Narragansett Bay Estuary Research Articles

Seasonality of nitrogen sources, cycling, and loading in a New England river discerned from nitrate isotope ratios

Abstract. Coastal waters globally are increasingly impacted due to the anthropogenic loading of nitrogen (N) from the watershed. To assess dominant sources contributing to the eutrophication of the Little Narragansett Bay estuary in New England, we carried out an annual study of N loading from the Pawcatuck River. We conducted weekly monitoring of nutrients and nitrate (NO3-) isotope ratios (15N / 14N, 18O / 16O, and 17O / 16O) at the mouth of the river and from the larger of two wastewater treatment facilities (WWTFs) along the estuary, as well as seasonal along-river surveys. Our observations reveal a direct relationship between N loading and the magnitude of river discharge and a consequent seasonality to N loading into the estuary – rendering loading from the WWTFs and from an industrial site more important at lower river flows during warmer months, comprising ∼ 23 % and ∼ 18 % of N loading, respectively. Riverine nutrients derived predominantly from deeper groundwater and the industrial point source upriver in summer and from shallower groundwater and surface flow during colder months – wherein NO3- associated with deeper groundwater had higher 15N / 14N ratios than shallower groundwater. Corresponding NO3- 18O / 16O ratios were lower during the warm season, due to increased biological cycling in-river. Uncycled atmospheric NO3-, detected from its unique mass-independent NO3- 17O / 16O vs. 18O / 16O fractionation, accounted for < 3 % of riverine NO3-, even at elevated discharge. Along-river, NO3- 15N / 14N ratios showed a correspondence to regional land use, increasing from agricultural and forested catchments to the more urbanized watershed downriver. The evolution of 18O / 16O isotope ratios along-river conformed to the notion of nutrient spiraling, reflecting the input of NO3- from the catchment and from in-river nitrification and its coincident removal by biological consumption. These findings stress the importance of considering seasonality of riverine N sources and loading to mitigate eutrophication in receiving estuaries. Our study further advances a conceptual framework that reconciles with the current theory of riverine nutrient cycling, from which to robustly interpret NO3- isotope ratios to constrain cycling and source partitioning in river systems.

Blue crab (Callinectes sapidus) population structure in southern New England tidal rivers: Patterns of shallow-water, unvegetated habitat use and quality.

The blue crab, Callinectes sapidus, has a broad geographic distribution encompassing coastal waters of the eastern United States and Gulf of Mexico, but intraspecific patterns of habitat use and quality are lacking at northern latitudes. This study examined the population structure of blue crabs in the Seekonk and Taunton Rivers (Rhode Island and Massachusetts, USA): two tidally influenced rivers contiguous with the Narragansett Bay Estuary and dominated by shallow-water, unvegetated habitats. Crabs were collected fortnightly from May through August (2012-2016), and abundance- and growth-based metrics were used to assess riverine habitat use and quality. These metrics were also analyzed with respect to crab life history traits and in situ abiotic conditions to elucidate patterns of habitat selection throughout ontogeny. Crabs measuring 8 to 185 mm carapace width (CW; n = 2,577) were collected, and two distinct age-classes occupied the rivers during the spring and summer (maximum abundance ~ 5 crabs/10 m2). The younger age-0+ cohort was numerically dominant (~ 88% of total catch) and comprised of male and juvenile female crabs (mean ± SD abundance = 0.28 ± 0.26 males/10 m2 and 0.14 ± 0.12 juvenile females/10 m2). Males accounted for the majority of age-1+ crabs (~ 83% of cohort), yet sexually mature females were also observed (9% of cohort; mean ± SD abundance = 0.04 ± 0.06 adult females/100 m2; size at 50% maturity ± 95 CI = 129.0 ± 0.2 mm CW). Crabs were spatially segregated along a salinity gradient with males and juvenile females prevalent in oligohaline waters (upper river salinity ~ 5 ppt) and adult females mainly concentrating in higher salinity areas (mid- and lower river salinity ~ 11-21 ppt). Seasonal and interannual patterns in crab abundance also differed by sex and ontogeny. Peak catches of males and juvenile females occurred during the spring and mid-summer, and annual abundances were positively related to dissolved oxygen (DO) concentrations. In contrast, mature females were most abundant during August and years with elevated water temperatures. The absolute and relative growth rates of juvenile crabs equaled 0.9 ± 0.3 mm CW/day and 1.5 ± 0.6 % CW/day, respectively, and were directly related to DO levels. A synoptic examination of crab abundance and growth across a broad geographic range indicated that shallow-water, unvegetated habitats presently serve as functional nurseries in southern New England tidal rivers.

