Nitrogen Flow and the Interaction of Boston Harbor with Massachusetts

Estuaries Vol. 20, No. 2, p. 365-380 June 1997

Nitrogen Flow and the Interactionof Boston HarborWith Massachusetts Bay

JOHN R. KELLY1 3 Willow Lane Rye, New Hampshire 03870

ABSTRACT: This paper summarizes evidence that most of the considerable nitrogen loading (-8, 470 mmol total N m-2 yr-1) to Boston Harbor (Massachusetts, USA) is expelled to shallow shelf waters of Massachusetts Bay, where it strongly influences ecological dynamics. Examination of nitrogen concentrations in the harbor, compared with loading, indicated that removal processes are active in the harbor. Comparison to other estuarine systems showed that the harbor's nitrogen concentrations are consistent with its loading, if they are corrected for tidal flushing effects on the water residence time. Furthermore, extensive measurements of sediment denitrification confirmed that rates of N2 gas loss are high in an absolute sense (-600-800 mmol N m-2 yr-l) but nonetheless remove only a small portion (<10%) of the annual land-derived nitrogen loading. Burial in sediments apparently removes only about 2% of the N input, implying export to offshore environments as the major removal process (-88-90% of N input). Western Massachusetts Bay receiving waters were examined for a signature of export from the harbor. Data consistently show a gradient of decreasing nitrogen concentrations from the harbor to about 10-20 km into the bay. In many cases, plots of nitrogen concentrations versus salinity show nearly conservative mixing character, which implies virtual export. Seasonally, the data suggest most of the export from the harbor in winter is as dissolved inorganic forms (NH4+, NO3-, NO2-). In summer, export is dominated by the outflow of organic nitrogen forms. Chlorophyll export is evident as well, suggesting that the nutritional coupling of the harbor and bay in summer involves organic fertilization of the bay's surface water. Finally, high-resolution studies over different stages of the tidal cycle help refine understanding of the advection of chlorophyll and stimulation of in situ chlorophyll growth at the seaward edge of the tidal excursion into the bay.

Introduction to the harbor is exported to the bay. Observational evidence Estuaries often receive very high nutrient load- shows that the quality of nitrogen export varies ing compared to other ecosystems (Kelly and Levin seasonally. Special water-quality mapping 1986; Nixon et al. 1986a, b). Worldwide, Boston studies are presented that resolve ecological fea- Harbor, Massachusetts (USA), is one of the most tures at fine scales and illuminate the influence of the highly nutrient-loaded estuaries. Most of the nutri- harbor's summertime export upon nitrogen cy- in western ent loading to Boston Harbor comes from effluent cling Massachusetts Bay. discharge, so current and future wastewater man- Data Sources and Methods agement practices affect nutrient concentrations in Boston Harbor and its offshore shelfwater This paper synthesizes a large body of field, lab- adjacent and data associated with an exten- system in western Massachusetts Bay. A variety of oratory, analyses sive marine carried out studies recently have been conducted in the har- monitoring program large- from 1991 to 1994. Data are drawn from a bor-bay region and this paper provides a synthesis ly variety of that are available (see Acknowl- of results related to nitrogen cycling. reports publicly Some individual results are The paper begins with fundamental information edgments). study pub- lished, while some are in or on Boston Harbor nitrogen loading. Knowing the preparation already allows one to examine concentrations and submitted to the open literature. Detailed methods loading are available in the cited but flows of nitrogen within the harbor in a reports, important budgetary elements are in the context of some context. Where does the input go? Are there nitro- highlighted results and, moreover, brief method de- gen sinks within the harbor? What is the relation- specific are for and/or ship between harbor nitrogen cycling and the bay, scriptions provided major unique which receives harbor outflow? measurements that provide the foundation for conclusions of this The focus in this paper is western Massachusetts synthesis. Bay as well as Boston Harbor, because a variety of Sampling Sites evidence shows that most of the nitrogen loading Monitoring stations were located throughout Boston Harbor, Massachusetts Bay, and some of 1Author: tele: 603/430-8378; fax: 603/430-8378; e-mail: rkel- Cape Cod Bay and included a variety of measure- [email protected]. ments that are not discussed here (e.g., benthic

? 1997 EstuarineResearch Federation 365

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 366 J. R. Kelly

-71.10 -71.05 -71.00 -70.95 -70.90 -70.85 -70.80 -70.75 Fig. 1. The study area in Boston Harbor and western Massachusetts Bay. The seaward boundary of the harbor is arbitrarily defined by a line from Deer Island, at the northern harbor's channel to the bay, to Hull, a hooked peninsula bordering the southern harbor's channel to the bay. A string of islands extending from the harbor into the bay separates northern and southern regions of the harbor. Dark crosses mark water column stations where measurements in 1994 included total nitrogen. Of the three harbor water column stations, only the Deer Island station was sampled prior to 1994. This station, at the edge of the northern harbor, lies just seaward of several major MWRA effluent outfalls. Thin crosses show additional water column stations where standard hydrocast sampling was conducted, but only dissolved inorganic forms of nitrogen were measured. Dots locate sediment stations for denitrification and benthic flux studies. Continuous towed instrument sampling was conducted along a track (dashed line) from the entrance to inner Boston Harbor through the northern channel to a point in the bay almost 20 km from Deer Island; bottom bathymetry along this track is shown in Fig. 11.

infauna, winter flounder, organic contaminants). similar to in situ harbor temperatures. Efflux of N2 The data subset examined focuses on Boston Har- from surface sediments (-5 cm) into overlying wa- bor, western Massachusetts Bay, and the exchange ter and gas phases were corrected for diffusion by of material, particularly nitrogen (N), between the parallel flux determinations on anoxic control estuarine harbor system and its adjacent shallow cores (Nowicki 1994). Rates for Boston Harbor shelf. Besides information on N loading, the paper sediments were reported by Kelly and Nowicki relies on measurements of water quality as sampled (1992, 1993). Denitrification rates (as loss of N2 gas by vertical hydrocasts and continuous in situ sam- to overlying water) were measured at three pri- pling techniques (Fig. 1). Benthic flux measure- mary stations representing different sediment ments were made at several stations in the harbor types in the northern and southern harbor; how- (Fig. 1). ever, a total of six locations throughout the harbor were sampled (Fig. 1). From September 1991 Sediment Denitrification and Benthic Flux Studies through October 1994, denitrification rates for Measurements of sediment denitrification were about 40 station-occupations were obtained, span- made during 1991-1994 (Nowicki et al. 1997) us- ning all seasons. Rates of benthic metabolism and ing a direct gas flux technique (Nowicki 1994) nutrient flux made for the same stations during modified from Seitzinger et al. (1980). Replicate 1991-1994 are summarized by Giblin et al. (1997). sediment cores were collected by diver. In the laboratory, the surface 5 cm of the sediments were Water Quality Measurements transferred intact to a 7.8-cm-dia glass chamber, Water quality sampling and laboratory analytical where N2 release rates were measured under gas- methods followed general oceanographic conven- tight conditions over several days at temperatures tions and were reported by Albro et al. (1993). Tra-

