Geology topics

Research about Long Island Sound

Source-linked reports with geographic coverage including Long Island Sound.

At least 19 recordsLinked to original sources

USGS2024

Simulated mean monthly groundwater-transported nitrogen loads in watersheds on the north shore of Long Island Sound, 1993–2022

Elevated nitrogen loads are pervasive in the Long Island Sound, an estuary that receives freshwater and nutrients from both surface-water and groundwater discharge. Surface-water nitrogen loads to the Long Island Sound are relatively well characterized, but less is known about groundwater-transported nitrogen loads. Prior work on the northern shore of Long Island Sound (Connecticut and areas of New York and Rhode Island) suggested that groundwater travel times are relatively short (median less than 2 years) and that decade-long nutrient legacies are not widespread. Because the travel times are short, groundwater flow and nutrient loads likely vary substantially between months. In the current study, the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency’s Long Island Sound Study and the Connecticut Department of Energy and Environmental Protection, developed a set of models to better characterize spatial and temporal patterns of groundwater-transported nitrogen loading from atmospheric deposition, septic systems, and fertilizers within the study area. The models provide an estimate, with uncertainty, of groundwater-transported nitrogen loads in the study area, filling a key gap in the nitrogen budget for Long Island Sound. The models also highlight the spatial and temporal variation in nitrogen loading throughout the study area. The modeling workflow involved four models. (1) A soil-water-balance model was developed by using the Soil-Water-Balance software to simulate groundwater recharge across the study area for water years 2005 through 2022. The simulated mean monthly recharge from the soil-water-balance model was used as input into a groundwater-flow model. (2) The groundwater-flow model was developed by using the MODFLOW 6 software and data for water years 1993 through 2022 and simulates average monthly hydrologic conditions. The groundwater-flow model was calibrated by using the Iterative Ensemble Smoother method within the PEST++ software. The Iterative Ensemble Smoother method generates an ensemble of sets of parameter values, with each set producing reasonable simulated hydrologic parameter values. (3) An ensemble of MODPATH particle-tracking simulations were run to generate particle flow paths and travel times, with each simulation using a different set of the flow model parameters. (4) A nitrogen load model uses the MODPATH simulation outputs to track nitrogen from the land surface through multiple attenuation zones until it discharges into fresh or saline surface water. As with the groundwater-flow model, the nitrogen model simulated average monthly groundwater-transported nitrogen loads for water years 1993 through 2022. One novel aspect of the nitrogen load model is that the nitrogen attenuation parameters were calibrated to observed nitrogen loads. Across the ensemble of simulated nitrogen loads, the median study-area-wide monthly simulated nitrogen loads from the aquifer to Long Island Sound throughout the year ranged from 900 to 18,600 kilograms of nitrogen per day, with a median load of 5,100 kilograms of nitrogen per day. The simulated loads were based on average monthly conditions for water years 1993 through 2022. Loads were highest during the winter and early spring and lowest during the late summer. However, simulated travel times for groundwater and nitrogen loads discharged to Long Island Sound during summer were longer than travel times for groundwater and loads discharged during the winter, indicating that, on average, groundwater discharged during summer traveled along different, and longer, flow paths, than groundwater discharged during winter. This indicates that summer loads would respond more slowly to changes in nitrogen inputs at the water table than winter loads. Over the entire study area, approximately 15 percent of the simulated load is from atmospheric deposition sources, 30 to 40 percent is from fertilizer, and 50 to 60 percent is from septic systems. The final analysis of the study involved simulating the change in groundwater-transported nitrogen load in response to upgrading septic systems or reducing fertilizing inputs to areas of turf grass. Both management interventions reduced the groundwater-transported nitrogen load, and reductions were greater in areas with greater loads from septic systems or turf-grass fertilizers. The delay between management actions and substantial reductions in groundwater-transported nitrogen loads varied seasonally; loads during the late summer months remained elevated longer than the winter loads.