Dynamics of wind-driven estuarine-shelf exchange in the Narragansett Bay estuary

Physical exchange between estuarine and continental shelf waters impacts flushing dynamics of the estuary and determines rates of ocean inputs of nutrients and plankton. To investigate the occurrence and propagation of shelf water intrusions into the Narragansett Bay estuary, we collected velocity data near the estuarine–shelf interface during three summer periods. These data were compared to environmental forcing factors, including wind velocity, tidal mixing and river discharge. Results suggest a background cyclonic flow within the two passages of the estuary based on mean inflow in the channel on the eastern side of the estuary and mean outflow on the western shoals. Within the lower estuary this background circulation was perturbed by channel-parallel winds. On the shelf outside of the estuary, winds parallel to the coast were associated with cross-shelf flow of deep water. Strong pulses in estuarine–shelf exchange flow fell into two wind-driven modes: responses to direct forcing by down-estuary wind or rebounds following relaxation or reversal of up-estuary wind. Rebound events were common, providing the most dramatic perturbations to the mean background estuarine circulation. A reduction in exchange between Narragansett Bay and shelf waters during prevailing up-estuary winds in the summertime and short-lived pulses in exchange flow under wind reversal events are expected to affect nutrient fluxes and dynamics of hypoxia in the estuary.

Relationships of Modeled Nitrogen Loads with Marsh Fish in the Narragansett Bay Estuary, Rhode Island

The human population and associated watershed development has risen steadily since the 1850s in Rhode Island. With these increases, human-derived wastewater has also risen dramatically, resulting in increasing nitrogen loads to estuarine systems. In this study, we examined relationships of modeled watershed nitrogen loads of 6 coastal subwatersheds

Invasion dynamics on a temperate rocky shore: from early invasion to establishment of a marine invader

Populations of invading Asian shore crabs (Hemigrapsus sanguineus) and resident crabs (European green crab Carcinus maenas or species in the family Panopeidae) were monitored for up to 12 years along a south to north orientation on the open coast of Massachusetts and within the Narragansett Bay estuary, Rhode Island. At all sites, densities of resident crabs declined as H. sanguineus increased in abundance. Population dynamics were divided into 3 stages of the invasion (early, mid, late) based on statistically different densities of invading and resident crabs. Early in the invasion on the open coast, the relatively few H. sanguineus present had a wide range of individual sizes. By late in the invasion, relatively small crabs [ 10 mm CW were present late in the invasion. In Narragansett Bay, a recruitment peak of H. sanguineus occurred shortly before it surged in population size, and large crabs were abundant late in the invasion. Geographic comparisons of H. sanguineus populations in southern New England showed similar growth trajectories. Monitoring populations of resident and invading species at multiple locations from early invasion through clear establishment of the invader allows a more complete understanding of the population dynamics of marine species invasions.

Spatial and temporal trends in stable carbon and oxygen isotope ratios of juvenile winter flounder otoliths

Isotopic ratios of fish otoliths have been used in numerous studies as natural tags or markers to aid in the study of connectivity among fish populations. We investigated the use of spatial and temporal changes in the stable carbon and oxygen isotope ratios of otoliths to differentiate juvenile habitats of winter flounder (Pseudopleuronectes americanus). Young-of-the-year (YOY) juvenile winter flounder were collected annually over a three-year period from 18 stations along the coast of Rhode Island, USA. Sagittal otoliths were removed from fish and analyzed for stable carbon (13C/12C or δ13C) and oxygen (18O/16O or δ18O) isotope ratios using continuous flow isotope ratio mass spectrometry. Differences in isotope ratios were observed among stations and along salinity gradients in the Narragansett Bay estuary and an estuarine river system (Narrow River). Overall, the isotope ratio patterns observed among stations were consistent over the three sampling years; however, differences were noted in isotope ratios and the magnitude of the isotope ratio gradients among years. Significant positive correlations were noted between salinity and δ13C for two of the three years. For each of the three years sampled there was a highly significant positive correlation (2002, r = 0.93, P < 0.01; 2003, r = 0.85, P < 0.01; 2004, r = 0.97, P < 0.01) between δ18O and the salinity of the collection site. Also, there was a significant negative correlation between the number of months of above average river flow and δ18O for the three sampling years (r = 0.99, P < 0.05). These findings suggest that yearly changes in the volume of freshwater inputs to these estuarine habitats may be related to the differences observed in otolith δ18O isotope ratios. Because of these year-to-year differences, sampling of each cohort may be necessary in order to use this isotopic technique for winter flounder connectivity studies.