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions EstuaryN Flows to ShallowShelf 367 ditional vertical sampling included measurements where values in parentheses indicate standard er- of temperature and salinity with a CTD (SeaBird rors. The regression slope was significant (p < SBE-9). Density was calculated following Fofonoff 0.001), but the intercept was not significantly dif- and Millard (1983). The sampling system also in- ferent (p = 0.30) from zero. cluded a dissolved oxygen sensor (SeaBird SBE- 13), a fluorometer for measuring in situ fluores- Results and Discussion cence (Chelsea III), and a transmis- Aquatracka FRESHWATER FLOW AND NITROGEN LOADING someter for attenuation of red light (SeaTech 25 EARLY1990s) cm-pathlength). GO-Flo or Niskin sampling bottles (CIRCA (5-1 or 10-1), attached to a rosette, were used to Alber and Chan (1994) summarized both fresh- sample water at about five depths spaced through- water flow and nitrogen data for -1990-1993. To- out the water column at each station. Sampled wa- tal freshwater flow averaged -44 m3 s- 1, dominat- ter was used for analyses of N forms, other nutri- ed by inputs from tributaries (-21 m3 s-1; 48% of ents (P, Si), and a variety of other analyses, includ- total) and from effluent (39% of total). Inputs ing (in vitro) extracted chlorophyll a (Parsons et were calculated for northern and southern harbor al. 1984). NH4+ (Lambert and Oviatt 1986) and subareas (Fig. 1). Most of the total freshwater flow NO3- + NO2- (Lambert and Oviatt 1986) were (34.5 m3 s-1, 78%) and the effluent freshwater flow measured at all depths and locations. Chlorophyll (11.6 of 17 m3 s-1, 67%) was to the northern har- a, dissolved organic N (Valderrama 1981), and par- bor. ticulate N (Lambert and Oviatt 1986) were mea- Alber and Chan's (1994) nitrogen loading esti- sured only at two depths of most stations (Fig. 1), mate for Boston Harbor included contributions near-surface and mid-depth at a subsurface chlo- from Massachusetts Water Resources Authority rophyll maximum if it was present. From 1992 to (MWRA) treatment plant effluent, combined sew- 1994, water quality surveys were conducted in Feb- er overflows, stormwater runoff, airport runoff, ruary, March, April, June, August, and October at tributary flow, atmospheric deposition, groundwa- the stations of interest in the region (Fig. 1). An- ter discharges, and other permitted (non-MWRA) nual cycles (1992-1994) have been reported (Kelly National Pollutant Discharge Elimination System et al. 1993; Kelly and Turner 1995a,b). (NPDES) discharges. Calculated total loading for the harbor and its subareas are given in Table 1. of High-resolution Mapping These estimates represent watershed and direct at- the Harbor-Bay Region mospheric loading; an estimate of the gross input In 1994, 12 towed-instrument studies were con- from the ocean at the harbor-bay boundary was not ducted to gain more insight on the nature of har- attempted. bor-bay coupling at finer scales (Kelly et al. 1995). The harbor's N loading is dominated by MWRA Briefly, a towfish with in situ sensors was oscillated effluent, representing about 89% of the total input from near-surface to near-bottom with the vessel of 12,807 mt N yr-1. Most (76%) of the MWRA underway (-4-7 kts) along transects running from effluent (8,571 of 11,350 mt N yr-1) discharge is within Boston Harbor to a point about 20 km into to the northern harbor. Alber and Chan's (1994) western Massachusetts Bay (Fig. 1). During this error analyses suggest a N loading uncertainty of "tow-yo" sampling, data from the sensors were about ? 22-26% (Table 1). Hunt et al. (1995) continuously recorded and combined with navi- measured MWRA's effluent and estimated annual gational and depth positions. For analyses, the N effluent input for 1994 to be 8,220 mt N yr-1, readings were averaged by 2-s bins, resolving -5- about 28% less than Alber and Chan's effluent av- 6 m horizontally and <1 m vertically. The July 1994 erage. Actual variations loading in daily, as well as survey presented here included an early morning analytical uncertainties in estimation of the efflu- transect near low tide and a mid-afternoon transect ent concentrations and extrapolation uncertainties approaching high tide. During profiling opera- in calculating loading (from concentrations and tions a JRC JFV-120 dual-frequency color video flows), will determine variability in total harbor echosounder provided bathymetric measurements. loading estimates. Overall, the annual N loading Fluorescence readings were calibrated (post-sur- has been strongly characterized and likely lies well vey) to chlorophyll a (Chl a) concentrations mea- within ? 30% of the average estimate (Table 1). sured by in vitro extraction from vertical hydrocast The loading of total nitrogen (TN = all dis- samples of the previous day. For the July survey solved and particulate, organic and inorganic calibration, the predictive linear regression was forms) is given in Table 1. Alber and Chan (1994) Chl a (pLg1-1) = 0.28 (? 0.26) suggested that almost 60% of the effluent loading + 1.34 (? 0.13)Fluorescence was dissolved inorganic nitrogen (DIN = NH4+ + (n = 12, r2 = 0.91) NO3- + NO2-). Hunt et al. (1995) partitioned ef-

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 368 J. R. Kelly

TABLE 1. Nitrogen loading to Boston Harbor and other estuaries.

System Annual Loading, Form Reference Boston Harborb Area Mean 8,470 mmol m-2 yr-1 TN Alber and Chan 1994 Area Low 6,594 mmol m-2 yr-l TN Alber and Chan 1994 Area High 10,674 mmol m-2 yr- TN Alber and Chan 1994 Volume, Mean (1,728 mmol m-3 yr- ) TN Alber and Chan 1994 Area Mean 5,500 mmol m-2 yr-l DIN Alber and Chan 1994 Volume, Mean (1,122 mmol m-3 yr-1) DIN Alber and Chan 1994 New York Bayc Area 31,930 mmol m-2 yr- DIN Nixon and Pilson 1983 Volume (4,550 mmol m-3 yr-1) DIN Nixon and Pilson 1983 Northern San Francisco Bayc Area 2,010 mmol m-2 yr-l DIN Nixon and Pilson 1983 Volume (290 mmol m-3 yr- ) DIN Nixon and Pilson 1983 Narragansett Bayc Area 950 mmol m-2 yr-l DIN Nixon and Pilson 1983 Volume (100 mmol m-3 yr-1) DIN Nixon and Pilson 1983 Chesapeake Bayc Area 510 mmol m-2 yr-l DIN Nixon and Pilson 1983 Volume (80 mmol m-3 yr-1) DIN Nixon and Pilson 1983 Kaneohe Bayc Area 230 mmol m-2 yr-l DIN Nixon and Pilson 1983 Volume (40 mmol m-3 yr-1) DIN Nixon and Pilson 1983 a Note all parenthetical values give volumetric loading. b Uses a total harbor area of 1.08 X 108 mc (Menzie et al. 1991) and a mean depth of 4.9 m (Signell and Butman 1992). c Includes annual input from land drainage and point sources. Does not include precipitation input. fluent nitrogen in samples taken monthly through- northern Harbor, receives an enormous input of out 1994 and found that 70% was DIN, with the nitrogen. remainder about equal portions of dissolved organic nitrogen (DON) and particulate nitrogen IN SITU WATERCOLUMN CONCENTRATIONSOF (PN). NITROGEN Boston Harbor loading (TN and DIN) is com- In spite of very high input, Boston Harbor water pared to a few other estuaries on areal and volu- has not exhibited concomitantly high in situ nitro- metric bases (Table 1). Most of the effluent load- gen concentrations. Robinson et al.'s (1990) data ing to Boston Harbor is delivered to a small initial for eight stations collected over about 2 yr of har- mixing area just inside of Deer Island in the outer borwide monitoring (1987-1988) yield an annual northern harbor (Fig. 1), so rates in Table 1 are, mean harborwide DIN concentration of 10 ,uM. in some areas of the harbor, conservative. Regard- When phytoplankton PN estimated from chloro- less, Boston Harbor as a whole, and especially the phyll was included, the annual mean DIN + PN concentration was - 11.4 ,LM (Kelly 1991). Surveys in 1994 were conducted seasonally (n = 5 or 6 TABLE 2. Mean concentration of N forms at stations in Boston surveys) and provided comprehensive partitioning Harbor in 1994. of N forms in water samples for three harbor sta- DIN PN DON TN tions (Kelly and Turner 1995b). Mean concentra- Station Na (jiM) (RJM) (RpM) (FM) tions (Table 2) were similar to those of Robinson Northern Harbor et al. from the late 1980s. Slightly higher average F23P 60 10.2 3.4 12.1 25.7 DIN and TN concentrations were obtained for the (23) F30B 18 11.9 4.2 7.9 24 northern harbor, compared to the southern har- (12) bor (Table 2). DIN was 40-50% of TN at the three Southern Harbor stations. Nixon and Pilson (1983) and Nixon F31B 15 9.4 3.1 7.5 20 (1983) provide annual mean DIN concentrations (10) for a number of major estuaries in the United States. Many estuaries in Nixon's summary, includ- Mean 93 10.5 3.6 9.2 23.2 ing New York Bay, Delaware Bay, Chesapeake Bay, (45) Patuxent River Estuary, Potomac River Estuary, and a The number of samples depends on the form of N. The San Francisco Bay, have lower loading rates (Table higher number is for DIN, measured at 3-5 depths on 5-6 sur- 1) but have average DIN concentrations >20 ,uM- veys. The lower number is for organic forms measured only at double or more the value for Boston Harbor. surface and mid-depth. Duplicate measurements were made at station F23P, which lies near Deer Island at the edge of the The annual volumetric loading to the harbor is northern harbor (Fig. 1). 1,728 ,uM yr-1 for TN and 1,122 mmol ,iM yr-1 for

