly flucLuating environment. PaEchiness can thus be explained withour considering the patch strucÈure of the environment, or special behaviour within or between species. Of course, if these phenomena occur they will contribute to Patchiness Thepopulationdynamicsof.o.carinataands.exspjnosusat Gumeracha will be discussed more fully in subsequent sections of this generally chapter . D. catinata, although presenL throughout the winter, exhibited a diphasic annual population cycle with peaks in mean density during autumfi (March-May) and late winËer-early spring (September-October) ' This agreed with observations on the seasonal disÈribution of the species (Burns, in various other hraËer bo¿ieì in Australia and New Zealand L979; particular, Tirnms, 1970; Bayly , Lg62; Byars , 1960; Jolly , 1952) . In Burns (1979) recorded population peaks of O- carinata during February- (1970) March and rate october in Lake Hayes, New Zealand. vijayaraghavan reported a single annual peak of O. carinata in a small, shallow pond in density India. Maximum population density was similar to peaks in mean Average at Gumeracha but occurred aE a \n/ater temPerature of 25oC' density throughouE the year \Álas much lower (i.e. IO-20/L) than at Gumeracha. Mean density of s. exspinosus in the Gumeracha ponds peaked year during mid-summer, although the species vlas present throughout the ' cycles No comparative quantitative data is available on annual population of this species ' In the absence of quantiEati.ve data on the abundance of nauplii cycles and copepodite stages 1ittle can be concluded concerning population of a. leuckatti and B. triartic,.tTata in the Gumeracha ponds. M- feuc]:arti second period r¡ras perennial with maximum recruitment during summer' A of lower recruitment may have occurred during late winter-spring. Timms t27 . (1970) repor¡ed that this species was most abundant from November Èo March but that peaks at other Èimes ürere not uncormon. Green 0974) reported that breeding in this species was most intense during spring and sununer. Although ovigerous females were not recorded in pond 2 from mid-December 1977 until mid-May 1978, recruitment occurred during January and April I978. This could have resulted from the hatching of resting eggs (Hutchinson, L967) or from recruiEnenÈ of a dormant phase (nauplii or copepodids) (Green , 1974; Hutchinson, L967). B. triarticuLata exhibited major population peaks in pond 2 during April and November 1977. However, several minor increases in mean density suggested that recruitment was repeated. Geddes (1968) reported that adults, copepodids, and nauplii of this species ¡¿ere PresenÈ throughout the year in Marshall Reserve pond, Victoria, and thaÈ a peak in breeding occurred in August-SePtember. Temperature has been reported as Èhe most important single factor regulating zooplankton populations in some natural ponds (O'Connell and Andrews, L977; Byars, 1960). It is, perhaps, unrealistic to attempt to isolate any single factor as most important since the evolution of planktonic populaÈions occurs in response to a suite of factors, including food level and interspecific interactions. Cladoceran mortality at pH in excess of 10.5 has been reported by O'Brien and De Noyelles (Ig72). D. carinata generally occurred below a pH of 9.5 in the Gr¡meracha ponds, although one collection \,ías rnade at pH 10.5. The decline of D. carinata in pond 2 during Iate 197 7 occurred as pH approached and exceeded 10.5. The onset of O. carinata population increases in pond 2 ín 1977 and 1978 ocourred later than in pond l ' In both years pH exceeded 10.5 in pond 2 and D. carinata did not aPpear until pH fell belor¿ 10.5. If pH had been a major factor affecting the occurrence of D. carinata at Gumeracha fundamentally different population cycles would have been expected in each pond due to pH differences. 128. ponds even though Ho¡.¡ever, population cycles \¡/ere very similar in both the pH of pond 1 never exceeded 10.5. Furthermore, if direct pH mortality had been important a correlation between pH and mean density would not have been expected below Èhe criÈica1 pH level' The negative relaËionship found between pH and mean density of D. catinata during 1978 was due t.o the negative correlation beÈween mean density and temperature rather Ehan pH induced mortality (temperature and pH were positively correlated during 1978). Mortality of Oaplvtia in t'lSPs may the occur due to NH, toxicity at pII above 8.0 (Dinges, L973)' However, critical NH, concentration varies between species of Oaphnia and may be as high as 5 mg/1. It is unlikely thar NH, concentraEions in the of Gumeracha ponds hlere ever high enough to result in direct mortality D. carinata. D. carinata hlas a f acultat,ive browser in the Gumeracha ponds; after the decline of the phytoplankton standing crop animals ingested sediment. Atthough the sediments would never have become a limited greaf resource in an absolute sense, population densiEy may have been so at times that there vtas simply insufficient bottom area for all animals in the population to obtain adequate nutrition. Maximum mean density 100 animals per of. o. cal.inata (approxi-mately 1000/1) corresPonded to the bottom square centimetre of pond bottom. Animals did not forage on conÈinuously so the whole population would noE be feeding simultaneously' disturbed However, at high population densities the probability of being by another animal while feeding would increase. D. carìnata may have shortage been limited at high population density by a relative resource (see 4. 3. 3) . Physico-chemicalfacEorsappearedtobeunimportantin accounting for the variance in mean density of S' exspinosus aL Gumeracha. The disappearance of this species from pond 1 in 1978 could significant have been related to the decline of. p. ochreatus. The only L29. factor affecting the abundance of this'species aE Gumeracha appeared Eo be a negative interaction with .p. carinata. It is unlikely that the negative correlaÈion between mean densities of the two species was the result of temperature effects. Although maximum mean density of S' exspinosus occurred during suÍrmer, the species exhibited a second population increase in pond 1 during nid 1977 aflet the decline of D. carinata. It has been demonstrated that simocephalus vetufus is invariably replaced, by Daplnia puTicarja in mixed laboratory culture (Frank, Lg52). HorÈon et a7. (f979) have suggested that Frankrs results were due to S. vetuTus, an obligate susPension feeder, being at a competitive disadvantage in the unstirred medium of the experimental environment. D. pu7ícaria, a facultative browser, $/as able Èo utilize sedimented food and therefore maintain itself for longer' Such an explanaÈion could not account for the second population increase of S. exspinosus in pond 1 during mid 1977 at a time when suspended food rvas extremely low. It is tempting to suggest that the decline of S. exspinosus (maximum length 3.5 mm) in pond I during the increase of D' carinata (maximum length 5.6 nm) in February-March 1977 was due to competitive displacement by the larger species in accord with the síze- effíciency hypoÊhesis (Brooks and Dodson, 1965). However, the size- efficiency hypoÈhesis has not generally been supported by experimental findings (".g. Neill, Ig75). It now aPPears that zooplankton competitive ability is a complex interplay between size-selective vertebrate and invertebrate preda¡ion (Lynch, I979; Dodson et al., 1976; Dodson, 1974), reproductive effort (Lynch , Lg77), and growth ràte (Novakova et â1. ' 1978) ' The decline of S. exspinosus will be discussed further in section 4'4 where birth and death rates are Presented. If the decline of this species v/as due to predation the mortality rate \,/ould be expected to increase in the presence of the predator (..g. Kerfoot, 1977)' If the decline r¿as due to comPetition the birth rate would be expected to 130. decline as resources became lirniting' Loedolff(1965)concludedthaÈtemperat'urealonewasthemost importanÈ factor controlling the density and appearance of cladocerans in I{SPs. It is obvious from the studies at Gumeracha that, while temperature is imporLant, zooplankton communities in l'ISPsi as in natural eJaters, may be influenced by other factors. These facÈors must also zoo- be considered r^¡hen designing eff luent polishing schemes utilizing plankton communities. In the absence of experimentally deËermined filtering rates, the effect of zooplankton gÏ.azers upon phytoplankEon sÈanding crop in the Gumeracha ponds must be inferred from correlations of population density. D. carinata appeared to be the major grazet in the Gumeracha ponds and terminated phytoplankton blooms ' The sequence of events during the decline of phytoplankton blooms at Gumeracha hlas very similar to Èhat described by Pennington (1941). That is, as the density of Ð. carinata increased, phytoplankton standing crop declined, the water turned a dark colour, ancl dissolved oxygen concentrations fe11 to very low levels. D. carinata collected at thaÈ time were brighÈ pink in colour due to the synthesis of haemoglobin in resPonse to lowered of ambient oxygen concentrations' (Fox, 1948). Although Ehe percentage phaeopigments in the total chlorophyll a pool was significantly correlated with the density oÍ. p. carínata, such a relationship is not always an accurate indicaÈor of grazíng pressure. In shallow ponds, a poor (Glooschenka' correlation may result from resuspension of sediments 1972; Moss, I970) while a high correlation may result from zoop'lankton feeding on detrit aI algaI ce11s already rich in phaeopigments (Glooschenka, Ig72). Both processes probably contributed to relatively high percentages of phaeopigments in the Gumeracha ponds during winter (rigure 3.4) . 131 . The filtering raLe of oaplnia (the volume of medium conLaining 1975) is the number of cells consumed in a given time: I'IeEzel, light' influenced by temperaEure, PH, food concentration' food tyPe' (Hayward Gallup' I976; oxygen, body length, and reproductive state and 1961; Ivanova' Kring and O'Brien, 1976a,b; Starksweather' L975; Kibby' 1969; Burns andRigler, Lg67)' AlEhough D' catinata is L969; Burns ' (maximum length larger than any species of the genus previously studied ranged îxom 2'65- aÈ Gumeracha was 5.65 mm), mean body length of adults (section From Hayward and 3.40 nnn during the present study 4'3)' would Gallup iGg7û it was estimated that an average adult D' carínata (approximately ingest B-10,000 cel1s/individual/hour at ce11 densities were prevalent 25,000/rn1) and temperaEures (approximately t5oC) that duringperiodsofpopulationincrease.Eachanimalwouldthusfilter 150 individuals 0.25-0.30 ml/hour or 6-7 mLlday. AË mean densities above the entire volume of the llítÍe D. carinata could probably have filÈered of Scenedes¡nus acutus Guneracha ponds ín one day or less. outdoor cultures biomass at optimal areal density (growth rate below maximum) have minimum D' catinata doubling times of about 3 days (stengel and soeder, 1975) ' phytoplankton standing populations appeared to be quite capable of reducing crop in the Gumeracha Ponds ' in l,Ihile grazíng by D. carinata terminated phytoplankËon blooms theGumerachapondstheonsetofbloomswastriggeredbytemperature ratherthanreleasefromgrazíngPressure.Thedominantzooplankter duringsummerperiodsofphytoplanktonabundancewasM.]-euckarti,a effluent quality carnivore. As a result, significant deterioraËion of dueÈohighphytoplanktonstandingcropsoccurredduringSummer.D. catìnata,themajorg:.aze'.'\¡/asnotPresentduringmostoftheperiod ofphytoplanktongrowth,andwasthusunabletocontrolphytoplankton of Ehe phytoplankton standing crop on an annual basis ' Carbon limitation mayalsohaveoccurredintheGumerachapondsduringperiodsofintense L32. grazírlg by D. carínata. controlled carbon enrichment experiments would be required Eo separate the effects of carbon li¡nitation and gtazír.g' Grazing was, therefore, one of a suite of factors controlling phyto- plankton abundance. The effects of zooplankton upon effluent qualiÈy at Gumeracha were manifested through the reduction of phytoplankton sEanding crop' D. carinata contributed to major reductions in BOD, SS, and TOC in pond 2 during late March-April 1977 and in both ponds during the same period during Lg78. It was shown in chapter 2 that reduction of BOD, SS, and months This TOC was highest in the Gumeracha ponds during the winter ' Híghest was related to periods of macrophyte development in chapter 3' D' reduction of organic Parameters also coincided with periods of high calîinata population density. However, percentage reduction of BOD, SS, D' and Toc in pond I was high throughout June-November 1977 even though carinata was absent. The standing crop of P. ochteatus in pond 1 was high during that period. Despite a high standing crop of D. catinata in pond 2 during June-November 1977, Percentage reduction of BoD, ss, was consistenE \^/ith and TOC was lower in that pond than in pond 1. This a lower standing crop of P. ochteatus in pond 2. Howevet, D. catinata gtazíng contribut,ed to improvement in'effluent quality during periods of during as evidenced by increased reduction of BoD, ss, and Toc in pond 2 p. pond March and April Ig77. The growing season of ochreatus in that did not commence until l"I'ay 1977 ' That D. carinata did noE contribute greatly Ëo the reduction of decline organic parameEers during winter is not unexpected. After the of phytoplankEon standing croPs , D. carinata (a facultative browser)' less foraged on the bottom and ingested the secliments. Consequently, chief time would have been spent filtering in the water column' As the filtration mode of BoD and ss reduction by cladocerans appears to be rhe of sestonic particles, the shift in feeding behaviour of D' carinata 133. r.rould decrease its conÈribution to BOD and SS reduction' Loedolff (1965) reported a good inverse correlation betvreen BOD and total cladoceran standing croP in I.ISPs in southern Africa. It is likely, however, that high standing crops of phytoplankt.on nere Present throughout the year in Loedolff's ponds (c.f. shillinglaw and Pieterse, Ig77). Under such conditions, phytoplankton standing croP, and therefore BOD, would reflect grazírtg pressure' . Removal of NO, and soluble and total PO4-P was highest in the Gumeracha ponds during phyËoplankton blooms. Consequently, grazíng by D. carinata resulted in a reduction in nitrogen and phosphorus removal. Elster (tgOS) reported that grazíng by Dapfutia in !üSPs resulted in high nitrogen and ptrosphorus concentrations in effluents. The data of Loedolff (1965) also showed Èhat effluent phosphate was highest when standing crop of cladocerans vtas maximal' Removal of NH} TKN, and org-N was highest in pond I at Gumeracha during the latter half. of. L977 when D. carinata was absent. Removal was lower in pond 2 during the same Period even though density of D' carinata was high. Removal in pond 2 during 1977 incteased with the onset of p. ochreatus growth. As for organic parameters' P. ochreatus was the major agent of reducdion of nitrogenous comPounds in the Gumeracha ponds during the wincer of. 1977. However, a comparison of influent and effluent concentrations does not accurately reflect the importance of a population as a nutrient store. The nutrient store represented by annual net production of D. catinata and S' exspinosus y'etained in the Gumeracha ponds is compared with the amount of nutrient in the ponds annually in subsequent secÈions of Ehis chapter. 134 . 4.3 Population Dvnamícs and Prod uction of Daphnìa carìnata 4.3.1 Methods 4.3.1.1 Size Dístríbution. Information on the age and size sÈructure of a population is essential for an accurate analysis of population fluctuaËions. It is difficult to describe the age stÏucture of Daphnia populaËíons as members of thÍs genus do not exhibit any age-specific characters. Indivíduals nay be aged in the laboratory by following moulting and instar duration. Such a technique Ís impractical in the fÍeld. The appearance and devel-opmenÈ of successive generations may be followed in the field by monitoring the changes ín nurnbers of a¡rimals Ín arbítrarily defíned size classes. This approach was adopted during the Present studY. (1932) Body length of D. carinata was measured afÈer Anderson as the longest dÍsËance from the top of the head to Ëhe base of the caudal spine (see Mitchell, 1973). Measurements were made at 20 times magnification using a micrometer eyepiece. At ËhÍs magnification, 10 eyepiece units were equivalent to 0.526 ¡nn. Post embryoníc animals (juveniles and sexually mature adults) were placed Ínto 9 length classes each of l0 mícrometer units in width (Table 4.7) i the lower lirnit of the first juvenile size class.was 15 eyepiece units. The lower lirnit of sÍze class 4 corresponded to carapace length at. the onset of reproduct,íon. ftnmature or embryonic stages (passed in the brood chanùer) of D. carinata were also assigned to size classes for length - dry weight determinaÈions. The development of Ëhe parthogenetic eggs of t (1977). The D. carinata has been descríbed by Murugan and Venkataraman puTex descrj'bed by developmental sequence is identical to that of. o. was Edmondson (1955). For convenience, Edmondsonrs classifícation as adopted duríng the present study. Embryoníc sÈages hTeÏe classed foLlorvs: early - eggs round or slightly elongate; middle - ernbryo Tabl-e 4.7 Length classes for mature D- catinata Míd-c1ass Length class I'licrometer units IImt length (nm) I 15- 25 0..759 L.325 r.04 JuveniLe 2 25- 35 L.325 1. 855 I .59 3 35- 4s 1.855 2.385 2.12 4 4s- 55 2.385 2.9r5 2.65 5 55- 65 2.9t5 3,445 3. 18 Sexually 6 65- 75 3.445 3.975 3.71 mature 7 75- 85 3.975 4 .505 4.24 I 85- 95 4 .505 5.035 4.77 9 95- 105 5.035 5.565 5 .30 135. elongate r^Iith distÍnct head bulger separaÈe anËennal ramí bearing terminal setae, and developing caraPace and caudal spine; late - embryo wtth wel-I developed eye pigment and differentiated Èhoracic appendages ' The laËe embryonic stage is clearly disËinguishable from the first aduLt st,age as in the former the caudal spine is curled ventro- anteriorally beween the caraPace values ' Embryos (n = 339) were dissected out of the brood chanbers of female D. carinata col-lected from pond 1on 21 May, 1976. Each embryo was classified according Ëo the scheme above and measured using a m micromeËer eyepiece. The mean length of each stage l^Ias: early, O'249 (t standard error equal to 2.O% of the mean' n = 95); rniddle, 0'378 rm (t standard error equal to 2,47" of the mean' n = 115); l-ate' 0'616 nn (t standard error equal ao of. the mean, o = L29). To check this 1.97. procedure, embryos ¡¿ere assígned to 0.02 nn length classes; length- frequency analysis revealed peaks Ín number at lengths of 0.27' O'37, of and 0.63 rnn. These peaks corresPorlded closely with the mean lengths Edmondsonts embryonic stages. The upper length lirnit of the late embryonic stage r¿as 14.5 eyepiece uníts and the length of the newly hatched neonate was 0.759 rnn. Neonate length of D. carinata aE mm Gumeracha was slíghtly highefl than the value of 0.57 reported for 1-ength of Èhe same species by Murugan and Venkataraman (L977). Neonate (maxirnum D. catinata at Gruneracha was midway beËween that of D' thomsoni (fron body length 4.8 m) and D. magna (maximum body length 6.0 rnur) Green, 1956). Afterthenurnberofanimalspersamplehadbeencountedfor each sampling date, the 9 samples were pooled and subsampled (or volumetrically as in 4.2.1. At leasÈ 150 animals were measured The mean total number if l-ess than 150) and assigned to le.ngth classes" length of sexually mature adults (size classes 4-9) on each sampling (N) and date was calctrlated from the number of animals per size class 136. the mid-length of each sÍze class (t) ' That is, mean bo{Y length of the adult population was equivalent to r[(Nr.L1) + (Nz'L2) + (Nn.Ln) l XN 4.3. L.2 Reproduction. The number of femal-es in reproducËive condj-tíon (carrying eggs, rniddle or late stage ernbryos, and ephippia) in each of the 9 samples, v7as noted for each sampling date. The abundance ôf ovigerous and ephippial- females was expressed as the percentage of the total nunber of maÈure females. LossofeggsfromthebroodchamberoccurswhenDaphniaare preserved in formalin (e.g. Prepas, 1978; Prepas and Rigler, 1978). Live maÈeríal was, therefore, used where possible for the deternination of brood síze. Animals r^rere collected by oblique haul-s from the pond 150 nesh) tr{hen boËtom with a zooplankton net (25 crn mouËh diameËer, Um ' preserved material was used, only anímalS With caraPace valves close together and showing no apparent sígns of disturbafice I¡Iere selected' were on1-y fernales carrying eggs (not middle or laLe stage embryos) sel-ected. For each sampl-ing date at least 50 ovigerous females I¡Iere out of the measured and the number of eggs counted (after dissection not brood chamber). In the case of pt"""tved anirnals, loose eggs $IeÏe included in counts. Brood size (and eonceivably, the number of on ovigerous fernates) may, therefore, have been slíghtly underestimated underestimation some occasions. This would have resulted in a slight production' of birth and mortalíty rates, turnoveï tirne, and, therefore, from the total Mean brood size on each sampling date was calculated females' nurnber of eggs counted divided by the total number of ovigerous 4.3.1.3 Populatíon Parameters. D. carinaÈa reproduces contínuously; birth and death Ïates cannot be determined solely from counts' aS can be done with cohort breeders. The egg-ratÍo method, L37 , devised for roÈifers by Edmondson (1960), provides a technlque for expressing reproductive intensiËy in anímals that carry their eggs' This technique has been applíed Èo populaËions of Daphnia by Kwik and Carter (1975), Clark and Carter (1974), George and Edwards (1974)' (1964), employed Cr,urmíns et a7. (1969), !ürighÈ (1965), and llall and was during the Present studY. If the nurnber of eggs ín the populatíon (E) and the initial populaËion sj-ze (No) are known, and egg development time (D) is (B) or the number of measured experÍmenÈally, the finite birth rate ' newborn per individual per day, can be calculaÈed from D--. E "-D.N o (b')' An estimate of the instantaneous (potential) population growth rate or the rate at ¡^rhich the populaÈíon would increase if it maíntained birth rate B' can be cal-culated from b'=1-og.(1 +B) This formul'a stightly underestimaÈes br (Ednondson, 1972) ' The prime sÍgn has been used to indicate thaË population parameters have been calculated from estimates of popuJ-ation number. The calculation of bt and a age distribution, but may be applied assumes zero mortality "a"ufu to non-steady-state populatíons as an approximation (George and Edwards, I974; Edmondson, 1968). If successíve pairs of population densitj-es are known, the actual or net rate of populatíon growth (rt) can be calculated from log^N."et - 1og"eo N r-=-_--_,, population densitY where No is ínití41 population density, and Na is after ti¡ne t. The diff erence be-Ëween ínstantaneous (or potenEial) PoPulation gïor^Ith rate and actual population growth rate is a measure of 138. instantaneous mortality rate (dt), or dl = br - rr . predicted That is, the observed population change is subtracted from the population increase to reveal mortality frorr natural causes and predaËion. IfthepopulaËíonisinasteadySÈate,dlequalsbl.Ifthe is popul-atíon is increasing, bl exceeds dl, whil-e if the population A negatíve dr decreasing d, exceeds br. In both cases dr is posíÈive' value indicates that the observed popul-ation grol^Ith rate exceeds the potential popul-ation growth Ïate. Such a sítuaÈíon could possibl-y be adults' but associaÈed with the íncreased survival of non-reproductive (Curnmins et a7 is more likely to reflect errors in densiÈy esËimates ' ' of 1969) or the underestímatíon of birth rate due to the hatching ephíppialeggs(clarkandCarter,lgT4).Theleastreliablestatistic based upon t$lo associaÈed with the egg-ratio method is dt as it is quantiËies already calculaÈed wíth error (Ednondson' L974) ' Thenurnberofeggsinthepopul-at'ion(E)oneachsamplíngdate litre multiplied was calculated from the nurnber of ovigerous females Per tímes were determined by mean brood size on thât date. Egg development ín the laboratorY. 4.3.r.4 Calculation of Production: Po ation Turnover-time l"lodel . populaEion turnover NeÈ production or. D. catinata was calculated using used to calculate rates as derived from birth rates. This method has been (1974) the production of Daphnia populations by George and Edwards ' (1965) method' instantaneous Cummins et at. (1969), and I^lright . In this (D), or deaths morÈality rate (dt) is converted to a finíÈe death rate per fÍnÍte time interval, from D = 1 - .