Ontogenetic patterns in bluefish (Pomatomus saltatrix) feeding ecology and the effect on mercury biomagnification

In this study, bluefish (Pomatomus saltatrix; age 0-7, n = 632) and their prey (forage fish, macroinvertebrates, zooplankton; n = 2,005) were collected from the Narragansett Bay estuary (RI, USA), and total Hg concentration was measured in white muscle and whole-body tissues, respectively. Bluefish Hg concentrations were analyzed relative to fish length, prey Hg content, and ontogenetic shifts in habitat use and foraging ecology, the latter assessed using stomach content analysis (n = 711) and stable nitrogen (δ(15)N) and carbon (δ(13)C) isotope measurements (n = 360). Diet and δ(13)C analysis showed that age 0 bluefish consumed both benthic and pelagic prey (silversides, sand shrimp, planktonic crustaceans; δ(13)C = - 16.52‰), whereas age 1 + bluefish fed almost exclusively on pelagic forage fish (Atlantic menhaden, herring; δ(13)C = - 17.33‰). Bluefish total Hg concentrations were significantly correlated with length (mean Hg = 0.041 and 0.254 ppm wet wt for age 0 and age 1 + bluefish, respectively). Furthermore, Hg biomagnification rates were maximal during bluefish early life stages and decelerated over time, resulting in relatively high Hg concentrations in age 0 fish. Rapid Hg accumulation in age 0 bluefish is attributed to these individuals occupying a comparable trophic level to age 1 + bluefish (δ(15)N = 15.58 and 16.09‰; trophic level = 3.55 and 3.71 for age 0 and age 1 + bluefish, respectively), as well as juveniles having greater standardized consumption rates of Hg-contaminated prey. Finally, bluefish larger than 30 cm total length consistently had Hg levels above the U.S. Environmental Protection Agency criterion of 0.3 ppm. As such, frequent consumption of bluefish could pose a human health risk, and preferentially consuming smaller bluefish may be an inadequate strategy for minimizing human dietary exposure to Hg.

Survival of F-RNA coliphages and three bacterial indicators during wastewater chlorination and transport in estuarine waters

Three bacterial water quality indicators,Clostridium perfringens, enterococci, and fecal coliforms, were compared to F-RNA coliphages for their survival during chlorination at several municipal wastewater treatment plants in Rhode Island and seasonally during transport in a section of the Narragansett Bay estuary. F-RNA coliphages were used as the best available indicator for the survival of Noroviruses (formerly Norwalk-like virus), the most frequently identified agent for the most prevalent waterborne disease (an acute but benign gastroenteritis), which has yet to be propagated in tissue culture and for which there is no lower animal model. Inactivation of the enterococci and fecal coliforms during wastewater chlorination was much greater than that of the F-RNA coliphages whose inactivation was essentially the same as that of C.perfringens. Survival of the F-RNA coliphages andC. perfringens during winter transport down Narragansett Bay were comparable to each other and greater than that for the enterococci or fecal coliforms. During the summer,C. perfringens survived longer than the other three indicators, possibly because the virus-like (F-RNA coliphages) and the two vegetative bacterial indicators were more susceptible than theC. perfringens spores to the lethal effects of sunlight and elevated water temperatures during the summer. Based on these findings, F-RNA coliphages seems to be a reliable indicator of viral contamination and die-off in estuarine waters.

Report from Estuarine Research Federation 2001: An Estuarine Odyssey

Every week since January 1959, a trawler has left Wickford Harbor, Rhode Island, to make a 30-minute net tow in the Narragansett Bay estuary and in Rhode Island sound. The net collects animals three inches and larger living on and just above the bottom, explained Perry Jeffries, biological oceanographer at the University of Rhode Island, in a session titled “Detecting Estuarine Change.” “Because we do the same thing week after week, we can observe gradual and long-term changes. No record comparable to this 43-year-old data set exists for any coastal area.”