Connecticut, Rhode Island↗

USGS2020

Nitrogen budgets of the Long Island Sound estuary

Nitrogen (N) inputs to coastal ecosystems have significant impacts on coastal community structure. In N limited systems, increases in N inputs may lead to excess productivity and hypoxia. Like many temperate estuaries, Long Island Sound (LIS), a major eastern U.S. estuary, is a N limited system which has experienced seasonal hypoxia since the 1800s. This study is the first effort to constrain the total N cycle in this estuary. The approach utilizes data collected over the last two decades in the LIS time series with hydrodynamic model results to generate both monthly and annual N budgets between 1995 and 2016. Of the total N that is delivered to LIS through rivers and atmospheric inputs, 40% is exported to the adjacent continental shelf on the order of 10.8 ± 8.9 × 10 6 kg N/year. Of this export, 41% is dissolved organic N, 29% is particulate organic N, 32% is nitrate + nitrite, and −3% is ammonium. The remaining 60% of the N delivered to LIS is either buried in sediments or lost through denitrification. This inferred internal loss rate is equivalent to 5.4 g N/(m 2 year). This study serves as an example of the significant inter-annual variations that estuarine budgets undergo as efforts to understand coastal biogeochemical cycles move forward.

Connecticut, New York↗

USGS2020

Degradation of RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) in contrasting coastal marine habitats: Subtidal non-vegetated (sand), subtidal vegetated (silt/eel grass), and intertidal marsh

Hundreds of explosive-contaminated marine sites exist globally, many of which contain the common munitions constituent hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Quantitative information about RDX transformation in coastal ecosystems is essential for management of many of these sites. Isotopically labelled RDX containing 15 N in all 3 nitro groups was used to track the fate of RDX in three coastal ecosystem types. Flow-through mesocosms representing subtidal vegetated (silt/eel grass), subtidal non-vegetated (sand) and intertidal marsh ecosystems were continuously loaded with isotopically labelled RDX for 16–17 days. Sediment, pore-water and overlying surface water were analyzed to determine the distribution of RDX, nitroso-triazine transformation products (NXs) and nitrogen containing complete mineralization products, including ammonium, nitrate+nitrite, nitrous oxide and nitrogen gas. The marsh, silt, and sand ecotypes transformed 94%, 90% and 76% of supplied RDX, respectively. Total dissolved NXs accounted for 2%–4% of the transformed 15 N-RDX. The majority of RDX transformation in the water column was by mineralization to inorganic N (dissolved and evaded; 64%–78% of transformed 15 N-RDX). RDX was mineralized primarily to N 2 O (62–74% of transformed 15 N-RDX) and secondarily to N 2 (1–2% of transformed 15 N-RDX) which exchanged with the atmosphere. Transformation of RDX was favored in carbon-rich lower redox potential sediments of the silt and marsh mesocosms where anaerobic processes of iron and sulfate reduction were most prevalent. RDX was most persistent in the carbon-poor sand mesocosm. Partitioning of 15 N derived from RDX onto sediment and suspended particulates was negligible in the overall mass balance of RDX transformation (2%–3% of transformed 15 N-RDX). The fraction of 15 N derived from RDX that was sorbed or assimilated in sediment was largest in the marsh mesocosm (most organic carbon), and smallest in the sand mesocosm (largest grain size and least organic carbon). Sediment redox conditions and available organic carbon stores affect the fate of RDX in different coastal marine habitats.

Connecticut, New York↗

USGS2013

Limited denitrification in glacial deposit aquifers having thick unsaturated zones (Long Island, USA)