-dt ' 139. The turnover time of the population (T), or the tÍme for. the population to replace itself, is calculated from r = * (days) percentage turnover per day Ís trrus { ' 100. Net production raÈe (exclusive of respiration) can then be calculated by urultiplyíng daily percentage Lurnover by standíng crop biomass ' standing crop biomass on each sampling date was deÈermined from per litre and the number of post-embryonic indivídual-s in each size-class and the mean weight of each size class. The relationship between length dry weighÈ for D. carinata was deËermined in the laboratory. to 4.3. r.5 Eeg Development Time. A direct method was used determine the development time of parthenogenetic eggs of D. catínata' and The time inÈerval beÈween the release of eggs ínto the brood chariber ínfluenced the emergence of neonates was measured. Development Ëime is mainly by temperature; maternal nutrition after egg release has little effect(Edmondsonandtr'IinbergrL}TI)'Differencesineggsizebetween (Bottrell populaËions of a species may ínfluence development time et a7" L976; Munro and trühite, Ig75). For the determínation of development time, D. carinata in both the Gumeracha ponds was treated as a single population. ovÍgerousfemaleswerecollectedfromtheponds,returnedto eggs ín the the laboratory withín the hour, and only Índividuals bearing earliest stages of development (that is, eggs spherical and ín undivided size staÈe: after Murugan and Venkataraman, Ig77) were selected' Brood petri dísh filled with \^ras counted and each female r¿as placed in a 2o nnl ensure pond water which had been fíltered and examÍned microscopically to and 5 drops thaÈ no neonaEes \¡rere present. A small amount of sediment added to of an algal suspension (Scenedesmus cultured from pond 2) were placecl constanf eaeh peÈri dish. Petri dishes (plus lids) were in 140. tenperatures cabinets (t0.5oC; t hour dark - 15 hour light cycle) aÈ the temperatures at which animals had been collecËed in the fíe1d' Experiments rùere run at 10, 13, 16, 18 and 23oC' T\uo separate experiments, each consisting of l0 females' r¡Iere run at all tempet"t"tt"' the Developing eggs rTere examined at 12 hourly intervals excePt during laÈer stages of development when observaÈions filere more frequent' Inappl.yínglaboratorydeterminedeggdeveloPmenttimesÊoa field situation, allowance must be made for the therrnal hisËory of eggs if the anjmal exhibits marked verÈical migration over a wide temperature range (prepas and Rigler, 1978). The Gumeracha ponds were isolhermal maximum on many occasíons and during periods of thermal stratifícation tenperaÈure differences between the epi- and hypol-imnion were 5oC' Under these conditions the ponds could be Èreated as a síngle layer and of the depth-averaged r¡later temperature \¡Ias an adequate rePresentation Keen (1979) thermal hisrory of eggs (af ter Edmondson and tr'linberg, 1971) ' is has shown Èhat different thermal regimes, even if rnean temPerature tíme' consÈant, can produce signifieant differences ín egg development However, even fl-uc¡uations of up to 8oC only produced a development tirre difference of 1.8 hours. In view of the other assumptíons ínvolved in the turnover-time method of production calculation, such an error ís insignificant. In Èhe present study, an aÈtempt \^Ias made to select eggs in the earliest stage of development for the deternination of egg developmenttime.obviously,eggshadbeeninthebroodchamberfor correction some time prior to the coulmencement of experiments. A from facËor of an extra 3 hours for each 4oC decrease in temperature and Edmondson: 29"C (ca\culated from Murugan and Venkataraman: 1977, the 1955) was used to compensaEe for the period of time between depositionofeggsínthebroodclramberandthecornmencementof experiments. The actual correctíons were as follows: r4l. 23oc, laboratory time plus 0.31 days, 180C, laboratory time plus 0.46 days, 160C, laboratory tíme plus 0.53 days, 13()C, laboratory ËÍme plus 0 .59 days, 10(,c, laboratory tíme plus 0.69 days. 4.3.1.6 Length - Drv Weigh t Relationship. Female D. carinata were collected from the Gumeracha ponds at various times during Èhe study, returned to the laboratory, washed with distilled ttater, and sorted lnto size classes. Ovigerous and non-ovigerous adults (above size class 4) were sorted independently. Animals were placed inÈo small , pre-weighed aluminir:n foil cups' the nurnber peÏ cup depending upon síze. The larger size class animals '(classes 7 and B) could be welghed individually. For size classes 1 to 3, the number of anirirals pooled in a cup ranged from 1l to 509, but \¡/as generally about 50. For size classes 4 to 7, the nr¡mber per cuP ranged from 3 to 93, but was generally about 25. Ernbryonic st.ages were also weíghed after dissection out of the brood chamber. The number of embryonic stages per cup ranged fron 30 to 163,.but Iüas generally about 50. All- weights represenÈed averages for several animals. Animals lfere dried at 60oc for 24 hours. Higher temperatures hrere not used to avoid volatilization and decompositíon of fats and, therefore, weight underestímation (after Edmondson and lüinberg, L}TL). Cups plus dried animals were placed in a dessicator over silica gel and then weighed on a Cahn gram electrobalance (model G). l4ode1: 4.3. 1 . 7 Calculation of ProducÈion: Biomass Turnover Certain probleurs are associated with the use of the population turnover- t,ime model for calculating production (see lnlaters , 1977; Edmondson, Ig74). Príncipally, the underlying assumptions of the model (that b', Ít and dt are constant during the interval between sampl-ing, and that the populatíon is in a steady-state with a stable age distribution) aTe L42. rarely, if ever, met in a field situation. Steady-state populations of (slobodkin' Daphnia may be obtaíned only ÈemporariLy ín the laboraËory an aPProximation. 1954). The turnover-tíme method is, Ëherefore, I" view of these problems, a second rrethod whích made no assumpÈions concerning populatíon demography was also used to calculate the production of D. eatinata. The second method, developed by trlinberg et a7. (1965),is to based upon biomass turnover-tíme or the time taken for an anímal pass through successive developmental stages. The turnover-time of has each stage is, therefore, equivalefit to its duration. This method generally been used to calculate the production of cohort breeders' e'g' Daphnía eopepods (Burgis, Lgl4), buÈ has been applied to populaLions of (Duncan, L975; Hillbricht-Il-kowska et a7.,1966) and other contiir'uous1-y reproducing cl-adocerans (Lim and Fernando, I97B; Janicki and Dacosta' L977; Pedersen et a7., L976)' Inthismethod,developmentalstagesmaybeinstarsor arbitrarily defined size classes. The latter were used in the present class (T) study and were the same as above. The duration of each size canbemeasuredinthelaboratory.Fromthelength-dryweight relationship, the weight change upon Passíng through each size class class (^!ü) can be calculated. If the density of anímals in each síze (N) is known, daily production of each size class is then equivalent tostandingcropbíomassdividedbyduration.Netproductíonofthe population on each sampling date ís the sum of the production of all size classes Present, that i's' *r=0", + ... "":*"1 "t,r*r=o"l. * Tz Tn ',- 1-aboratory The only assumption made in applying this method ís that food development Èimes are similar to those in the field. Therefore, quallty and qrranËity in the experimental situation will be important' r43. Egg production musË be esEim¿ted separately in the biomass turnover meÈhod. For Èhis purpose, all enbryonic stages I¡Iere classed as one developmental stage and the initial weÍght of an egg r'Ias assumed to be zero. 4.3.1.8 Growth. The duration of successive size classes of 24'5oC' D. carinata r,ras determined in the laboratory at 10, 14.5, 18 and from the Anl-nal-s used in experiments at 10oC and 14'5oC l^Iere collected field at Èhe same t.enperatuïes. Animal-s used in experiments at 18oC (10-15oC) and acclimated afrd 24.5oC were collected at lower temPeÏatures for 5 days with gradual temperature Íncreases. Experimental anímals were collected during June, July, and August, L978' when chlorophyll a concentrations úrere extremely low. At those Èimes, D. catinata rnrould have been foraging amongst the sediments' Fivefemalesofvaryínglength,thesmatrlestbeíngearlysíze class 1 (15 eyepiece units in length), were measured as in 4.3'1'1 and placedínal30ml,pomadejarcontaínínglcmofpondsedímentand85m,e, offilteredpondl^/ater.Jartopswerecoveredbutnotsealed. 6 replicates hlere run at each temperature (i.e. 30 females) ' Jars were placed in constant temperature (to.soc) cabinets under constant illuminatÍon. Animals \^Iere removed and measured daily, the rnrater in the jars agiÈated, and animals replaced. The intestines of anímals rn¡ere foraging dark brown Èhroughout the experiments and animals were observed moulting; amongst the sedinents. Mature females released young duríng all neonates !¡ere removed' Animals could be maintaíned in Èhe experimental situation for of about 30 days. Therefore, the observed daily growth increments dífferent animals r^rere added sequentially to provide overall grovlth of curves. Each daily point on the lengÈh versus time curve fÀras a mean several values. The duration of successíve size classes was reacl directlY off the growth curves' r44. 4.3. 1.9 Nitro en and Phosphorus Cont.ent. Total nitrogen content of. D. carinata (as percentage of dry weight) was determined using a Kjeldahl digestion technique (as for P. ochreatus, 3.2.4)' Animals were collected fron the ponds duríng August, t976, and March, l"lay, and June 1977. AnimaLs from all size classes were pooled, washed with distilled Írater, drièd at 6OoC fox 24 hours, and homogenísed in a tissue grinder. A known weight of. O. earinata tissue r¿as then digested ín potassium sulphate and sulphuric acid' Total phosphorus content of D. carinata (as percentage of dry from weight) was determined after 61'pr (1976). Aninals were collected the ponds duríng March and April Ig77, and treated as above' A known weight of tíssue was digested in sulphuric acid and 10% copper sulphate' and phosphate determined using Èhe molybdate/acid Èechnique 4.3.2 Results for 4.3 .2,r Size Distríbution. Length-frequency hÍstograms D. carinata in pond 1 are Presented in Tigure 4.Ig' and are discussed in relaËion to populaÈíon density curves (Fig' 4'5)' The hígh proportionofjuveniles(sízeclassl)inearlyJuly'I976'indicated aperiodofuarkedrecruitment.ThroughoutAugust,septemberand october, 1976, size classes 1 Èo 4 were fairly equally represented and qras in the size distribution was f.aírLy const.ant; the populatÍon thus of a faixLy stable state, although some variation occurred. A períod recruitment (high proportion of juveniles) commenced in early November' through Lg76, aft'er a decline in population densiÈy, and continued fel1 December. The proportion of animals ín sÍze classes 5 and above' in off rapidly during Èhe latÈer hal-f of L976 indicating that mortality Èhose classes was high. Recruitment from the hatching of ephippial eggs occurred duringearlyFebruaryrlgTTrandtheproportíonofjuvenileswashigh and' on 16 February. All size classes weÏe represented on that daÈe I 00 òe 2.7.76 8.12.76 ?ß.3:77 n.4.ß 19.7.78 c) 0) d q.) t{ 0 t- h - 9.8:78 1I.8.76 10.5.æ 2..r2fr B.t+n L. 30¡.8 7+5.ß t6.2.Ê 2.4:r7 8.9.76 13.9.æ 5.6.78 æ.3.78 29-9.ß 23.n a.6.78 r:].4.æ 8.tt.E t6.3-7Ì 5.7J8 L r r r lt I I I I I W5-678e 2 5 8 Size Class pond 1' FIGURE 4.19 Length-frequency distribution of D. carinata in r4s. therefore, some of the juveniles present would have hatched from parthenogenetÍc eggs. D. catinaËa was not recorded ín samples on 2 February, L977. The presence of size class 9 individuals on 16 February indicated that growth had been extremely rapíd or that sarnplÍng error had occurred on 2 February. RecruÍtment was hígh throughout March, 1977, as population density reached a peak. Mortality of larger size classes r¡ras high. Maxi¡rum population densíty during 1977 occurred when the population I¡/as conposed largely of juveniles. A sÍmÍlar situation has been reported for D. hgaTina (George and Edwards, Ig74). Growth of the population through successive length classes can 1977 although recruitmenË be followed from early March until- late April, ' was continuous. RecruitmenË decreased in late April (size classes 3 and 4 became mosË abundant) just Prior to a populaÈion decl-ine. MorÈality was high duríng May and the population enÈered a diapause phase. Recruitment from the hatching of ephippial eggs occurred in mid-late March, 1978. A period of high recruitment from parthenogenetic eggs continued through April as population density increased. As in early Ig77, a period of rapid growth in length occurred early in the populatíon cycle, although sampling error could also have been involved. High population densities during 1978 occurred when the proportion of juveníles ín Èhe population r¡/as high. Recruitment üras continuous and fairly constant during May and June, 1978, declined sl-ightly during Ju1y, and increased during late August, 1978. Recruítment decreased during mid-September, 1978, just príor to a population decline. A period of high uorÈality occurred duríng laÈe September as the population entered suumer diapause. Length-frequency histogrnms for D. carinata 1n pond 2 are presenËed in Figure 4.20, and are díscussed in rel-ation to population density curves (Fig. 4.6). Recruítment from the hatching of ephíppial eggs occurred during míd-March, \977; some of the juve-niles on 30 March 100 N 29ß:ft 5-L0.n à 6.6.æ O 303.77 É 0) (/ 0) L 2,6.78 t¡ 0 t f! T t.ß:r7 13.\.n 12.7.77 t9:7.?g ù7.n 7.4n 9.8.æ 2.4:78 r0ß.7ì 10.5.æ t.6.n 30.s.æ 24AJ7 L As.A z.9n 13.9.78 Size Class FIGURE 4.20 Length-frequency distríbuÈion of D. carinata in pond 2. 146. could have hatched from parthenogenetic eggs as sexually mature females trere preserrÈ at thaÈ time. RecruitmenÈ \,fas hígh during early April as populatíon density increased. Maximum populat.ion density occurred during late April when the proPortion of juveniles in the population was high. As in pond 1, mortality of the larget size classes was high. Recrultment ceased alÈogether (no juveníles) ín nid-June during a signíficant decline in population density. Recruitment l47as high duríng late June and laÈe July, 1977, as population densíty increased' Gror¿Èh of the population through successíve length classes could be foll-owed from late JuIy to míd-Septenber. Recruitment was continuous from July to October, Ig77, but varied in intensity. RecruíÈment decreased during late October, and ceased altogether during early Nove¡nber, L977 ' At that time the population l{as senescenË (composed of older anínals) ' and mortality was hígh as the population entered summer diapause. Recruitmentfromthehatchingofephippialeggsoceurred duríng nid-Aprí1, lg7B. Juveniles hatched from parthenogenetic eggs probabl-y also contributed to recruitment by late April (sexually mature females present). Recruitment was hígh during May, 1978, as population density increased and reached a maxímum. Mortality amongst larger late anÍmals \¡ras very high during May. Recruitment decreased during June and July, Ig78, as populaÈion density decreased. Recruitment buL íncreased duríng early SepÈernber as population densíty increased, juveniLes were declíned somewhat, at the end of that month. Although present in late September, the population had declíned by early October' 1978, Thus, a períod of high mortality occurred jusÈ after 30 september, as the population enËered surÎmer diapause' SeasonalvariationinmeanbodylengÈhofmaturefemale shown in D. carinata (síze class 4 and above) in Lhe Gumeraeha poncls is L47. Figure 4.2L. Mean body length of mature animals ín pond 1 varied between 2;76 mm and 3.40 m; maxima oecurred during míd-February, L977 (3.40 nm; depth averaged úrater t,enperatuïe hras 23.5oC), and early July, Ig78 (3.27 um; average water tempeïature rùas 9.QoC). In pond 2, mean body length of mature animals varied between 2.65 um and 3.36 m; maxima occurred during nid-April, 1977 (3.30 mm; average water tenperature \llas 16.7oC), early July, L977 (3.26 m; average hrater temperature lras 10.3oC), and late May, 1978 (3.36 mrn; aveTage water temperature hlas 12.5oC). The range of mean body length was símílar in both ponds and duríng both 1977 and 1978. Mean body lengÈh maxima were also símiLar buË occurred at different times ín each pond. one female (size class 3) carrying eggs ïras collected from pond I on 16 March, L977. This was the only occasion on which an ovigerous female smaller Ëhan size class 4 was recorded from the Gumeracha ponds. Size class 8 and 9 females rilere recorded from pond I during February and March, 1977. The peak ín mean body length during mid-FebruaTy may have reflected increased growth rates at high temperatures due to reduced instar duration (Green, 1956). Generally, body lengËh at the onset of mat.urity remaj-ned constant. Therefore, mean body length maxirna at much lower temperatures refleeted increased longevity and contÍnued moultíng in adults' even though growth rate would have been lower. This pattern of growth has been recorded in D. hgaTina (George and Edwards, 1974) and D. nagna (Green, 1956). Longevity an Daphnia is temperature dependent (Hebert, 1978c). Mean body ]-ength of mature D. catinata in the Gumeracha ponds has, therefore, been plotted against average \nraÈer temPerature in Figure 4.22- A linear regression of xûean body length on average vrater temPerature for pooled data showed that varíatíon in temperature accounted for none of the variance ín mean body length. The effect of lag is importanE when consideríng Èhe j-nfluence of temperature upon the growth of individual-s 3.4 F rt o il T , rl fr 3.2 tl tl tl ? tl I rl É I I -o ¡J I d ò0 o tu, I F I I É 3.0 t t I o I I I I I F{ I \ , I I , h I I € I ¡t I I tl a o t I p I I o , É I I d 2.8 / I 'fI, I q) I I o ã I o I I b 2 6 DJ DJ r97 6 L977 L978 Tlne (rnonths) pond (¡) FIGURE 4.21 Mean body length of adult D. catÍnata in I and pond 2 (tr). 3.4 a a I 3.2 É a Ê a o a .d a a ¡J a bI) É 3.0 c, a Fl a >' E a po a a Ê d 2.8 q) a a 2 6 0 5 10 25 Temperature ( "c) FIGIIRE 4. 22 Mean body length of adult D. catinata versus depth- averaged water temperature in the Gumeracha ponds' 148. and populations (Hazelwood and Parker , L963; Deevey' 1960). Deevey showed that the size of aclult copepods rilas more strongly correlated with average t,emperature during the month precedíng sarnpling than with tenperature at the Èíme of sampling. A linear regression of nean bády lengÈh of D. carinata on mean monthly depth-averaged llaÈer temperature (for month prior to sampling; data pooled for both ponds during 1977 and 1978) showed that variatíon ín mean nonthly I¡Iater temperature accounted for only l% of the variance in mean body length. A lack of oxygen may retard growth in Dap?nia (Green, 1956). MinÍmum mean body length of D. catinata in pond I during 1978 occurred on 27 April. Dissolved oxygen concentration was very low on that date due to a declíne in phytoplankton standing crop. However, mean body length minirna occurred in pond 2 during perÍods of high dissolved oxygen concentration (1977 and 1978) ' Food is also an important determinant of growth. Ilowever, no sÍgnificant correlation (Spearmant" p) was found between mean body length of p. carinata and chlorophyll a concentration in either pond during L977 or 1978. D. catinata foraged amongst the sediments duríng most of Ëhe population cycle. Although temporal variation in the nuËritional value of sediments may occur in large lakes (e.g. Bowen, lgTg), this r¿as considered unlikely in the Gumeracha ponds due to the constancy of organic inPuts. number of 4 .3.2.2 Reproduction. Seasonal varíation in the ovigerous and ephippial female D. carinata' expressed as percentage of mature adulÈs, in the Gumeracha ponds ís presenÈed in Figure 4'23' The percentage of females carryíng middle and late stage enrbryos was always greaËer than the percentage carryíng eggs. The early stages of egg of development r¡lere, therefore, more rapíd. A peak ín the percentage ovígerous females occurred in pond 1 in earl-y November, L976' during a period of recruítment and increasing populaÈion densÍty. Ephippial 100 ?ond 2 males present 80 60 40 n I ll ,n', \ , \ 20 ^ \ q) \ \ \ è0 \ (6 ! \l 0 AJ O lr Pond 1 0) males ent Pr Pres 80 60 rì Ir 40 r\ ,l Ir lì /\ t\ 20 ii I I I I I 0 D J DJ L97 8 r97 6 r977 Time (r:nonths) expressed as a T'IGI]RE 4. 23 The number of ovigerous (-) and ephippíal (----) o. carinata Percentage of the number of adult females in Èhe Gumeracha ponds. r49. femal-es trere present Èhroughout the latt.er Part of L976. The percentage of ephippial feruales reached a peak in late Septenber, I976 during a decrease in population density, and also increased in late Decernber prior to the population decline. The pelcentage of ovigerous femal-es increased rapídly during February and March, L977 when recruitnent was hlgh and population density increasing. A smaLl increase in the just percentage of ovigerous females occurred in early,April, 1977 ' prior to an increase in populaÈíon densiÈy' Ephippial females were present in pond 1 from mid-February, 1977, peaked in early March, and declÍned gradually thereafter. several peaks in the percentage of ovígerous females occurred in pond 1 during L978. The peak in late May occurred prior to an increase in population density; peaks in late June, late Ju1-y, and early September occurred during periods of declining populatíon density. The PercenÈage of ephíppial femal-es peaked in late Apríl and lare August during population density peaks. During 1978' Èhe percentage of ovigerous and ephíppial females exhibited an inverse relationship. Males r¡lere generally rare buÈ from late April , I978, pereentage of constiÈut ed, L-2% of the total D. carinata population; the Thus' mal-es peaked aE 67. of the ÈoËa1 population during mid-September' a pronounced sexual phase occurred during the latter part of the D. carinata population cycle in pond 1, 1978' several peaks in the Percentage of ovígerous females occurred in pond 2 during Lg77. The peak in late April coíncided rn¡íth a peak in Eo 7% popul-aËion density. The percentage of ovigerous females declined during mÍd-June. No juveniles were pÏesent in the population at that time; thât is, recruitment had ceased. The percentage of ovigerous females increased markedly in late June and late July during periods of hígh recruitment and incre-asing population density. No ovÍgerous females population rüere recorded in early september or early october" However, density díd not decrease at those tímes suggestíng increased survival of 150. larger animals. Juveniles were present even though no females in the populatÍon üIere carrying eggs. Thís suggested that some recruítment occurred from the hatchíng of ephippial eggs. Peaks ín Ëhe percentage of ovígerous females in pond 2 during 1978 occurred in late Apríl, late May, and early AugusÈ during periods of hígh recruitment and increasing population density. The decrease in percenEage of ovÍgerous females in June and July, 1978 was refl-ected in reduced recruitment (increase in proportion of larger size classes) and a decrease in population density. The percentage of ovigerous females also decreased during late August and September; the population became senescent and declined at that, time. Peaks in the percentage of ephippial fenales in late April and late May, L978, were coincident wíth peaks ín the percentage of ovigerous females. The Percentage of ephippial females also increased during early September as Èhe population hras decliníng (percentage of ovigerous females and recruitrnent both decreasing) ' As in pond 1, males vlere rare in pond 2 until April of. L978. After that tÍme, males constitut eð, l-2% of the total population but increased to 5% of the population in mid-September' Seasonal variation in mean brood síze of. D. catinata (animals fromboth ponds pooled) is shown ín Figure 4.24. Mean brood size fluctuated from 3.0 to 35.2 pet female in 1977 and from 4'0 to 48'3 per female Ín 1978. Seasonal variatÍon was simílar duríng 1977 and 1978. 1978, at Highest mean brood size occurred in February, 1977, and April, increased the cormrencement of population cycles as population density rapidly. Mean brood síze decreased markedly as populaÈion density l-ncreases approached maximal values and remained low thereafter' Srnal-l in in brood size occurred during períods of population density íncrease July, Ig77, and August, 1978. Mean brood síze woul-d have been high in pooled, pond 2 during early April, Ig77. As animals from both ponds were low brood sizes in pond I masked true brood size in pond 2. Ilowever, 50 40 c, N .rl cr\ J 0 'o o o t¡ ,ô a. 0 I d ¡ CJ \ T IO \ \ .I I l/\ \r-]l t-l 0 J 1977 D J 1978 D Tine (nonths) FIGIIRE 4.24 I"lean brood size of D. catínata in both Gumeracha ponds. 50 ¡ 40 q¡ I N .F{ Ø30 € o o pþ a2o I ¡ T (ú q) T ! i0 l-l I I T ¿<+ I 0 0 5 10 15 20 25 Temperature (oC) FIGURE 4.25 Mean brood slze of D. carinaÊa versus depth-averaged \.tater temperaEure. 151. the fncrease in mean brood size in mid-April, 1977 probably reflected Ëhe contribution of high values from pond 2 animals. Brood sj-ze in Daphnia is ínfluenced by temperaÈure, body sízet and food; conditions which favour growth also favour egg production (Green, 1956). Brood size I^Ias deËermined from animals carrying eggs in the earliest Stages of development, It is unlikely Ëhat eggs had been in the brood chauber longer than about 12 hours when (see 1' 5) Depth- collect.ed, even at lo\ÀIest !ìIater temPeratures 4 ' 3' ' an averaged hrater temperature on the date of collecËíon was, therefore' adequate representation of the thermal history of eggs. Mean brood size in D. carinata during L977 artd 1978 has been plotted against depth averaged ürater tenperature in Figure 4.25. A linear regression of mean brood size on average temperature yielded a relationship of the form, That ís, mean brood size = -5.29 + I.32 . Èemperature' 12 = 0.29. variation in water telDperature accounted for on]-y 297" of Ehe variance in mean brood size. Egg nurnber ís posiÈively correl-ated with body size ín several species of Daplnia (George and Edwards, 1974; Green, 1956). Log mean brood sÍze per size class (averaged over the entire study period) is plotted against rnid size class length (m) in Figure 4.26. A linear regression of 1og average brood size on body length yielded a relaËionship of the form, 1og brood síze = -0.64 + 0.52 ' body length, t2 = 0.99' variation in body length accounted fot 997¿ of the variance in 1-og brood síze. Brood size increased continuously as body length íncreased' fxom Maxirnum brood size recorded for an índividual female D. carinata in the Gumeracha ponds was 147 (síze class 9). Seasonal variation It can be average brood size per size class is shown in FÍgure 4.27. were due seen that increases ín mean brood síze of the whole population to increases in the number of eggs carried by mature females of all when mean sizes. Mean brood síze of Ehe population generally increased o 100 O o o rú Fl q, (¡) N O T{ o ¡1 (¡) A o q) N il o E, o I 0 o o t{ F o 'ô0Q) (ú t{ q, Þ I 4 56 7 B 9 Length s 3 4 5 Length (ron) FIGURE 4.26 Average brood si-ze per size class versus míd-size class length ín D. carinata' t t 100 o (r) tr o (d FI o U tr ^ c) N .rl ül F Ä 4 ÊAJ o I N .rl I U) I A € 10 tr o o A ! ,.o q) ò0 I lr t T 0) ß/ ^ ^ o t I J 1977 DJ r978 Time (months) FIGIIRE 4.27 Average brood size per size class of D. carínata in the Gumeracha ponds. Size class: 3ro 7 , tr 4rL 8 t e 5'tr 9 , ô 6, A L52. body length in pond I and/or pond 2 íncreased. Average brood size per sÍze class also increased when mean body length was high; mean brood size maxima occurïed ít 1977 and 1978 when size-class 9 ovigerous females were presenÈ. That is, the egg layÍng capacity of the populatíon decreased as mean body length decreased' I{ithin a suítable temperature range' the number of eggs produced by Daphnia appears .to be ProPortional to food availability (Vivjerberg, L976 Ha1-l, 1964; Ingle, trÙood and Banta' 1937) ' A mÍnimum food level may exist below which egg production ceases entírel-y (Lampert, 1978). Food quality affects egg production in a manner analogous to food quantity (vivjerberg, L976i Arnold, 1971) ' The feeding behaviour of D. carinata changed during the course of population cycles; it is, therefore, dÍfficult to relate brood size to food avaí1-ability. Mean brood size of p. carinata ín'1978 was highest when chlorophyll- a concentratÍons hrere high and declined as phytoplankton standíng crops decreased and animals sr¡itched Èo foraging amongsÈ the sediments. However, mean brood size in pond 1 during February, 1977, washighdespitelowch]-orophyllaconcentraÈions.Meanbodylength carinata was also high in pond 1 at that tjme. Mean brood size in D' The effect at Gumeracha did not appear to be dependent upon food type. of food availabilíty will be discussed further in secËion 4'3'3' of development 4.3.2.3 E g.A Development Tíme. The mean duration Figure 4'28' (plus 951z confídence liniËs) of D. carinata eggs ís shown in prior to Èogether with values corrected for tíme in the brood chamber incubation. Both curves have been drawn by eye: The number of observations (eggs hatched) at each temperature hlere: 10"C, n = 95; 13oc, n = 183; 16oC, n = 114; lB"C; n = 72) 23oC' r = 234' Egg The relationship developmenÈ Eirne decreased as temPerature increased. by a between egg development time and teDPerature is best described curvilineat Logarlthmic functíon (that is, a second order polynornial) \ \ 8 \ \ to \ T 6 o >. d .d 'o c.) T Ê .Fl ¡J T rJ rE É 4 OJ ÉÈ o F{ 0) \ \ aOJ 2 20 2 0 5 10 15 Temperature (oc) arid corrected development FIGT]RE 4.28 Measured deveropment tlme (r), plus 952 confidence l-imits, time ( tr ) for the parthenogenetic eggs of D ' carinata ' 153. (Bottrell et a7., L976). Such a relaEionshíp could not be determíned for the data presented above as data PoínÈs T¡lere not equal1-y spaced. The corrected curve \7as very similar to the general farnilial curve presented by BoÈtreLL et a7. (1976) - 4.3.2. 