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions Estuary N Flows to Shallow Shelf 369

DIN (Table 1). This is many times the average mea- 1II()( ( - sured concentrations of 23.2 tuMand 10.5 txM for x- 4, TN and DIN, respectively (Table 2). Dividing the 3 volumetric loading by the average concentration z 100- 1, _ ' - 2, " provides an estimate of the turnover time neces- - - to maintain concentrations as low as mea- 4110 100 1000 sary - sured; for these data, the results were 4.9 d for TN 10 - 1' and 3.4 d for DIN. To explain these results we must identify processes that can remove or assimilate water column N within about 3-5 d on average. A major biological removal mechanism is nitro- in gen uptake by plankton primary production Loading (mmol m-3 res time-1) processes, but to provide removal of TN the uptake must be also be followed by deposition to bottom X - D TN sediments. A simple calculation can assess the potential of this cycle, by looking at the first step, Fig. 2. DIN concentration as a function of N loading for a primary production. Kelly and Doering (1995) number of estuaries in the United States. Data for Boston Har- have summarized recent net primary production bor are provided in this paper. Other systems were summarized Nixon where the concentration data were measurements for a station at the edge of the har- by (1983); possible, vertically and horizontally averaged. Nixon multiplied annual bor. As an example, in 1994, production was -266 input by a "mean hydraulic residence tim ated as the gC m-2 yr-~. Converting to nitrogen, assuming a mean freshwater replacement time = mean freshwater volume/ Redfield (C:N, atoms = N mean freshwater input) to estimate loading for 1 Narragan- stoichiometry by 6.625), = = = for net amounts to 682 pLM sett Bay, 2 New York Bay, 3 Delaware Bay, 4 Chesapeake uptake production yr- 5 = Patuxtent River 6 = Potomac River 7 for the harbor. This amount a substan- Bay, Estuary, Estuary, represents = Pamlico River Estuary (mid and lower portions only), 8 = tial fraction of DIN loading (-61%) but only 40% Apalachicola Bay, 9where pMobile Bay, the Northerntran Francisco of TN loading. Using the uptake and the average Bay, 12 = South San Francisco Bay, and 13 = Kaneohe Bay. TN TN concentration, the implied turnover rate, on and DIN each are shown for Boston Harbor (14). For Boston rather than the freshwater a average, is -12 d and therefore the initiating first Harbor, replacement calculation, range of 2-10 d (mid-point of 6 d) was used based on estimates step of the biological removal cycle is too slow on of the tidal flushing (see text). The dashed line depicts a 1:1 average to be a consistent removal mechanism. In correspondence between loading and concentration. summer, primary production and the biological cycle can be an important removal process (de- scribed later), but in any recent year of measure- this, tidal flushing occurs in the fundamental time- ments (e.g., Kelly and Doering 1995), average daily frame (i.e., days to week) required to maintain the production rates have not been high enough to observed low concentrations of TN and DIN. maintain average DIN concentrations as low as ob- Comparing the data of Boston Harbor to a sum- servations. mary of 12 coastal systems (Nixon 1983), Boston In contrast, the physical process of tidal flushing Harbor showedanomalousbetween loadingw) N concentrations occurs regularly, on a timescale fast enough to be for its N input. However, if loading is corrected by a consistent removal mechanism, and in Boston an estimate of water residence time for each sys- Harbor generally determines the water residence tem, Boston Harbor (with relatively fast flushing) time (Signell and Butman 1992). Various studies falls approximately in line with other data (Fig. 2). and calculations (e.g., Kelly 1991; Shea and Kelly The pattern in Fig. 2 is consistent with experimen- 1992; Signell and Butman 1992; Signell personal tal marine mesocosm studies (Kelly et al. 1985) communication) have suggested that the expected showing that average TN concentrations were lin- flushing (water residence) time of the entire har- early proportional to increasing N loading when bor is on the order of days (-2-10). Flushing var- flushing rate was controlled. Nixon (1983) esti- ies with winds (speed and direction) and with mated flushing as the mean freshwater replace- spring versus neap tides (Signell and Butman ment time (a method which is essentially blind to 1992). Sluggish backwaters in inner portions of the the mechanism(s) of flushing), whereas the esti- harbor which have weak tidal currents must flush mate of flushing for Boston Harbor comes more more slowly than the harbor average. In contrast, directly from modeling of tidal exchange. In con- material released in the strong tidal channels near trast to Boston Harbor, some of the systems in Fig. the harbor mouth at Deer Island must be flushed 2 are more riverine and more strongly flushed by more rapidly than the harbor as a whole. The lo- advective freshwater flow. In principle, the agent cation of the principal MWRA effluent discharge for flushing is less key than the timeframe, so the of nitrogen is off Deer Island (Fig. 1). Considering different methods (Fig. 2) should provide compa-