The goal of this study was to demonstrate how the extent of denitrification, which is indirectly related to dissolved organ carbon and directly related to oxygen concentrations, can also be linked to unsaturated-zone thickness, a mappable aquifer property. Groundwater from public supply and monitoring wells in Northport on Long Island, New York state (USA), were analyzed for denitrification reaction progress using dissolved N 2 /Ar concentrations by membrane inlet mass spectrometry. This technique allows for discernment of small amounts of excess N 2 , attributable to denitrification. Results show an average 15 % of total nitrogen in the system was denitrified, significantly lower than model predictions of 35 % denitrification. The minimal denitrification is due to low dissolved organic carbon (29.3–41.1 μmol L −1 ) and high dissolved oxygen concentrations (58–100 % oxygen saturation) in glacial sediments with minimal solid-phase electron donors to drive denitrification. A mechanism is proposed that combines two known processes for aquifer re-aeration in unconsolidated sands with thick (>10 m) unsaturated zones. First, advective flux provides 50 % freshening of pore space oxygen in the upper 2 m due to barometric pressure changes. Then, oxygen diffusion across the water-table boundary occurs due to high volumetric air content in the unsaturated-zone catchment area.

Long Island Sound↗

USGS2013

Sea-floor character and geology off the entrance to the Connecticut River, northeastern Long Island Sound

Datasets of gridded multibeam bathymetry and sidescan-sonar backscatter, together covering approximately 29.1 square kilometers, were used to interpret character and geology of the sea floor off the entrance to the Connecticut River in northeastern Long Island Sound. Although originally collected for charting purposes during National Oceanic and Atmospheric Administration hydrographic survey H12013, these acoustic data, sidescan-sonar imagery, and the sea-floor sampling and photography stations subsequently occupied to verify the acoustic data (1) show the composition and terrain of the seabed, (2) provide information on sediment transport and benthic habitat, and (3) are part of an expanding series of studies that provide a fundamental framework for research and resource management (for example, cables, pipelines, and dredging) activities in this major east coast estuary.

Connecticut↗

USGS2013

Sea-floor geology and topography offshore in northeastern Long Island Sound

Datasets of gridded multibeam bathymetry, covering approximately 52.9 square kilometers, were used to interpret character and geology of the sea floor in northeastern Long Island Sound. Although originally collected for charting purposes during National Oceanic and Atmospheric Administration hydrographic survey H12012, these acoustic data and the sea-floor sampling and photography stations subsequently occupied to verify the acoustic data are interpreted (1) to define the composition and terrain of the seabed, (2) to provide information on sediment transport and benthic habitat, and (3) as part of an expanding series of studies that provide a fundamental framework for research and resource management (for example, cables, pipelines, and dredging) activities in this major east coast estuary.

Connecticut;New York↗

USGS2012

Sea-floor geology of Long Island Sound north of Duck Pond Point, New York

The U.S. Geological Survey, the National Oceanic and Atmospheric Administration (NOAA), and the Connecticut Department of Environmental Protection are mapping the sea floor in coastal areas of the northeastern United States. As part of the project, more than 100 square kilometers of multibeam-echosounder data, 23 sediment samples, bottom video, and 86 still photographs were obtained from an area in Long Island Sound north of Duck Pond Point, New York, in the study area of NOAA survey H11999. This report delineates the sediment types and sea-floor features found within this area in order to better understand the sea-floor processes occurring in this part of Long Island Sound. The sea floor in the study area is dominated by ubiquitous sand-wave fields and three northeast-southwest trending bathymetric depressions. Barchanoid and transverse sand waves, including sinusoidal, bifurcating, arced, and straight-crested morphologies, are variably present. Asymmetrical sand-wave profiles indicate a westward to southwestward direction of sediment transport in most of the study area; current ripples and megaripples on the stoss slopes of the sand waves indicate transport is ongoing. The majority of the sediment on the sea floor is sand, although bouldery, gravelly, and muddy sediments are also present. Gray, cohesive mud crops out on the walls of some of the scour depressions associated with the troughs of large sand waves. Clasts of the muddy sediment scattered on the sea floor around the depressions demonstrate the intensity of the scour and suggest erosion of the underlying distal deltaic sediments.