4 Population Parameters. Seasonal variation in lnstantaneous (or potentíal) growËh rate' bt, actual growth rate, rt, and estimated insÈantaneous death rate' dr' for D. carinata in pond I is shown in Figure 4.29. Maximum bt values preceded population density mar corïesponded wÍth a decrease in the percenËage of ovigerous females in ,the population. bt declined gradually from June to September, L978. br was very high in mid-May, L977 and the demíse of the population in pond 1 at that time appeared to be fundauentally different from the decline observed in late 1978 when b I was low. Changes in death rate generally paralleled changes ín birth rate. Hígh mortalÍty in late February, L977, and late March, 1978, was associated with hígh proportions of juvenÍles. Ilowever, hígh mortality in late April to míd-May, L977, and late Septernber, L978, occurred when larger síze classes \^rere more abundant. That ís, mortalíty of juveniles appeared to be high duríng periods of íncreasing populaËion density whíle adult mortality \^Ias resPonsible for population declines' dr also includes prenatal mortality (George and Edwards, L974). Highest mortality occurred during periods of increasing population densíty I'/hen mean brood size was high. This suggested that egg mortality may have contributed consíderably to dr values. 0 0.3 0.2 0 0 I I I J 0 I l¡ I I p I -0. I 0 I I 4 ¡'t ll I -o-2 lr I tl I t, I 0 t, I I -0.3 ¡l t tl I t I I t I -0.4 I I ^ t t 0 0.6 I il I .d 0.4 it ti I ll o.2 ti ¡ \l h / i I \¡ I I I 0 J DJ I97B D r977 Tine (rnonths) FIGURE 4.29 Populatíon parameters b ' (----), r' (-), and df (-'-) for D. carinata in Pond 1. 154. tligh juvenile nortalíty in pond I during February, L977 a¡d. March-April, 1978, coincided wíÈh peaks in abundance of M. Teuckarti' Birth rates were high at Èhose times suggesting ËhaÈ predation may have contributed to decreased r' values in March, 1977, and April' 1978' However, dt was not significanËly correlaÈed with population density of M. Teuckartj ín pond I duxíng L977 (p = -0.11, P > 5"Á). A positíve correlation existed between dt and population densíty of U' Teuckarti during 1978 (p = 0.54) but thÍs was not significant aÈ the 5% level. very high mortality of D. cazínata in May 1977 was associaËed with a reduced birth raÈe and a decline in recruitment' Seasonal variaÈion inbt, rt and dt of. D. carinata in pond 2 generally Ís shown in FÍgure 4.30. As in pond 1, maxÍmumbr values preceded peaks in populatÍon density; from initial high values, bt declÍned as populaÈion cycles proceeded. bt increased as the population entered a second najor cycle during the latter half of 1977. ThÍs followed a significant decrease in population density during May. population declines in May-June, L977, and June-AugusÈ, 1978' T¡¡ere associaÈed with decreases in bt. However, bt T¡Ias extremely high duríng Èhe population decl-ine in mid-November, 1977 ' Although dt increased durÍ-ng the population decline in May- at that time June, Lg77 , this r.ras not marked. The population decline (and was due to a decrease in the percentage of ovigerous females therefore br) and the cessation of recruiÈment' br and dr were both very high during the populatíon decline Í-n November, L977. Ilowever, no juveniles vrere recorded on B November, 1977 sv'ggesting that egg mortality was high. The population decline during June-July, 1978 was al-soduetoadecreaseinthepercenÈageofovigerousfemales,as reflected in reduced br values, and a decrease in recruitment' dr values Íncreased during Ëhat period but \^Iere not high' br íncreased during AugusË, I}TB prior to an increase ín popul-ation densíty' During 0.8 0.3 o.2 0.6 0.1 J 0 p $' 0.4 -0. I -o.2 1 I -0.3 o.2 I I I :0.4 \ t t^I \ t \ t 0 -0.5 I 0.8 i I I 0.6 I i € i I 0.4 ¡ rl tit o.2 t\i ! I I .l\ 0 J r977 DJ 197 B D Time (nonths) FIGURE 4.30 Population Parameters b' (-), r C--) , and d' (-'-) for D. carinata ín Pond 2. 155. the popul-ation decline in laËe September, 1978, dt increased, b' decreased (percentage of ovigerous females decreased), recruitmenÈ decreased, and the population became senescent' dt was not significantly correl-ated with density of (p M. Teucq Mean and maxímum values of the populaÈion parâmeters bt, It, and dr fox D. carinata in the Gumeracha ponds duríng L977 and L97B ate presented in Table 4.8. Mean and maximumbt, ft, and df values inboth ponds were higher in L977 ttlar- in 1978. Al-though maximum values of b" rr, and dr in pond 2 wete greater than in pond 1 during 1977, meatt values in pond 1 were higher. Both mean and maximum values of br, rt, and d' r^rere hígher in pond I during l97B' 4.3.2.5 L th-Dr l^I t Relatíonshi . A double logaríthmic Plot on of mean dry weight (ug) pex size class (plus 957. eonfidence liníts) mid-size class length (to.) for embryoníc, juvenile and adult D' catinata from Gumeracha is presented in Fígure 4.31. Mean dry weights of ovigerous and non-ovigerous adult females have been plotted separately' (I^1) A linear regression of the naLural logarithrn of mean dry weighE on the natural l_ogarithm of míd-síze class length (L) for embryonic stages yíeLded a relatÍonshíp of the form, ln trl = 1.6335 + 0.0941 ' 1n L' 12 = O.26. Variation in lengLh accounted for only 26% of the varíance the 1n mean dry weight of embryonic stages. confidence limiËs for weíght of embryonic stages overlapped and weight did not change significantly during eurbryonic development. Linear regressions of ln mean dry weight on ln mid-size class length for adul-Ès yielded relationships of the form, ln tr{ = I'3877 + 2'8335 'lnLrx2=O.99 for ovigerous f emales, and ln I'I = 1'4011 + 2'7476 'lnL,12=0.99for Table 4.8 Mean and maxímum values of population parameters bt, !r and dr, for D. carinata in the Gr:meracha ponds duríng 1977 and 1978 POND 1 POìID 2 L977 I97B r977 197 I br x 0. 331 0.1I1 0. 191 0.072 Max o.778 0.348 0.834 o.2r2 r ¡* 0.119 0.110 o.o77 0.051 I"lax 0.193 o.27r o.252 0.211 dr x o.337 0. 101 0. 191 0.o72 Max o.766 0.210 0.994 0.196 * Mean positive r I 100 ò0 = +J 'o0 o T{ c¡ Þ Þ\ âH 10 t T o I 0 I I 10 Length (rnm) earl middle Late 1 2 3 4 5 6189 Embryonic Adult Length Class FIGURE 4.3I llid-size class length-dry weight relationship for ovigerous (a) and non-ovigerous(O) D. carinata' 156. non-ovigerous females. Sl-ope coefficients less than 3 indicated thaÈ, for adult D. carìnata, weight increases were relaÈively smaller as length increased (Daborn, L974). The nean weight of ovigerous females, averaged over all mature size classes, hlas 8.8% (! a standard error equivalent to 18% of Èhe mean) greater than for non-ovigerous females. The relatíonships beÈween mean dry weight and length for D. carinata from Gumeracha were similar to length-weight relationships for other meribers of the genus from a wide variety of habitats (sumnarized by Bottrell et a7., L976). The weight data presented above has been averaged over time and' therefore, masks any seasonal variation that may have occurred in the length-weight relaÈionship' 4.3.2.6 Growth. Mean length (eyepiece units and nm) of female D. carinaÊa has been plotted agai-nst time (days) for each temperature in Fígure 4.32. Growth curves \^rere as)rmptotic (or nearly so) as is typical for species of Daphnia (e.g. Munro and Inlhite, 1975; Anderson et a7., 1937; Anderson, 1932; MacArÈhur and Bailie, L929). Síze cl-ass duratíon (read directly from growth curves) and cumulative duratíon at each temperature is shown in Fígure 4.33. Growth Iüas most rapid in early síze classes; grorÀ7th rate decreased and size class duration íncreased as mature animal-s aged. Growth raÈe increased as temperature increased up to 18"C. Consequently the duration of size classes at decreased as temperaÈure increased. Animals attained a greater size hígher Èempeïatuïes but lived 1-onger at lower temPeratures ' This pattern of growth has been reported for other species of Daphnia (Munro and hlhite, Lg75; Anderson eÈ al., 1937). Had it been possible to maÍntain animals in the laboratory for longer periods, animals at lor^rer gro\¡Ith temperaËures may have reached l.arger final sizes despite lower rates (e.g. Green, 1956; I4acArthur and Bail-íe, 1929)' Growth rate of D. carinata at 24.5"C was low (between rates at 10oC and 14'5'C); the duration of length-classes íncreased at 24.5"C. D. rnagna and D. pulex lr t tt Itr I BO lt I ¡ ¡ 4 xl¡r'¡¡.1 I rt , rt'lrt ltl t I ,a rf -----ar atlr llttttl *ìtrr ttl rr"t rr 60 llll r ll l¡r 3 ú) ral +J l/ .r{ lrl É É tr¡ o I x O I t*¡ 0) ¡J 'rl t b0 Ê Ê 0) 40 q, 2 à F¡ q) ^rj_- fl--- ¿J ò0 1.. É " q) rri -- F¡ , :1'- t.'l - rf- I 20 t- 0 0 100 0 20 40 60 B0 ti¡ne (days) 24.5 co (-) FIGURE 4.32 Growth of D- carinata at lOoC (.), 14.5 co(r), 18"c ( t ), and (daYs) |ld Cumulative duratÍon (days) Cumulative duratlon H C) òJ ¡\ o\ oo o o o o *,so.99ãËoooooo F L¡J fll N L^) Durarion (agVs) UJ Duratlog (days) o o N) ltr U) oH. H o F1 N ts oo tl-- o o o c) .oIJ N) c) \ì-ro P QÞJ À. OJØ (/) u...r\ FJ T, ,\\ þ. 3ÈùÉ r 't f-t- d I .ñDJ O) (¡t Þ_ P. o H o\ 'Þ. u) H. tÞ Þ [-r g@ 0) 0) J (n o. (h s (Jr \ o .Ê)H c) ñ N) H' t\) t-¡l o o l) o- (, d .pr lJl ' r't r Þ- H. o (-¡r Þ "Þ "à tÞ Or ! 157. both exhibj-t lower growth rates at 30"C than at 25"C (Brown, L929), Survívorshíp of D. carinata (percentage of animals remaining alíve) Ís pl-otted against time for each temperahrre in Figure 4.34. Mortality was similaT aE 10oC, !4.5"C, and lBoC' but increased markedly at 24.5"C. Hígh ternperatures IùeIe detrimental to the survival of D. carinata and laboratory observations rrere supported by fÍeld studíes of seasonal occurrence. Growth experiments at temPeratures between 18"C and 24"C would be requíred to determine the exacË criËical temperature above which thermal stress caused high mortality. Although growth rate was híghest Ín the laboratory at l8oc, field studíes suggested that the optimum t.emPerature for Èhe growËh of. Ð. carinata (as evídenced by peak popul-ation densities) was about 15"C. phosphorus conLent 4 .3.2.7 Nitro g. en and Phosphorus Content. Mean fox D. carinata (all- size classes pooled) from Gumeracha was 1 '37" of dxy weight (* standard error equívalent to 6 .L7" of. the mean). Mean nitrogen conËent oÍ. D. catinata was 6 .6% of dry weight (1 standard error equal to 6.5"/" of the mean). The nutrÍenÈ content of D. carinata was similar to that reported for D. catawba from a tempeÏate, o1ígotrophic lake (Makarewicz arrd Likens, L979). Nitrogen content of ¿. carinata was consíderably lower than has been reported for zooplankton (includÍng Daphnia) elsewhere (Vivjerberg and Frank, 1976; Khan and Siddiqui, L97l; Krishnamurthy, L967; calculated from B].azka, 1966). Ilowever' varíation in analytícal methodol-ogy and the expression of results renders these studies less dj-rectly comparable. Phosphorus content of D' catinata was lower Èhan reported for Daphnia by Vivjerberg and Frank (1976) but greater than reported for mixed freshr,rater zoopl-ankton by Khan and Siddiqui (1971). Suffi-cient comparable data is not available at present to determine whether the nutrient conEent of zooplankton ís related to habitat nutrient status- 100 OJ .rl 80 F{ (d ò0 .rl .rlÉ 60 rö É c) -A tr ^- À--a q) 40 I ò0 \l d Ð É A\. a) -¡-ti-¡- U ¡.- tr 20 AJ ^-a-a-a \^ ê{ h- -a- .^--a ¡ I 0 0 5 10 15 20 25 30 Time (days) FIGTIRE 4. 34 Survivorship (percentage remaining alive) f.or D. car¡nata et lOoC ( ), 14.5oC (A), 18oc ( tr), arLd 24.5oc (t ). 158. 4.3.2.8 ProducËion Population T time Method. Seasonal varíatíon in sÈanding croP biomass (ng dry weight/L) and net daily production rate (mg dry weight/ f,/d,ay) of D. carinata Ín Èhe Gumeracha ponds are shown in Figure 4.35. production calculations, based on the population turnover-time method, f.or D. carinata in both ponds are Presented in Appendíx 4. Biomass ín pond I was low during February and March, 1977, despite high populaËion density. This resul-ted from a high proportion of juveniles in the popuLation. Maximum biomass occurred in Apri1, 1977, coincident rÀ7íth a population density peak and higher ProPortions of larger síze classes. In pond I during L978, biomass peaks coincided with population density maxima. Maximum biomass in both 1977 a¡d I97B occurred some months after Èhe decline of phytoplankton standing crops' Mean and maximum daily biomass ín pond I were 8.459 mg dry weight/!' arld 29.529 mg dry weight/l respectively i¡ L977, and 9.223 ng dry weíght/!, and 29.106 mg dry weíght/9, tespectívely in 1978. Mean and maximum biomass were similar during both years. Net daily production fol-lowed a patÈern very simil-ar Ëo biomass. Production has been calculated over the time inÈerval between sampl-ing dates and plotted at the rnid-poinÈ of the sampling interval. Although mean biomass beÈween samplíng dates l^/as used to calculate production, acËual biomass on each samplíng date has been plot¡ed. Therefore, production increases appear to lag behínd biomass increases. Peaks in neË daily production occurred at times of population clensity maxima. Net daily productíon rate in pond I varied from zero to 7.896 mg dry weight/y/day in L977 and from zero to 2.439 mg dry weíght/9,/day in 1978. The range of net daí1y production to biomass ratios (P/B) in L977 was 0.L26-0 '535; mean daily P/B was O.282, equivalent to an average biomass turnover-time during the growing season of 3.5 days. The range of claily P/B ratios in 1978 was 0.003-0.250; mean daily p/S v¡as 0.099, ecluival-enÈ to an Pond I 8 I 30 t tl I I I I I 6 I I I I 20 I I I h I 4 (Ú I ¡ 'Ú ¡ èl oì ¡ I {J ¡J I F 10 I .rlò0 ò0 l¡t 0) ={0, , 2 B B , I ) h I t.¡ l¡ ,¡,tl t 'Ú É ,l t tl ö0 o0 il E a t 0 É o o o Pond 2 .rl (ú +J É I C) o ¡ u Ì{ 20 i fl 2 'o FA il o !r , $.{ f¡ Ê{ tl I I I I I I I I I I I t I I 10 I --l I I I t t ¡l I t I I t , t t I I I I 0 0 J DJ r978 D 197 7 Tírne (months) FIGURE 4.35 standing crop biomass and daily production of D. carinata (population turnover-tÍme method) in the Gumeracha ponds, Biomass (-) , production (--:-) . 159. average biomass Èurnover time of 10.1 days. Maximum daily production in pond 1 was hígher ín 1977 than in 1978. Although mean daily biomass was similar in both years, average turnover Ëirne was shorter in 1977 ' In pond 2 duríng L977 and 1978, biomass peaks coincided with populatíon density maxíma, and occurred after the decline of phytoplankÈon standing crops. Mean and maximum daily biomass in pond 2 lrere 3.738 rng dry weight/.0 and 10.986 mg dry weight/ß respectively in Lg77, anð.7.713 ng dry weÍght/9. ar.ið 21.105 ng dry weight/Î, respectively in 1978. Maxinum and nean biomass ín pond 2 wexe lower ín 1977 than in Lg78, and lower than in pond I duríng both years. Net daily production followed a pattern very sÍmilar to biomass, and produetíon peaks occurred at times of populatíon density maxima. NeÈ daily production rate in pond 2 varied fxom zero Eo 2.315 ng dry weight/9"/day in 1977' and from zero to 1.679 mg dry weightlg'/day in 1978. The range of daily P/B ratios ín L977 was 0.004-0.630; mean daily P/S was 0.153' equívalent to an average biomass turnover time of 6.5 days. The range of daily p/B ratíos in 1978 was 0.001-0.178; mean daily PIB was 0.068, equivalent to an average biomass turnover time of 14.7 days. Maximum daily net production in pond 2 was greater in 1978 than ín 1977. Although average biomass turnover time was longer Ín 1978' mean daily biomass was much higher than in Ig77. Maximum daíly production rate in pond 1 r¿as higher than ín pond 2 during L977 and lg7}. Thís reflected higher mean daily bÍomass and shorter turnover times ín pond I during both years. A linear regression of pooled daíly P/B ratios from boÈh ponds durÍng L977 and 1978 on depth-averaged !üater Èemperature shorn¡ed Ëhat variatíon In temperature accounÈed for only 23:z of the variance in P/B ratío ' Total monthly and annual net production (r¡g d y \rt/9.) of D. carinata ín the Gumeracha ponds was calculated by determíníng the area under the net daíly production rate curves using an Ott compensating po1-ar planímeter, Cype 30 115. Total net procluction T¡Ias convertecl to 160. , g dry weight/rn¿ of pond surface area; weíghted mean monthly biomass , (g dry weÍght/rnz) was calculated by measuring the area under the daily biomass curves and divíding the total by the number of days per month' ïhe results, together wlth monthly and annual P/B ratíost are presenÈed Ín Table 4.9. In pond I during Lg77, monthly net production was hÍghest in M"y; this reflecÈed a peak in daily net production just prior to a rapid population decline. In Lg78, monthly net production was híghest in May 1977 peaks in buË decreased gradual-1-y Ëhereafter. In pond 2 during , with monthly neÈ productíon occurred in May and August and coÍncided ÈÍmesofpopulatíondensitypeaks.In|978,nonthlyneÈproductionwas highest in June, coíncident with a peak in populaÈíon densíty' Annual net producrion in both ponds duríng 1977 was higher than during 1978' more rapidly The D. carinata population in each pond turned over much ln 1977. Annual net production of ¿. carinata in pond 1 during both in both years exceeded productíon in pond 2. f:rt 1977, annual P/B ratio pondswassimilarbutaveragebiomasswasmuchhigherinpondl.In P/B ratio was 1978, average biomass in boÈh ponds was sÍmílar but annual higherinpondl.HigherannualproductíonofD.carinatainpondl biomass in !,IaS' therefore, .ilue to the Same rate of turnover of a hígher 1978' Lg77, and more rapid turnover of a símílar biomass in Bíomass TurnoverMethod.Growt'hofo.carinatainthelaboratory\^IaS Èhe optimal most rapid at lBoC. However, field studies suggested that the calculation temperature for growth was closer to 15"C. Therefore, in size-class duration of neÈ production using the biomass turnover method, in the at fíeld temperatures \¡Ias determined from the duration observed presented laboratory at I4.5oC and the formula (based on Kroghts curve) formula is in Edmondson and trlinberg (197t, p. 20). Although this generallyappliedinthecalculationofeggdevelopment,therelationship foX zooplankton between temperature and developmental rate is similar Tabl-e 4 .9 tíon Toral monthly and annual- net production (P, g dry weight/ur2) based oi F"1"+3 .turnover-time method, nean monthl-y and annual biomass (Sr g dry weightlm') , and P/B ratios for D. carinata in the Gumeracha ponds duríng 1977 and L97 8 POND 1 POND 2 B PIB P B PlB P t977 L978 I977 L978 r977 I978 t977 r978 L977 I 978 r977 r978 Jan. Feb. 14.4 1.1 13. I ¿ ¿ * March 30.4 * 4.9 6.2 ¿ * 2.6 April Lt5.2 L7 .9 16 .0 8.2 7.2 2.2 L7 .9 7.0 4.9 8.8 5.1 ]..0 May 184.6 28.4 t5.z 11.4 T2.L 2.5 25.0 13.8 16.9 5.7 2.6 June 60.4 20.3 3.0 r-7 44.0 0.3 2.7 L.4 July 16.8 8.4 2.O 1.9 12.7 0.7 9.2 4.4 4.L 2.r Aug. 9-1 7.7 L.2 15.3 9.3 3.7 4.0 32.8 8.8 8.5 3.9 3-9 2.3 S ept. 19.0 4.8 3.7 0ct. 1.5 0.2 7.5 42.9 1.1 10.3 0.3 4.2 18.4 Nov. 25.7 r.4 Dec. 35.5 12.3 Annual 344.6t 153.1 e.9 8.7 37 .L3 17.6 163.2 89.7 4.6 7.3 * Too small to be measured planimetrically I Total annual production (¡P) 2 Mean annual biomass @ 3lp B. 161. eggsandadults(Mclarenr1963)'The'criticaltemPeratureabovewhich could not be thermal stress reduced grohtth raÈe and inereased mortality fixed accurately from laboratory grov/th experimenÈs ' It was assumed rate vTas that Èhe relaËionship between ÈemPerature and development constanÈoverthetemPeraturerangeencounteredbyD.carìnataínthe fiel,d. rhis assr:mption appeared to be justifíed as egg developrnent $Ias critical temperature more rapid at 23"C than at 18"C. However, if the therefore for D. catinata was substantially lower Et'an 24oc, growÈh and production,willhavebeenoverestimatedathighertemperatures.As temPerature this was production \¡ras highest during periods of 1ow $Iater riot considered a serious source of error' SeasonalvariationíndailyneÈproduction(mgdryweigtlt/9'/ day)ofD.carinaËaintheGumerachapondsísshowninFigure4.36. Productíoncalculations,basedonthebiomassturnoverrnethod,for productíon rate ín D. carinata aïe presented in Appendix 5. Net daí1y it 1977 and from pond 1 varied from zero Eo 2.707 mg dry weight/y/day zetot.ol.3T4ngdryweight/9'/dayinlgTS.TherangeofdailyP/B was 0 equivalent ratios In 1977 was 0.136-0 .7O9; mean daily P/B '272, toanaveragebiomassturnovertÍmeof3.Tdays.ThefangeofdailyP/B was 0.155, equívalent to ratios in 1g7B was 0.01g-1.163; mean dail-y P/B NeÈ daily producËíon an average biomass turnover time of 6.5 days. in 1977 and rate in pond 2 varied from zero to 1.453 rng dry weíghtl¿"/day The range of daily P/B from zero ro 0.809 urg dry weight/9,lday in 1978. ratiosín1977was0.002-0.186;meandailyP/Bwas0'079,equivalent toanaveragebiomassturnovertimeof12.6days.Therangeofdaily ?/B was 0'079' P/B ratios in 1978 was 0'012-0 '329; mean daily equÍvalentËoaîaveÏagebiomassturnovertimeof12.6days.Highest dai.lyP/Bratiosoccurredinbothpondsduringtheonsetofpopulation cycles. Pond I 3.0 2.O x çd ol I 0 Ð ò0 '-l c) F 0 >' t¡ .d 1.5 Pond 2 ò0 É É o .rt L, o 1.0 E o H Ê{ 0.5 0 J igtt DJ L978 D Tirne (months) FIGURE 4.36 Daily production of D. carinata (biornass Èurnover rnethod) in the Gumeracha ponds. L62. DailynetproducÈíonratescalculatedusingÈhepopulation turnover-time method always exceeded daily rates calculated using the production rates bfomass tuïnover meÈhod. Differences between daÍly net r'ere most marked in pond l during late April-May, L977, and mid-June' and early 1978, and in pond 2 during late september-late ocËober, L977, June, 1978. These perÍods coincided wíth high populatíon densitíes and high b t values) , large numbers of eggs in the population (and therefore but 1ow recruítment (that is, low rt values)' DailyneEproductionraÈescalculatedusingthebiomassturnover contríbution DeËhod showed that egg production often urade the largest Ëopopulationproductionofallsizeclasses.Dailynetproductionof the total eBBs, expressed as Percentage of daily net production of + population, ranged from 31 to 777" (mean = 517"' standard error 6 747" (mean = equivalent to 12% of the mean) in pond 1 during 1977, to 27iÁ,!standarderrorequivalentluo22T"ofthemean)duringl97B,and to 267" of the from 9 to 617" (mean = 3L7", t stanclard error equivalent (mean 25%, t standard mean) in pond 2 during Lg77, and from 8 to 66i4 = llighest percentage error equivalent to 25% of the mean) during 1978- at the contributíon to total population productíon generally occurred to total population conmencement of populatÍon cycles. The contribution productíon generally decreased with increasing síze class ' TotalmonthlyandannualnetproductionofD.carinata\¡'as (calculated using determÍned from the curves of daily production rate production the biomass Ëurnover method) by planimetry. Total net and (g dry weight/rn2) is presenÈed wiËh weighted mean rnonthly biomass annual net production monthly and annual P/B ratios in Table 4.10. Total during both years in both ponds was highet ín 1977 than in Ig7B, and in pond 2' total annual net production in pond L was greater than by the population Annual production patterns were the same as indícated usj-ng the turnover-time method. Total annual net productj-on calculated Table 4.10 Total nonthly and annual net production (P, g dry weight/rn2) based on þiomass turnover method, mean monthly and annual bionâss (¡, S dry weight/m2), and P/B ratios for D. carinata ín the Gumeracha ponds during L977 a¡d 1978 POND 1 POND 2 P B PlB P B PlB r97 7 L97 8 L977 1978 r977 r978 1977 L978 r977 197 8 r977 r978 Jan. Feb. 7.5 1.1 6.8 J + March 23.7 & 4.9 4.8 * April 48. 1 25.2 16.0 8.2 3.0 3.1 18. I 0.4 7.O 2.6 May 41. B 23.L L5.2 11 .4 2.8 2.0 12.l 15.1 4.9 8.8 2.5 r.7 June 26.L 20.3 1.3 0.2 16.8 0.3 L6.9 o.7 1.0 July 7.5 8.4 0.9 1.3 5.2 0.7 9.2 1.9 0.6 Arrg. 7.L 7.7 0.9 5.8 5.0 3.7 4.4 1.6 1.1 SepÈ. 6.0 4.8 1.3 20 -9 4.7 8.5 3.9 2.5 t.2 Oct. 0.2 0.2 1.0 36 .0 o.2 10 .3 0.3 3.5 o.7 Nov. 4.s r.4 3.2 Dec. Annual- 121.11 95.2 932 8.7 13.03 10.9 98.9 47 .4 4.6 7.3 2r.4 6.s * Too small to be measured planimetrically I Total annual production (tP) 2 þÍean annual biomass (Ð 3lp B 163. population turnover-time method hras' on averager tr¿ice as high as toÈal annual net productíon calculated using Èhe biomass turnover method' Mean and maximum daí1y P/B ratios based on the biomass turnover method were similar to, or slightly higher thafi, mean and method' maximum daily P/B ratios based on the populaËion turnover-time Ilowever, daily net production rates calculated using the population turnover-tíme method greatly exceeded daily rates calcul-ated using the bj-omass turnover neÈhod when population density (and biomass) was high and a large number of eggs ÍIere present in the population. The biomass turnover method showed that egg production made a significanÈ contribution to Èotal population production. Therefore, when egg or embryo mortalíty was underestimated production would have been greatly overestímated. The populatíon turnover-time model assumes a stable age distrj-bution, that ís, that rnortaliÈy of all size classes is constant' Seasonal_ variation in the number of eggs (calculated from percentage of ovigerous females and mean brood size) and the number of juveniles (síze-class 1) in the populations of D. carinata at Gumeracha is shown in Figure 4.37. Comparison of egg number curves with populatíon density curves showed that the rate of decline ín the nr¡mber of eggs was often more rapíd relaÈive to the decline in numbers of adults. This suggested deparËure from a stable age dístribution wiÈh increased mortalÍÈy of eggs or ernbryos (c.f. Threlkeld, I979a). Comparison of egg numbers with the number:s of juveniles showed Èhat consíderable mortal_Íty of eggs or neonates occurred in pond 1 in April, L977, and April-' late May, IaËe June, and July-August , L978, and in pond 2 in ]at'e early July, early August, late SepËember and early october, 1977, and early August, Ig7B. These periods generally coincided with high bl the values and preceded peaks in daily productíon rate calculated usíng population turnover-tíme method. Hígh mortality (40-90%) between eggs (Prepas and neonates of Daphnia has been reported elsewher:e and Rigler' POND 1 POND 2 1000 , I tl rl lt tl rl 'tl I ;rI ,¡tl ;r ti rl t¡ I I I I I il I I ;i I 100 v I Ír I I G) I t.