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 370 J. R. Kelly rable estimates, especially given that they are crude and N2 loss represented about 30-50% of the total approximations for each system that do not con- nitrogen flux from sediments (Kelly and Nowicki sider well the small-scale heterogeneities of circu- 1993; Giblin et al. 1994, 1995). lation, mixing, and freshwater input variability. Mean daily rates should not be simply extrapo- Further examination of the pattern in Fig. 2 is war- lated to derive an annual value: rates in higher or- ranted, particularly as understanding of estuary- ganic conditions rise exponentially, not linearly, shelf exchange processes improves. For the pur- with temperature (Nowicki 1994), and a spatial pose of this paper, Fig. 2 is first-order evidence con- mosaic of sedimentary environments, with differ- sistent with suggestions of the importance of water ent characteristic flux rates, are present in Boston residence time in coastal ecosystems, including Harbor (Knebel et al. 1991). Recognizing these Boston Harbor (cf. Valiela and Costa 1988; Nixon factors, annual estimates have been derived from et al. 1996). the harbor data. For example, one harborwide an- The above calculations and comparisons lead to nual value (666 mmol N m-2 yr-1) was obtained by the tentative conclusion that tidal flushing is a ma- extrapolating over time using temperature-flux re- jor influence on Boston Harbor's nutrient status. lationships and over space by developing sediment Rather than an internal (within harbor) sink, there organic carbon content-flux relationships (Kelly seems to be a more principal role of tidal flushing and Nowicki 1992). and removal of nitrogen loading (by advection) to A second annual value was obtained by appor- the offshore system, western Massachusetts Bay. tioning rates to classes of sedimentary environments, that is, those being "depositional," "sedi- ANNUAL BUDGET FOR NITROGEN ment reworking," or "erosional/nondepositional" SINKS IN THE HARBOR as classified by Knebel et al. (1991). Fractional ar- Primary production initiates the biological re- eas of 51%, 29%, and 20%, represent depositional, moval cycle, but the actual internal sink occurs sediment reworking, and erosional/nondepositional within harbor sediments, through permanent buri- classes, respectively. It was possible to develop a al or denitrification. Denitrification flux incuba- flux-temperature relationship for a very high or- tions were conducted near in situ temperatures; ganic, depositional sediment. In contrast, a sandy, measurements in 1991-1994 spanned the temper- erosional/nondepositional sediment station had ature range -1?C to 18?C-similar to the seasonal rates that were more constant and independent of range in bottom water of the harbor. Individual temperature. Using all 1991-1992 depositional Harbor stations had rates ranging from nondetect- class flux-temperature pairings (n = 16 replicate able to 9.9 mmol N m-2 d-1. There was substantial measurements), flux data were convolved with the spatial and interannual variability in denitrification annual bottom-water temperature cycle. An inte- rates. Many individual measurements exceeded 3 grated value of 772 mmol N m-2 yr-1 was calculat- mmol N m-2 d-1; these substantial rates are within ed. In contrast, an approximation for the nonde- the high end of the range reported for subtidal positional case was 400-500 mmol N m-2 yr-1. It estuarine sediments (cf. Seitzinger et al. 1980; Seit- was assumed that the sediment reworking class had zinger 1988; Nowicki 1994). Highest rates in Bos- a rate intermediate to the other two classes. Using ton Harbor were observed under conditions of Knebel et al.'s (1991) fractional areas for extrap- summertime temperatures, with high sediment or- olation, an annual estimate of 660 mmol N m-2 ganic content (-3% C), and with the presence of yr-l was derived for 1992 (Kelly and Nowicki 1993). infauna (e.g., Nereis and/or Ampelisca mats) that The station providing the primary basis for the de- were actively burrowing or irrigating surface sedi- positional class had high fluxes relative to other ments. Mean rates were highest in 1993 when Am- measured depositional-class sediments with mod- pelisca flourished throughout the year at one high erate-to-high organic contents. Moreover, Knebel organic station (cf. Giblin et al. 1994; Kropp et al. et al.'s (1991) erosional/nondepositional class in- unpublished data). Mean values for each suite of cluded some hard-bottom area, but for the com- measurements (n = 10 to 15) in calendar years putations the class was assigned a rate typical of 1992-1994 ranged from -1.6 mmol N m-2 d-1 to hard-sand, low organic sediments. Considering 2.9 mmol N m-2 d-~. Denitrification rates mea- these facts, the derived denitrification estimate for sured by the gas flux technique, when compared the whole harbor must be biased high. to rates calculated indirectly by stoichiometric Additional data (1993-1994) and computational modeling, showed some scatter among individual schemes (B. Nowicki, personal communication) measurements, but annual averages were compa- lead one to conclude that integrated annual de- rable (Giblin et al. 1992, 1993, 1994). Generally, nitrification in harbor sediments created a N2 gas N2 flux was slightly less than DIN release to the loss of -600-800 mmol N m-2 yr-~ during the pe- overlying water from sediment remineralization, riod of measurements. Simple sensitivity analyses

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions EstuaryN Flows to ShallowShelf 371

Denitrification 45 Input -600-800 N2 i 40 35

8,470 TN 30 5,500 DIN J252 25

Offshore 20

>7,460 - 15

+ 10

0 Jan Mar May Jul Sep Nov Burial Feb Apr Jun Aug Oct Dec ----- __------_ _ -- - -TN DIN | -200 Fig. 4. Annual cycle for TN and DIN in Boston Harbor water. Data are from 1994. Points and bars indicate the mean and Units of mmol N m-2 y-1 range of concentrations measured at 2-5 depths at the three Fig. 3. A simple annual nitrogen budget for Boston Harbor harbor stations given in Fig. 1. emphasizing internal sinks and export for N input. Fishing and dredging are additional, but minor, N removal terms (see text). All rates are mmol N m-2 yr-~. includes pre-modern conditions and must be a minimal estimate of recent accumulation. The related to computational schemes suggest that un- high-range estimate covers recent decades but certainty around integrated annual rates might be does not account properly for bioturbation effects +10-20% (Kelly and Nowicki 1993). Considering and therefore is "apparent" and a maximal esti- this, annual rates could be as high as 1,000 mmol mate. Suspended loading from land sources to N m-2 yr-1. Boston Harbor was estimated as 900 g dry solids A mid-range value of 700 mmol N m-2 yr-~ rep- m-2 yr-1 (Menzie et al. 1991). Spread across the resents 8% of the annual TN input to the harbor harbor, this would provide about 0.1 cm yr-~ for (Fig. 3). In comparison, Adams et al. (1992) used sediment accumulation. On the one hand, some a simple box model with flushing rates similar to of this suspended matter loading is organic and Signell and Butman (1992); their model predicted will be decomposed before burial; on the other that sediment denitrification accounted for about hand, Menzie et al.'s (1991) estimate does not in- 5% of the N input, with their model sensitivity clude input from marine erosion (Knebel et al. analyses suggesting 22% as the upper bound. In 1991). On balance, the rate of 0.1 cm yr-1 value short, an extensive set of data and modeling pro- may be high but is a reasonable first-order approx- vide a body of evidence to show denitrification as imation. From a variety of studies, the average or- a minor sink (<10%) for nitrogen in the harbor. ganic C content of recent (near-surface) harbor The Boston Harbor budget also confirms a con- sediments is -2.5%; use of surface concentrations tention that sediment denitrification may not pro- may slightly overestimate content of buried sedi- vide enough nitrogen removal to alleviate eutro- ments, but depth profiles are often not distinct phication effects in some coastal waters (Nowicki enough to determine a "background" concentra- and Oviatt 1990; Nowicki 1994). tion appropriate for burial below a bioturbation Permanent burial in harbor sediments repre- zone. Typically, the C:N content of harbor sedi- sents a smaller nitrogen sink than denitrification. ments has been about 8 by weight (cf. Giblin et al. Many researchers have grappled with estimating a 1994, 1995). Using the 900 g dry solids m-2 yr-1, net sediment accumulation rate for Boston Har- representing accumulation of 0.1 cm yr-1, burial is bor. The most reliable estimates for annual sedi- 200 mmol N m-2 yr-1. This sink removes about 2% ment accumulation harborwide range from 0.02 of the N input to the harbor (Fig. 3)-a percent- cm yr-I to 0.2 cm yr-~ (Knebel et al. 1991), similar age in line with burial determined for other north- to the range for Narragansett Bay, Rhode Island east temperate coastal estuaries (cf. Knebel et al. (Santschi et al. 1984). The low value of the range 1991). Consistent with other studies (e.g., Kelly

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 372 J. R. Kelly

-71.10 -71.00 -70.90 -70.80 -70.70 -70.60 -70.50 Fig. 5. DIN concentration gradient in western Massachusetts Bay. Means are from surface data of six surveys throughout the year. Sampling extended throughout Massachusetts Bay. and Nixon 1984), most of the nitrogen deposited sidered it is evident that the harbor is an inefficient to Boston Harbor bottom sediments is not retained nitrogen trap. Annual budgeting therefore con- in the sediments but remineralized to inorganic N; firms the earlier tentative conclusions: internal on average roughly 40% of the total inorganic N sinks are relatively minor and export is the domi- flux from harbor sediments is N2 gas (Giblin et al. nant nitrogen removal process. 1997). Other processes for removal of nitrogen within SEASONAL INFLUENCE OF BIOLOGICAL PROCESSES ON the harbor are fishery harvest and dredging. Sim- THE HARBOR NITROGEN BUDGET ple calculations showed that shellfish harvests re- Because denitrification in most of the sediments move minimal nitrogen (<0.25%) and that dredg- within Boston Harbor is sensitive to temperature ing, conducted periodically, may provide a long- and the activity of infaunal organisms, rates rise in term removal of 1-2% of inputs (Kelly and Now- summer, to represent removal of -12% of the ni- icki 1992). It is unknown whether dredging and trogen loading, expressed as an annual average burial estimates are independent of each other or (Kelly and Nowicki 1993). However, concentra- represent double counting; regardless, for our pur- tions and loading of MWRA effluent TN also can pose they are clearly minor removal terms. rise -1/3 in summer compared to winter (Hunt Summary of significant removal terms (Fig. 3) et al. 1995), so higher absolute denitrification rates indicates that advection of > 88% of the input may may be commensurate with increased summer ef- be required to balance the budget. Removal esti- fluent loading. mates have uncertainties, but efforts have been Other in situ biological processes in the harbor made to bias them high. Input estimates also carry may affect the quality of nitrogen exported season- uncertainties (Table 1) but when everything is con- ally to western Massachusetts Bay by altering the