New York↗

USGS2011

Character of shell beds flanking Herod Point Shoal, southeastern Long Island Sound, New York

High biogenic productivity, strong tidal currents, shoal topography, and short transport distances combine to favor shell-bed formation along the lower flanks of a cape-associated shoal off Herod Point on Long Island, New York. This shell bed has a densely packed, clast-supported fabric composed largely of undegraded surf clam ( Spisula solidissima ) valves. It is widest along the central part of the western flank of the shoal where topographic gradients are steep and a stronger flood tide results in residual flow. The bed is narrower and thinner toward the landward margins where currents are too weak to transport larger valves and topographic gradients are gentle, limiting bed-load transport mechanisms by which the shells are concentrated. Reconnaissance mapping off Roanoke Point suggests that shell beds are also present at the other cape-associated shoals off northeastern Long Island, where relatively similar geomorphic and oceanographic conditions exist. These shell beds are important to the Long Island Sound ecosystem because they provide complex benthic habitats of rough and hard substrates at the boundary between the muddy basin floor and mobile sand of the shoals.

Connecticut, New York↗

USGS2008

Estuarine sediment transport by gravity-driven movement of the nepheloid layer, Long Island Sound

Interpretation of sidescan-sonar imagery provides evidence that down-slope gravity-driven movement of the nepheloid layer constitutes an important mode of transporting sediment into the basins of north-central Long Island Sound, a major US East Coast estuary. In the Western Basin, this transport mechanism has formed dendritic drainage systems characterized by branching patterns of low backscatter on the seafloor that exceed 7.4 km in length and progressively widen down-slope, reaching widths of over 0.6 km at their southern distal ends. Although much smaller, dendritic patterns of similar morphology are also present in the northwestern part of the Central Basin. Because many contaminants display affinities for adsorption onto fine-grained sediments, and because the Sound is affected by seasonal hypoxia, mechanisms and dispersal pathways by which inorganic and organic sediments are remobilized and transported impact the eventual fate of the contaminants and environmental health of the estuary.

Connecticut, Massachussetts, New York↗

USGS2008

Quaternary geology and sedimentary processes in the vicinity of Six Mile Reef, eastern Long Island Sound

Six Mile Reef, a sandy, 22-m-high shoal trending east-west and located about 7.8 km off the Connecticut coast, has a core of postglacial marine deltaic deposits mantled by tidally reworked modern sediments. Sedimentary environments off the eastern end of the shoal are characterized by processes associated with long-term erosion or nondeposition, a mobile-sediment-limited seafloor armored by gravelly sand, and scattered elongate fields of barchanoid sand waves. The barchanoid waves reach amplitudes of 20 m, are concave westward, and occur in individual and coalesced forms that become progressively more complex westward. The seafloor on and adjacent to the shoal is characterized by processes associated with coarse bedload transport and covered primarily with asymmetrical transverse sand waves. The transverse waves exceed 8 m in amplitude, have slip faces predominantly oriented to the west and southwest, and have straight, slightly sinuous, and curved crests. Megaripples, which mimic the asymmetry of the sand waves, are commonly present on stoss slopes and in troughs; current ripples are ubiquitous. The amplitude and abundance of large bedforms decrease markedly westward of Six Mile Reef. The seabed there is covered with small, degraded ripples, reflecting lower-energy environments and processes associated with sorting and reworking of seafloor sediments. Megaripples and current ripples on the sand waves suggest that transport is active and that the bedforms are propagating under the present hydraulic regime. Net bedload sediment transport is primarily to the west, as evidenced by textural trends of surficial sediments, orientation of the barchanoid waves, and asymmetry of the transverse waves and of the scour marks around bedrock outcrops, boulders, and shipwrecks. One exception occurs at the western tip of the shoal, where sand-wave morphology indicates long-term eastward transport, suggesting that countercurrents in this area shape the shoal and are important to its maintenance.

Long Island Sound↗

USGS2006

Physical properties of Long Island Sound sediment cores

This report presents data on x-radiography, water content, and sediment texture from sediment cores collected in 1996 in Long Island Sound, offshore of Connecticut and New York (Figure 1). Core locations and analytical data are presented in both graphical and numerical form. The physical properties data presented here are a subset of a larger dataset consisting of results from these cores and other sediment samples. (See Poppe and others (1998) and Mecray and others (2000) for samples collected in Long Island Sound from 1996-2001 by the USGS .