¡ \ I t) I I .Fl I I I I tJ I Fl I I I I I t{ I I rj ¡ c) I I ll t o. I I I tl I t I I ir c,) r^t I Fa I I z I I l0 I I I I JF MA ¡f J JFMAMJJAS ON MAMJJASON A MJ J AS O 1977 1978 L977 1978 Time (months) ponds. FIGURE 4.37 The number of eggs (-) and juveniles (---) of n. carinata in the Gumeracha t64. L97B; Hall, L964). Mortality may have occurred during embryonic stages (in the brood chanber) or amoïLgst newly hatched neonates ' Female Daphnia may abort eBBs, although this generally occurs Ín response to high temperatures (Threlkel-d, 1979b). Thus, the populatiol t,,t,tot"t- time method of production calculation overestinated production of D. carinata during periods of íncreased egg mortality and departure from a stable age distribution. on several- occasions the nurnber of juveniles of D. catinata in the Gumeracha ponds exceeded the number of eggs in the population' This could have resulted from Èhe underestimatÍon of brood size (e'g' due to egg loss on preservation) or repeaÈed recruitment from the hatching of ephippial eggs. Víjayaraghavan (1970) has suggested that contínuous recruitment from the hatching of ephippial eggs may be characteristic of D. carinata and the present sÈudy seems to suPport thís. This phenomenon aPpeaÏs to occur ín other Daplnia specíes (Duncan, lg75). Temperature changes or desiccation may not be necessary to índuce hatching ín Èhe ephippial eggs of Daphnia (trlood and BanËa' t937, 1933). ThebiomassturnovermethodappearedtoprovídemoÏe realistic est.Ímates of annual net productíon than the population turnover-Èime method. Total annual net production of D. carinata during L977 was 174.384 kg dry weight in pond 1 and 123.131 kg drv weight in pond 2. Total annual net production of. D- catinata in pond I repïesented a nutrient stoïe equivalent to 4.637" of total- Po4 - P retaíned in the pond during 1977, and 2.20% of TKN and 1.32% of total nitrogen (NO¡ + TKN) reÈained during 1977. Total annual net producËíon ofD.caI'inatainpond2representedanutrientstoreequivalenËto (NO: TKN) retained 3.06% of roral'o4-P and 17.567" of total nitrogen + in the pond during 1977. HarvesË of D. carinata did not rePresent a sígnificanÈ pathway lot nutrient removal from Ëhe Gumeracha ponds' r65. Total annual neË production or D. carìnata in pond 1 during !977 was equivalent to 57" of total annual net primary production and 4257" of. total annual net phytoplankton producÈion. The latter result is not surprising as durinB most of the populatíon cycle D. carinata obtained nutrition from the sediment.s. Total annual net productíon of D. carinata in pond 2 duríng 1977 was equivalent to 3.68% of Èotal annual net prímary production and 3.94"/" of total- annual net phytoplankËon Broduction. 4.3.3 Díscussion 1\uo types of population cycle are conmon amongst Nearctic and palaearcÈic specíes of Daphnia (subgenus Daphnia) (IIebert, 1978c). In both types, Daphnia may overwinter or hatch from ephíppial eggs in spring. During early spring a high proportíon of females are ovigerous and mean brood size is high. Popul-atíon density increases rapidly to reach a peak in early summer but during the latter phase of the population increase both brood size and the proPortion of reproductive fenales decline. Frorn peak summer densitÍes populations uay (1) collapse, and then undergo one or more similar cycles later in Èhe year, or (2) decline slightly but remain fairly stable until the onset of winter. In boËh cases there is a transition from low density spring populations with high mean brood size to high density sulDmer populations with lower egg production. The population cycle of D. catinata (subgenus ctenodaphnja) at by Gumeracha r^7as, in form, similar to the general cycle exhibited Nearctic and palaearcËic Daphnia and conforrned with (1) above. After (to a an initial, rapid increase in densitY the population declined varying degree) and then underwent a secondary increase and similar cyele later in the yeaï. During the onset of the populatíon cycle the percentage of ovigerous females and mean brood size !üere high but both decreased as population density increased. However, the population t66. cycle of. D. carinata díffered fundarnentally from Holarctic species in seasonality. D. carinaËa was a cold Ílater form and populatíon peaks occurred in laÈe autumn-early winter. D. catinata \nlas not plesent during suntrneï and populations \¡Iere reestablished from diapausing ephippial eggs in autumn. At Gr¡meracha, the popul-ations of D. carinata were inteïmit.tent. in a permanent habitat. Iligh surmer temperatures' rather than low winter temperatures, !{ere unfavourable for this species. In pond 1 during May and Ju1y, 1978, and ín pond 2 during April to June, Ig77, and May to June, 1978, a dramatic reduction in reproducËion occurred shorÈly after peaks in population densi¡y' bt and r' (and population density) decreased at those times while d' was litt1e altered. This pattern of populaÈÍon change is characËeristic of Mphnia in food-liniÈed situatÍons (e.g. George and Edwards, I974) ' D. carinata f.otaged amongsL the sediments during mosÈ of the populatíon cycle. As díscussed in sectÍon 4.2.3, it is un1íke1y that D. carinata could have depleted the sedimenÈs to a límíting level. It is nore líkely that a relative resource limítation occurred due to large numbers of animals att.empÈing Èo feed on the sediments simultaneously. Populations of D. puTex (a facultative browser) in aerated InISPs may also be food-Iimited at times (Daborn et aI , 1978). Although Frank et a7. (1957) reported density-dependence of br and r' in laboratory cultures of D. puhex, this was unlikely aÈ the densj-ties of o' catinata encountered aÈ Gumeracha. DuringthepopulationdeclineínpondlínlateApriland May, Ig77, and in pond 2 in early November, 1977 ! events differed considerably from the above síËuation in that dt increased markedly rnrhile b' remained high. This suggested that predation by M' leuckatti of may have contributed to the population decline. Ilowever, mortalíty neonates could have been caused by other factors, for example, a relative food shortagei while sufficient food could be obtained by L67 . adults to produce eggs, those eggs may have been unable to survive Past hatching. M. Teuckarti is carnivorous only as late stage copepodids and adults (Gophen, L977). Therefore, total ntrmbers are not an accurate reflection of the predation Pressure exerted by this species. In the absence of more deÈailed information on the age strucÈure of M. Teuckarti ín the Gumeracha ponds, the lack of correl-ation between the density of this specíes and Ëhe density of D. catinata is not suTPrísing. A1-though carnivorous cyclopoíds include smaller cladocerans in their diet (Lane, I97B; Gophen, 1977; Kerfoot, I977a) they appear to edríbit extreme selectivíty for the nauplii and copepodids of other copepods, even if cladocerans are more abundant (Brandl and Fernando, 1975; Confer, 1971). Dodson (L974) has divided cyclomorphíc plankters into three groups: (1) organísms too small to experience vertebrate predation (l-ess than 1 um in length) and which elaborate spines or other structures to frustrate ínvert.ebrate predators; (2) inËermediate sized organísms (1-2 nm) that face boÈh vertebrate and invertebrate predatíon and which reduce the visible part of their body by elaborating helmets to avoid vertebrate predaÈors; and (3) large cladocerans (greater than 2 mm) which can live only in the absence of intense vertebrate predatíon and resemble truly cyclomorphic forms only in small, inmature stages , D. carinata should obviously fall r¿ithin category (3). If D. carinafa was subject to predation by M. Teuckarti, Èhe immaËure stages míght be expected Ëo exhibit cyclomorphic changes. However, the present author has shown that juvenile and primiparous stages of D. carinata at Gumeracha maíntain constant caïapace width to body length ratios throughouE the year despíte uorphological changes in adulÈs (see Mitchell, 1978). This suggested that predation by M. Ieuckarti did not sígnificantly infl-uence the populations of Ð. carinata at Gumeracha. In this regard, hemipËerans and odonatans also prey upof- Daphnia (t"tc¡,r¿l-e and LawÈon, 1979; Johnson, 1973) and 168. notonectÍd predation exerts consÍderable influence uPon Èhe morphology of adult D. carinata (OtBrien and Vinyard, 1978). Hemipterans and odonatans occurred in the Gumeracha ponds but were noÈ studied quantiËatívely, although Agraptocotixa sp. and Anisops sp. apPeared to be most abundant from IaÈe spring through suÍmer. The intensity of thÍs fo:m of invertebrate predat.ion pressure at Gumeracha remains unknown Population declines in both ponds during late 1978 r¡ere accompaníed by gradual decreases ín bf and rr and a gradual increase in dt. Populations became senescent at thaÈ tíme as reproduction gradually decreased in response to unfavourable environmental condiÈions. ThaË ist temporal changes in D. carinata populatíons at Gumeracha resenbled those operating for other species of Daphnia ín natural habitats of.ten characterízed. by variable food supplies and predation pressure. variation ín mean brood size of D. catinata at Gumeracha was typical of Daphnia in food-limited situations (c.f. Daborn et a7',1978; de Bernardí and Canali, 1975 George and Edwards, L974; Clark and carter , Ig74; I^lright, 1965). In such siÈuations, brood size ís highest at Èhe conmencement of population cycles, declines rapidly thereafter and remains fairly constant with some minor flucÈuations' food Brood size is dependent upon energy intake and fecundíty reflects avaílability. Low mean brood size is, Ëherefore, exPected in a population that has reached the carryíng capacity of its environment (clark and carter, I974; Ilall, Lg64). Generally, the reduction of brood size to a low, constant. leve1 occurs in Nearctic and Palaearctic Daphnia during the surmner suggestíng that populatíons are in equilibriun with their food supplies (Hebert, 1978c; Hal1, 1964). However, equilíbrium is unlikely to occur for long perÍ-ods (íf at att) in the field (Slobodkin, lg54). In D. catinata, equilibrium conditions may have occurred briefly duríng winter' L69. bt values for D. carinata at Gumeracha were similar to those for D. pulex in aerated I,trSPs (Daborn et aI , 1'978). Ilowever r' values for D. carinata h7eïe generally lower, and dt values therefore, higher' The ftnding ÈI-rat ït, b| and dt values fot D. carinata in pond 1 exceeded values for pond 2 agreed with the results of Daborn et a7 ' (1978) who reported lower values ín the second pond of a two-Pond series. rt, br and dt values for D. catinata at Grmeracha lIere generally high compared to other studies o1 Daphnia ín natural vrater bodies; bt and dt values during 1977 wete higher than reported ín most studies while 1978 values r¡lere lower (c'f 'Kwik and Carter' 1975; Clark and Carter, 1974; George and Edwards, 1974; l{right' 1965; Hall, 1964). populatíon density oÍ o. carinata at Gumeracha r,ras similar to Èhat of D. pulex in aerated !üSPs (Daborn et al , 1978) but greatly (c'f' Allan' exceeded that reported for Daphnia in any natural water body L977; de Bernardi and canali, 1975; Kwik and carter, L975; Clark and 1966; I^Iright, L965; Carter , L974; George and Edwards, 1974; Korínek, at IIal1_, 1964). Accordingly, mean and maximum biomass of D. catinata any member of Gumeracha greatly exceeded that. previously reported for the genus (c. f . George and Edwards , L97 4; Duncan , 1975; I^Iright, 1965) ' from Annual productíon of cladocelafi populations has been reported g weight/n2 0.7 to ll0 g dry wei-gh t/^2, the usual maximum being 30 dry (see review by l^Iaters, Lg77). Prior to this study, the maximum annual production calculated for a population of Daphnia usíng the populatíon turnover-time method was 110 g dry weíght/mz fot D. gaTeata menðlotae Ln (cuunnins et aI., 1969). Mean annual net production of o. carinata turnover-time the Gumeracha ponds, calculated using the population production of method, r¡/as IBB g dry weight/*2' Thus, mean annual net any species of D. carinaËa at Gumeracha is the híghest yet recoÏded for Daphniaoranyspecies.ofplanktoniccladoceran.Totalannualnet 170. productlon of D. carinata in pond 2 during 1978 was less Èhan that reported for D. galeata mendotae by Curnrnins et a-l . (1969). Annual P/B ratios fox D. carinata in boËh ponds durí-ng 1977 wete very high, but the 1978 value in pond 1 was closer to average (approximately 20) (c.f. I,laters, Lg77). Annual p/B for D. catinata in pond 2 during 1978 was bel-ow average. As discussed above, bt, rt and dr values for D. catinata from Gumeracha were lower than reported for some natural populations of Daphnia. Average and maximum mean brood síze of O. carinata exceeded values reported in other studies of Daphnia from natural situations (c.f. Allan, L977; de Bernardi and Canali, L975; Kwik and Carter, 1915; George and Edwards, I974; trrlright , L965; Hal1, 1964). High brood size in D. carinata from Gumeracha could reflect the large size of the specÍes. However, mean brood síze of Ð. carinata was sírnilar to Ehat of D. puTex (a srnaller specíes: Green, L956) in aerated l'ISPs (c.f . Daborn et aI.r 1973). Brood size of D. pulex from natural habitats ís much lower Ëhan reported by Daborn et aI. (1978) (see Hebert, I97Ba; Green, 1956). While average brood size fot síze class 8 and 9 females of O. carinata from Gumeracha was higher than previously recorded maxima for the species (Hebert, 1978c), brood sizes of síze class 4 to 7 females were lower than recorded for females of the same length from other habitats (Hebert, 1978c; Navaneethakrishnan and Michael, 1970) ' Thus, high food conditions in WSPs aPpear to result in increased brood sizes, although this may be related Èo more favourable conditÍons for grol¡/th. An increase in brood size r¿ill increase the number of eggs in the population and, therefore, increase bt. If r' is constant, dt will atso increase. The turnover-time of the population will decrease' and daily percentage tulnoveï, and Èherefore production, will increase' Thus, high fecundíty, resulting in rapíd turnover of a very high t7 L. standing crop biomâss apPeared to be responsible for Èhe hígh product'ionofD.catinataatGumerachaduringL9TT.Thiswas reflected ín high annual P/B ratios. IIigh fecundity in D ' carinata appears to be a speeific trait, but some environmental modification mayhaveoccurredintheGumerachapondsduetohighfoodcondiÈions. High production in 1978 resulted from moderate turnover of a high bíomass. Meanannualrret'productionofD.carinata,calculatedusing the biomass turnover method, was 91 g dry weight/rnz. Total annual production of D. carinata ín both ponds during L977 anð in pond I during 1978 exceeded the production (but noË greatly) of D. cucuTlata ínaeutrophicEuropeanlakecalculatedusingthesamemeËhod (Híllbrichr-Ilkowska et al., 1966). Total annual production of for D. carinata in pond 2 durÍng 1978 was similar to that reported D. cucullata. Armual plB xaxíos for D. carinata were low compared to values presenred by Hillbricht-Ilkowska et a-2. (1966). Daily neÈ productioTrratesofD.catinatainbothpondsweremuchhigherthan (Duncan' reported for three species of Daphnia in a London reservoir Lg75) calculated using the bíomass turnover method' ThemajorassumptionofthebiomassÈurnovermodelísthat growthinthelaborat'oryissimilartothatínthefíeldundernatural situation is' condítions. Food qualíty and quantity in the experimenÈal therefore,ofparamountimportance.IngrowthexperimentsconducËed duríngthepresentstudy,D.carinatawasfedonpondsediment'. fot Daphnia Although the relat,ive nutritional value of dífferent algae 1971), no has been invesLígated (e.g. Arnold, l97l; Schindler, qualities of algae comparíson has been made of the relative nutriËional had no and detritus. van Heyningen (1954) suggested Ëhat detritus finding nutrítíonal value Íor D. puhex. This is not in accord wíth the the sediments of Horton et a7. (1979) that D. pulex frequently ttt'ILízes t72. r,rhen suspended food is low. Pacaud (in Hutchinson, L967) reporÈed that Daphnia fared better on a diet of flagellates that detrítus. However, as Horton et aI. (1979) have shown, the ability of different species of Daphnìa to utilize the sedíments varies. Maxímum biomass of Daphnia appears Ëo occur when food quality is highest; this may even occur prior to the development of highest nu-nerical densíty (George and Edwards, Lg74). On this basis, detrítus may ha"e been a higher quality food for D. carinata than algae; maxj¡num biomass at Gumeracha occurred several weeks afËer the declíne of phytoplankton sÈanding crops. It is lÍkely the growth raËe, and thus production rate' of O. carinata would have varied while feeding on phytoplankton' Growth rate and. longevity of Daphnia in laboratory cultures 1943)' may both decrease as density increases (Frank et a7., 1957i' PraÈt, In growth experiments conducted during the presenË study, the density of D. catínata was equivalent to 60 animals per litre. Thís density would not have been high enough to cause a depression ín growth rate (c'f' Frank et a7., Lg57). In fact, experimental densities were much lower than commonly encountered at Gr¡neracha. Thus, in the experimental situation food may have been superabundanË and grol^¡th rates may have been overestímated. The present study showed that the population turnover-time method of production calculation gave annual production values for D. carinata that were about twice as high as given by the biomass turnover method. Thís resulted from the overestiutation of daily production rates during periods of high egg or neonate mortality' The generalÍty of this finding must await furÈher investigatíon and will probably depend upon the prevalence of periods of departure from a involve stable age distribution. Both methods of production calculation assumptions, those for the biomass turnover method probably being least unrealístic. Obviously, the above f inding has imporÈant impl-icati-ons r73. for all studies invol-ving esÈímates of secondary production. It would be desirable for future studies to incorpolate both metho 1002. 4.4 Po tíon amics and Produc tion of Sinnce Lus exs nosus 4.4.L l"lethods Body lengÈh of s. exspinosus I4Ias neasured (at 20 times magnificatíon) as the longest distance from the top of the head to the tip of the posterior carapace protuberance. Mature animals were placed into 13 síze classes, each being 5 eyepiece uníts or 0.265 mrn inwidth (table 4.11). The lower limit of size class 4 corresponded to carapace length at the onset of r"ptàduction. That is, animals less than 1.325 m ín length r¡rere never observed to carry eggs. Two irnmature (ernbryonic) stages \¡rere recognised and designated "early" (including eggs) and ttlatet'. Length frequency dístributíons and mean length of adults on each sampling date were determined as ín 4'3'1'1' The percentage of mature adult fernales in reproductíve condítion and mean brood size on each sampling date (after 29 June, 1977) were determined as in 4.3.I.2. The populaÈion PaÏameters bt, rr, and d, were calculated as in 4.3.1.3, and daily net productíon (mg dry weig'rit/g,/day) deLermined using the population turnover-time method as ín 4.3.1.4. ThedevelopmenttímeofparthenogeneticeggsofS.exspinosus hatched \¡/as not measured directly in the present study. Length of the membrane) at embryo of S. exspinosus (having moulted the nauplius Gumeracha (0.398 mm) and mean length of neonates (0.663 mm) were simílar to values for s . vetulus (Hoshi, t95O) and s. acutirostris (Murugan and Sivaramakrishnan, Ig73). Temperature-corrected egg development times Table 4. l1 Length classes for S- exsPinosus Míd-class Length class Micrometer units DM length (nm) Early 0-5 o -o.265 0. 133 Enbryonic t Late 5-10 0.265-0.530 0.398 I 10-15 0. 530-0. 795 o.663 Juvenil-e 2 t5-20 0. 795-1 .060 0.9 28 3 20-25 I .060-1 .325 1.193 4 25-30 1.325-1.590 1.458 5 30-35 1.590-1.85s t.723 6 35-40 I . 855-2. 120 1.988 7 40-45 2.L20-2.385 2.253 I 45-50 2.385-2.650 2.518 Sexually 2.783 mature 9 50-55 2.650-2.9r5 10 55-60 2.915-3.r80 3 .048 11 60-65 3. 180-3.44s 3.313 L2 65-70 3.445-3.7rO 3.578 13 70-7 5 3.710-3.975 3. 843 I74. for S. veÈuJ,us and S. acutirostris were very similar (calculated from Murugan and sivaramakrishnan, 1973; Hoshi, 1950). Egg development times for S. serruJ.atus reported by Ang and Fernando (1973) were much shorter aË high temperatures. Thereforer e88 development times for S. exspinosus were calculated from the figure of 1.92 days for S. acutirostrjs aE zgo| (from Murugan and Sivaramakrishnan, 1973) using the equatíon (based on Kroghts curve) presented ín Edmondson and I,Iinberg (1971, p. 168). This equation r,tras found to overestlmate measured egg development times for D. carinata by a mean value of 0.16 days; egg developmenÈ times for S . exspinosus r¡¡ere corrected accordingly. The relationship between mid-size class length, and mean size class dry r^reight f or S. exspinosus htas determined on pooled ovígerous and non-ovigerous females (collected from Gumeracha during'August, Lg77) as in 4.3.1.6. 4.4.2 Results s. exspinosus occurred only briefly in pond 2 during January, 1977; the following concerns only population cycles in pond 1. 4.4.2.1 Size DistribuËion. Length-frequency histograms for s. exspinosus ín pond I during 1977 ate shown in Tigure 4.38. In late October - early November , 1976, recruitment from the hatching of resting eggs initiated the population cycle. Recruitment decreased and mortality anongst larger size classes \¡Ias reduced in December, 1976. RecruítmenÈ íncreased during January, 1977, and large numbers of juveniles contributed to the populatíon density peak in mid-January' Recruitment continued during I'ebruary while juveniles from the mid-January peak was high íncreased ín length. Mortality of the larger size classes duríng that period. Recruitment occulred during March and Apri1, 1977 , but mortality of larger síze classes \^Ias extremely hígh. Population density declined to less than I animal per litre at that time. 2.3.T1 v.7.n 23.\.77 2f .10.76 L t I 7.r2.77 8.¡t.76 ¡. æ.3n t* l¿ h. a.8,n 2,12.76 E- I 5.t.77 t": t3.\.n q. t.78 L L""" ¡L lB.1 .78 t.6.n J"" I 2.2.n t t I b''o',t ll. - b- 15.3.78 29,6.T1 ß,2.n I lr I ,0"' t h, trlrllttlll lllltltll|-l LLLTJJJJTLJ uJruiJ-UJ 89 lll r23 4s6 789 l0 | 2345 67 891ß 12345 67 89 t0 t2 34 56 7 Size class in pond l' FTGURE 4.38 Length-frequency distributíon of S' exspinosus L75. Recruitment decreased during June and animal-s increased .in length' Recruitment increased somewhat during early July, conËributing to an increase in popul-ation density, but declined thereafter and remained lor¡ until late October. Although recruitment ülas low from July to October, mortal-ity amongst the larger size classes also decreased and population density remained Laí:rly constant. Recruitment íncreased duríng October-December but mortality of larger size classes also increased. Peak population density in late December, 1977 ' $7as due to large numbers of juvenÍ-les. Recruitment declÍned during January, 1978' and mortality of larger size classes \¡Ias high. Both factors contlibuted to the population decline in January and February. A small burst in recruitment occurred from the hatchíng of ephippíal eggs in March, I978' However, high moïtalíty prevented the develoPment of large numbels' Recruitment ín s . exspinosus I¡Ias continuous. However r reproduction appeared to be synehroni zed Xo some extent in that periodic bursts of recruitment (and high adul-t mortality) were interspersed with períods of reduced recruiËment and low adult mortalíty' seasonal variation in mean body lengÈh of mature female s. exspinosus in pond 1 duríng 1977 ís shown in Figure 4.39. Mean body length of S. exspinosus ranged from 1.46 to 2.35 mr. Maxima occurred in l_ate December, lg76 (2.13 nrn: depth averaged $Iater temperature was 23.0"C), early August , Ig77 (2.35 rmn: depth averaged \^7ater temperature water was 12.0'C), and early October, tg77 (2.16 mm: depth averaged , temperature I¡Ias 16.1'C). It appeared that, as was the case for D. carinata, hígh mean body length in S. exspinosus could occur at high temperatures due to rapid growth, or at low temperatures due to íncreased longevitY. MeanbodylengthofmatureS.exspinosushasbeenplotted against depth-averaged rn/ater temperature on the date of samplíng in Figure 4.4O. A línear regression of mean body length on hTater 2. É li ,c ¡J 2.0 èo r oÊ F{ €h o F I Ê d I c) ã I 1.6 \rr,r I \ I L.4 L97 6 t97 7 L97 8 Tine (months) FIGLRE 4.39 Mean body length of adult S. exspinosus in pond l. 2.2 a E ,c 2.O {J o0 Ë a o r{ .o>r I B po a Ë (ú c) 1.6 L.4 0 510152025 TemPerature ("C) FIGURE 4.40 Mean body length of S. exspinosus versus,depth-averaged lrater tenPerature in Pond 1. L76. Èemperature shoÍred that varÍation in temperat,ure accounted for ort1ry 77" of the variance in mean body length. A linear regression of mean body length on depth-averaged \ÂIater temPerature over the month prior Ëo sampling shorred Ëhat variation in mean monthly water temperature accounted for only L4% of. the variance in mean body length. These results contrast wirh the finding of Green (1966) that mean body length of S. r¡etu-l.us is negatively correlated with htater tenperature above lBoC. Mean body length vras negatively correlated with chlorophyll a concentration (p = -0.56, 57. > p > I%) ' 4. 4.2.2 Reproduction. seasonal variation in the number of ovigerous and ephíppial female S. exspinosus (expressed as percentage of number of mature adults) in pond 1 is shov¡n in tr'igure 4.4I. The percentage of ovigerous females reached peaks in late october, L976, early January, early Novernber, and late December, 1977, during periods of pronounced recruitment príor to population density -increases' The percenÈage of ovigerous females decreased from late January Ëo early April , Lg77 (3"/") during a major declÍne in populati-on density. Ovigerous females íncreased in April and May during a period of pronounced recruitment but only gradually increasing population densíty (high rnort,ality amongst Iarger animals). Although the percentage of ovigerous females (and therefore recruitment) declined during June, 1977, population density increased in laÈe June due Ëo íncreased survival of larger animals. Ovigerous females peaked in late July but decreased ín August.. Ovigerous females increased during October and early November. AlEhough recruiÈment was high, mortality of larger animals increased and population density was litt1e altered' The percentage of ovigerous females declined markedly in laËe November - early December and population densiEy decreased slightty; confidence vlere presen't lirniÈs \Àrere very wide at that time. No ovigerous females af.er January, lg7B. Recruitment in mid-March vras from ephippial eggs. 80 60 c) ò0 d IJ É q) u 40 H q) È I I I I I I I I I I I I ¡ I t I I I I 20 I I ¡ ii I I ¡ l ,l I I I l t tlI I I , I I t I I I I I , I I , t t I t ì I I I l I I I l I , I I , I 0 DJ DJ L97 6 r977 197 I Tirne (rnonths) FIGURE 4.41 The number of ovigerous (-) and ephippíal (---) s. exspinosus expressed as a percentage of the number of adult females ín pond 1' r77 . peaks in the percentage of ephippial females coincided with, or occurred just prior to' decreases in population densíty' Variation in mean brood size of S. exspinosus in pond I from late June , Ig7l, is shown in Figu re 4.42. Mean brood síze decr."""