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions EstuaryN Flows to ShallowShelf 373

Fig. 6. NH4+ concentration gradient in western Massachusetts Bay. Means are from surface data of six surveys throughout the year. Sampling extended throughout Massachusetts Bay. partitioning of nitrogen forms in the water. For ex- ganic-rich sediments sometimes released >10 ample, wintertime net primary production (NPP) mmol N m-2 d-1 (volumetrically, >2.0 jxM d-1), rates (pre-spring bloom) were on the order of 0.3 which is over 40% of the daily loading. Summer- gC m-2 d-1, whereas summer rates averaged over time NPP therefore is, in principle, capable of 1 gC m-2 d-1 and were sometimes >1.5 gC m-2 d-1 maintaining steady-state water column nitrogen (Kelly and Doering 1995). At 1.5 gC m-2 d-1 (-3.8 concentrations by assimilating all new loading and JLMN d-l1), NPP could assimilate summertime wa- sediment remineralization within about 2 d-equal ter column TN in about 5 d and DIN in about 1 to or less than the time it takes to tidally flush the d. In part, the turnover due to NPP in summer is harbor. Most of the NPP is continuously reminer- more rapid because water column concentrations alized (in water and in sediments), so the biologi- were at annual minima (Fig. 4). The fact that a cal processes largely cycle, rather than remove, ni- water column very strong seasonal cycle occured in DIN concen- trogen. But instead of maintaining ni- trations is itself evidence that biology has an influ- nitrogen in the DIN fraction during summer, tends to be held within such ence on the harbor's nutrient cycle. Biology may trogen organic forms, biomass and dissolved nitro- also influence TN concentrations, for they also as plankton organic As a seasonal were lower (-5-10 jiM) on average in summer gen (DON) (Fig. 4). consequence, variations in biological activity are effective at in- compared to winter (Fig. 4). Summertime NPP the concentration and partitioning of ni- rates >3 JLMd- 1 could nearly assimilate measured fluencing trogen forms in the water within Boston Harbor. daily inputs to the harbor (expressed volumetrically = -4.7 jiM d-1 TN, 3.1 jLMd-1 DIN). Mea- EVIDENCE IN THE RECEIVING SHELF SYSTEM sured summer benthic DIN release rates (Giblin et If the nitrogen export were as large as suggested al. 1995) were greater than denitrification flux; or- by the harbor budget, there would be obvious trac-

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 374 J. R. Kelly

-71.10 -71.05 -71.00 -70.95 -70.90 -70.85 -70.80 -70.75 Fig. 7. TN concentration gradient in western Massachusetts Bay. Means are from surface data of six surveys throughout the year. Sampling for TN was limited to Boston Harbor and western Massachusetts Bay.

es of it within western Massachusetts Bay. In the periods when there was a defined outflow from the 1970s Pandan (1977) noted a nutrient (including harbor, evident as a lower salinity surface plume NO3-) concentration gradient from Boston Har- bending southward along the coast. bor into Massachusetts Bay. Not all nitrogen forms were measured in studies of that time, but DIN, SEASONAL VARIATIONS IN EXPORT TN, and associated partitioned forms of nitrogen During the colder seasons, inorganic and organ- recently have been monitored in Massachusetts ic nitrogen forms often appeared to mix roughly Bay. Using annual averages for available near-sur- conservatively from the edge of the harbor into face data from 1990 and 1992-1994, spatial pat- surface waters of western Massachusetts Bay. As an terns have confirmed that the harbor acts as a example (Fig. 8), February DIN concentrations in strong source of nitrogen into the western Massa- near-surface waters were linearly correlated with sachusetts Bay region (Figs. 5, 6, and 7). Consistently, linity (r2 = 0.71; n = 10; p < 0.001), as were TN the annual mean concentrations of DIN at the concentrations, albeit with higher variability (r2 = edge of the harbor have been -6-8 uM higher 0.41; n = 10; p < 0.03). The pattern supports the than conditions about 10-20 km into the bay. concept of dispersion into the bay and dilution of Mean annual TN concentrations declined about fresher, high-nitrogen harbor water with back- 10-13 ,LMover the same distance from the harbor. ground bay water. In this case, biological activity in NH4+ was usually <1 JiM in most of the bay but the harbor (as well as the bay) was relatively low; showed distinct enrichment near the harbor. NH4+ the data support the notion that physical processes is a main component of effluent DIN (as well as largely dictate the distribution of nitrogen. Export remineralized nitrogen) and offers a simple short- of DIN, as well as other forms, was efficient under term tracer of harbor export. Generally, the area these conditions and the bay was largely inorgani- with elevated TN, DIN, and NH4+ concentrations cally fertilized by the harbor. has extended further from the harbor, southward In contrast, summertime biological processes are along the coast. This average feature was not pres- capable of influencing concentrations faster than ent at all times of the year but can be attributed to physical processes cause dispersion. With generally

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions EstuaryN Flows to ShallowShelf 375

February 1994 June 1994

J -J 1J 30- 0 30

25- 0 0 25

20- * 0* Z 20 15- 15 z F-z 10- 10 5- 5 0 i ; 0 I 1 30 31 32 33 30 31 32 33

February 1994 June 1994

35 , ., 30- 30 25- 25- :3 20- 20- z 15- z 15- C2 10- n 10- d 5- 5- L 0 o J 0 l I ", 30 31 32 33 30 31 32 33 Salinity (uM) Salinity (uM) Fig. 8. Nitrogen concentrations as a function of salinity during winter and summer. Data include near-surface samples in Boston Harbor and western Massachusetts Bay (dark-cross stations, Fig. 1).

depleted DIN concentrations, there can only be 20 minor export of DIN. In June (Fig. 8) low DIN concentrations were observed at all salinities and 18 - there was not a significant relationship between = = 16 - DIN and salinity (r2 0.4; n 16; p < 0.46). How- ever, there was a significant linear correlation be- 14 - = = A tween TN and salinity in June (r2 0.59, n 16, the narrow range of 12 - D p < 0.0003), in spite of salinity O " that was (Fig. 8). z sampled 10 - Seasonal trends for winter and summer 1994 c 0 = '. CO % in a) 8 - were fairly representative of similar surveys pre- s oO vious years. Especially in summer, a strong shore- - 6 to-sea TN gradient has been a persistent and reg- A A 4 - ? ularly observed feature. As an example, data for A +_ AA the summer of 1992 are shown in Fig. 9. On av- 2 - - the approximately linear decrease of TN +- erage, 0 I I' '1I i i + into the bay suggested a principal process of dis- 30.6 30.7 30.8 30.9 31 31.1 31.2 31.3 31.4 persion of nitrogen in a manner similar to that of Mean Salinity (PSU) the fresh water emanating from the harbor. The trend is apparent for both organic nitrogen forms, I o A DIN I TN DON PN + j DON and PN, suggesting that the harbor acted to this sea- N concentrat ions in west- organically fertilize the bay in summer. At Fig. 9. Summertime surface-layer the lowest ern Massachusetts Bay as a function of salinity. Daita from the son, DIN concentrations were routinely upper water column (-10-15 m) have been verticaally averaged of all measured forms and did not consistently for June and August 1992 surveys during thermaIlly stratified show a gradient. conditions. In 1992, sampling was conducted only to the edge Overall results indicate that the annual nutrient station in ti northern of Boston Harbor but included the and the of were affected by channel off Deer Island. One station (salinity 30.9 5oe PSU) budget quality export had DIN measurements. Data were compiled by K