Gene flow versus local adaptation in the northern acorn barnacle, Semibalanus balanoides: insights from mitochondrial DNA variation.

In reciprocal transplant experiments, Bertness and Gaines (1993) found that Semibalanus balanoides juveniles that had settled in an upper Narragansett Bay estuary survived better in that estuary that did juveniles from coastal localities. The observed pattern of survivorship led to the claim that local adaptation may result from a combination of limited gene flow between and strong selection within these habitats. Here we test the hypothesis that limited gene flow has led to habitat-specific population differentiation using sequence and restriction fragment length polymorphism analyses of the mitochondrial DNA D-loop region of S. balanoides. Samples were analyzed from replicated coastal and estuary localities in both Narragansett Bay, Rhode Island, and Damariscotta River, Maine. The patterns of F(ST) indicate that gene flow between coast and estuary is extensive (Nm > 100) and is not lower in the estuary with lower flushing rates (Narragansett Bay). Given the high estimate of genetic exchange, adaptations for unpredictable environments seem more likely than local adaptation in this species because loci that respond to selection in one generation are essentially homogenized by the next seasons' settlement. Nevertheless, these estimates of neutral gene flow can help identify the strength of selection necessary for local adaptation to accumulate in Semibalanus.

GENE FLOW VERSUS LOCAL ADAPTATION IN THE NORTHERN ACORN BARNACLE, SEMIBALANUS BALANOIDES: INSIGHTS FROM MITOCHONDRIAL DNA VARIATION

In reciprocal transplant experiments, Bertness and Gaines (1993) found that Semibalanus balanoides juveniles that had settled in an upper Narragansett Bay estuary survived better in that estuary that did juveniles from coastal localities. The observed pattern of survivorship led to the claim that local adaptation may result from a combination of limited gene flow between and strong selection within these habitats. Here we test the hypothesis that limited gene flow has led to habitat-specific population differentiation using sequence and restriction fragment length polymorphism analyses of the mitochondrial DNA D-loop region of S. balanoides. Samples were analyzed from replicated coastal and estuary localities in both Narragansett Bay, Rhode Island, and Damariscotta River, Maine. The patterns of FST indicate that gene flow between coast and estuary is extensive (Nm > 100) and is not lower in the estuary with lower flushing rates (Narragansett Bay). Given the high estimate of genetic exchange, adaptations for unpredictable environments seem more likely than local adaptation in this species because loci that respond to selection in one generation are essentially homogenized by the next seasons' settlement. Nevertheless, these estimates of neutral gene flow can help identify the strength of selection necessary for local adaptation to accumulate in Semibalanus.Corresponding Editor: J. Neigel

The Use of Satellite Data to Quantify Thermal Effluent Impacts

Thermal effluent from a large coal-fired electric generating facility located on Mt. Hope Bay in the Narragansett Bay (Rhode Island, U.S.A.) has been implicated in a large decline in fish populations in this region. Detailed information on the spatial and temporal properties of this thermal input (approximately 5 million m3day−1of thermal effluent 7°C above ambient) is, however, lacking. In this paper it is shown that the spatial extent and magnitude of the thermal impacts can be quantitatively determined by exploiting the strengths of remotely sensed data. Seasonal trends of surface temperature in the Narragansett Bay estuary were derived from a composite of 14 thermal infrared satellite images (Landsat TM Band 6) with a spatial resolution of 120m. The derived temperatures were validated against independent measures of surface temperature for a number of sites within the bay, and it was shown that the satellite measures were within 1°C of the in situ temperatures. Relationships among thermal properties and physical characteristics were identified through a comparison of the seasonal temperature patterns of 12 regions within the bay. As expected, depth was the primary factor in determining the magnitude of seasonal temperature variation in the estuary, while advective exchange with the coast ocean was the second most important factor. Although the behaviour of Mount Hope Bay was significantly correlated with the other upper estuarine regions, the bay did not experience autumn cooling, which is characteristic of upper estuarine waters. From late summer through to autumn, the average temperature difference between Mount Hope Bay and Upper Narragansett Bay was 0·8°C, which can be attributed to warming from the thermal effluent of the Brayton Point Power Station in Mount Hope Bay. An unsupervised (statistical) classification of temperature as a function of season revealed the natural boundaries between areas with different seasonal temperature signals, and statistically identified Mount Hope Bay as a unique area in the upper estuary which had anomalously high temperatures throughout the year. Among the scenes included in the unsupervised analysis, Mount Hope Bay was on average 0·8°C warmer than the rest of the upper estuary, and the total area affected is 36km2.