å rapÍdly during July; thereafter, mean brood sÍze showed a less rapÍd but contínued decrease until the population declíned Ín January, l97B' that AJ-though maxímum mean brood size of D. catinata was much hígher than of s. exspinosus, average mean brood size of. the two species were not signíficantly different during 1977 (Mann-Whitney U test' p > 0'05) ' Body size, temperature, and food are all important factors influencing brood si-ze ín sinocephaTus (Green, 1966). Brood size, and deËermíned individually on |íve S. exspinosus collected in June July, Lg77, has been plotted against body length (tto) ín Figure 4.43. A linear regression of brood size on body length gave a relationship of Èhe form, brood size = 24.85' length - 39' 88, tZ = O'79' That is' variation ín body length accounted fot 79% of the variance in brood síze. The intercePt on the X-axis (1.6 mm) showed close agreement with bodylengthattheonsetofreproducÈion(1.45rnm).Themaximum lndividual brood size recorded for s. exspinosus from Gumeracha was 42 in a síze class 12 female (2.92 nm body length) ' LogmeanbroodsizepersÍzeclassraveragedovertheentire study period, has been plotted against mid-size class length (nun) ín Figure 4.44. A linear regression of log average brood size on mid-size class length gave a relationship of the form, log mean brood Síze = class O.4g . 1-ength - O.zg, ,2 = 0.g7. That is, variaÈion in mid-síze length accounted f.or 977" of. Èhe variance ín average brood size per size c1ass. A stïong positive relationship exísted between body 1-ength brood and brood size ín s. exspinosus. However, in the field' mean (p = 0'68' size ancl mean bocly length \^/ere not significantly correlated p > 57"). 20 T \ 16 I o .rlN o \ € T2 o o pt{ ¡ It É (ú 8 o I \ I 4 0 J r977 L97 B Tirne (nonths) pond 1' FIGURE 4.42 llean brood size of s. exspinosus in T 40 I I ¡ 30 T t o E N rat I T{ r¡, I o I.â ,l €20 t-I o l/t o H FÉ¡ I ,'4 t t_t 10 a/l I l,/¡ t's¡s tr I,¡I 0 I 2 3 Body length (nm) FIGIIRE 4.43 Brood size versus body length of 5. exspinosus in pond 1' 100 (¡) o ,4 ilN o o € o o tr Þ 1 0 q) /t/ è0 o ' d tr 0) o I 4 5 6789 10 Size class Length (nrn) FIGURE 4.44 Average brood size per size class versus míd-size class length of S. exsPinosus- 178. A strong negative correlation hras found beËween mean brood size of S. exspinosus and chlorophyll a concentration (on the date of samplíng) (p = -0.96, p < 0.17"). This suggested that s. exspinosus may also have gained nutrition from the sediments. Log mean brood size of S. exspinosus has been plotted agaínsÈ depth-averaged \,Íater temPerature on the date of sarnpling in Figure 4.45. A lÍnear regressíon of 1og mean brood size on average \'üater temperature gave a relationship of the form, Lo9 rnean brood síze = L,64 - 0.05 temperatute, 12 = 0.78. That is, variation ín average water temperature accounted for 78"/" of. the varÍance Ín log mean brood síze, Thus, a strong negative relationship existed between mean brood size and tlater temPeratule. On a seasonal basis ín the field, this appeared to override the relationship between brood size and body length. Low mean brood size ín S. r¡etulus also occurs at high temperatures as females become maÈuïe at a smaller size thereby restríct,Íng egg-laying capacity (Green, L966). For the calculation of population paramet.ers, mean brood size on each sampling date from Nove¡nber, 1g76, until June, L977, was back-calculated from the relationship between 1og mean brood síze and depth-averaged vlater temperature. 4 .4 .2.3 Popula tíon Parameters. Seasonal variatíon ín instantaneous gro\¡/th rate, b!, actual growth ÏaÈe, rt, and instantaneous deaÈh rate, dt, of S. exspinosus in pond I ís shown in Figure 4.46. Peaks in rt during rnid-January, late June, and mid-December, Lg77, corresponded wíth peri-ods of hígh recruitment and, therefore, high or increasing population density. The population decline in March, Ig77, I^las due to a decrease in the percentage of ovígerous females and concomitanÈ reductions in bt and rt. rr hras low from July t.o November , Lg77; recruítmenË l¡/as generally low and survival of the larger .size classes high during that period. Maximum I00 o c, N .r{ o o o 'do o 10 ¡{ F t Ë d o q, è¡ o I 6 810 L2 14 16 18 20 2? Temperature (oc) FIGIIRE 4.45 Mean brood size of 5. exspinosus versus depth-averaged T,rater temPerature in Pond 1' o.2 0.1 I l_ L J 0 ¡l 0.4 0.1 I 0.3 il I 2 a I ii ^ ,. I p I I I 1i- ll I t¡ ll i I l¡ ,l 0.3 o.2 I ¡l t t, I , I I l, i I l t, í'i rl I \ I r! I It i.,^j I r I Í Li 0. I t \ ) I t 0 0.4 ii I ¡i i1 ¡l 0.3 ]\ I I I I I li I € I I I !¡r o.2 tit \ I .zl I \. I ¡! iii 1 I i\ \i\ \7 I tti i ! !lr ir/ \ i \l 0.1 1 \ I T I 0 DJ J r977 t97 B Tiure (months) (-.-) FIGI]RE 4.46 Populatíon parameters br (--- ), r' (-), and d' for 5 . exspinosus in Pond 1. I79. r, was 0.238, and mean positive rt lvas O.O77. Mean and maximum bl values were 0.2L4 and.0.410 respectively. Seasonal change in d' generally followed a similar Pattern to br' Mean and maximum dt values were 0.197 and O.432 respectively' The declíne of bt and rr during February and early March, 1977, coincided with an increase in abundance of D' catinata' However' bt increased during late March, 1977, while D. carinata I'7as still present. rt increased markedl-y ín 1at.e June after the decline of D. catinata. Ilowever, neither bt, Ït, nor dt was signíf ícantly correlated with population densiÈy of O. carinata during 1977 (Spearman's p¡ p > 0.05). The percentage of ovigerous females in the populatíon of hígh S. exspinosus decreased markedly in January and March, 1977 ' A percentage of non-reproductive adults is cournon in food-lírnited populatíons of Daphnia (Hebert, 1978c; Slobodkin, 1954). Events in L977 resenbled Ëhe population of 5. exspínosus during the early part of I D carinata those in the food-límited D . carinata populations. b of ' I 1977 (Mann- was significantly greater than b of s . exspinosus during lfhitneyUtestrP>0.05)'AlthoughmaximumrrofS'exspinosushras both greater than maxímum rt of D. catinata, mean positive rt values of U p > 0'05)' species r^rere not significantly d{f ferent (}4ann-Whitney test' dr values for both species were only just not significanÈly dífferenË during 1977 (Mann-Whitney U test, p > 0'05)' ThepeakindlofS.exspinosusinmíd-February,1977, coincided wiËh a pealc in population densiÈy of. U' Teuckarti' However' cltrring Jantrary, Ig7B, dr decreased as the density of u. Teuckarti increased. d' of s. exspinosus and population density of u' Jeuckarti (p p > 5i¿) r,rere not significantly correlated during 1977 = 0'34; ' The number of eggs ancl juveniles (size class 1) in the populationofs.exspinosusinpondlduring|gTTisshowninFigure Èhe fate of declíne 4,47 . The rate of decrease in egg number exceecled I tl tt tl rl I I t I t 100 I ll It I ¡l ¡ I I ¡ I I I I t q) I t{ I .rl+¡ FJ ,i tr ,l .rt q) \ tt^ ,'I À t tl ¡l v¡ I t{ tl q) \ I !r I F t t i ¡ ir JE I tl z 10 t i\r^t I l't { I I I I I I I I I ¡ I I I I ,r I ¡ I t I I t t I I t I I I I I I I , I I ¡ I I , I rl t t I l¡ I I I I ¡ , I ^ , I , I I I I , I , , I I , , ¡ , , I , , , I 1 J t977 DJ I97 B Time (months) FIGURE 4.47 Number of eggs (-) and j uveniles (- --) of ^S. exspixosus in pond 1 180. in population density during February, August and Septemberr- October and November, and late Decernber, 1977. This suggested departure from a stable age distribution at those tímes. Comparison of egg number wíth Èhe number of juveniles showed that considerable mortal-ity of eggs or neonaÈes occurred in earl,y February, late March, and from AprÍl to early Decernber, Lg77. This expl-ained 1ow rr values duríng the latter períod. Lor^r nurnbers of juveniles and Èhe presence of larger size class females from Apríl to Decenber suggested starvation of neonaÈes under low food conditions even though some females were still abLe to obtaín sufficient food for growth and egg productíon (e.g. Neil1, L975). plot 4 .4.2.4 Length-D rv !ùeight Relatíonship. A double 1o garithmic of mean dry weight (ug) per size class on mid-size class lengËh (mm) for embryonic, juvenile, and adult s. exspinosus from pond I Ís presented in Figure 4.48. A línear regÏession of the natural logaríthm lengËh of mean dry weíght (I^I) on the natural logarithm of ¡nid-size class (L) for embryoníc stages yielded a rel-ationshíp of the form, 1n tr-l = 0.g585 - 0.0971 ln L, r2 = 0.31. That is, variation in length accounted for only 3I% of the variance in weight of embryonic stages. animals some weight loss appeared to occur in late ernbryoníc stage ' overlapped However, confidence 1ímits for the weight of embryonic stages during and weight changes vTere not significant. A weight loss may occur the embryoníc development of some cladocerans (Green, 1956). Alinearregressj-onofthenaturallogarithmofmeandry weíght on the natural logarithm of mid-size class length for ovígerous ln W = and non-ovigerous females yíelded a relationship of the form, z.l4z3 + 2.B460. ln L, t2 = 1.00. slope- coefficients for the regression line of r,reight on length for D. catinata and s. exspinosus lIere sírnilar' catinata' However, the Í-ntercept for 5. exspinosus vTas hígher than for D' Larger intercept.s generally occur as body sÍze decreases among and cladocerans (Bottrell et a7", 1976). !üeíght of the ernbryonic stages 100 o ã00 t +, T ,G o ô0 il o B lL h T âl..l t0 /io I _o o I 0.1 I Length (rnm) e 1y 1a I 2 3 4 6 7 I Eubryonic Adult Length class FIGURE 4.48 Mid-size class length-dry weight relationship for pooled ovigerous and non-ovigerous S. exspinosus' 181. neonate of D. carinata $rere higher than for Ëhe correspondi-ng stages in s. exspinosus. However, above a length of 0.9 mn, ^9. exspinosus hTas more than tr¡ice as heavy as D. catinata of the same length even though D. carinata aÈtained a larger maximum body length' That ist s. exspinosus \¡ras a shorter, stouteÏ animal . sinacephaTus has a heavier exoskeleton than Daplnía (Hutchínson, L967). 4 .4.2.s Productíon ?opulation Tur nover-Time Method. Seasonal variation in sÈanding croP biomass (mg dry r^reight/Í,) and daily net production rate (mg dry weight/ ,,/day) of 5. exspinosus in pond I during 1977 ís shown in Figure 4'49' production calculations, based on the populatíon turnover-time method, for s. exspinosus are presented in Appendix 6. Biomass peaks coincíded with population density maxima. Bíomass \^Ias highest (7.349 rng dry weight/[) ín January, 1977, when population densiÈy was maximal. Mean bíomass during 1977 was 1.093 mg dry weight/g. Maximum and mean bíomass of s. exspinosus \¡rere much lower Ëhan fot D. carinata ín pond 1 duríng 1977 due to 1or¿er population densities. Daily net production rate closely followed biomass fluctuatíons. Net production rate varíed from order of 0.004 to 0'785 rng to 0.385; mean daily P/B ratio was 0.L76, equívalent to an average carinata biomass tuïnover-tírne of 5.7 days. Mean daily P/B ratio for Ð. in pond 1 during 1977 was hÍgher than for s. exspinosus and average for the biomass turnover-time was 3.5 days. However, daíly ?/B ratios (Mann-\{hitney two species \^rere not significantly differenÈ ðutíng 1977 UtestlP>0.05).Thus,t'hehigherproductionofD.carinataresulted biomass' from the same rate of turnover of a much higher standíng crop A línear regression of daily P/B r-atio for s. exspinosus on depth-averaged l^/ater temperature showed that variation in temperature I 0.8 I I I' ii ¡l lr tl h lr (ú 6 I 0.6 .Ú oì ,1 I ,l ol IJ ll +J l" I 00 l¡ '-l I .¡b0 o rl I B 0) tì I Þ à I il I h .dH ¡l 4 Ir ,l o.4 õ I ô0 ri tr I ô0á I I U) Ø I É t o cd .r{ 1 É I .lJ o t 1 U 'rl I I a Fq I E 2 I I { 0.2 o I I l¡ t{ I Êr I I I I I , , I , , , 0 0 J DJ t97 7 L978 Time (roonths) FIGURE 4.49 Standing crop biomass and daily producÈion of 5. exspinosus (population Èurnover-time method) in pond 1. Biomass (-), production (- - - -) . r82. accounted for only 3% of. the varíance in daily P/B ratio. IË was shown above that ternpeïature accounted for only a small proportion of the variance in the daily P/B ratÍo of p. caÏ.inata. These results contrasted wíth rhe findings of Janicki and Da Costa (1977) and Duncan (1975) that daily PIB raÈíos of. Bosmina and Daphnia showed a strong positive relationship with temPerature' Total monthly and annual net-production of s. exspinosus \^Ias determined by planimetry. Net productíon I¡Ias converÈed to g dry weight/ .2 of. pond surface area, and Èhe results, togeËher wíth weighted mean monthly biomass (g dry weight/rn2) and monthly and annuaL P/B ratios, are presented in Table 4.I2. Monthly net production was highest in January, August and october, 1977. Total annual net production of s. exspinosus in pond 1 during 1977 was onfy 207" of total annual net productíon of D. carinata. Annual P/n ratio for S. exspinosus hlas higher Èhan for D. carinata but nonthly P/B tatj:os l¡Iere higher for D. carinata. As was the case fot Ð. catinata, peaks in daíly net production rate of s. exspinosus occurred during periods of high egg mortaliÈy and departure frorn a stable age disËríbution. The applicaËion of the populaÈion turnover-time method for the calculation of productíon ín S. exspinosus v/as subject to the same sorts of error as for D. carìnata. Total annual rret production of s. exspinosus \^las' therefore, overestimated due to failure to take increased egg mortality ínto account. The population turnover-time method overestímated total annual net production of D. catinata by 1.6 to 2.8 Èimes' Therefore' total annual net producÈion of s. exspinosus ín L977 was probably closer 1 during to 30 g dry weight/rn2. Total annual net production in pond conËent 1977 woul-d, therefore, have been 43 kg dry weíght. The nutrient and was of s. exspinosus \^las not determined during the present study, phosphorus assumed to be similar to D. carinata. The nitrogen and TabLe 4.12 Total monrhly and annual net producÈion (P, g dry weight/ur2) based on population turnover-tíme method' mean monÈhly and annual bíomass (B, g dry weight/rn2), and P/B ratios for S. exsPinosus in Pond 1 during 1977 P B PIB r977 r978 L977 L97 I t977 T97B Jan. 10.0 1.3 4.r 0.2 2.4 6 .5 Feb. 8.4 1.0 8.4 March 0.4 0.1 4.0 Aprí1 0.1 0.02 5.0 May 0.5 0.1 5.0 June L.2 0.4 3.0 July 5.1 L.9 2.7 Aug. t6.2 3.2 5.1 Sept. 7.9 2,O 4.0 Oct. L2.7 2.O 6.4 Nov. 3.8 0.6 6.3 Dec. 3.1 0.9 3.4 Annual 69,4t 1.3 r.42 49.63 I Total annual producÈion (xP) 2 Mean annual biomass (Ð 3¡P B 183. conÈent (as percentage of dry weight) of D. carinata (see 4.3.2.7) was used ín the following calculations. Total annual. net production of S. exspinosus in pond I duríng 1977 tepresented a nuLrient store equivalent to 1.L4% of total PO4-?' O.54% of TKN, and 0.321Å of total nitrogen (TKN + NO3-) retained in the pond during 1977. Ilarvest of S. exspinosus did not rePresent a signíficant pathway for nuÈríent removal- from the Gumeracha poncls. Harvest of Èhe total- annual net production of. D. carinata and s. exspittosus from pond 1 in 1977 would have removed 5.777" of total PO4-P' 2.747" of TIG{, and 1.647" of total nítrogen (rrn + NO3-) retaíned in the pond durine 1977. Thus' production of herbivorous zooplankton did not represent a significanÈ nuÈrient sËore in the Gumeracha ponds, and harvest of Èhis group would ponds noÈ have provided a useful pathway for nutrient removal from the ' Total annual neÈ production of s. exspinosus in pond L during 1977 was equi-valent Eö I% of total annual neÈ primary production and would L05% of total annual- neÈ phytoplankton production. The laËter ToÈal suggest ÈhaË S. exspino.Sus \¡IaS not an obligate suspension feeder. annual net productíon of o. carinata and s. exspinosus in pond 1 during !977 was of the order of 2t6 kg dry r^reight. T,he ecological eff iciency of the pond, or the effíeiency of energy Ëransfer between the primary and secondary trophic levels, as exPressed by the ratio of net zooplankton production to neË primary production, was equivalent Êo 0 .064 . 4.4.3 Discussíon AlthoughS.exspinosusandD.carinatabothreproduced continuouslyatGumeracha'somesynchronizaiuj:onwasapparentin S.exspinosusandreflectedinperiodícburstsofrecruiËment. population cycles of the two zooplankters were similar durÍng the early part of Ig77. The rapid decline in the percelltage of ovigerous 1977' female-s of 5. exspinosus foll-owing the population peak in January, 184. suggested that food-limitatiorl \Álas responsible for the decline in population density. Food-l-imiÈat,ion may have arísen as a result of competition with D. carinata, although this was not reflected in population parameÈers. Although it has been suggesÈed that Sjmocephalus is an oblÍgate suspension feeder (Horten et a7.,1979>, observations by pacaud (in Hutchínson, Lg67) and the population increase of s ' exspinosus in July and August, Ig77, suggesÈ that this specíes may also be a facultative browser to some extent. Thus, S. exspinosus and D- carinata may have competed for access to the sediments. The decrease in mean brood size of S. exspinosus during the latter part of 1977 a]-so suggested food-linitation or, at least' some degree of food-restriction' s. exspinosus may not have been able to utilize the sedimenËs as effecÈiveLy as o. carinata alÈernative explanatÍon for the population decline of S. exspinosus in January and February, 1977, ís the oversaturation of so¡ne specialized niche. This could explaín why populatíon density r,ras lower from July to Novernber than in January, 1977 ' Ttte outcome of competitive interacÈions is determÍned by size-sel-ectíve predation and reproductive rate (Lynch, 1979, 1977; Kerfoot, 1977a). In the absence of vertebraËe predation, intense invertebrate predation can result in the replacement of a smaller by a larger specíes (Lynch , lgTg; Dodson, Ig74b); larger body size confers protection from invetebrate predators (Dodson' I974a). Although the death rate of small cladocerans may increase in the presence of copepod predators (Kerfoot, Ig77), dt values for S. exspinosus and population density of M. feuckarti l¡7ere not correlated aË Gumeracha' However' as not discussed in 4.3.3, total population density of M. Teuckart:l need reflect the p::edation pressure exerted by the species. Although mean brood sjze of s. exspinosus and D. carinata hTere not significantly di_fferent in pond I during 1977, the birth rate (b') of o. carinata was I significantty higher than for 5 . exspinosus ^ An increase in b rnay be 185. achieved by increasing the number of eggs in the population (E) (lndependently of increasing No), or decreasing egg development time (D). Egg development times of D- carinata and s . exspinosus are probably very sÍmilar (c.f. Bottrell et a7., 1976). The percenÈage of ovígerous females in the population of D. catinata in pond 1 during Ig77 (mean = 697") was signifícantly greater than the Percentage ín the populaÈion of S. exspinosus (mean = 367") (Mann-Whitney U test' p < 0'01) ' Thus, the number of eggs (E) in the population of D . carinata exceeded that ln s. exspinosus for any given populatíon density; this explained the higher birth rate of D. carinata. A hígher birth rate may have given D. carinata a competítive advantage with respect to s. exspinosus' This was not reflected in increased rt values fox D' carinata as might have been expected had the larger species been at a competitive advantage (e.g. Goulden et aJ., 1978) . CompetitÍve interactíons are exceedingly complex and although conditions may be favourable for the adults of a given species, survival of earlier stages may be reduced' the Such a situation can result in a larger species becoming extinct in presence of a smaller one (Lynch, l97B). Obviously, a more involved expe-rimental study would be required to elucídate the nature of competitive and predatory interactions amongst the zoopl-ankton cornmunity of the Gumeracha ponds. Principally, these would involve determining the age sÈructure of. M. Teuckarti populations' prey selection experiments Ínvolving juvenÍles of S. exspÍnosus and D. catinata, and under mixed and single species culÈures of S. exspittosus and D' carínata abundant food and food-limited condiËions' comparative data on the population dynamics and production of liÈtoral cladocerans aIe scarce. Food-limitation and predatíon have been eutrophíc shown to be important in límiting S. serru-?atus in meso- and (b') ponds in Canada (Ang and Fernando, Lg73). Mean birth rate of s. exspinosus at Gumeracha was much lower: than for s. serru-zatus' As 186. mean brood size of 5. exspinosus (9.6/feurale) exceeded that for S. serru-Z.atus (3.7/female) in the Canadían ponds (calcul-ated from Ang and Ternando, 1973), hígher birth rate in S. serrulatus may have resulted from shorter egg developmenÈ times for that specíes (c'f' Ang and Fernando, Lg73). Ai-though brood síze in s. exspinosus at Gumeracha was similar to brood size in S. acutirostris (from a small lndian pond) up to a body length of 2.5 mm, above thís length brood size 1n S. exspinosus rfas higher (c.f. Murugan and SÍvaramakrishnan, 1973). This also appeared to hold wíÈh respect to S. veÊu-zus from some habitats (Green, 1956) but not from others (Green, 1966). Brood size in S. exspinosus at Gumeracha was similar to that recorded for the same species at some sites in a polluted sÈream in the Middle East, but l-ower than recorded from other sites (Mohammad , 1979) ' Thus, food availability in the Gumeracha ponds did not appear to be exceptionally high. Ang and Fernando (1973) díd not indicate Èhe method used to calculate Èhe production of S. setrulatus, and although they referred Total to ''grossrr production, íncluded no information on respiraËion. annual. net production of S. exspinosus in pond 1, calculated using the populatíon turnover-time methodrv¡as much lower than total production of S. serru-Latus during the growing season in the eutrophic Colurnbía Lake' but similar to total annual production of S. settulatus in the mesotrophic Miller rs Lake. 4.5 General Discussíon The zooplankton conununity of the Gumeracha ponds exhibited low diversity in terms of species nurnber, but contained represefitatives of Although the ponds all_ the major ecological groupíngs of zooplankters. were dominated numerically by a single species (o. carinata), the dynamics of the cornrnunity as a r¡hole vTere complex. Thís has important implícatíons for the use of zooplankton in pond managenent. The 187. findings of the present sÈudy do not supPort the conclusíon of Loedolff (1965) that temperature is the major factor deterrnining the occurrence and abundance of zooplankton in WSPs. Iühile ËempeTature may be important in determining the occurlence of some species, abundanee (popu1-ation densíty) is influenced by food level, competition, and predatíon. Thus, zooplankton populations in !üSPs would require careful management to mainËain an optimal standing crop of a desired species ' Perhaps most surprising r¿as the finding that, even in I'trSPs with high organic ínput'S, zooplankton populations cou1d, at tiDes, become food-lirniLed. Food-líruitation of Daphnia in aerated oxidation ponds has been reporÈed elsewhere (Daborn et aJ ', 1978) ' In a by managenenÈ context, thís problem could, perhaps, be overcome repeated croppíng aÈ critical times duríng the population cycle. The population would be maintained in a vigorous growth phase (i.e. as at percenËage of the commencemenË of populatÍ-on cycles) with a high ovigerous females and hígh brood sizes. Annual producÈion would thus be Íncreased, although standing crop biomass at any given time vrould be reduced. Periodi-c cropping would, of course, be essenËial for nutrient removal. TheD.carínatapopulationsatGumerachaterminated phytoplankton blooms but the speeies lÍas prevented from c-ontrolling phytoplankton standing crops during surnmer by high temperatures ' rntensive culture of Ð. carínata for algal removal would require the would inhibit mainÈenance of temperatuÏes around 15',C. Obviously, this the development of phytoplankton blooms which were ÈrÍggered at about macrophytes' lBoC at Grrmeracha. As with fil-amentous algae and submerge Gumeracha, supraoptimal, rather than suboptimal' e/ater temperatures r88. ínhibited the growÈh of. cTadophota, P. ochreatus and D. carinata during the period of phytoplankton bl-ooms. The reduction of organic material in the Gumeracha ponds was highest during spring-winter-autumn r'rhen standing crops of p. ochreatus, CTadophora an;d D. catinata were high' phytoplankton had a significant detrimental effecÈ on effluent quality' Accordingly,itnightbeexpectedthaÈal-galproblernsinAustralian and that I^ISP tr{Sps would be exacerbaËecl in areas of higher temperature function on an annual basis rnight be more effectíve in cooler areas ' This conflicts with the widespread viær that !