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 376 J. R. Kelly

7 0

- 6 ? -10 it W _ -I5

-20- 0 - c_ s-4 -25 (1) 03 - E .2 -

C.2 -U ' -35 D? -40- 1 - -45-

0 I I I I I I i I ' I , I ' I i -57 0.. - 11- 111- 1- ...... ''I''. I'll - I I I 30.6 30.7 30.8 30.9 31 31.1 31.2 31.3 31.4 -71.02 -70.97 -70.92 -70.87 -70.82 -70.77 -70.7 Mean Salinity (PSU) Longitude Fig. 10. Surface-layer chlorophyll concentrations in western REGION + + + Boston Horbor ? Chonnel Massachusetts Bay as a function of salinity. Data as per Fig. 9. 0 0 0 Boy Fig. 11. High-resolution "tow-yo" sampling along survey transect from Boston Harbor to Massachusetts Measured tides. Additional inference with to summer Bay. respect bottom topography is displayed. In situ sensor data have been export and its potential effect on the bay can be summarized as 2-s bin-averaged data, marking the general drawn from Fig. 9. For either TN, DON, or PN, if V-path of oscillation of the towfish through water column. Dif- one drew a line from concentrations at lowest and ferent symbols codify data by three geographic regions for anal- The area "outside" the harbor salinities, a number of at interme- yses (see Fig. 13). immediately highest points is a shipping channel in the westernmost bay. diate salinity are well above the line. This feature suggests an accumulation area, or an unknown source, for organic N forms at stations within the deeper water of the bay, a mid-depth chlorophyll region of active tidal excursion of water from the maximum (-2-3 pxg1-1) was evident, but a semi- harbor (e.g., Signell and Butman 1992; Kelly et al. isolated patch of high chlorophyll (>6 pIg 1-1) was 1995). Summer chlorophyll concentration patterns noted in bay surface waters several kilometers east with salinity were similar to TN (Fig. 10). The av- of the channel (see Fig. 11) leading from the edge eraged chlorophyll data showed a general linear of Boston Harbor into the bay (Fig. 12a). The area trend with salinity, but, like TN, enriched concen- with high chlorophyll concentration was persistent trations again were indicated at intermediate salin- near a sharp density front, which itself became par- ity. tially isolated from inshore water by a thermocline upwelling into the channel as the tide flooded EFFECTS OF TIDAL EXCHANGE DURING SUMMER (Fig. 12b). The center of the chlorophyll patch - Since strong export has been indicated, one may and the density front (UT 23.5) were displaced ask what responseis observable in the receiving sys- concomitantly several kilometers shoreward with tem. High-resolution harbor-bay transect studies the flooding tide, almost to station F24 (Fig. 12b). (Kelly et al. 1995) offer initial results on this ques- Moreover, chlorophyll concentrations within the tion. For a July 1994 survey (Fig. 11), sampling was patch increased through the day as shown by the conducted around low tide (leg 1) and nearing high tide sampling (Fig. 12b). It was also noted high tide (leg 3), as indicated in inserts to Figs. that the water from within the thermocline surged 12a and 12b. Using the oscillating towfish data, into the harbor with the flooding tide (Fig. 12b). chlorophyll concentrations and density were spa- Figure 13 shows chlorophyll as a function of sa- tially contoured for each survey leg (Figs. 12a, b); linity for the condition when the tide was low and a comparison of chlorophyll to salinity for leg 1 is the tidal excursion of lighter, less saline seawater in Fig. 13. was furthest into the bay. There were high chlo- Typically high summer chlorophyll concentra- rophyll values at low salinity in the harbor and low tions (>6 pxg1-1, peaking at >10 pg 1-1) were not- values at higher salinity in the channel and in the ed in the harbor. The bay was thermally stratified, bay. The main body of data showed a nearly inverse whereas the harbor was vertically well-mixed. In chlorophyll-salinity relationship. These data gen-

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions EstuaryN Flows to ShallowShelf 377 Chlorophylla (a) 0 - t - sI -10- .-. - E -20 liii I CF -c -30 - -t I C0 -40 -.

-50- 4 1 I ? 11 Om 6000m 12000m 18000m 24000m

Sirrma-T

O F30-

-10--

E -20 . : . : . :.. ' ; : .: i .! il, -L v-, -30-- 0 ' -EJ 2 2: 2' : ...... ! 1 -4O -- \ - i 4,: :1i 2: 2; 2:4i ~: : i: :: ;: F.. -50 -I [: : I,i1 i! - I L

Ormr 6000m 12000m 18000m 24000m

Chlorophyll a (b) Ni6P (b)