Long Island Sound↗

USGS2006

Interpolation of reconnaissance multibeam bathymetry from north-central Long Island Sound

Introduction The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Connecticut Department of Environmental Protection (CT DEP), has produced detailed maps of the sea floor in Long Island Sound, a major East Coast estuary surrounded by the most densely populated region of the United States (fig. 1). The current phase of this cooperative research program is directed toward studies of sea-floor topography and its effect on the distributions of sedimentary environments and benthic communities. Because anthropogenic wastes, toxic chemicals, and changes in land-use patterns resulting from residential, commercial, and recreational development have stressed the environment of the Sound, causing degradation and potential loss of benthic habitats (Koppelman and others, 1976; Long Island Sound Study, 1994), detailed maps of the sea floor are needed to help evaluate the extent of adverse impacts and to help manage resources wisely in the future.

Connecticut, New York↗

USGS2005

Surficial geologic interpretation and sidescan sonar imagery of the sea floor in west-central Long Island Sound

The United States Geological Survey (USGS) is working cooperatively with the National Oceanic and Atmospheric Administration (NOAA) and Connecticut Department of Environmental Protection (CT-DEP) to conduct detailed studies of the surficial geology in Long Island Sound (LIS). The study goals are to interpret sedimentary environments within the Sound, to further understand processes controlling sediment distribution, and to provide a framework for future studies. Sidescan-sonar mosaics produced by USGS and NOAA show detailed acoustic images of the sea floor with 1- m resolution. These images, along with data obtained from sediment samples, seismic-reflection profiles, and seafloor video, are used to interpret the surficial geology. As part of this cooperative program, since 1995, 12 sidescan-sonar surveys of the LIS sea floor have been completed (Poppe and others, 1997; Twichell and others, 1997; Poppe and others, 1998a; Poppe and others, 1998b; Twichell and others, 1998; Poppe and others, 1999a; Poppe and others, 1999b; Poppe and others, 2001; Poppe and others, 2004; Zajac and others, 2003). The purpose of this report is to release digital versions of the imagery and interpretations from NOAA survey H11044 originally published in McMullen and others (2005). Survey H11044, which covers an area of 293 km 2 in west-central LIS , includes the area of the previously published Milford Survey (Twichell and others, 1998) and the westernmost part of the New Haven Harbor Survey (Poppe and others, 2001). These two surveys detailed surficial geology and mapped sediment distributions. In this study, we map the sediment distribution across a broader, previously unstudied area and the sedimentary environments.

Connecticut↗

USGS2003

Responses of infaunal populations to benthoscape structure and the potential importance of transition zones

Relationships between population abundance and seafloor landscape, or benthoscape, structure were examined for 16 infaunal taxa in eastern Long Island Sound. Based on analyses of a side-scan sonar mosaic, the 19.4-km 2 study area was comprised of six distinct large-scale (> km 2 ) benthoscape elements, with varying levels of mesoscale (km 2 -m 2 ) and small-scale (< m 2 ) physical and biological habitat heterogeneity. Transition zones among elements varied from ~50 to 200 m in width, comprised ~32% of the benthoscape, and added to overall benthoscape heterogeneity. Population abundances of nine taxa varied significantly among the large-scale elements. Most species were found at high abundances only in one benthoscape element, but three had several foci of elevated abundances. Analyses of population responses to habitat heterogeneity at different spatial scales indicated that abundances of eight taxa varied significantly among spatial scales, but the significant scales were mixed among these species. Relatively large residual variations suggest significant amounts of mesoscale spatial variation were unaccounted for, varying from ~1 km 2 to several m 2 . Responses to transition zones were mixed as well. Abundances of nine taxa varied significantly among transition zones and interiors of benthoscape elements, most with elevated abundances in transition zones. Our results show that infaunal populations exhibit complex and spatially varying patterns of abundance in relation to benthoscape structure and suggest that mesoscale variation may be particularly critical in this regard. Also, transition zones among benthoscape features add considerably to this variation and may be ecological important areas in seafloor environments.