Chemical speciation of dissolved Cu, Zn, Cd, Pb in Narragansett Bay, Rhode Island

The chemical speciation of `dissolved' Cu, Zn, Cd, and Pb was determined by differential pulse anodic stripping voltammetry (DPASV) at three sampling sites in the high salinity region (24–30 psu) of the Narragansett Bay estuary. Speciation results show that organic chelates of these four trace metals are the dominant forms in conventionally filtered ( 99% for Cu in these estuarine waters. Dissolved Zn ([ZnT]) varied from 72 nM at the Upper Bay site to 16 nM at the Lower Bay site, the concentration of the Zn-binding ligands ([LT]) varied from 48 to 11 nM with a relatively uniform conditional stability constant (KZnL,Zn′cond=109.0 M−1). At the Upper and Lower Bay sites, where [ZnT]>[LT], there was less organic complexation (50 to 60%) of [ZnT] as compared to the Mid-Bay (bloom) station, where [ZnT]<[LT] and the degree of organic complexation was considerably higher (97%). The concentration of Cd-binding ligands was nearly constant throughout the bay (ca. 4 nM with mean KCdL,Cd′cond=108.9 M−1) and present at much higher levels than the dissolved Cd ([CdT]=0.80–0.29 nM, decreasing down bay). Titration results for Pb were modeled by two classes of Pb-binding ligands. Dissolved Pb ranged from 0.32 to 0.13 nM and the strong class of Pb-binding ligands (L1) was in slight excess of these values (ca. 0.8 nM) with a mean KcondPbL1,Pb′=1010.0 M−1. A weaker class of Pb-binding ligands (L2) existed at 4.0–8.2 nM with a mean KcondPbL2,Pb′=108.8 M−1. Titration data for Cu were interpreted as being influenced by three classes of Cu-binding ligands (L1, L2, L3), whose sum was always in excess of the dissolved [CuT] (12.7–27.9 nM). Our DPASV estimates of [L1] were 16–38 nM with a KcondCuL1,Cu′≥1012 M−1. There were higher concentrations of intermediate and weaker classes of Cu-binding ligands: [L2]=40 to 15 nM with a mean KcondCuL2,Cu′=108.8 M−1 and [L3]=100 to 54 nM with a mean KcondCuL3,Cu′=107.7 M−1. The two stronger classes of Cu-binding ligands (L1 and L2) resulted in CuL1 and CuL2 as the dominant dissolved Cu species. Free ion concentrations were calculated for all four metals at the three sampling sites: [Cu2+]≤10−12 M, [Cd2+]≤2×10−12 M, [Pb2+]∼10−12 M, while [Zn2+] ranged from 0.3–13×10−9 M. For Cu, Pb, and Cd, these ambient values are below the concentrations of toxic responses reported from laboratory studies of marine microorganisms. At the Upper Bay site, any toxic effect of the elevated free zinc ion concentration is likely to be alleviated by the antagonistic effect of high dissolved Mn.

Distribution, Abundance, and Habitat Characteristics of Juvenile Tautog (Tautoga onitis, Family Labridae) in Narragansett Bay, Rhode Island, 1988-1992