E -c C- C) C

Cm 6000m 12000m 18000m 24000m Siama T o P3GB

~~~~4-10- '2 - 2 2

-50 -i:,.

Om 6000m 12000m 18000m 24000m

Fig. 12. a) Fluorescence (as chlorophyll a, JILg1-1) and seawater density (oT) as contoured from high-resolution sampling near low tide on July 28, 1994. b) Fluorescence (as chlorophyll a, jig 1-1) and seawater density (aT) as contoured from high-resolution sampling approaching high tide on July 28, 1994.

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 378 J. R. Kelly

W9409 Leg 1 (Low Tide)

15 14- 13- 12- 11- + 4i- ++ HIGH 10- >0 + +, ++k I + 9.0- C)_ 4OW'" 8.0- f 0 + 7.0- WV4 0 LOW4 + W o 6.0- (-- (0 5.0- 4.0- LOW -^ 3.0- 2.0- LOW -* 1.0- .00 I ,, i I I I II I I I i T I II I I ]- T I ]I I [ I I I T I I I T I I 1 I I T II' T I I I ] 30.0 30.4 30.8 31.2 31.6 32 Satinity REGION + + + Boston Harbor ? ? * Channel 0 0 0 Bay

Fig. 13. Fluorescence (as chlorophyll a, iLg 1-) as a function of salinity from high-resolution sampling near low tide on July 28, 1994. Data were coded by region as shown in Fig. 11.

erally are consistent with the notion of strong mix- production (without correcting for advective or ing and dilution of harbor chlorophyll (with TN) grazing changes) near 3 gC m-2 d-1, a high value into the surface layer of the bay during summer. A but within the range of measured net primary pro- slight concavity in the salinity-chlorophyll relation duction rates in the western bay region (Kelly and at mid-salinity may result from mixing of a low- Doering 1995). chlorophyll source into the channel from the edge The high-resolution data confirm dispersion of of the harbor where the MWRA effluent is dis- chlorophyll (and by proxy, TN) into the surface charged. Another cluster of points with low chlo- layer of the bay and also identify a potentially pro- rophyll was noted for surface bay water under strat- ductive region at the edge of the tidal front where ified conditions at - 16,000 m along the transect high chlorophyll concentrations are persistent. (Fig. 12). Based on temperature-salinity plots (Kel- Factors enabling high chlorophyll and high pro- ly et al. 1995), this bay water did not mix with the duction may include removal of light limitation harbor-bay tidal region. A principal exception to (harbor water is turbid), access to greater nutrient conservative mixing was the anomalous cluster of supplies (from the harbor via organic matter re- points with high chlorophyll (Fig. 13) at interme- mineralization if not small pulses of NH4+ export; diate salinity (e.g., 31.4 PSU). These data, confirm- also perhaps from upwelling of the thermocline ing the observation using averaged summer data bringing higher nutrients near the surface), and (Fig. 10), demonstrate that the high chlorophyll at stability of the water column (cf. Kelly 1993). Re- the seaward edge of the tidal front (near the gardless of mechanisms, the high-resolution data 12,000 m mark, Fig. 12) was not produced by sim- clarify the nature of the Boston Harbor-Massachu- ple mixing. setts Bay interaction by identifying one aspect of Comparison of low-tide and high-tide tracks the response of the bay to high nutrient export at (Fig. 12) indicated flood-tide movement of water a tidal-diurnal scale of observation. shoreward along the whole transect and also sug- Conclusions gested in situ chlorophyll growth during the day and Perspective could have produced the locally observed, high The evidence is overwhelming that Boston Har- chlorophyll concentrations. A simple calculation bor is an inefficient trap for the huge mass of ni- from the observed chlorophyll change (leg 3-leg trogen that presently flows into it from its water- 1) within the advecting patch implies net primary sheds. Consequently, it exports most of its nitrogen

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions EstuaryN Flows to ShallowShelf 379 loading to western Massachusetts Bay. Export qual- ALBER,M. ANDA. CHAN. 1994. Sources of contaminants to Bos- ity varies seasonally, with high DIN export in win- ton Harbor: Revised loading estimates. Massachusetts Water Resources Authority Environmental Quality Department ter, prior to a spring bloom in the harbor. In con- Technical Report Series No. 94-1. Massachusetts Water Re- trast, organic export dominates in the summer. sources Authority, Boston, Massachusetts. The main agent for export is tidal flushing. This ALBRO, C.J. R. KELLY,J. HENNESSY,P. DOERING, AND J. TURNER. study is a prime example of the importance of rap- 1993. Combined work/quality assurance plan for baseline wa- id in some shallow tidal Re- ter quality monitoring: 1993-1994. Massachusetts Water Re- flushing embayments. sources Authority Environmental Quality Department Tech- sults also demonstrate the extension of a water- nical Report Series No. ms-14. Massachusetts Water Resources shed's influence not just upon estuarine receiving Authority, Boston, Massachusetts. waters but also upon the adjacent coastal shelf wa- FOFONOFF,N. P. ANDR. C. MILLARD,JR. 1983. Algorithms for ters. computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science. 44. UNESCO, Finally, results are of interest with respect to Paris. changing perspectives on estuaries. Decades ago GIBLIN,A. E., C. HOPKINSON,AND J. TUCKER.1992. Metabolism some estuaries were characterized as marvelous and nutrient cycling in Boston Harbor sediments. Massachu- nutrient traps, where countercurrent and salt- setts Water Resources Authority Environmental Quality De- flow aided and accumula- partment Technical Report Series No. 92-1. Massachusetts Wa- wedge high production ter Resources Massachusetts. tion of matter (Odum 1959). In de- Authority, Boston, intervening GIBLIN,A. E., C. HOPKINSON,ANDJ. TUCKER.1993. Metabolism, cades, we have recognized that many estuaries, like nutrient cycling, and denitrification in Boston Harbor and Boston Harbor, receive massive flows of nutrients Massachusetts Bay sediments. Massachusetts Water Resources and are more like material "transformers" (e.g., Authority Environmental Quality Department Technical Re- Series No. 93-2. Massachusetts Water Resources Author- Valiela and Teal 1979) or partial "filters" (e.g., port ity, Boston, Massachusetts. Kennedy 1984). It is generally recognized that we GIBLIN,A. E., C. HOPKINSON,J. TUCKER,B. NOWICKI,AND J. R. need to know much more than land-derived load- KELLY.1994. Metabolism, nutrient cycling and denitrification ing and watershed inputs to understand estuaries. in Boston Harbor and Massachusetts Bay sediments in 1993. This study is a case in point that we need to study Massachusetts Water Resources Authority Environmental not the but also its interaction with the Quality Department Technical Report Series No. 94-5. Mas- just estuary sachusetts Water Resources Authority, Boston, Massachusetts. sea. Some estuaries function as a strong hydrolog- GIBLIN,A. E., C. HOPKINSON,J. TUCKER,B. NowicKI, ANDJ. R. ical conduit to the sea with respect to some mate- KELLY.1995. Metabolism, nutrient cycling and denitrification rials, even when they are only weakly flushed by in Boston Harbor and Massachusetts Bay sediments in 1994. runoff from the land. Massachusetts Water Resources Authority Environmental Quality Department Technical Report Series No. 95-13. Mas- sachusetts Water Resources Authority, Boston, Massachusetts. ACKNOWLEDGMENTS GIBLIN,A. G., C. S. HOPKINSON,AND J. TUCKER.In press. Ben- The author was funded by the Massachusetts Water Resources thic metabolism and nutrient cycling in Boston Harbor, Mas- Authority (MWRA) as technical director on two contracts to Bat- sachusetts. Estuaries20:344-362. telle Ocean Sciences, Duxbury, Massachusetts. The MWRA has HUNT, C. D., D. E. WEST,AND C. S. PEVEN.1995. Deer Island a publicly available technical report series that includes all stud- effluent characterization and pilot treatment plant studies: ies cited in this synthesis; listings may be obtained from Ber- June 1993-November 1994. Massachusetts Water Resources nadette McCarthy, Environmental Quality Department, Massa- Authority Environmental Quality Department Technical Re- chusetts Water Resources Authority, Boston Massachusetts port Series No. 95-7. Massachusetts Water Resources Author- 02129. I thank Mike Connor, Mike Mickelson, Ken Keay, Meryl ity, Boston, Massachusetts. Alber, and Wendy Leo of the MWRA. Relevant field studies were KELLY,J. R. 1991. Nutrients and Massachusetts Bay: A synthesis conducted by Battelle Ocean Sciences (BOS), the University of of eutrophication issues. Massachusetts Water Resources Au- Rhode Island (URI), the University of Massachusetts-Dartmouth thority Environmental Quality Department Technical Report (UMD), and the Ecosystems Center, Marine Biological Labora- Series No. 91-10. Massachusetts Water Resources Authority, tories (MBL). I thank Barbara Nowicki, Peter Doering, Candace Boston, Massachusetts. Oviatt, and numerous staff and students at URI; Jeff Turner and