üsPs are more effective in climates r^rith high temperatures and incidenÈ solar radiation' A more extensive seasonal survey of trISPs a1-ong a climatic gradient in southern Austral-ia would Prove interesting in this regard' Althougho.catinataplayedamajorroleinthereductionof phytoplankton standíng crops and made substantial contributions to Èhe gxazing' improvement of effluent quality duríng periods of intensive the dj-rect importance of zooplankton in pond function throughout the rest of the year vras not great. Rernoval of organic materíal during periodsofhighstandingcroPsofo.catinataappearedtobeeffecÈed largelybysubmergedmacrophytes.Ilowever,herbivorouszooplankton' of such as D. carinata, mâY contribute indirectly to the improvement effluentquality.Bytermínatingphytoplanktonbloomsínaerobic}JSPs' DaphniacanreducebiogenicturbiclityandimprovelightPenetrationin ponds. This may permit the germination and establíshment of submerged macrophytesÈhatcouldnoËoccurintheabsenceofDaphnia.McNabb a (Ig76) concluded that Daphnja was essential for the rnaintenance of develop in suítab1e lighÈ regime which al-lowed submerged macrophyËes to full-y aerobíc maturation ponds in Michigan' Annual net producËion of p' catinata and S ' exspinosus representedacombinednutrientstoreequivalenttolessthan6T"of retaíned in the PO P and less than 27" of to-ual nítrogen rotal 4 - 189. would Gumeracha ponds during Ig77. Harvest of herbivorous zoo'plankton not have provided a useful PaÈhltay for nutrient removal from the zooplankton Gumeracha ponds. Due to high populaËíon turnovel rates, harvest would need to be conducted every few days. This would íncrease the operational costs of Ëreatment plants to some extent but would probably be a low-technology process. The incorporation of nitrogen and phosphorusintounícellularalgaeappearedtobethernosteffective nutrientremovalpaËhvTayintheGumerachaponds.EffluentNO,and periods of high soluble PO4 - P concent,rations were lowest during phycoplankton standing crop' Therefore, a system íncorporating stage zooplankton culture ponds for algal control as a final treatment nutríent míght be expected to exhibit poor performance with respect to removal_. The rate of nitrogen and phosphorus recycling by zooplankton is such that a large proportion of Èhe nutrients ingested ís rapidl-y regeneratedinthesolubleformorlosÈtothesedimentsvia Peters and incorporatíon into faecal pellets (Ganf and Blazka, I974; relative Rigler , Ig73; Peters and Lean, 1973) ' Depending upon the net movement of magnítude of Èhe soluble and particulaËe components ' nÍtrogenandphosphorustothesedimentsmayoccur.NiËrogenand I'ISPs would be phosphorus release from the sedimenËs in fully aerobic most effective expected to be low (see 2.2.3). In such a situation, the emptying of the pond means of nutrj.ent removal rníght be via periodic procedure and mechanical removal of the sediments. This operational wouldrofcourserincreasetheareal-requirementsofthetTeatment plant as extra ponds would be necessary to allow periodic bypassing' Futureresearchinthisareamightinvolvefield-scale on experíments upon Ëhe effects of moderate gtazíng Pressure gtazer densityt net phytopl.ankton populatj-ons in I'trSPs' Up to a certai:n prirnary productioh may be enhanced by the preserrce of herbívores is Ëhus (Porter , 1976; Cooper , Ig73) ' Self-shading by Phytoplanlcton 190 . prevented; the efficiency of photosynthesis and the intensity of the decomposition of organic materíal may be increased (Gliwicz, 1975) ' cropping of zooplankton would be requíred to reduce the intensÍty of grazíng pressure and, as discussed above, Ëhis would be expected Lo lncrease Ëhe production of the group. As a result' a ne\^I steady-staÈe with respect to nutrient cyclíng and partitioning amongst the components need for of the IaISP ecosystem might be establÍshed. There is an uÏgent more intensive study of nutrient cycling and partítioning within tr{SPs during dífferent phases of the armual pond cycle. Via this Ëype of manipulaÈion it may be possible to obtaj-n the benefíciaL effects of unicellul-ar algae in tr{sPs at lower standing crops, thereby reducing operational- Problems. Studies of the productívity of different trophic levels in the hypereutrophic environment of tr^ISPs allow comment upon relatíonships (in between productivity and lake trophic state. Patalas Makarewicz and Likens, LgTg) has suggested that there is a tendency for the daily ?/B ratio of the zooplankton community to increase in proportion to the productivity of the lake. That is, high P/B ratíos are expected ín eutrophic lakes. Peders en et a7. (1979) were unable to support Èhis hypothesis.MeandailyP/BratioforS.exspinosusduringl-977was o.L76 and for Ð. carinaÈa during 1977 anð, I97B xanged from 0'068-0 '282' eutrophíc These ratios were characterísÈic of zooplankton in meso- to lakes (c.f. Pedersen et al ,1976, Table B) with the híghest mean P/B fot O. carinata exceedÍng that for the mosÈ eutrophic lake' As year to year fluctuation may be considerable a generalisation of the type said, suggested by Patalas is difficult to substantiate. It may be P/B raXíos from hovrever, that if Patalast hypothesis l^7as correct, all than Gumeracha might have been expected to be considerably higher previously recorded. This clíd not appear to be the case' a7" It has been postulated (ttitt¡richt-I1kor^rska, in Pedersen et 191. Lg76) that energy transfer efficiency between the primary and secondary trophic levels (ecological efficiency) would decrease with increasing lake trophic state. tr{hile the data of Pedersen et a-7. 0976) and llall et a7. (1970) supported this postulate, Makarewicz and Likens G979) arrived at the opposite concl-usion. Bcological efficiency in pond 1 at recorded Gumeracha during 1977 was 0.064. ThÍs was general-ly lower than for oligo- and mesotrophic lakes (c.f. Pedersen et a7., 1976, Table 9)' On That ís, tr{SPs do not aPpear to be highly efficient ecologically" this basis alone, it woul-d not be expected that a hígh proportion of the nutrients store management of maturation WSPs is thus examined' r92. Chapter 5. Fish 5.1 Introductíon The concept of utilizing domestic sewage for fÍsh culture ís not ne\^r, nor is the observaÈíon that fish uray grow rapidl-y in se\¡7age fextíLized ponds. The practice of fish culture in ponds connected with latrines and animal pens is widespread and long-standing in Asian countries (Híckling, 1968). Fish culture ín ponds to vrhich livestock manure and human se\^Iage are added has been practiced for some tíme in Israel (e.g. Schroeder and Hepher, L976). It ís only comparatively recently, however, that the direcÈ culture of fish ín operational ÍISPs has been attempËed. The only notable exceptÍon ís the culËure of Cgprinus carpio in large ponds that are part of the system treating domestic sewage from Munich (ttickling, 1968). several specÍes of fish, of wídely dífferíng feeding ecology, may occur naturally in !JSPs. These include detrítivores: C. carpio an¡d lctal-utus me7asl carnivores: Mugì7 cephaTus, Gambusìa affinis, perca fluviatifis, Leuciscus cephalus, SaLmo ttutta, and Lepomis cganelTus; and herbivores: Ruti-Z.us rutj-Zus, and several indigenous Asian cyprinids (after Carpenter et a7., I976; Goulden, L976; S]-ack, L974; Chatterjee et al., 1967). Additionally, many species have been deliberately íntroduced and successfully maintaine-d in tr'lSPs. These Ínclude R. rutjlus, P. fluviatifis, S. ttutta, and Gasterosteus L. cePhalus and I{itliar'st acuieatu;.t(I^Ihite/ t978), TiTapia nil-otica, Ictalutus punctatus, Notemigonus crgsoTeucos, and Pinephales ptomelas (CarpenLer et a7., Lg76), c. carpio (Noble, 1975), c. catpjo and Labeo rohita (Kríshnanroorthi et aI., I975), Retropinna retropinna, Carassius auz.atus' grass carP (presumably and Sal.mo gairdneri (Slack, I974; Teoh, 1974) ' Ctenophargngodon idella) (Ponyi et al., 1973), salmon (Anon', 1972)' L. rohj-ta and ca t]a catl-a (chatterj ee et a7., 1967) , Mictopterus safmoides, TiTapia mossambica, TiTapia sparmani, arrd Le¡nmis macrochirus 193. (Itey, 1953). These studies have shown that, given suiÈable physico- chemícal conditions, fish will survive, grow rapidly, and may attain spawning condition ín !üSPs. Fish production in WSPs is very high conpared with natural waters and unfertilized fish ponds, and may even exceed producrion in ferr ,lízeð. fish pond" can sËabiLize ar¡d íncrease dissolved oxygen concentration and pH (schi;oeder, L975; Slack, L974; Teoh, L974). The exact process effecting this change is not made clear in these paPers. schroeder (1g75) reported that phytoplankton and zooplanlcton standíng clops decreased in the presence of fish, vrhíle Teoh (1974) reported increased zooplankton abundance and reduced phytoplankton abundance. Schroeder (1975) suggested that increased oxygen concentrations would allor^¡ the pondtosatisfythewasteBODmorereadily,andthathighpHwould improve nutrient removal due to loss of NH, to the atmosphere and the precípitation of PO4 - P. Ho¡.¡ever, no <1ata vüere Presented to substantiate L94. and total these predictions. Removal of BOD, SS' total nítrogen phosphorusinal^IsPhasbeenreportedashígherwhenfishwerePresent (carpentet et ali, than during a similar períod in the absence of fish 1976).However,thecontrolwasnotrunconcurrentlyinthisstudy pond was not taken into and Èhe effects of other organisrns in the presence of fish is account. Although these studies suggest that the benefícialforpondfunction,!trhiteG975)hasdemonstratedthatsize- selectivepredationuponzooplanktonbyfishcanlimittheabilityof phytoplankton. rncreased the zooplankÈon as a whole to cofitrol the of fish to a phytoplankton abundance may result from the introduction I^]SP.ThiswouldobviouslybedetrimenËaltopondfunctionandreduce effluent qual-itY. profound The latter resulË is not surprising in view of the effectsoffishpredationuponaquatíccomnunitiesínnaturalwater bodíes.Intensefishpredationgenerallyeliminateslargerspeciesor animals (e'g' size classes of zooplankton, thereby favouring smaller Archibald,lgT5;DeBernardíandGuissani,lgT5;Hillbricht-Ilkowska 1967; Grygierek et a7" L966; and tr^Ieglenska, I973; Galbraith ' Straskrabarlg65;BrooksandDodson'L965;I{rbaceketa7"1961)'The of smaller specíes uay abundance, biomass, fecundity, and production 1975; Ilillbricht-rlkowska íncrease ín Èhe presence of fish (Archibald, and Dodson (1965) originally and I,{eglenska, lg73). Although Brooks suggestedthattheabsenceofsmallerspeciesofzooplanktonínthe presenceoflargerspecieswastheresultofcompetitivedisplacement advantage is (that is, the size-efficiency hypothesis) ' competitive Both vertebrate and determíned by many factors (see Chaptet 4) ' invertebratepredationareimPortantinstructuringzooplankton fBrien a-2 L979; Zatet' 1975) comnunities (Lynch , lgTg; O eÈ " ' Nevertheless,theeffectofplanktivorousfishuponphytoplankton elsewhere populations observed by I'tlhite (1g75) has been described 195. (Anderson et a7., I97B Hurl-bert et a.I., 1972). Benthivorous fish nayalsoíncreasephytoplanktonpopulationsduetoÏegeneratíonof phosphorus from the sediments (Lamarra, 1975) ' Thus' the benefits of fish for IntSP functi-on seem far from cl-ear' Fish rnay represent a significant. nutrient pool Ín some natural h¡aters. Kitchell et a-2. (1975) have shown that over half the total epilimnetic standing croP of phosphorus may be contained ín fish biomass slowly under some circumsËances. This phosphorus store is remine'raLLzed may maíntain compared to invertebrate consumers, and consequently, fish (Kítchell a large reservoir of nutrienÈs throughout an annual cycle et a7., lg7g, Lg75). A large part of the phosphorus contained in fish to rapid biomass is bound in bones and scales and is, thus, resisÈent represent degradatíon (Kitchell et af., L975). The harvesÈ of fish may apotentiallyusefulpathwayfornutrientremova].from}lSPs. Theeffectsoffishintroductíonuponpondfunctionarrd effluentquality!/erestudiedatGumeracha.Theinfluenceofan omnivore, Carassius autatus, on planktonic communíties and water by the annual chemistr:y vrere monitored. The nutrient pool represented netproductionof,C.auratus\¡IascomParedwithannualpondnutríent retention to determine the usefulness of fish harvest for nuÈrient the value removal . In Ëhis manner, an aÈtempt \^IaS made to evaluate of usíng of fish as a tool for the management of ltrSPs ' The advantages fish for pond management, should this prove effective, are obvíous' Fish are long-Iived and relatively easily harvested. Ponds can be restocked with fish of any size aE any desired density immediately as after followíng harvest. Thus, pond efficiency rtould not declifle' a1low for bypassing macrophyte or zooplankton harvest, and extra ponds to would not be required" 196. 5.2 Methods 5.2.r Enclosures and Experimen tal Desisn. The effecËs of c. auratus on pond function and effluent quality vüere investigated usíng an enclosure technique. That is, fish were introduced into effects enclosures constructed within the poncls at Gumeracha, and the were upon the chemisÈry and biology of hTateÏ within the enclosures moniÈored. Enclosureshadtobelargeenoughtotakeareasonablenumber of fish, but \^rithin the límits of Èhe projectts resources' optirnal (approx. g stocking rate for the rapid growËh of fingerlings 20-100 liveweighË,appÏox.5-l5cmstandardlength)ofmanyspeeies,íncluding ís about c. auratus, in shallow ponds under intensive culture conditions t. I975; 1 fish/m- pond surface (after Krishnamoorthi et aJ., I975; Noble, Reich, I975; Bardach et aI., 1972; Nambíar, L97o; Ilickling, 1968' 1962; Swíngle, 1968; Vaas-Van Oven, 1957; Lin' 1955)' It was surface area decided that a diameter of 4.5 m would give a suffícient , (16rn.).Enclosures(Fig.5.1)werecirculartoavoidcornereffects' The ends of and construcËed of heawy (010) black plastic sheetiDg' the top and 14.5 m lengths of plastic v/ere overlapped and heat-welded; 15 cm ancl heat- boÈtom of the plastic sheeting were folded over about this gave a wide, welded Èo form envelopes. llhen finally constructed at the top shallow cylinder (approx. 4.5 nr diameter:) 1.3 rn tall, open A nylon rope !/as and bottom. Fish thus had access to the sediments. and run around the circumference of each enclosure in the top envelope pond bottom' I m lengths attached to 1.8 mwooden stakes driven into the around Ëhe of I cm diameter steel reinforcíng rod were placed círcumferenceofeachenclosureinthebottomenvelopetosink enclosures firml.y inËo the sedjments' Signíficantqualitativeandquantitativechangesinplanktonic wate-r i's communities and \,zater chemistry may occur r¡hen standing .5n l;3 m I FIGIIRE 5.1 Experinental fish enclosure design Enclosures Pond 2 Siphons Enclosures Pond 1 Siphons Humus tank FIGURE 5.2 ExPerimental desÍgn r97. enclosed (Smyly, Lg76; Lack and Lund,1974; Lund, L972). These changes arise as a result of the prevention of nutrient renelíal- To avoid these effects and to make the sítuation v¡ithin enclosures comparable to a functional I^ISP, a flow-through sítuation was produced in each enclosure. A 16 cm square window \nras cut into the side of each enclosure (just below the water level) and covered with I crr plastic mesh. The Gumeracha ponds are gravity fed; siphons (1 cm diameter plastic hose) ü/ere run from Ëhe pond 1 ínfluent sump inÈo each enclosure in pond I and from pond 1 into each enclosure in pond 2. The rate of flow through the siphons gave a retention time within enclosures that r,¡as similar to retention tíme of the ponds. Retention times in pond 2 enclosures \^rere s1-ightly lower than in pond 1 due to a greater head of $/ater from pond I to Pond 2- Four enclosures \¡rere constructed ín each pond: 3 experimental (p1us físh) and I control (no fish). To examine the effect of fish densiÈy, and therefore to determine optimal stocking rate, experimental enclosures \rere stocked at rates of 0.5 fish/rn2 (B/enclosure), I firs]n/t? (16/enclosure), and Z físh/m2 (32/encLosure). The overall experimental design is shown in Figure 5.2. To prevent the access of predatory r^rater birds into enclosures, floating covers hrere constructed of.2.5 cm stretched mesh fish netting saddle-sÈítched to circular frames'of plastic hose and bouyed by polystyrene floaÈs. Dense growths of stigeocTonium sp. and uTothrix sp' formed on some of the floating covers ín Ju1-y, 1978. These growths had signif icant eff ects uPoll !,Iater temPerature and dissolved oxygen concentration in enclosures (see 2.2.2). Enclosure covers were raísed clear of the v/ater surface after Ju1y, 1978, and algal growth died off' auratus 5 .2.2 Exper imental Fish. several wild populatíons of C. I,rere sampled to find a source of large numbers of suitable and símilar sLzed fish (6-10 cur). All fish usecl ín the experiment r¡/ere collected 198. from the same population. This population was from a smal1 (approx' , Ranges 3OO mz), deep (approx. 3 n) farm dam near Uraídla, Moun¡ Lofty (138" 30150" E, 34" 48' S). The bore-fed darn has clear l^later which is underlain by a gravel and clay substrate. AË the tine of fish collection (February, IgTB) the entire pond bottom \/ülas covered by a dense, submerged stand of vaTTisneria spiraTis. Fish were captured using a cylindrical- trap (12 cn aperture, 1 mn mesh) ' Fish $7ere returned to the laboratory and anaesthetized in 50 pprn 14s222' Each fish was then weighed, measured (standard length), and tagged. Taggíng passed through the rÄras carried out using 5 cm lengths of nichrome wire dorsal musculature between the proximal part of the pterygiophores at the base of the posterior poÏtion of the dorsal fin. A numbered plastic sleeve was slipped onto one protruding end of the r¿ire and the two ends then interlocked. Fish were then placed into an outdoor holding tank (2.2 x 0.5 x 0.7 rn) and fed rrAqua-Lab Supreme" fish pe1-lets. Fish were left in the tank for several days to determine whether severe handling effects or tag loss occurred. All fish recovered from handling and only 2 of the LI2 tagged fish dropped tags ' At the termination of the field experiment' recaptured fish showed no ill effects from tagging. No r^rounds or fungal infections were observed around the point of wire entry. Animals that had dropped fish tags showed only minor, localised scale damage. 227. of recaptuled and tag had dropped tags. Tag ]-oss varies r^líth tag type' fish species, (Laird and attachment siËe, and may be as high as 9O7. in some cases present study scott , Ig78). The system of tagging employed duríng the $ras reasonablY effecÈive. and biomass 5.2.3 Exper imental Procedure. The stocking density ofc.auratusineachenclosureisshowninTable5.l.Aconcerted effortwasmadetoensureEhataslmilarsizerangeoffÍshwas introduced to each enclosure. Fish were introduced to pond 1 enclosures Table 5.1 Stocking density and biomass (g) of C- auratus in enclosures at Gr:meracha POND 1 POND 2 Standard length(cn) weight (e) Stocking Standard length (cn) Weight (g) Stocking Stocking biomass biomass Enclosure (e) density Mean Range Mean Range (e) Mean Range Mean Range 22-84 268 8.6 6 .4-L2.5 24 2 10-64 193 E I 8 10 7 B. s-14 .3 44.8 L6 1 10-50 242 Ez t6 9 2 7 .6-L2.2 25.2 t3-49 403 7.4 6 .0-12 .0 I6 2 B-59 519 E 32 I 3 6.7-13 .1 20.3 9-63 668 7"3 5.5-12.4 .] E No fish 4 * Control- t99. on 6 March, Lg78, and to pond 2 enclosures on 13 March' 1978. The experiment üras terminated on 27 Septernber, 1978. Fortnightly measurements of l^Iater temperåture and disSolved oxygen concenÈration were made (as in 2.2.I) at the surface and successive 10 cm depth intervals in each enclosure. A 1200 m.l, water sample was also Èaken from the surface of each enclosure and the following parameters PO4-P' determined as Ín 2.2.1: PH, ss, toÈal (unfil-tered) BOD, solubLe total oxidized nitrogen (No¡ + No2 ), TC, TOC and TIC' 600 nl, surface vlateI samples r¡ere taken fortnightly (after filtration through 150 pm zooplankton mesh). chlorophyll a 'h/as determíned as in 3.2.I, and aLgaL ceIl density deÈermined as t-n 3'2'2' A slngle sample of the zooplankton of each enclosure was taken fortnightly with the tube sampler (see 4.2.1). An attempt was made to the homogenize Èhe zooplankÈon within each enclosuÏe' príor to taking varíous sample, by moving the sides of the enclosure back and forth aÈ points around íts círcumference' The major zooplankter in all enclosures vras D. carinata. The numerical density of that species in female enclosures \^7as determined as in 4.2.L. The percenÈage of adult D. carinata in reproductive condition, and the length-frequency distribution (plus mean length of adulÈs) in enclosures \¡/as determined as ín 4 .3.l. 1 and 4 .3 .L .2. The original experimental design called for ruonthly recapture of fish to determíne growth rates. Several methods were employed during the course of the experiment in an attempt to recapture fish' These included electro-shocking, físh traps, and seine netting' No fish rn'ere recaptured from any enclosure using these methods. It was later (a discovered that the wave-form generaÈed by the electro-shocker at cybertronic Mark 12 S) was entirely inappropriate for the condítíons TDS) Half-pulsed Gumeracha (still, fairly turbid \^/ater of moderate ' direct currenË (or half-r¡/ave ïectífied alternating current) would have 200 been most suitable under those conditions (after Helawell, 1978; Vincent, L}TI). The experiment $/as t.erminated on 27 September' L978, by applying "Pro-Noxfishrr (active constituent rotenone' 2.5% WIV) Èo each enclosure at a rate of 10 ppm (dose strength from F. Reynoldst N.S.I^I. State Fisheries, pers. colnn. , L97B). Potassium perrnanganate was added to each enclosure at the same rate (10 ppm) approximately l- hour after treatment to neutralise the rotenone. Fish reËurns from the enclosures are sho\^lll in Table 5.2. Additionally, dead fish were reËríeved from some enclosures on 11 October, 1978, as follows: pond 1 enclosure 2: I fish, enclosure 3: 10 físh; pond 2, enclosure 2: 1 fish, enclosure 3: I fish. It was concluded that fish not recaptuïed either died during the experiment or escaped from the bottom of encl_osures due to an imperfect seal with the sedinenÈs. , Recaptured fish were treated as follows. SÈandard length (c¡n) was measured on all fish, and 6 large' syrmetTical scales removed from the left síde of the body between the l-ateral line and the anterior half of the dorsal fin (after Tesch, 1968). Scales \fere cleaned and examined microscopically usíng transmítted líght; annuli were determined after Tesch (1968). Live weight (g) was measured on fish collected on 27 September. The dígestíve trac.ts of those animals were removed and representative samples of materitl- ftot the fore and hind gut examined microscopically. This material was analysed semi- quantítatively using the points method (after Hynes, 1950). 5.3 Results Due to the death or escape of fÍsh from some encl-osures the effect of varying fish density on pond functíon could not be determíned' The effects of C. autatus could, in some measure, be gauged from a comparison of physico-chemical alld biological conditions in enclosure 2 with conditions in the control enclosure in pond I " In the following sections t'controltr refers only to the control enclosure in pond 1 and Table 5.2 Returns of C. auratus from experimental enclosures ín Lhe Gumeracha ponds ot 27 September, 1978, afLer treatment with rotenone POND 1. Stocking Enclosure density Recaptured Recaptured Tagged I untaggea Tagged Untagged 8 I 1 E I Ez 16 10 4 1 El 32 1 20L. ttfísh" refers only to enclosure 2 in pond 1. 5.3.1 Physíco-Chemical Charac teristics in Enclosures. Depth- averaged lrrater temperature ("C) and dissolved oxygen concentration (mg/ø) in fish and control enclosures are shown Ín Figure 5.3. Variation in both ParameËers T¡las similar to that ín the pond proper duríng the same períod (Fig. 2.6). Dissolved oxygen concentration was high at the start of the experiment (> 15 mg/g) but declined markedly in both enclosures during Apri1, 1978. Dissolved oxygen concentration was l-or¿ (< 2 rrg/L) ín May, íncreased steadily from June to rnid-September, and then increa.sed markedly in early October. There rnras no signíficant difference between (20-30 ffLg/9,) at rhe start of the experiment, declined markedly during laÈe April, and remaj-ned at low, fairly constant concentrations thereafter (< 5 ntg/p"). SS ín both enclosures followed a símílar pattern to total BOD: SS was high at Èhe start of the expeÏiment (> 80 mg/[), declined during Apr:il, and remained low thereafter (approx. S-10 mg/¿) ' Varíatíon in pH, BOD and SS in boÈh enclosures \^tas similar to variatíon ín those parameters in the pond proper during the same period (Figs. 2.I5-2.17). There \^ras no sígnif icant diff erence between pH' BOD or ss in fish and control enclosures (Mann-tr^lhitney u test, p > 0.05). Variation ín soluble POO - P and total oxidized nitrogen in fish and control enclosures ís shown in Figure 5.7 . Sol-uble P04 - P was low in both enclosures at the start of the experiment (< 2 mg/L), rrl H o Dissolved oxygen concentration (mg/1,) Temperature (oC) F H o tJr 5 l¡l o\ oo o È. o\ æ l¡ (, OUoo ÞE o5O(-r 3lrtÞ F1 < rrHÞo Þ P. 0j I o0a I 3lD I o" P. !< 0l Hrr1 H.O FI ØH ts. É rT oL{ H 1g ^\O ¡úlo ocoË{ i/H 5 Þ ñ. ;J rl ÞJ rt I U) I O.B I o oo0) Þ r.to, ñoo. HP. U) ^íJlO lH ah v(Dt< o. Þoo oXH< o oooûa ÉJ d o Ø L2 t0 A B 6 FIGiIRE 5.4 pH of waÈer in fÍsh (-) and control e--) enclosures. ( ) 30 o¡ 20 , I o0 É oÊ rq r-{ d ¡J o 10 H I 0 M A MJ J A S 197 B Tirne (nonths) FIGURE 5.5 Total BOD of vlater in fish enclosufes. -1 BO '60 èì ö0 É v) 40 v) 20 0 M A MJJ A S T97 B Tine (months) FIGIIRE 5.6 SS concentration in f ish (--) and control (-- -) enclosures. L2 cl t Ò0 , É , , .t) a ¡r o I .ËÊ Ø o I ,-dÈ I a) {J d Ê tJ) o .d À o 4 .c ]J , o¡r I \, 0 t\ , , , I oì 30 ô0 E Ë o 00 o u Ð .r{ É .d 20 o N .rl 'ú .rl J oX 10 M AMJJ A S T97B Tirne (months) FIGURE 5.7 Total orthophosphate-phos¡;horus and oxidized nitrogen concentration in f ish (-) and control (---) enclosures. 202. increased markedly during April and May (reachíng a peak of II-I4 ng/ 9. Ín late May), but declíned steadily thereafter. There lüas no significant dífference between soluble POO - P concentration ín fish and control- encl-osures (Mann-WhiÈney U test' p > 0.05). Total oxidized nit.rogen in both enclosures \¡7as also low at the start of the experiment and increased during May. Total oxidized nitrogen in both enclosures reached a peak ín late May (30-35 rrLC/9') but decreased somewhat thereafter. There was no significant clifference between total. oxidízed nitrogen concentratíon in fish and control enclosures (Mann-I^Ihitney U testr p > 0.05) . Variation in TOC and TIC in fish and control enclosures is shown in Figure 5.8. TOC was fairly high ín both enclosuTes (approx. 50 mg/Î.) at the sËart of the experiment buL decreased markedly in April- TIC r¿as 1ow in both enclosures (< 5 rng/!,) at the staÏÈ of the experiment, increased to a peak in late April (approx. 38-40 mg/L), but cleclined thereafter. There \^ras no sígnifícant difference between > TOC or TIC in fish and control encl-osures (Mann-tÙhitney U testr P 0.05). That is, physico-chemical conditions ín enclosures l¡/ere similar to those in pond I proper and enclosures therefore replicaÈed the pond situation fairly accurately. At a stockíng rate of I físh/m2, C. au¡¿tus had no significant effect upon physico-chemical conditíons within enclosures. 5 .3.2 Phytoplankton in Encl0sures. varíatíon in the concentration of active chlorophyll a (*g/*3) in fish and control enclosures is shown in Fígure 5.9. The experiment corunenced during a phytoplankton bloom Ín pond I and, consequently, chlorophyll a concentratíon was hígh 2 (> 700 *g/rJ) in both enclosures. Chlorophyll a concentration declined markedly to very low levels (. 10 rg/*3) in late April, and remaíned low until termination of the experiment. There \¡Ias no significant difference betweerr Chlorophyll a concentrations in fish and control enclosures 60 tl ol I I Èo so I ¡ t É o I ,o H+o o o .r{ Ë 3o¡o t{ o 'lSzo o H 10 ^40oì ò0 Ë ç 30 o ..o tJ (ú o o 20 .r{ Ê (Ú ô0 }{olO Ê 'r{ F{ d Ë0 H ìf A MJ J A T97B Time (¡nonths) FIGIIRB 5. 8 Total organic carbon and total inorganic carbon concentration in fish (-¡ and control (---) enclosures. 800 I I I I t t t 600 I I I ca I E I ò0 I I Ê t I ß I I F{ 400 I FI I h t I .g I È I I o I I ¡{ o I I f-'{ I , ,c I I (J I I I I I 200 t I I I I , I 0 M A MJJ A S o r97 I Time (months) FIGI]RE 5.9 Active chlorophyll a concentration in físh (:-) and control (---) enclosures. 