Estuarine nursery areas are critical for successful recruitment of tautog (Tautoga onitis), yet they have not been studied over most of this species' range. Distribution, abundance and habitat characteristics of young-of-the-year (YOY, age 0) and age 1+juvenile tautog were evaluated during 1988–1992 in the Narragansett Bay estuary, Rhode Island, using a 16-station, beach-seine survey. Estuary-wide abundance was similar among years. Greatest numbers of juveniles were collected at northern Narragansett Bay stations between July and September. Juvenile abundances varied with density of macroalgal and eelgrass cover; abundances ranged from 0.03 fish per 100 m2 to 8.1 fish per 100 m2. Although juveniles use eelgrass, macroalgae is the dominant vegetative cover in Narragansett Bay. Macroalgal habitats play a previously unrealized, important role and contribute to successful recruitment of juvenile tautog in Narragansett Bay. Juvenile abundances did not vary with sediment type or salinity, but were correlated with surface water temperature. Fish collected in June were age 1+ juveniles from the previous year-class (50–167 mm TL) and these declined in number after July or August. The appearance of YOY (25–30 mm TL) in July and August was coincident with the period of their greatest abundances. A precipitous decline in abundance occurred by October because of the individual or combined effects of mortality and movement to alternative habitats. Based on juvenile abundance, a previously unidentified spawning area was noted in Mount Hope Bay, a smaller embayment attached to the northeastern portion of Narragansett Bay. In August 1991, Hurricane Bob disrupted juvenile sise distribution and abundance, resulting in reduced numbers of YOY collected after the storm and few 1+ juveniles in 1992.

Recruitment to American Lobster Populations along an Estuarine Gradient

This study evaluates patterns in the distribution and abundance of newly recruited (young-of-the-year) and older American lobster (Homarus americanus Milne Edwards) along a 22 km length of the Narragansett Bay estuary, Rhode Island, with particular attention to substratum associations. This not only represents the first assessment of benthic recruitment of this species along an estuary, but it is also the first study of lobster recruitment in southern New England. Censuses were conducted by divers in a substratum-specific manner. in cobble-boulder habitat, with the aid of a diver-operated suction sampler, I found newly recruited (5–10 mm carapace length) lobsters to be most abundant on the open coast, with numbers diminishing to zero in the upper bay. Visual censuses of older lobsters in the same habitat revealed a similar pattern. On featureless sedimentary habitats new recruits were absent and lobster densities were at least two orders of magnitude lower than in rocky habitats. In Narragansett Bay, rocky habitats comprise a small proportion of the bottom. The availability of such habitats, the relative importance of larval supply and potential physiological stress in limiting recruitment up-bay remain unclear.

The sources of PCBs to the Narragansett Bay estuary

The major rivers and municipal treatment facilities that discharge directly into Narragansett Bay have been surveyed to determine the amount of PCBs associated with their discharges under dry weather conditions. The Blackstone River, which empties into the northernmost sector of the bay system, was the largest source of riverine PCBs, contributing ∼ 70% of the 12 kg of Ar 1254 transported by the evaluated rivers per year. An additional 2.5 kg, annually, may be coming from freshwater inputs not explicitly measured in this study, giving a total fluvial input of ∼ 14 kg Ar 1254 per year. A single wastewater treatment facility, the Fields Point plant, which also discharges into the northern sector of the bay, contributed 70% of the 5.9 kg year −1 of Ar 1254 attributable to municipal inputs. Therefore, an estimated 20 kg of particulate Ar 1254 enters the bay, annually, from these sources, under dry weather conditions. Ar 1254 inputs represented ∼ 70% of the total Aroclors present in the samples (i.e., Ar 1242, Ar 1254, and Ar 1260). Of note was the almost exclusive presence of decachlorobiphenyl in the river samples.

Lignin geochemistry of sediments from the Narragansett Bay Estuary

Cupric oxide oxidation has been employed to characterize the lignin geochemistry of Narragansett Bay sediments. Lignin concentrations throughout the estuary are low when expressed on a carbon-normalized basis, but can be characterized as enriched when expressed on a mass-normalized basis. This implies substantial dilution of the sedimentary lignin by inputs of lignin-poor carbon. Lignin concentrations do not correlate with the 13C isotopic composition of the sedimentary organic matter. These results are consistent with a sediment lignin component consisting of varying amounts of vascular plant debris and lignin-depleted organic matter, the latter originating from both marine (planktonic) and terrestrial (uncharacterized) sources. Compositional plots of lignin-derived phenols show that sediments in the upper estuary are influenced to a greater extent by gymnosperm lignin sources than those in the mid-and lower estuary. Given the extent to which the upper estuary is affected by pollution sources, inputs from anthropogenic discharges are the most likely cause of these compositional differences. However, an evaluation of processed paper products as an “anthropogenic” lignin source indicates that the lignin content of these materials is insufficient to account for the levels found in the sediments. Subsurface lignin compositions at an upper estuary site reveal that lignin originating from the inferred anthropogenic sources disappears at a depth shallower than that which would be expected based on the distribution of other trace organic pollutants (hydrocarbons and several synthetic organic compounds). We speculate that differences in either the depositional history or the degree of preservation of these two compound classes are responsible for the observed trends.