KELLY,J. R. 1993. Nutrients and Massachusetts Bay: An update David Borkman at UMD; Anne Giblin, Chuck Hopkinson, and of eutrophication issues. Massachusetts Water Resources Au- Jane Tucker at MBL; and Carlton Hunt, Damian Shea (now thority Environmental Quality Department Technical Report North Carolina State University), John Hennessy, Scott Libby, Series No. 93-17. Massachusetts Water Resources Authority, Roy Kropp, and Rosanna Buhl at BOS. Special thanks to Carl Boston, Massachusetts. Albro (BOS) who developed the high-resolution sampling and KELLY,J. R., C. S. ALBRO,P. DOERING,K. FOSTER,J. HENNESSY, data acquisition system, and produced Fig. 12 for this paper. L. REED,AND E. REQUINTINA.1993. Water column monitoring Study conclusions are solely the perspective of the author and in Massachusetts and Cape Cod Bays: Annual report for 1992. do not necessarily reflect the opinion or perspective of the Massachusetts Water Resources Authority Environmental MWRA. Quality Department Technical Report Series No. 93-16. Mas- sachusetts Water Resources Authority, Boston, Massachusetts. GEYER.1995. LITERATURE CITED KELLYJ.R., C. S. ALBRO,AND W. R. High-resolution studies of water quality in Boston Harbor and Massachu- ADAMS,E. E., J. W. HANSEN, R. L. LAGO,P. CLAYTON,AND X. setts Bay during 1994. Massachusetts Water Resources Au- ZHANG.1992. A simple box model of the nitrogen cycle in thority Environmental Quality Department Technical Report Boston Harbor and the Massachusetts Bays. Civil Engineering Series No. 95-22. Massachusetts Water Resources Authority, Practice7:91-103. Boston, Massachusetts.

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions 380 J. R. Kelly

KELLY,J. R., V. B. BEROUNSKY,C. A. OVIATT,AND S. W. NIXON. NIXON,S. W., C. D. HUNT, ANDB. L. NowICKI. 1986a. The re- 1985. Benthic-pelagic coupling and nutrient cycling across an tention of nutrients (C, N, P), heavy metals (Mn, Cd, Pb, Cu), experimental eutrophication gradient. Marine EcologyProgress and petroleum hydrocarbons in Narragansett Bay, p. 99-122. Series26:207-219. In P. Lasserre and J. M. Martin (eds.), Biogeochemical Pro- KELLY,J. R. AND P. D. DOERING.1995. Nutrient issues update cesses at the Land-Sea Boundary. Elsevier Press, New York. 1995: Metabolism in Boston Harbor, Massachusetts Bay, and NIXONS. W., C. A. OVIATT,J. FRITHSEN,AND B. SULLIVAN.1986b. Cape Cod Bay Massachusetts (USA) during 1992-1994. Mas- Nutrients and the productivity of estuarine and coastal marine sachusetts Water Resources Authority Environmental Quality ecosystems. Journal of LimnologicalSociety South Africa 12:43-71. Department Technical Report Series No. 95-19. Massachusetts NIXONS. W. ANDM. E. Q. PILSON.1983. Nitrogen in estuarine Water Resources Authority, Boston, Massachusetts. and coastal marine ecosystems, p. 565-648. In E.J. Carpenter KELLY,J. R. ANDS. A. LEVIN. 1986. A comparison of aquatic and and D. G. Capone (eds.), Nitrogen in the Marine Environ- terrestrial nutrient cycling and production processes in nat- ment. Academic Press, New York. ural ecosystem, with reference to ecological concepts of rel- NOWICKI,B. L. 1994. The effect of temperature, oxygen, salin- evance to some waste disposal issues, p. 165-200. In G. Kul- ity, and nutrient enrichment on estuarine denitrification rates lenberg (ed.), The Role of the Oceans as a Waste Disposal measured with a modified nitrogen gas flux technique. Estu- Option. NATO Advanced Workshop Series, D. Reidel Publish- arine, Coastal, and Shelf Science38:137-156. ing Company, Dordrecht, Netherlands. NOWICKI,B. L., J. R. KELLY,E. REQUINTINA,AND D. VAN KEUREN. KELLY,J. R. AND S. W. NIXON. 1984. Experimental studies of 1997. Nitrogen losses through denitrification in Boston Har- the effect of organic deposition on the metabolism of a coast- bor and Massachusetts Bay. Estuaries20 (in press). al marine bottom community. Marine EcologyProgress Series 17: NowIcKI, B. L. ANDC. A. OVIATT.1990. Are estuaries traps for 157-169. anthropogenic nutrients? Evidence from estuarine meso- KELLY,J. R. ANDB. N. NOWICKI.1992. Sediment denitrification cosms. Marine EcologyProgress Series 66:131-146. in Boston Harbor. Massachusetts Water Resources Authority ODUM, E. P. 1959. Fundamentals of Ecology. Second edition. Environmental Quality Department Technical Report Series W. B. Saunders Company, Philadelphia, Pennsylvania. No. 92-2. Massachusetts Water Resources Authority, Boston, PANDAN,J. W. 1977. New England Offshore Environmental Massachusetts. Study. Final National Oceanic and Atmospheric Administra- KELLY,J. R. AND B. L. NOWICKI.1993. Direct measurements of tion Report, United States Department of Commerce. Nation- denitrification in Boston Harbor and Massachusetts Bay sedi- al Oceanic and Atmospheric Administration. Pacific Marine ments. Massachusetts Water Resources Authority Environmental Environmental Research Laboratory. Seattle, Washington. Quality Department Technical Report Series No. 93-3. Massa- PARSONS,T. R., Y. MAITA,AND C. M. LALLI.1984. A Manual of chusetts Water Resources Authority, Boston, Massachusetts. Chemical and Biological Methods for Seawater Analysis. Per- KELLY,J. R. ANDJ. T. TURNER.1995a. Water column monitoring gamon Press, Oxford, England. in Massachusetts and Cape Cod Bays: Annual report for 1993. ROBINSON,W. E., T. J. COFFEY,AND P. A. SULLIVAN.1990. New Massachusetts Water Resources Authority Environmental England Aquarium's Ten Year Boston Harbor Monitoring First (March 1989), New Quality Department Technical Report Series No. 95-16. Mas- Program. Report 1987-July England sachusetts Water Resources Authority, Boston, Massachusetts. Aquarium, Edgerton Research Laboratory, Boston, Massachu- setts. 02110. KELLY, R. ANDJ.T. TURNER.1995b. Water column monitoring J. P. S. M. ANDC. HUNT. 1984. Ac- in Massachusetts and Cape Cod Bays: Annual report for 1994. SANTSCHI, H., NIXON, PILSON, cumulation of trace metals and total Massachusetts Water Resources Authority Environmental sediment, (PB, Cu) hydrocarbons in Rhode Island. Estuarine, Quality Department Technical Report Series No. 95-17. Mas- Narragansett Bay, Coastal and Shelf Science19:427-449. sachusetts Water Resources Authority, Boston, Massachusetts. SEITZINGER,S. 1988. Denitrification in freshwater and coastal KENNEDY, V. S. (ED.). 1984. The Estuary as a Filter. Academic marine ecosystems: and Press, Orlando, Florida. Ecological geochemical significance. Limnologyand Oceanography33:702-724. KNEBEL,H., R. R. RENDIGS, AND M. H. BOTHNER. 1991. Modern SEITZINGER,S., S. NIXON,M. E. Q. PILSON,AND S. BURKE.1980. sedimentary environments in Boston Harbor, Massachusetts. Denitrification and N20 in near-shore marine sed- 61:791-804. production Journal of SedimentaryPetrology iments. Geochimicaet CosmochimicaActa 44:1853-1860. C. E. ANDC. A. OVIATT (EDS.). 1986. Manual of bio- LAMBERT, SHEA,D. ANDJ. R. KELLY.1992. Transport and fate of toxic and in coastal areas. Marine logical geochemical techniques contaminants discharged by MWRA into Massachusetts Bay. Research Series No. 1, 2nd edi- Ecosystems Laboratory Report Massachusetts Water Resources Authority Environmental of Rhode Island, Rhode Island. tion, University Narragansett, Quality Department Technical Report Series No. 92-4. Mas- S. ANDB. 1991. MENZIE,C. A.,J.J. CURA,J. FRESHMAN, POTOCKI. sachusetts Water Resources Authority, Boston, Massachusetts. of Massachusetts Water Boston Harbor: Estimates loadings. SIGNELL,R. P. ANDB. BUTMAN.1992. Modeling tidal exchange Environmental Resources Authority Quality Department and dispersion in Boston Harbor. Journal of GeophysicalRe- Technical Report Series No. 91-4. Massachusetts Water Re- search97:15,591-15,606. sources Boston, Massachusetts. Authority, VALDERRAMA,J. C. 1981. The simultaneous analysis of total ni- NIXON, S. W. 1983. Estuarine ecology-A comparative and ex- trogen and total phosphate in natural waters. Marine Chemistry perimental analysis using 14 estuaries and the MERL micro- 10:109-122. Final to United States Environmental Protec- cosms. Report VALIELA,I. ANDJ. E. COSTA.1988. Eutrophication of Buttermilk tion Agency, Chesapeake Bay Program under grant no. Bay, a Cape Cod coastal embayment: Concentrations of nu- X-003259-01. trients and watershed nutrient budgets. EnvironmentalMan- NIXON,S. W., J. W. AMMERMAN,L. P. ATKINSON,V. M. BEROUNSKY, agement12:539-553. G. BILLEN,W. C. BOICOURT,W. R. BOYNTON,T. M. CHURCH,D. VALIELA,I. ANDJ. M. TEAL. 1979. The nitrogen budget of a salt M. DITORO,R. ELMGREN,J.H. GARBER,A. E. GIBLIN,R. A.JAHN- marsh ecosystem. Nature 280:652-656. KE,N.J. P. OWENS,M. E. Q. PILSON,AND S. P. SEITZINGER.1996. The fate of nitrogen and phosphorus at the land-sea margin Receivedfor consideration,January 16, 1996 of the North Atlantic Ocean. Biogeochemistry35:141-180. Acceptedfor publication, October18, 1996

This content downloaded from 158.121.199.176 on Wed, 29 Jan 2014 10:51:19 AM All use subject to JSTOR Terms and Conditions