203. (Mann-lJhiÈney u tesÈ, p > 0.05). variation in chlorophyll a concentrations in enclosures lras very similar to variation ín chlorophyll a in the poncl pïoper during the same period (Fig' 3.2). The composítion of the phytoplankton wiLhin enclosures $ras similar to that in the pond proper during Èhe same Period. The bloom at the start of the experiment was composed mainly of S. opoTiensis, s. quadricancla, s. acutifo¡mjs and s. acuminatus. During periods of lor,¡er temperatures and low chlorophyll a concentrations díatoms, mainly Nitzschia sp., Navicula sp., cgmbeTla sp. and Diatoma sp., predominated. variation in total cell density ín fish and control enclosures is shown in Figure 5.10. Total cel1 density was high in both enclosures at the sËart of the experiment (rvhen chlorophyll a concentration was hígh) but decreased during April as the phytoplankton bloom declined. Although some variation occurred between cell densitíes in enclosures in May, total density was not signifícantly different in the fish and control enclosure (Mann-Ifhitney U test, p > 0.05). Variatíon in Scenede,smus species composition in fish and control enclosures is shown in Figure 5.11. Species succession in both enclosures $Ias similar, and the same as that observed ín the pond propeï during the same period (Fig. 3.5). c. auratus had no sígnifícarrt effect upon chlorophyll a concentration or phytoplankton specíes comPosítion in the experímental enclosure. The variation ín chemistry of enclosures \l7as the result of variation in the standing crop of phytoplankton. The decrease ifi díssolved oxygen concentration, pI{, BOD and SS during the course of the experíment was clue to the decline of phyÈoplankton standing crop in April. Soluble POO-P and total oxidÍzed nitrogen were low at the start of the experiment due, to incorpoÏation into algal cel1s. Nuti:ienË r:emoval. decreasecl as the phytoplankton stalrding crop declined" Físh Control 10000 10000 t t I a t , I t oì , I I t I è¡ I I o 100 0 1000 , I E ¡ ¡ I ¡-.¡ I .¡ I ÚJ ¡ à li ¡ IJ c.J 'rl I q !" I l.i -t É I -l Ea.) I ¡ CJ 1 Li o Fl I I I Fl I F.{ I 0.) cd I (J ¡ +J I 100 i 'l o I I 100 I H -ì I I I I I I It I rt I I l I i I t I I I , I I I l I I I I I , t I I I I I I I I I l I I I I I l I I I I I l I , I I I I I I t I I I I I I I I I I I I l 10 10 MAMJ MAM JM A MJ TÍme (rnonths) Time (nonths) FIGURE 5.10 Total algal cell density in fish (-) FIGIIRE 5.11 Successlon of scenedesmus species in fish and control G--) enclosures. and control enclosures. S - opnTiensis (-) , S quadricaudra (---, acuÈ iformis (""") . , s. ' ,5 . ecumina t ¿¡s (-. -) . 204. Qualitatively and quantitativel-y, the phytoplankton population $Tithin the enclosures resembled that in the pond proper. That is, no significant alteration of the phytoplankton occurred due to enclosure effects. 5.3.3 Zoop lankton ín Enclosures. Variat.ion ín the density of Ð. carinata in the fish and control enclosures is shor¿n ín Figure 5.12. In both enclosures, D. carinata populations developed from the hatching of ephippial eggs in early April. Population density increased markedl-y during late April. The D. catinata populaÈion in the fish peaks one ín late April (298/ L) and one enclosure showed two densíÈy ' in early June (625/9,) after a mar:ked population decline. Population densíty in the control enclosure increased rnore rapidly Ëhan in the fish enclosure but showed only a single peak (42819") in May. Population density ín both enclosures declined steadily from June until mid- September. Thereafter, populations rapidly disappeared from both enclosures. There \^ras no significant dif f erence between the densíty of o. catinata in the físh and control enclosures (Mann-I,tlhitney U testr p > 0.05). Non-sígníficant correlationsT¡/ere found between the density of D. carinata and ch1-orophyll a concentraÈion in the fish (Spearmants p = -0.43r P > 0.05) and control (Spearmants p = -O,22r P > 0.05) enclosures' The length-frequency dístributíon of D. calinata ín both enclosures is shown in Figure 5.13. The proportion of post-embryonie individuals in dj-fferent size classes varied throughout the experiment. However, no consistent trend emerged with respect to síze distribution in the físh enclosure. That is, the populatíon length distribution was not skewed torqards smaller indíviduaIs, and D. catinata greater: than 2 rnm in body length were recorded in Ehe presence of C. autatus throughout the experiment. Variation in the mean body length of 1000 tr,-_ì t I I I t I I I t t I 'r.' t I , 100 I ) I , , t èl I I ì , o I Ë I I >. I {J I \ .r.{ I t o I I oÉ I â I I I I t I I IO t I I I I I I 1 MA M JJ AS o 197 B Time (months) (-) and control (---) FIGURX 5.12 DensiEy of D. catinata in f ish enclosures ' Fish Control 13q.æ Z.t+.79 n,\,78 t0.5.n 10.5.78 a,5.'n 2+.5.78 t-t 6.6,78- l- L-r.21,6.æ L.6.78 t--Ë. I- t9.7.78 L.-Ë. 13.9,ß L 13.9,æ r2345 67I9 r23 4567 B9 I I 2.1nm 2.r lnm Size class of D' carinata in fish FTGTJRB 5.13 Lengtlr-frequency distríbution and contr:ol enclosul:es ' 205. D. carinata in both enclosures is shown in Figure 5.I4. Apart from an initial peak in body length in the control enclosure, the range and patÊern of variatj.on in mean body length was similar in both encl-osures. There \^ras no significant difference between mean body length Ín the fish and control enclosures (Mann-Itlhitney U testr P > 0.05). 'fhus, predation by c. auratus upon D. carinata díd not appear to be íntense, and, if it occurred at all, v/as not size-selective. Variation in the Percentage of ovigerous and ephippíal adult female D. carinata in both enclosures is shown ín Fígure 5.15. Although there I^ras no signifícant difference between the Percentage of ovigerous females in the fish and control enclosures (Mann-Itlhitney U testt p>0.05),thepercentager¿asoftenlornrerínthefishenclosure. There was no signifícant difference between the PercenÈage of ephippial females ín both enclosures (Mann-trrrhitney U testr P > 0.05), although the percenÈage hras often higher ín the fish enclosure. This suggests Èhat the presence of fish may have made conditions unfavourable for D. carinata, but indicates that C. auratus did not prey selectively upon the darker ephíppial females. Although not studied íntensívely, Èhe preselce of físh appeared Ëo have no major effect upon the external morphology of D. carinata. That is, no narked formation of helmets or oËher carapace proÈuberances v/as observed. Thus, C. auratus did not exert sígnificant trophic effects upon the zooplankton or phytoplanktonic cormnunities in the experimental enclosure. At a stocking rate of 1 fish /^2, C. auratus had no significant effecÈ upon pond function and, therefore' upon effluent qual-iËy. 5.3.4 Fish Growth and Production in Enclosures. Al-1 fish recaptured, on 27 September, L978, Ieere in reprocluctive coDdition. Testes of male fj-sh were large, pinkish in colour, and equivalent to (on average) 5.97. of. total li.,re weight (t standard error e-quivalent to e I t ¡ ¡ I I I I I 3.5 I I E I I .-d I +J t ö0 I É I q) ¡ r{ t- I >' I 'd rl- o p o Ë (ú 3 0 tc) \ \ tr¡ 2 5 A M J JA S o r97 I Time (roonths) FIGIIRB 5. 14 Mean body length of n" carinata in fish (g-f ) and control (tr--tr) enclosures. Frl H 6) F L¡J Percentage ovigerous Percentage ephipplal \JI 1..) N Or æ N) 5 o\ æ ts O O O O O o O o O (Jl OE 'd rD !¡.Fr P.O E5'do H.ñ ûJ 0) 0q P.O Þ Hì Hr o0,ts. 5o- HB ats H. lrr á lo o Éro ÞQ O \.1 Éor É coq I g, FJ 11 Ì-. o5 U) O0r 5cl rr 0J C{ ñoo Pg) 1qH lF. Þ rJ \, OO oo Þoa ooa v) H cf) cDoÉH H o v) 206. l|:l of the mean) " Ovaries of female fish distended the body cavíty (egg" r^rere orange in colouration and clearly vísible) and were (on average) equivalent to 21.9% of. total live weight (t standard error equívalent to I27" of the mean). Although the gonads of cypriníds may develop gradually during winter, final ripening occurs 10 to 15 days prior to spawníng (Nikolsky, 1963). Mean depth-averaged temperature duríng the fortnight prior to the recapture of C. auratus at Gumeracha \¡ras 12.5"C. Thus, physico-chemical conditions and food levels in pond 1' 1nrere apparently suiLable for the survival and reproduction of C' auratus' Recaptured fish exhibited marked weighÈ gains and increases in length. The mean lengËh of fish recaptured from pond I - enclostre 2 was 11.7 cm (range 10.5 to 14,2 cm), and the mean rveight of fish was 66.4 g (range 43-128 g). Total recaptured biomass was 929 g (including weighr of gonads). fne meaì length of fish recaptured from pond 1 - enclosure 3 was 11.9 cn (range 10.9 to 13.7 cm). The mean weight and mean length of fish recaptured from pond 1 - enclosure 2 were significanËly greater than mean weíght and length when introduced (Mann-I{hitney U test, p < 0.05). The mean length of fish recaptuled from pond 1 - enclosure 3 was sígnificantly greateÏ than when introduced (Mann-l^Ihítney U test' P < 0.05). Examinatíon of the scales of Ïecaptured fish revealed an apparenf- change ín the spacing of circuli after introduction to the pond at Gumeracha. Two growth patterns were evident. In the first, a transition occurred from a region of more closely spaced circulí to a regj-on of rnore widely spaced circuli hTith no cutting over. That is, a annual change in growth had occurred but this r,ras not the same as an growth check. In the second pattern, a tlansitíon occurred from a regíon of wídely spaced circuli to another region of wíde1-y spaced círculi rvíth a grorvth checlc. Fish were íntroduce-cl at Gumeracha just prior to a decrease in water temperature. Thus, a transitíon from a 207 . surtrner gro\¡/th pattern (widely spaced círculí) to a slower, wínter growth pattern (closely spaced circuli) after a growth check rnrould have been expected. TransitÍon from rapid sumnner growth to another period of rapid growÈh, despite reduced water ËemPerature' appeared to have occurred after the íntroduction of. C. autatus at Gumeracha. For compaïative purposes the growth of C. auratus ¡^ras studied in the Uraidla population and in populaEions frorn ì4í1lbrook Reservoir, and a shallow back\^rater of the River Murray at Cobdogla (see Mitchell' LgTg*). Age r¡as determined from scale readings and gro\¡/th deterrn-ined from the back-calculation of length at the time of formation of successive- annuli using the modified direct proportionality formula (chugunova, I97O; Tesch, 1968) . Significant differences in length- weight relationships and grovrth rates occurred between popul-ations. FÍsh from Uraidla gre\^r at the slowest rate of all popul-ations studied. The time of recapture of C. autatus from Gumeracha would have corresponded to the period of annulus formation. The length and weight of recaptured fish hlas assumed to represent size at the end of the yearts growth. The mean length (plus 95% confidence lirnits) of recaptured C. auratus has been plotted agaínst age, and compared with back-calculated growth hisLory of other populations (including that at Uraidla) from South Australía in Figure 5.16. The growth rate of C. auratus in the Gumeracha pond increased appreciably above that of the Uraidla population, that is, the population from which anímals were origína11y collected. Mean live weight (minus gonad weight) of recaptured f ish has.been plotted agaínSt age and compared r^7ith \^Teight versus age data for the Uraidla and Cobdogla populations (calculated from growth curves and length-weight relationships in Mitchell, 1979) in *This paper is presented in Appenclix 3. -T a--' -l'-' 30 ' --cl 'J" 'ù"' o-' -1---'rn__-+-- i----.-'--E -'-u ,'! E" É o I 'f/ I 20 T '.É{J t-L òt) É , 0) Fl lrt I I o t ,J_ t 10 , _--L I 0 0 2 46 B 10 Age (years) FIGIIRE 5.16 Growth of C. auratus in the Gumeracha pond (^) compared wíth growth at Uraidla (A), Cobdogla (E)' and in Millbrook Reservoir: ( f ). 208. Figure 5.17. Live weight of C. auratu.s at a given age (above the second year of life) increased markedly after íntroduction to the Gumeracha pond. The daily net production of. c. auratus (g live weight/m2 /day) Ín pond I - enclosure 2 during the course of the experiment was calculated from Recovered Biomass (e) - Initial (Stockins) Biomass (e) Area (ur2¡ . Time (days) The weight of gonads was included in recovered bíomass as suggested by Chapman (L967). The duration of the experiment \¡/as 204 days. Dail-y net production of C. auratus during the experiment was 0.16 g live , weíght/m'/day. If this rate of production had been maintained throughout the year, annual net production would have been 58.4 g live ) weight/m'/year. Fish growth is directly proportional to food íntake and assimilation above maintenance requirements (Nikolsky, 1963; Brown, Ig57). Oxygen consumptíon (a measure of standard rnetabolisrn) of C. auratus increases by a factor of 2 fot each 10oC increase in hrater tempeïature up to 30"C (Beamísh and Mookherjii, 1964; Fry and Hart, 1943). Thus, food intake and growth rate of C. auratus woul-d have íncreased as maintenance requirements increased in response to higher temperatures. Annual productíon of C. auratus, íncluding periods of surnmer growth, would probably have been slightly higher than the above figure, provided food levels were adequate to meet and exceed mainLenance r equire-ments . Had the annual rate of net production of C. auratus in pond 1 - enclosure 2 been uaíntained in the pond proper, total annual net production in pond I r¡ould have been 84 kg live weight. The nutrient content of C. auratus tissue \,/as not determined duríng the present study. The nutrient content of freshr¿ater fishes varies with food quality and quantity (Papoutsoglou and Papapararskeua-PaPÒutsoglou , l97B) 3 hd H LÍve weight (e) Cj d o\ 0o o N) 5 O O frl o O O o (¡l o ts I \¡ I I I $TJ F t 50H. I o.5 < I Èo I c) o a{ ì R Í¡P.voQ oc:'o ÞoHO.'f 3< \ \ aE O \ \ >H \ vo ã \ . ÊtDÉ Þ 0a {o¡ o N) Þ- H' 0a rtO \ HI \ oo 0l .H H \ o ùoË. \ \ 0r 0r rtË \ c r'l -Þ hù (/) at I FhË I ñh I o I g Fr, H I do I F.|Ë I 0) P'11 I o-:t I FO Êr s Þ 6) AL >Ë vd 0t o Þ 209. total niErogen conLent of freshwater fishes ranges from 2.2 to 3.67" of liveweight and total phosphorus content from 0.3 to 0.8% live weight (calculated from Papoutsoglou and Papapararskeua-Papoutsoglou, I97 B, assunlng ËhaÈ proteín content is equivalenË to TKN x 6.25: same authors; Bu1l and Mackay, L976; calculated from C'oodyear and Boyd, L972, assuming that dry weight is equivalent to 207. of live weight: Lagler et a7., 1962, p,170). The studies quoted analysed whole fish' and therefore included bones an C. auzatus may have been slightly higher than these values. Total annual net production of C. auratus in pond I (as determined above) represented a nutrient store equivalent to O.277" of total nitrogen (tXU + NO3-) and 1 .02% of Èotal t04 - P retaíned in pond 1 during 1977. Harvest of C. auratus would not have removed a sígnificant Proportion of the nutrients retained in the pond annually. At the production rate exlaÍbíted in enclosure 2, fish harvesË did not represent a useful pathway for nutrient removal from the Gumeracha pond. Food items found in the intestines of C. auratus recaptured on 27 September, I978, included D. catinata, Afoneffa sP., ü. Ieuckarti, C. assìmiJrs, larval and adult chíronomids, fragments of. Scenedesmus cells and filamentotrs a1gae, diatoms (NavicuTa sp., Nitzschia sp., CgnbeTia sp., CgcToteTl-a sp., Amphora sp.) and detritus. The mean peïcentage of estimated volume of major food iteurs in ::ecaptured físh is shown in Figure 5.18. The dominant food items r^Iere D. carinata and detritus. Benthic or:ganisms, that is ostracods and chydorids' \,/ere the nexË most abundant food items. C. autatus ín the experr'-mental enclosure appeared to have been ingesting the sediments. Although D. carinata formed a large proPortíon of the food in C. auratus, f{ H 6) ã td v Percentage estimated volume H N) U) Þ. @ o oH o o o 6)c)Ëo o€a3 Flo D. carinata oP-Þúl !].f-t Ê¡ F. o !Þ A7one77a sp. Þoo O. Hr 0qç rl C. assimiTis o o Þ ct o Þ fragments rt Crustacean (/) o Ht tsrl o Larva o o o. 0, Chironomídae Ë H. H at 0r o ñ- 9 Adult Ë (/l U o Dytiscidae d o o Ërl pJ Filanentous algae 0q o o 6 rt P. Diatoms É 0¡rt o Ê. o DetriÈus H É ã o H¡ d o É rt o 2r0. ingestío¡ \¡ras not size-selective. As D. carinata foraged amongst the sedÍments when phytoplankton standing crops were low, it is likely that the O. carinata ín Ëhe ínÈestines of C. autatus were ingested íncídentally with the sediments. That is, C. auratus did not activåly prey upon D. carinata. 5,4 Díscussion c. auratus r^ras able to survive, make apprecíable weight gains, and reach spawning eondition in pond I at Gumeracha. The success of spawning would have been determíned by the availability of suitable spawning siËes and the occurrence of favourable physico-chemj-cal condítions for egg develoPment. . C. auratus is a phytophil and deposits its eggs on submerged aquatíc vegeËation or ori recently inundated terrestríal vegetation (Balon, 1975; Kukuradze and Mariyash, 1975) ' The species never lays its egg on the bottom. Spawning success at Gumeracha would, therefore, have depended upon the Pïesence of P. ochteatus. The provísíon of spawning sites is an indirect benefit of the presence of submerged macrophytes in tr^lSPs. I^trater tempelature and dissolved oxygen concenÈratíon are important factors affecting the development of fish eggs (Bagenal and Braum, 197S). Although Phytophils are generally (Balon, I975) oxygen levels at adapted to low oxyge-n concentraÈions ' Gumeracha after the decline of phytoplankton blooms could have been detrimental to egg survival or development. GrowÈh and production of C. auratus in pond I were determined from small sample sizes (n = 31 and n = 14 respectively) and must be regarded as tentative. However, growth rate of C. autatus from Uraidla increasecl after intr:oduction to the Gumeracha pond. The Uraidla population extribited the lowest grorvth rate of the natural populations studied (l,titchell , 1979), This appeared not to be due to temperature differences but may have reflected genetically deLermined varietal difference-s (c.f . Kukuradze aD.d Mariyash, I975). Growth rates of ztl. C. auratus at Gumeracha may have been more pronounced had fish from other populatiolts been introduced. Taggíng may affect the growth rate of fislr (Jones, 1977) and ideally, growth rates of tagged and untagged. físh should be compared. It is possible that the taggíng procedure may have retarded the growth of C. autatus at Gumeracha to sone degree. Study of the scales of C. auraËus from Gumeracha indicated that growth had increased after introductíon to pond 1. A typical winter gro\^rÈh pattern Inlas not apparent. Although seasonal changes in growth of fish correlate with Ëemperature varíatj-on and temperature influences maíntenance requirements and appetite (Brown, 1957), growth rate is also significantly influenced by food level. Variation in Ëhe wídth of scale circuli spacing appears to deperrd primarily on food availability (Silton and Robíns, I97I; Wingfield, L94O; Bhatia' 1931) and, if food is superabundant, seasonal periodicity in the spacing of scale circuli need not occur (Gray and Senta, 1931). Increased food availability in the Gumeracha pond (compared to the dam at Uraidla) gave rÍse to a period of rapid gror¡rth despite decreasing water temperature. All fish recaptured from Gumeracha were deep-bodied in appearance and resernbled Balonts (1977) "obeset' forms. These forms only aríse under condítions of extreme food abundance . C. auratus from Millbrook Reservoir, the population with the highest growth rate (Mitchell, 1979), r.¡ere also deep-bodied in apPearance. The annual production of C. auratus at Gumeracha was much hígher than generally recorded for freshwater fish from naÈural water bodíes (approx. 5 to 10 g live rveight/rn2 /yeaÐ (see reviews by laiaters, J.977 GuËreridge, Haskins and Davey, 1976; Le Cren, L972; Chapman, 1967: Brown, Ig57). The rnajor exception to this was the production of I,ítapia and carp in t-ropical ponds (40 to 2OO g live weight/m2 /year) (Brown, Ig57). The annual procluction of C. aurat-us at Gumeracha was generally greater than for fish in unfer:tílized físh ponds (10 to 20 g 212. t líve weíg]nt/m'/year) but similar to that in fertilized ponds (20 to 40 g t live weight/m'/yea'r) (c.f . Gutteridge, Haskins and Davey, 1976; Brown, 1957). The major exception to this was the production of cyprinids in fertilízcd ponds ín Israel and the tropics (> 200 g líve weight/m2 /yeat). The annual- production of C. auratus aÈ Gumeracha was símilar to the production of freshwater fish in some I'lSPs (c.f . Lrrhi-te and Inlilliams, l97B], Noble, Ig75), but lovrer than reported for others (60 to > 200 g live t weíght/ur'/yeax) (c.f. Gutteridge, Haskíns and Davey, 1976). The results of the present study confirm the conclusions of !ühite and l,{illiarns (1978) and Noble (L975) that high fish production can be obtained in hISPs without intensive management or supplement feeding. Operatíng cosLs of I^ISP aquaculture schemes would, therefore, be considerably lower than for conventional físh cul-ture systens. It appeared that C. auratus, at a stocking rate of 1 fish/rn2, had no signifícanÈ infl-uence upon pond function. That is, C. auratus could be cultured ín llSPs without signíficant detrimental effects on effluent qualíty. However, the presence of C. auratus would not improve effluent qualíty . C. autatus did not reduce the grazing pressure of the zoopJ-ankton upon the phytoplankton and so increase aLgaI standíng cïops as ïeporÈed for planktivores in I^lSPs by Ifhite (1975). C. auratus had no significanÈ effect on the density or size dístríbution of. p. catinata at Gumeracha. This conËrasted wÍÈh the findings of Archibald (1975) who reporËed intense selective predation of larger D. pulex by C. auratus of a simiLar size to that used in the present study. C. auratus does not possess a tlue stomach and relative gut lengrh is hígh (shuljak, 1968; Suyehiro, 1942). These features suggest that C. auratus characteristically has a cliet containing large amounÈs of indígesrible narerj-al (Kapoor et aJ", I975; Nikolsky, 1963). The gut contenÈs of C. auratus from Uraidla (l,titcnell , 1979) and Gumeracha indicated that the species ruas de-trítívorous and íngested the sedimenÈs. 2L3. D. carinata appeared to be Íngested incidentally and thís would explaín the lack of size-selectivity and cyclomorphic effects. Archibal-dts (1975) experÍmental design prevented the access of C. autatus to the sediments and may have induced some swítching in feeding behaviour. C. carpio, also a detríËivore, may increase the phytoplankton standing crop by regenerating phosphorus from the sediments and excreting PO4-P (Andersson et al., L97B; Lamarra Jr., 1975). The mode of feedÍng of. C. carpio íncreases the amount of organic maÈerial in suspensíon (Spodniewska, L962) and would be expected to increase BOD and SS. C. autatus apPeared not to exert Èhese effects at Gumeracha. Although C. auratus may íncrease turbidity in some siÈuations (Lake, Lg66) this clid not apPear to be pronounced at Gumeracha. C- auratus uray ingest more of the sediments than C. carpio which resuspends much sedimental material in the l^¡ater coh¡un. Thus, C. autatus appeared to be a more suitable species for culture ín I{SPs Èhan C. catpio which could have a detrimental effect on effluent quality. Although several stocking densitíes were incorporated into the experimental desígn' data have been obtained for only one stocking rate 1t fisn/m2). The effects of. C. autatus on effluent quality may vary at hígher densities. The harvest of c. auratus from the Gumeracha pond did not represenË a sígnificant pathway for nutrient removal" In this respect, the results of the prese-nt study agreed with the findíng of Bul1 and Mackay (1976) that rhe harvest of the total maximal fish yield from eutrophic and oligotrophic lakes ín Canada would have removed less than L% of. phosphorus and nitrogen entering the l-ake annually. Bull and Ifackay compared the nutrienË store represented by fish production with annual nutrient load and not, as in the present study, with annual nuÈrient retention. The nutríent store contaíned in fish pr-oduction in the Canadj-an lakes woul.d, therefore, have represented a somervhat higher peïcentage of annual nutrient retention. 2L4. The usefulness of p1-anktivorous and some deËrítívorous físh for the nånagement of I^ISPs aPpears Èo be doubtful-. Some species, such as C. auraÈus¡ may be cultured in I,trSPs Intithout significant effecËs upon effluent quality. Ilowever, of the specíes of fish tested in I{SPs to date, none have been shor¡n concl-usively to inprove pond function and increase effluent qualiÈy. One group of fÍshes that haver as yet' been unstudied in InlSPs are the phytoplankton fil-teríng cyprinids (e.g. Hg¡nphthalmichthgs molitrix). However, such species are resÈricted to the tropics ancl may be unsuítable for use in Èemperate climates. In any event, their inËroduction and use in non-endemic areas would engender many environmental and legal problems. 2L5. Chapter 6. Concluding Discussion The presenÈ study set out to províde basic informatíon on the ecological- interactíons bet\^Ieen organísms ín maturation I¡lSPs' and, in so doing, to establish a firmer basj-s for bj-ological princÍples of pond managemefit. The dynamics of organisms from different trophic levels were related to effluent quality, and therefore the efficiency of pond function, and the usefulness of those organisms as managenent tools evaluaÈed. Previous studies on bíologícal asPects of pond function have been based upon a priori judgements as to the likely ímportance of a species or Ërophic grouP in the. treatment pÏocess" Moreovel' organisms have been studied in isolation from the rest of the pond ecosystem. such studíes have failed t.o take into account the effects of other organisms present with the object of major interest. The present study attempted to investigate the overall pond ecosystem and to relate the role of the major ecologícal gr:oupings to the overall functioning of the system' can T1-re relaÈive usefulness of varÍous organisms for pond management only be evaluated in the light of this tyPe of investígatíon. obviously, such a study was ambítious and some groups \Á/ere studíed less intensívely than others. To some extent, this reflected the bías of the investigator. liovever, a concerted attempË has been made to provi approaches increase the financial and energetic costs of r^¡asÈe treatment and detract from the funclamental advantages of WSPs as simple, The impetus for the economica.I systems for waste tl:eatment. rnajor present study rvas the possibility of providing i^lSP man¿ìgement prínciples based upon the funclanlent,al ecological. interactjons wíthin ponds ' gre-atly Biologicai nranagement of trJSPs woulcr, not íncrease operati'ng cosËs 2L6. (provided that any technology involved was relatively simple) and coulcl have the added advantage of producing utilízabLe by-products. The najor operating problem of I^ISPs has been the presence of algae in effluents and the concomitant effects of effl-uent discharge upon ïeceivíng vraters. Algal control r^ras therefore a primary consideration Ín studying the ecology o1 WSPs with a víew to biological management. The stablLízation of organic matter is noË usually a primary requiremenÈ of maturation ponds. However, the present study has shown that, during phytoplankton blooms, effluent BOD, SS and TOC may íncrease substantially above infl-uent concentrations, thereby exceeding present r^rater quality criteria. The removal of organic maËerial was, therefore, also a consideration duríng the present study. The major functional requirement of maturation ponds is effluent políshing, ín particular nutríent removal; this was also of primary concern during the present study. Although nutríent removal is the prime function of maturatíon poncls, nutrient partitioníng, removal pathways, and removal efficiency have been virtually unstudied in this type of hlSP. The major ecologícal inËeractions influencing phytoplankton populations in the Gumeracha ponds are sunrnarized in Figure 6.1. This scheme may be used as a predictive model for the management of maturat.ion ponds to reduce phytoplankton standing crops. Phytoplankton blooms in the Gumeracha ponds were triggered by increasíng temperature but ¡ve-re Èerminated by zooplankton (¿. carinata) grazíng. D. carinata, a cold r^¡ater species, \¡Ias prevented from controlling phytoplankton abtrndance during sumnìer by high \dater temperatures. Greater tlnan 507" pond surface cove-rage by fílamentous algal mats (cl-adophora) during Ëhe critíca1 period for the onset of phytoplankton blooms and Èhe Presence of substantial stands of srrbmerged macrophyte (e- ochreatus) inhíbitecl the development of a summer phytoplanktorr bloorn. Thus, phytoplanlcton in WSps rnay be controlled by encouragíng the development of populations of Chlorophyll a (rg/*3) (-) Chlor:ophyll a (tg/*3) (-) N) 5' Or æ o f.J Þ. Oì @ o O O O O O o o O <) o O O O o o OO O o <) o o Percentage surface coverage bY Temperature ("C) (-'-'-) rrl Cladophora (-'-'-) H ¡.J â. o\ @ o N) (, 6) O o O o O O o o O -F 14 Þ \. \. î v) \. I ------\ o. 2 o H o Ht 3 gJ I (J. o É o o _./__ o ts o 0a F o 0) H q I H. I r-t o Cr d ! 