New York↗

USGS2002

Estimation of nitrogen yields and loads from basins draining to Long Island Sound, 1988–98

Monitoring data on total nitrogen concentrations and streamflow were used to estimate annual nonpoint nitrogen loads for 1988?98 at 28 monitoring sites and 26 unmonitored basins that drain to Long Island Sound. The estimated total nitrogen yields at monitoring sites were used with basin characteristics and ancillary data to develop a multiple-linear regression equation to estimate nonpoint nitrogen yields from monitored and unmonitored basins. The estimated nonpoint nitrogen load to Long Island Sound from the basins studied ranged from 21 million pounds in water year 1995 to 50 million pounds in water year 1990. Statistically significant regression variables include time, population density, annual mean runoff (minus wastewater return flow), pointsource nitrogen yields, percentage of basin area classified as urban/recreational grasses, percentage of the basin classified as agricultural land, and the ratio of deciduous to total forest area. Nonpoint nitrogen loads from monitored and unmonitored basins were computed using the regression equation by setting the point-source nitrogen yields and wastewater return variables to zero, and incorporating streamflow information from index stations in or near unmonitored basins. Nonpoint nitrogen load information obtained through use of this equation was summarized by six Long Island Sound management zones. Estimates of nonpoint nitrogen loads from these basins can be improved by additional sampling, and by developing data on nitrogen loads from municipal wastewater-treatment facilities outside of Connecticut, compiling information on annual interbasin diversions of flow, studying instream losses of nitrogen, and analyzing the processing and storage of atmospheric nitrogen in different forest types.

New York↗

USGS2001

Estimates of nitrogen loads entering Long Island Sound from ground water and streams on Long Island, New York, 1985-96

Fresh ground water that discharges from the northern part of Long Island's aquifer system to Long Island Sound contains elevated concentrations of nitrogen from agricultural fertilizer, domestic waste and fertilizer, and precipitation. The nitrogen contributes to algal blooms, which consume oxygen as the algae die and decompose. The resulting low dissolved oxygen concentrations (hypoxia) adversely affect plant and animal populations in Long Island Sound. The four major streams on the north shore of Long Island that have long-term discharge and water-quality records were selected for analysis of geographic, long-term, and seasonal trends in nitrogen concentration. Nitrogen concentrations generally decrease eastward among three Nassau County streams, then increase again at the easternmost stream, Nissequogue River in Suffolk County. A long-term (1970-96) increase in total nitrogen concentrations in the Nissequogue River also is evident. Seasonal fluctuations in nitrogen concentrations in all four streams reflect chemical reactions and microbial activity in the stream system, so total nitrogen concentrations in the three easternmost streams generally were lowest during summer and highest in winter, whereas those in the westernmost stream (Glen Cove Creek) were highest during summer and lowest in winter. The nitrogen loads discharged to Long Island Sound from each of the four streams for each year during 1985-96 were calculated from the annual mean total nitrogen concentration and the annual mean discharge. Nissequogue River's annual mean discharges were 3 to 6 times larger than those of Glen Cove and Mill Neck Creeks, and produced the largest annual loads of nitrogen--65 to 149 ton/yr (59,000 to 135,000 kg/yr). Cold Spring Brook had the lowest annual mean discharges and annual mean total nitrogen concentrations of the four streams; its annual mean nitrogen load ranged from 1.2 to 2.8 ton/yr (1,100 to 2,500 kg/yr). The nitrogen load carried to Long Island Sound by shallow ground water from the north shore of Long Island was calculated from simulated shallow-aquifer discharges from Nassau and Suffolk Counties (9,200 and 21,400 Mgal/yr or 34,800,000 and 81,100,000 m3/yr, respectively) and median total nitrogen concentrations at selected wells (2.2 and 4.3 milligrams per liter as N, respectively). The resultant nitrogen load was 84 ton/yr (76,500 kg/yr) for Nassau County and 384 ton/yr (349,000 kg/yr) for Suffolk County. The nitrogen load carried to Long Island Sound by deep ground water from the north shore was calculated from simulated deep-aquifer discharges from Nassau and Suffolk counties (13,200 and 47,300 Mgal/yr or 50,000,000 and 179,000,000 m3/yr, respectively). The median nitrogen concentrations of deep ground water for the two counties were 1.62 and 1.34 mg/L as N, respectively. The resultant nitrogen load from deep-aquifer discharge was 89 ton/yr (81,000 kg/yr) for Nassau County and 265 ton/yr (240,000 kg/yr) for Suffolk County. Nitrogen loads entering Long Island Sound from the shallow aquifer underlying three areas of differing land use along the north shore--a sewered residential area in Nassau County, an unsewered residential area in Suffolk County, and an agricultural area in Suffolk County--were evaluated. The agricultural area contains no major streams and, therefore, produces very little surface runoff to Long Island Sound and substantially greater shallow-aquifer discharge than in the sewered and unsewered areas. Ground water in the agricultural area also had the highest median nitrogen concentration (9.9 mg/L as N) of the three land-use areas and discharged the largest estimated nitrogen load to Long Island Sound--152 ton/yr (138,000 kg/yr), which represents about 40 percent of the estimated total nitrogen load from Suffolk County. Ground water in the sewered area had the lowest nitrogen concentration (1.9 mg/L as N) and discharged the smallest nitrogen load to Long Island Sound--7.28 ton/yr (6,600 kg/yr). The analysis indicates that land use on the north shore of Long Island can greatly affect the nitrogen concentration of water in the shallow aquifer and the resultant nitrogen load discharged to Long Island Sound from ground water.