Dissolved copper and copper-organic complexes in the Narragansett Bay estuary

The geochemistry of dissolved copper-organic complexes was investigated in the estuarine waters of Narragansett Bay. A transect survey was conducted in August 1980, while one mid-bay station was monitored from March through August of that year. The transect data indicated that most of the copper-organic complexes enter the bay via sewage effluent which is discharged into the Providence River at the head of the bay. Organic copper concentrations in the estuary ranged from 0.12 to 2.30 μg kg −1 and comprised from 14 to 70% of the total dissolved copper. The concentration of copper-organic complexes was not directly related to the amount of dissolved organic matter; and recently generated organic material from phytoplankton production within the bay had a negligible influence on the fraction of dissolved copper which was organically bound. The major source of total copper to the bay is anthropogenic inputs from sewage effluents. Particulate and dissolved copper concentrations ranged from 0.06 to 2.42 and 0.23 to 16.4 μg kg −1, respectively, giving average values of about 40% particulate and 60% dissolved copper. Particulate copper concentrations decreased rapidly from the upper to the lower bay as a result of both removal and dilution. About 75% of the dissolved copper entering the bay is rapidly removed in the Providence River and upper bay, and the remaining portion (which is largely organic copper) follows conservative mixing in the mid to lower bay. The data suggest that copper binding by dissolved organic matter may be an important control on the riverine flux of dissolved copper through estuaries into coastal and oceanic waters.

Geochemistry of C 25 and C 30 biogenic alkenes in sediments of the narragansett bay estuary

The distributions of a series of structurally related C 25 and C 30 biogenic alkenes in sediments of the Narragansett Bay estuary have been determined. The suite of alkenes detected differs both quantitatively and qualitatively from those previously reported in other estuanne and coastal regions. Four C 25 mono- and dienes and one C 30 diene comprise 73–91% of the total alkenes in all surface (upper 2.5–5 cm) sediments analyzed. However, significant geographic variations exist in the relative abundance of these five compounds throughout the estuary. A comparison of alkene concentrations with δ 13 C of the bulk sedimentary organic matter has shown that the geographic variations of some alkenes reflect the distribution of marine organic matter, suggesting a marine source for these compounds. The distributions of other alkenes are not similarly correlated. In particular, concentrations of the C 30 diene are relatively constant and exhibit no dependence on the origin of organic matter in these sediments. This distribution implies an in situ production of this alkene throughout the estuary. Analysis of several sediment cores reveals that alkene concentrations are generally highest at the surface and decrease to low, constant values within the upper 25 cm. An exception is the subsurface concentration of one C 25 diene, which exhibits an increase at the same depth in two separate upper bay cores.

Survival of natural sewage populations of enteric bacteria in diffusion and batch chambers in the marine environment.

The survival of natural populations of Escherichia coli and enterococci in sewage was measured in large-volume diffusion chambers in an estuary and a salt marsh. The 5-liter chambers, with polycarbonate membrane sidewalls, were found to be suitable for up to week-long experiments. Decay rates, measured monthly from February to August 1978, ranged from 0.042 to 0.088 h(-1) (time for 90% of the population to die = 25 to 55 h) for E. coli and 0.019 to 0.083 h(-1) (time for 90% of the population to die = 29 to 122 h) for enterococci and were significantly correlated with temperature. In contrast to the diffusion culture experiments, the decay of E. coli in batch culture did not correlate with temperature. Enterococci survived longer than E. coli in the Narragansett Bay (estuary) experiments, but survived less well in the more eutrophic salt marsh. The effect of light on survival was examined with light/dark experiments and sampling at frequent intervals over the diel cycle. Diel changes in survival were not evident in the Narragansett Bay experiments. E. coli, however, exhibited a diel pattern of growth during the day and death at night in the salt marsh. There was no significant difference in decay rates between light and dark diffusion chambers, nor were decay rates correlated with light intensity. In concurrent batch experiments, survival was significantly greater in the dark for both organisms. These results suggest that the effect of light is complex and that conditions in batch culture may modify the survival of enteric bacteria. Observations made in diffusion chambers may more closely follow the in situ survival of enteric microorganisms.