0) o at \ H. o ø jP. fi a l]. o C) \ â o H I Þ o / Ê) ¡d o 5 io. Þ lsfO\æO o o ooooo ts o o o o o Percentage boÈtom coverage Density of o. carinata by P. ochreatus C---) (no./1,) e--l 2L7. filamentous algae, submerged macrophytes, and zooplankton ín the ponds' Management of Ehese populations would be required to maintain optimal standing crops and would probably chiefly ínvolve periodíc croppíng.. ThÍs would be essential to prevent food limitatíon of zooplankton' Some problems could be encountered ín attempting to culture filamentous algae and submerged macrophytes simultaneously. It would be essentíal' for algal mats to remain on the pond surface during November and December, even if the filaments r¡ere in a senescent phase. The culture of Cladophora and P. ochteatus has been discussed in Chapter 3, and problems encountered in the management of D. catinata discussed in Chapter 4. Removal of BOD, SS, TOC and organic nitrogen at Gumeracha was highest during períods of dominance of P. ochreatus and D. carinatai BOD and SS concentrations of the final effluent satisfíed present quality criteria only during those periods. Effluent quality deteriorated substantially during phytoplankton blooms. In this regard, the Gumeracha ponds functíoned more efficíently aÈ lower water temperatures and in the absence of phytoplankton. Unicellular algae \¡Iere unnecessary for the stabiLízaËion of organic material whích appeared to be effected largely by P, ochteatus. Management of maturation ponds for Èhe effective stabilization of organic material would involve the encouragement of subrnerged macrophytes' and zooplankton (to a lesser degree). Such a management strategy would be compatible with, and ín fact r¿ould be dir:ectly dependent upon, the control- of unicellular algae" Partítioning of the total nitrogen (rxn + No3-) and total po. retaíned in the Gumeracha ponds during 1977 is shown in Figures 4 -P 6.2 and 6.3. The relatíve share (as a percentage) of total nitrogen and phosphorus for any species ís equívalent to the nutrient store represented by the total annual net production of that species" In pond 1, when phytoplankton standing crops were low, the greatest share Phytoplankton (1%) Phytoplankton (27.', Cladophora (I2%) P ochreatus (.I7.) Cladophora (47iÒ D carinata (I.37.) s exspinosus ( .37") P. ocÍreatus (2.6', NiËrogen Total P0 -P Total 4 D. carinata (4 .6', retained (i002) retaÍned ( 1 o0z) S. exspinosus(1.11 (Bs.3Z) (42.7i¿) Bacteria, benthos, other zooplankton, insectst Bacteria, benËhos, other zooplankton, l-nsecÈs, s ediments sediments FIGURE 6.2 Nutrient partitioning in pond 1 during L977. \ ?) Re cli Phytoplankton (5402) Phytopl-ankton (1202) (? ) (?) Total Ni-trogen Total P0. - P retained (1002) rerained4 (Loo"l) Cladophora (7%) Cladophor a (L"/") P . ochreatus (.9"/.) P . ochreatus(.6"/") D. carinata(3,L%) D. carinata(L7.6%) (t (?) BacEeria, benÈhos, other zooplankton, insect.s, sediments' Bacteria, benthos, other zooplankton, fnsects, sediments. FIGURE 6.3 Nutrient parËitioníng ín pond 2 during L977. zLB. of nitrogen and phosphorus retai-ned íA the pond was channelled into organisms not studied during the present ínvestj-gation (i.e. bactería, benthqs, insects) and to the sediments. After Èhis, the major nutrienË store, particularly for phosphorus, vlas rePresented by the production of CTadophora. Although the production estimate fot Cl-adophora was tentatíve, it. was probably an underestimate. An increase in the productior_ of Cl-adophora, for example by cropping, coulcl have provided a major nutrient store in the Gumeracha ponds and, therefore, a useful pat6way for nutrient removal. As filamentous algae is also important for the control of phytoplankton, the culÈure of species such as Cladophora appears to represent a useful tool for \^lSP management. Despite high annual net production c¡f D. carinaXa and C. auratus, harvest of these organisms and P. ochreatus appeared to be of little potential value for nutrient removal" The harvest of D. carinata, P. ochreatus, and CJadophora from pond 2 also appeared to be of little value for nutrient removal- phytoplankton production esÈímates T¡rere tentative but were of such magnitude as Êo suggest that a major proportion of the nutrients ret.ained in the pond \,/ere incorporated ínto unicellular algae. This !¡as consisLent with the fi.ndíng of Kimerle and Anderson (197L) that phytoplankton were a dominant energetic component of I{SP ecosystems. The proportion of nutrient-s íncorporaËed into phytoplankton in pond 2 appeared to great,ly exceed that i.ncorporated Í:nto CTadophora in pond 1' The harvest of unicellular algae appeared to be the most effective means of nutrient Iemoval frorn the Gumeracha poi-rds. This was reflected Ín low effluent concentrations of soluble PO4 - P and NOr- during phyt.oplanktonblooms"Hor¡ever,nutríentuptakebyalgalcellsdoesnot constitute removal frou effluents unless the algae are harvested continuously prior to dl,scharge. If algal harvest ís not practiced, the nutrient load of the influent ser^/age is exported (bound into algal 2L9. cells) to the receiving \¡rater body. Suitable technology currently exísts for the mechanical removal of algae from effluents. However, the financial and energetic investments required for mechanical harvest substantially increase lÙSP operating costs. Biological alternatíves for algal control involve filamentous algae, submerged macrophytes, and zooplankton. However, if a1-ga1- cont.rol, via inhibítion or consumPtion' rather than algal harvest is pracËíced, Ëhe capacity for nutríent removal from the pond system is reduced. Thus, algal- control (as opposed to algal harvest) and high nutrient removal appear to be incompatíble. The decísíon to introduce mechanical harvest into a gíven treatmenË system must' therefore, be based upon both economic and treatment requírement considerations ' If unicellul ar aLgaL harvest is not desirable, a pond ecosystem based upon filamentous algae, submerged macrophytes' and zooplankton is likely to prove more efficíent with respecÈ to overall v/aste treatment" I^Iith careful, effectíve management and harvest of filamentous aLgaL populations, ïeasonable nutrient removal could be achieved. The presenË study has examined the relative merits of various, naËurally occurring groups of organisms for the management of l{SPs on bíological rather than engilleering principles" Those gloups offering the most promise as pond management tools have been highlighted' It norv re;nains for the management princíples outlined ín the present study to be developed and applied by those bodies responsible for the treatment of \nlaste, on an oPerational day-to-day basís' 220. Appendix 1 Pond 1 L978 Pond I 1977 1000 2000 / s00 1000 X:t 2 / 0 0 0 600 1200 Pond 2 1977 Pond 2 L97B 4000 500 xlt 2000 250 .¿- 0 0 300 600 00 0 (no./.e,) Mean densitY (no . / 1.) I'lean density Mean crowding (Xx) versus mean density lor D. catinata in the Gumeracha ponds (---, random exPectation). Pond I 1977 ?ond 1 1978 Pond 2 L977 4000 50 50 25 x* 2000 25 0 0 0 300 600 714 15 30 Mean density (no./[) Mean crowding (X't) versus mean densiÈy for S. exspinosus in the Gumeracha ponds (---, random expectation) . N' N) F 222. Pond I 1977 240 Pond 1 L97B 800 x* 1200 7 / 4oo 0 00 350 700 Pond 2 1977 240 a Pond 2 I97B 160 , xx L20 BO /7 0 0 60 L20 10 140 (no Mean density (no. /.C) Mean densíty " /.9.) Mean crowding (X*) versus mean density for l'I . Teuckartj in the Gumeracha ponds (- - -, random exPectation) . 223. B. triarticulata Pond I 1977 Pond 2 L977 I2 L20 x)k 6 60 0 0 5 50 M. hirsuticornis 200 Pond 2 L977 Pond 1 L977 a I 800 100 x* 900 2 - 0 0 250 45 90 L25 (no./[) Mean densítY (no . /1.) Mean density and Mean crowding (X*) versus mean densíty for B' triarticul.ata M. hirsuticornis in the Gumeracha ponds (-- - , random exPectation). fta 100 f Pond I \ 1977' \ * 1978 x f \ Þ *r\t.. *( t\ \ o. F \ ¡ x f \ l.J a 1000 ta \ / + \ o/ \ + ++ \ a * i \ + 100 ¿l''* .t \ * /t * ol \ o + É \ >' JJ .rl 1 a U) 10 + Pond 2 É €GJ \ x . a 1977 .\ + X d x L97B a) f I ¿{ xt 10 I \ + 1 a 8 10 ll pH x x Pond 1 ¡ 10 1977 L978 x 1..) Pond 2 N) 5' r977 + 1978 * I 16 2 I 22 24 6 B 1012 14 T emP erature "8 ß ].S SO lved oxygen (me/.q) Mr:;,¡n ciens,Í ty o l' D. cel rjn,?ta rJerstls dcpth av('rilgecl wat-er trìm[)(]r:n Lrrrc nncl d lssolved o4yflen concentration, ancl PU 225. Pond 1 1977 . Pond 2 1977 3 t4 1978 x 1000 L97 B a 100 a a t a x 10 I , a o? I rll ì I 24 o 18 2 02224 8 10 12 14 16 rB 20 22 É Temperature ("C) >. +J 'rl o É 0) Pond I 1977' Pond 2 1977 + Pond I 1977 ' Pond 2 I97l + É (d T97BX 1978 x 9ro 00 a l- + x I 100 \ I + + \+ + \ t +Ì + \ I 2 I Díssolved oxygen (nel 9') pH Mean density of S. exspinosu.s veïsus depth-averaged water temperature and díssolved oxygen concentration, and pH' 226. Pond I L977 ' Pond 2 L977 ' I000 I97B x I97B x a r00 a x 10 a T ol I rtl J_ ì B 10 12 1416 18 20 222 4 B 10 12 14 16 rB 20 22 24 o Temperature (oC) É Þ\ il¿J U) É €q) 1977 Pond 2 L977 + Pond 1 1977 o Pond 2 1977 + É Pond 1 ' (ü I97B x q) L97B x t I 000 100 + + / + + + + a ++ a { x 10 / ¡ + + r: + + r / + f * + /* I i-. '{t - + o24 6Bt01214L6 B 9 10 I1 Dissolved oxygen (mg/ ) PH temperàture Mean density of M. hitsuticornis versus depth-averaged vlater and dissolved oxYgen' and PH' 227 . Pond 1 L977 . Pond 2 L977 . I000 1978 x 1978 x xx f t 100 x x * ¡ f al a IO * a r x f x x */ x x x ta aa t tttlrl rrl 1 t -J-. -[-I' .-,<--l--J èì B 1012 L4 16 182022 24 B 10T2 L4 16 r8 20 22 24 o Temperature ("c) É Þr {J 'r'l v) É OJ 'ú Pond I 1977 o Pond 1 1977 . Ê (ú I97B x l97B x o) I 0 00 I x x f a 100 7 x' * /. x x /.' x 10 x r.( x x 2 x t * x x 1 I x lr 0246810127416024 6 81012L476 Dissolved oxygen (^e/ L) Mean density of M. feuckarti versus depth-averaged vrater temperature and dissolved oxygen concentration. Pond 1 L977 . Pond I 1977 . 1978 1000 + 1978 + x I /r oì 100 a o a x JJ .¿ x Ø É a '( €c) 10 d x q) a o tx x I I 9 10 11 I 9 10 pH Mean density of M. LeuckarÈi versus pll l\) l\) @ Pond 1 L977 o 1000 Pond 2 1977 + + + + + + + + + oì + + + i00 + o + É + + .t t,à + + 'rl + UJ + 0.) + + + € + + + 10 d 0) + + + + a'ù + + + + I J-¡-I.-Llo-+ 8 10 t2r4L6 18202224 0 2 4 6 B 1012L4L6 I 9 10 11 Temperature (oC) Dissolved oxygen (ne/L) PH -+-+ Mean densiÈy of B. tríarticulata versus depth-averaged \,tater temperature and dissolved oxygen concentration, and pH. t\) N) \o 230. Apprrunrx 3 Papers presented in support of the thesis Mitchell, B.D., (1980) Waste stabilisation ponds. In W.D. Williams (ed.) An Ecological Basis for Water Resources Management (pp. 360-375. Canberra, Australia: Australian National University Press. NOTE: This publication is included in the print copy of the thesis held in the University of Adelaide Library. Mitchell, B.D., (1978) Cyclomorphosis in Daphnia carinata king (Crustacea : Cladocera) from two adjacent sewage lagoons in South Australia. Australian Journal of Marine and Freshwater Research, v. 29 (5), pp. 565-576. NOTE: This publication is included in the print copy of the thesis held in the University of Adelaide Library. It is also available online to authorised users at: http://dx.doi.org/10.1071/MF9780565 Mitchell, B.D., (1979) Aspects of growth and feeding in golden carp, Carassius auratus, from South Australia. Transactions of the Royal Society of South Australia, v. 103 (6), pp. 137-144. NOTE: This publication is included in the print copy of the thesis held in the University of Adelaide Library. Appendlx 4. ProducÈion o1 Daphnia earinata (?ond i) calculated using Èhe populatlon turnover-titre oodel Dep Èh- .Mean avera ged Mean Tine Blomass Produc tion Dãte (E) (D) (No) b br r d D T b ionas s t emper a lur e tenper a ture ( days ) (ue/ a) (ne/ Y/ àay) (ne/ v") ( "c) t8.9 0 0 0 t6, 2.77 73.5 21 2 63.4 a aa t3 7 0 382 0.3235 14 0.1870 0.1365 0.r276 7 ot, 507 0.254 0.032 a 11 a 111 2. 19.0 2T I90.7 t-ðr 2 01. 0 1 0.7781 It1 0.1929 0.5852 0 .4430 2 .26 3487 t.997 0. 884 16. a 11 17,7 18 4 15r.9 3. I5 297 2 0 ao1 0.2601 14 0.0269 ó.2332 0.2080 4 .8I 4961 4,220 o.877 a 1a 30. 18.3 1ô 0 2i8.4 3.25 I 85 7 0 157 0.1458 t4 -0.0336 o.I79L 0.1642 6 .09 460 3 4.782 0.785 13. 4.77 L6.Z t1 3 3r6.0 3.42 I9I 4 0 )qq o.2957 t4 -0 ,00 22 0.2979 0 .257 6 3 .88 7 669 6.136 I.58r t1 4.77 14.8 l5 5 18 2 0 41b 0.3¿78 i4 0.07 i i o.2Lr7 4 .r4 29 529 18.599 4 "L93 1. 6.11 il. I 0 5.80 0 0 37t 0.3199 J4 -0 ,4465 0.1664 c.5353 I .87 0 t4 .7 65 7.896 15. 3.78 tt o 0 0 0 29 . 3.78 r6.6 l9 3 5.0 I 96 3 I 0.338 ñ ,ot? I4 0.0808 o.2t04 0.1897 5.27 1b 0 .008 0 .002 13. 4.78 Ì4.9 I5 8 175.3 3 88 181 5 0.416 0 .347 5 t) 0.27 13 0.0763 0.0735 13.61 4557 I t ç7 0. I68 ta o ll 1 27 . 4.18 9 t94.9 ¿¡ 62 7025 0. 209 0.1898 l4 o , 1237 0.0661 0.0640 15.63 15894 70.226 0.65¿ r0. 5.78 r2 .4 T2 Ò 2r.6 5 30 255 0 0.036 0,0354 -0.1071 o . t425 0. r326 7 .53 5997 10.946 1 .454 21 . 5,18 t2.5 T2 5 353 .4 5 36 304 0 0.016 0.0157 T4 0.0r26 0.0031 0 .003 1 106 74 8.335 o.026 6. 6.78 11.4 IL 0 203.1 5 70 IIC6 9 O.2Ot1 0.1856 13 0. 0994 0.0862 0.0826 12 . I t 29106 19.890 |,642 2r. 6.]8 OQ 10 6 198.I 6 70 li! 2 0.027 0.0266 15 -0. i044 0.1310 o . Iz28 8.14 r059 5 19.85r 2 .439 nqo? ao a, 5. 7 .78 oñ 9 4 45 .0 1 94 225 I 0. 108 0.I026 14 -0.0019 0. 1045 ô 10.08 9.789 0.971 1?O O 19. 7 .78 I I 70 Lt2 3 0.023 0.a221 I4 -0.0r91 0.0418 0.0409 6638 7.8I0 0.320 9. 8. 78 1.2 7 9 /tr. ó 9 93 90 7 0.082 0.0788 2l -0.0306 0.1094 0.1036 9 .65 3982 5.3r0 0.550 30. 8. 78 9.I I 2 52 .5 9 50 416 7 0.089 0.0853 2T 0.0726 o.orzl 0.0126 79.31 I1470 t.tt6 0.097 13. 9.78 10 .6 9 9 24 ,3 l 37 82 0 .0 i69 l4 -0.1157 0 ,1326 0.t242 8.05 21 64 7.IT] 0. 88,i 11,10,78 r6.6 l0 Õ 0 Ò 70 0 0.044 0.0431 ló -0. 1576 o .2007 0. 1818 5 .50 0 1.382 0.251 ¡\) UJ ts (?ond Appendix 4. (Cont.) Productlon Ôf D' carinata 2) Mean Depth- B lomas s ?roduct ion Time T b lomass averaged È1ean (D) (No) B b t dr D (¡g/t) (ngl r/ day) Da Èe (E) ( days) (:¡gl temperaÈure teÐperature s ) ( "c) c 0 16. 3.77 t8. I 0 8.34 116 0.058 0.007 o .4 o.323 0.2799 t4 0. I520 o.1279 0 . I201 30. 18. 18 7 10. 0 3.10 J ,1 145 0.I2¿ 14 0.0337 0 .0 331 30. 18 7375 la 11 6 145. 3 3.60 286 .0 0.331 0.285 7 o.2520 4.17 I6. l32 0. I 070 9.34 8928 8. 152 0.873 aaa 8 3. 84 332 .6 0. I32 0.1240 lc 0.0 108 0. l 4.77 I5. 0 I5 9 184 L .556 0.892 123 0. 1I60 Jq -0.10I6 0.2176 0. r 956 5.11 8. 9 t2 0 1. 5. 70 10 0. 1. 6.77 o .0t 23 13.83 379 0.282 0.020 a J.  a1, 4 .4 0 .0I3 0.0r29 t4 -0.062i 0.0750 6.77 3 8 6 0 167 o .213 0.00 I 0 .07 57 t4 0.0717 c.0040 0 ,0040 250.00 )o t a a ô I 8. 6 8. 70 t2 .0 0.078 d. t )a 0.0r17 85.25 930 0.548 0.006 o 1 .48 .8 0.09 6 0.09r5 13 o .07 97 0.0118 7 .77 l0 3 9 J7. I 429 n Á7a 0.087 ,< 1 aQ .8 0.151 0.1406 15 -0 .00¿ I 0.r36_5 0.r216 7 .84 i.77 9 6 IO 0 r8.38 3598 2.O13 0.110 7T o 0, 121 0.114r L11 0.0582 0 .05 59 0.0544 10. 8.i7 It 5 l0 6 138. 7 6.70 n ?lo L 0.2453 0.2175 4.60 3tt65 3.532 I 11 17 8 56.6 5. 80 t29 0.287 t4 0.042i 24, 0 tl o.0921 0.0885 11.30 527 6 4 .371 0.387 56. 0 5.70 100 .0 0.o7J 0.07 42 l4 -0.0r85 7, 9.77 l2 0 T2 0 0,0547 18.30 I C055 7 .666 0 .4 1,9 o .2 0. 120 0.1133 T4 0.0570 0.0563 I rl < 2r. 9 .17 I5 6 I3 291 . 6 4.66 1 e? 7680 8.867 .2 0. 358 0.3060 t4 0.0031 0. 3029 0.2613 r0.17 T7 2 16 L t 14. 2 3.61 232 O, EI2 ). a 0.0444 0.09i0 0.0870 t1.50 10986 9.333 T7 I! 141. 6 3.40 590 0. i45 0. I354 ¿! 1ô, lO.7 /- t7 6 237 5.612 2 ,192 Õ r3 0.4951 0. 3905 2.56 15 16 c J.)ó 0.067 0.0649 -0.4302 8. 1r .71 I .9 0.6299 I.59 l 0.1t9 0.075 3.14 0 ,2 I.303 a.8342 t5 -0. I599 0 941 1I . t-7 21 1 I8 ) 0 0 0 13. 4.78 l5 - z 0 462 o.2 3l 2 50. 3 4.49 70 I 0.223 0. 2013 t4 0.2168 -0.0155 27 . 4.78 13. 1 t4 7 402 3.932 0 .00¿ l3 0.2I08 0 .001 1 0.0011 909 .09 0 l3 ,1 126. 7 5.05 322 0.236 0, 21I9 10, 5.78 13. 0.0523 T9, L2 9161 L 285 ¡.ú33 It .8 196. 0 5. 20 qlq 2 0.076 0.0733 Itt 0.0196 0.0537 24. 5.18 5 t2 13 .54 21106 t5 .137 1.118 Ir 1.6 0.0807 13 0 .0040 o .0167 0.0738 12. 0 lz ,3 164. 3 5 .50 6 0.084 6. 6.18 1< nql? 0. lc85 0.1028 9.73 11576 L6 .341 1.6ì9 .2 )J, 6 .23 207 2 0.059 0.0573 -ô 2I . 6.78 I0. 3 II t7.t2 806 5 9.E21 o,57 t /.tJU 97 0 .034 0.0334 78 -0.0268 0.0602 0.0584 1 .18 o 9 9 .7 t7. 0 0.073 t9. .005 6 0 .014 2 0.0141 70.92 2243 5 .I5tt o I10. 2 L57 I r0 I 0.020 0.0198 2l 0 9, 8.78 1. 9 8 11 .02 5955 4 .099 0.3i2 4 0.1124 21 0.0173 0.095 I 0.0907 10. I 9 .0 33. 3 8.45 158 0.i19 30. 8.78 0.04 53 0.0443 22.57 3655 It.705 o.209 12 0 ?a a 10 .7 16. It É,.60 130 ) 0.032 0.0315 14 -0.0138 t1. 5.62 0 1.728 0. 308 0 0.030 o.o2.a6 28 -0.1664 0. r960 0.1780 1r.i0.78 t8. 8 15 .0 0 4.16 N) (¡J N Appendix 5. ProducÈion of D. carinata (Pond 1) calculated using the biomass turnover model Initial Final 16 .2.77 2.3 .77 16 .3.77 Size l{eight DuratÍon Productíon weighÈ weight DensiÈy Class change (days) (ne/e"/day) (c) (e) (No . /.0) 151.9 3 .30 0.2302 E ÞÞ-ooc 0.0000 0 .0050 0.0050 63.4 2.30 0.1378 19 0.7 3 05 0.3t26 2.10 0 .0 108 16 6.3 3 94 0. 1604 168. 8 4.33 0.1481 1 0 .0050 0 " 00BB 0.0038 7.7 ,), t) 1 BO.B 5 .78 0.1873 2 0.0088 0 "0222 0"0134 J.OI 0.0082 1 5 25 0 .031 1 26.5 6 .50 0.0897 3. 0 "0222 0 "0442 0.0220 1.1 4 .0s 0.0060 3.1 5 9T 0 "0488 4 0.a442 0 .07 68 0.0326 0.6 4 .05 0 .0048 6.7 5 91 0 "0370 72.5 6 .50 o "0627 2 5 0.0768 0. 12 I5 o 1.0 7.2r 0 .00 62 5.5 10 51 o.0234 4.2 TT.57 0 .016 "0447 tt 6 0. 1215 0. 1800 0.0585 0.8 9.91 0.0047 14"44 0.0089 1.5 15.90 0.0055 0 .0099 7 0. iB00 0.2539 0.0739 0"2 12.62 0 .0c 12 1.0 18. 34 0.0040 2.7 20.24 1 8 c.2s39 0.3446 0.09 07 0.1 20.28 0 " 0004 1.0 29.55 0 .003 30 .3 -71 L3.4 .77 27 .4.77 29 .3.78 2iB. 4 3. 1B 0.3434 316. 0 3.75 0.4213 LI32.J 4.23 1 .3384 5.0 3 .60 0.0069 118 . 9 4. JJ 0. 1043 87. 7 5.76 0.0646 62. 2 5 .67 0.0417 3.1 4.9s o.0024 17. B 5.78 0 .04 13 27 9 6.89 0 .0543 81. 9 7 .57 0. 1450 16. 3 6 .50 0.0552 t2 I 7.75 0.0599 L32. 1 8.51 0 .3415 0 22 J 6.50 0 . 1118 31 0 7.75 0 " 1304 L47 . 7 8.51 .56s8 7 4 r1.57 0 .0 286 27 9 13.79 0.0904 65. õ 15 .14 0. i943 J B 1B .95 0 .0117 25.4 20. B0 0.0714 3 0 20.24 0 .01 10 0 24.t2 0 .003 I J. I 26.49 0.0085 l N) U)(, Aooendix 5 . (Cont. ) 13.4.78 Duration Production 27 .4.78 r0.5.76 24.5.78 Density (days) (nc/e,/ðay) (No . i r,) 175. 3 4.20 o "2087 r94.9 5.20 0.I874 21.6 s "43 0.019 9 353.4 5 "37 o.329r Ltz. 5 5.67 o.o7 54 649.3 6.98 0.3535 97.4 7 .40 0 .0500 139.8 7 .40 0.0718 19. B 7 .57 0 .03s0 160 .0 9 .35 0.2293 83. i 9"BB 0.L127 28.0 9.BB c.0380 a 15. 8.51 0 .0408 T4L "6 t0.52 0 34"4 11.11 0.0681 48.6 11.11 0.0962 a'l "2961 6 8.51 0.1057 s6.4 10.52 0"i748 28.6 11.11 0.0839 55 .9 1r.11 0. i640 ) 0 T5.T4 0.0059 1B .5 18. 70 0.0442 11. 5 19 .76 0 .0260 28.O 19.76 ,) 0.0633 0 20. B0 0. 005 6 3.7 27 "L6 0.0080 1. ö 42 s6 0.0038 6 .6.78 2r "6.78 5 "7 .78 19.7 .78 2C3.7 6.10 0. 1670 i98.8 7 .47 0.1331 4s. 0 8.45 0.0266 r39.9 8.95 a .o7 82 557 .9 B "23 0 "257 6 102.2 9.64 0.0403 68. 0 11 .01 0 .02 35 30 .5 11.81 0 .0098 110 1 L0.99 0.2799 29.L t2.87 0 .0303 84. 0 L4.70 0 .07 56 56.3 15 .76 0.0479 119 .6 L2.36 0.2129 L2.5 14.47 0 .0 190 19.6 16.53 0.026L 40.s L7 .72 0 .0503 B1 .9 i2.36 0.2160 JJ. J L4.47 0 "0750 10. 8 L6.53 0"0213 20.3 17 .72 c.0373 118 .4 2l "98 a.2408 4s. B 25.74 0"0795 23. 2 29.40 0.0353 2L.7 31.53 0.0308 to 8.3 35. 3B 0 .0 137 r9. 6 40.4r o "0284 43.33 0.0039 N) UJ N Appendix 5. (Cont.) 9.8.78 Duration Production 30.8"78 13.9.78 Density (days) (ne/t'/day) (No. /r,) 76.8 11 .0 0.0349 52.5 8.30 0.0316 24 3 6.70 0.0181 26.3 14.37 0.0070 20L.7 i1.01 0.0696 15 7 9 "r7 0 .0065 19.9 19. 1B 0 . 0139 68.3 14.70 0.0623 28 6 L2.24 0.0313 12.7 2I.57 0.0 130 75.0 16 .53 0.0998 17 7 13 "77 0.0283 16.7 2L.57 0.0252 40. 8 16 .53 0.0805 15 0 13.77 0 "0355 L2 "0 38.37 0.0 140 2A.4 29.40 0 .03 i0 4 I 24.49 0 "0088 ).¿ 52.7 4 0.0035 10.4 40.4t 0 .015 r 7 33.66 : 0.0012 Production of D. carinata (Pond 2) 30.3.77 L3.4 "77 27 .4.77 L.6 .77 r45. 3 3.57 0.2035 232.8 4.t5 0.2805 L.2 8 .60 0 .0007 i.o s.99 0 .0028 205. 9 4.73 0.1654 180.3 s "67 0.12C8 6.6 1i.01 0.0023 3.3 8.00 0.005s 27. 5 6 .30 0 .05 84 63.2 7 .57 0.i119 r.7 14.70 0 .00 15 11. 7 7.10 0 .0363 30 .6 B .51 0.0791 0.7 76.53 0 .0009 0.7 9 .00 0.0025 L2. 9 7 .LO 0.0592 25.9 8"51 0.0992 0.8 16.53 0 .00 16 10. 9 12.63 0.0386 25.9 1s.13 0.o765 0.3 29.40 0 .0005 13. 7 17 .36 0.0462 4.3 20 .80 0 .0121 0.1 40.4r 0 .000 I 1. 4 22.r0 0.0047 2.3 26.64 0 .0064 ., N 0 35.50 0 .005 I (, (¡t Appendix 5. (Cont.) Is"6.77 Duration Production 29 .77 DensiÈy -6 12.7 .77 27 .7 .77 (days) (ne/ ,"/day) (tlo . /.0) 3.0 9.4A 0.0016 B 6 8" 20 0.0052 37 "r 6.9s 0.a267 25 2 7 .70 0.0r_64 I 0 2 1r. 01 0 .0035 o, B .28 0.0042 22 6 I0.32 0 .0083 0 5 L4.70 0 .0005 17.2 T2.87 0.0r_79 3 5 L3.79 0 .00 34 18.86 0" 0017 0 4 L6. 53 0 0005 14 t.t " 2.8 "47 0 .0043 J I 15. s0 0.0054 1"5 18. 86 0 .0026 0 3 16" 53 0 - 0006 1.1 14.47 0.0025 I 6 15 .50 0.0034 4.7 33"55 0.0009 7 ?o 40 0 : - 0011 2.L, 27 "74 0.0036 0 3 27 "57 0.0005 0"7 46.tr 0.0009 1,1 35.38 0 "0018 0.3 45.04 0.0005 L0.8.77 24.8.77 7 .9.77 2t "9 .77 1 138. 6 .00 0. 1156 56.6 s.70 0.0496 56 .0 5.70 0 .049 1 29 L.6 3.94 0.3701 19. 2 8.23 0.0089 78.2 7 "80 0.0381 L9 .0 7 .80 0 .009 3 5 4.4 5.42 0 .0381 18. 5 10.9 9 0.0226 10. I 10 .41 0 . 0139 21 .0 10 .41 4.0270 I 3.1 7 .23 0.0243 5. 0 L2.36 0 .0089 18 .9 LI.7I 0 .0355 2I .9 LT "7I 0 .0413 50.0 8.13 0. 1353 L2. 1 12.36 0"0319 8.2 11" 71 4.4228 13 .0 LT.7L o.0362 10 0.2 8 .13 0.4018 L4, 2 27.98 0.0289 10. I 20.82 0.0232 I6 .0 20.82 c.0344 4"4 14.46 0.0r36 2. 2 30 -2I 0. 004 3 2.7 28.62 0 .005s .0 28.62 0.0164 '7 38.46 0.00 13 : : (,N) o\ Appendix 5. (cont. ) 5.L0 .77 26.L0 "77 8 .LI.77 27 .4.78 Density Duration ProducÈion (days) (u,e/ e"/day) (No. /r.) IT4. 2 3.43 0. 1665 r4L.6 3.35 0 .21r3 9.0 3 87 0. 116 50 .J 5 .05 0.0498 50. 0 4.73 0 "0402 i90 .6 4.55 0.1592 11 , 7.00 0 .0061 64" 0 6.31 0 . 1359 280.4 6 o7 0.6190 J .7 9.35 0.0053 74. 0 7. r0 o "2293 59 .6 6 83 0.L920 0"9 7.75 0.0026 3 .0 10 .51 0.0063 25 0 7.LO 0.1148 47 .8 6 83 o "2282 0.9 7 .75 0.0038 I a 10.5r 0.0059 6 0 12.63 o.a2r2 11" 8 L2 15 0.0434 0.3 L3.79 0.0010 .l 18.70 o.0026 U L7.36 0.0236 : 2 0 22.r0 0.0067 10.s.78 24 -5 "78 6.6.78 21.6 .78 126.7 5.08 0.t247 r96 .0 5 "25 0. 1867 164. 3 s.70 o.L44r 53 .5 6.9s 0.0385 23L.5 7 .00 0.1-257 336.4 7 .40 0 .L7 27 t79 5 7 .80 o .087 4 62.2 9.64 0.0245 ))a 9. 35 0.0328 23.8 e.qB 0 .0323 40 2 10.41 0 .05 17 20.7 12.87 0.02L6 19"0 10.51 0.0398 19.5 11.11 0.0386 51 4 LL,7I 0.0966 24.9 14.47 0.0379 26.4 10. 51 0.0818 7.6 11.11 0 "4223 84.4 IT "7I 0.2350 45.6 14.47 o.'J,c27 15.2 18. 70 0.0363 19 19 .5 .76 0 .044 i 73" 2 2C.82 0 "1572 45.6 25.74 0.0792 3.6 25.1r 0.0082 15 .3 27.16 0 .0330 L7. 9 28.62 0.0366 8"3 35.38 0.0137 ?o 32.73 0. 0088 3"8 34.58 0 .008 I N) U) ! Appendix 5. (Cont.) L9.7 .78 9 .8.78 30. 8.78 13.9.78 Ðensity Duration Productíon (days) (ne/ e-lday) (xo . / r.) 17. 0 7 .37 0.0115 110.2 9.95 0.0s54 33.3 7 .L5 0.0233 16.4 6.23 o.or32 t< o 9.64 0 . 01,02 65 .0 t2.56 0.0 197 46.4 9.64 0 .0 183 54.3 8.66 0.0238 J+. 5 12.87 0.0359 L7 .B 16.77 0.0L42 33 .8 L2.87 0.0352 36.4 rt.57 0.0422 18 7 14.47 0.0284 12.2 18. 86 a.0142 32.8 14.41 0.0499 16.1 13.01 0.o272 -7 2 14.47 0"0r.62 10"4 18.86 0 .0 180 25 t4.47 0.0s68 13 .6 13 .01 0 .034 1 o "2 o 6 25.7 4 0.0 149 33.55 0 .0063 19 .3 2s.74 0.0335 9"3 23 "r4 0.0180 B 35.38 0.0046 1.0 3s.38 0.0017 1.0 31.80 0.c018 : :, NJ t¡) co Appendlx 6. ?roductlon oî. Sinncephalus exspÌnosus (Pond 1) calculated using the populatlon turnover-tlme r¡odel Dep th- Mean Tlne B{omâss Product ion averaged Mean D T b lonass DaÈ e (tl (D) (No) B bt r dr (ve/ l¡el t / aay) temperature t eÍnperatur e (days) t) (mg/ f.) ( "c) I ,a 11 ) 18.7 I 393 r.77 2 I 1 0 .237 6 0.0235 0.0232 43.10 7 319 3.871 0.090 t9. r.77 23. 0 22.6 15r .6 3. 08 520.9 0.2983 0.261 l4 I I 788 4 .569 0.785 18. 9 21.0 r33.8 J.)I t 13.5 0.0829 0.0796 I4 -0-1088 0. r884 0.I7t7 5.82 A 7A)A 3 675 t.232 o.347 16. 2.17 5 2r .2 10.9 3.61 57 .7 o.3266 L4 -0.0483 0,3309 0.2817 .55 22 1232 0. 1r 59 8.63 I41 0.408 o.047 a 3. i7 lo 0 6.0 3.6r 2l .0 0.0523 0 . 0510 l4 -o .07 0 . o .287 8 4 .00 2L 0.081 0.020 16. 3.77 t7. 7 18. 4 I.8 4.41 0.9 0 .0648 0.0628 T4 -0.2250 0.250I 2. 85 q 0.0I3 0.005 JU. 1 ?; 3 18.0 0.8 4.63 0.4 0.4320 0.3590 ic -0. 0730 0 .4320 0.3508 0.2016 /, o< JZ 0.0r9 0 .004 r3. 4, t-'i 16. 2 I7.3 1.1 5 .00 i.9 0.4000 0. 3365 l4 0.1113 o.2252 ç 0 .004 11 r,.77 15.5 3.6 ). ót t.4 ñ noo 0.0948 14 -0.0218 0. 1156 0.1101 9 .08 0.032 14. 8 0.0I8 t. 6.77 l tt.8 20.5 8.46 A' 0. 3040 0.2651' Jq 0.0438 0.22t6 0.1988 5.03 t49 0.09c 4l 0.095 0.028 I5. 6.77 10. 0 9.4 6.9 tt .25 1.8 0.2953 0. 2588 IL -0.0883 0.3471 0.2933 J.qI o ñ? o.487 0.054 ?o 6, t'] o t 9.6 ,( Q 11.t5 0.3438 o .29 55 t4 0.1782 0.1173 0.I107 932 12 09 t-070 0.02I 12. 7.77 o 9 9.5 7r-6 11.15 62 .7 0.1066 0. t0l3 l3 0 . 0813 0.0200 0.0I98 50.50 0. 0 350 1I.76 2265 1.731 0. i48 a1 7 .77 o 1 9.6 L/J.U 11.i5 71.tl 0.1024 0 .097 5 t5 0.0087 0.0888 o o< o1 a 5.43 3507 2.886 0 -532 10. r2. 0 r0.6 114.8 o ,2435 0 .2r7 9 l4 0.0143 c.2036 0.1842 o1 , l¿ .9O 2296 t oô, 0.592 o i1 12.9 t2 .5 o). L 8.02 0.2623 0.2329 T4 0.00¿8 0.2281 0.2040 r036 2646 2.t17 | o -256 7. o 17 11. 3 I2. I 84.3 8.45 82.1 0. I056 0.1004 It1 -0 .0090 0.1094 0. 9.65 0 0 I4 .05 85 0. 1855 0. r 693 5.91 51 6 t .61I 0.27 3 21 . Q 7t- t4. I 13.1 7 .58 36.2 0.1355 .127 -0 0 .067 2 14.88 21 56 r .666 0. 112 5. 0 .11 i6. I t5.5 ll,t¿ .5 5. 82 56 .2 0. I c63 0.1010 t4 0.0314 0.0696 3.02 875 1.8r6 0.60I 26. o.?7 17. 6 r6.9 58.7 5.01 66 .8 0.507 Ì 0.4 I02 2l 0.0082 0.¿020 0.33r0 I3 0.2258 0.2021 4.95 416 0.ó61 0. 134 8. I.7 t- t7. 5 17.6 52 .4 4.85 30.9 0.1812 0.r665 -0.0593 1 3.87 530 0.¿88 0.126 23. | .17 10 0 18.3 34.5 4.52 41 .4 o .37 52 0.3r86 I5 0.0195 0.299 0.2585 186 0. i58 0.0ó8 7. 2.77 14. 4 r6.1 24.6 5.2r 17 .1! 0. r 599 0.1484 t4 -0.06r9 0.2103 0.1897 ( e, 2 t' 1518 0.852 0.031 ,) 2.17 t6. 9 15.7 12.4 216.2 0.2430 0.2r1 5 15 0.r800 0.03i5 0.0368 .I7 lo 1 4.01 134 0.826 0.206 4. 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