New York↗

USGS2000

Contaminant distribution and accumulation in the surface sediments of Long Island Sound

The distribution of contaminants in surface sediments has been measured and mapped as part of a U.S. Geological Survey study of the sediment quality and dynamics of Long Island Sound. Surface samples from 219 stations were analyzed for trace (Ag, Ba, Cd, Cr, Cu, Hg, Ni, Pb, V, Zn and Zr) and major (Al, Fe, Mn, Ca, and Ti) elements, grain size, and Clostridium perfringens spores. Principal Components Analysis was used to identify metals that may covary as a function of common sources or geochemistry. The metallic elements generally have higher concentrations in fine-grained deposits, and their transport and depositional patterns mimic those of small particles. Fine-grained particles are remobilized and transported from areas of high bottom energy and deposited in less dynamic regions of the Sound. Metal concentrations in bottom sediments are high in the western part of the Sound and low in the bottom-scoured regions of the eastern Sound. The sediment chemistry was compared to model results (Signell et al., 1998) and maps of sedimentary environments (Knebel et al., 1999) to better understand the processes responsible for contaminant distribution across the Sound. Metal concentrations were normalized to grain-size and the resulting ratios are uniform in the depositional basins of the Sound and show residual signals in the eastern end as well as in some local areas. The preferential transport of fine-grained material from regions of high bottom stress is probably the dominant factor controlling the metal concentrations in different regions of Long Island Sound. This physical redistribution has implications for environmental management in the region.

Long Island Sound↗

USGS2000

Clostridium perfringens in Long Island Sound sediments: An urban sedimentary record

Clostridium perfringens is a conservative tracer and an indicator of sewage-derived pollution in the marine environment. The distribution of Clostridium perfringens spores was measured in sediments from Long Island Sound, USA, as part of a regional study designed to: (1) map the distribution of contaminated sediments; (2) determine transport and dispersal paths; (3) identify the locations of sediment and contaminant focusing; and (4) constrain predictive models. In 1996, sediment cores were collected at 58 stations, and surface sediments were collected at 219 locations throughout the Sound. Elevated concentrations of Clostridium perfringens in the sediments indicate that sewage pollution is present throughout Long Island Sound and has persisted for more than a century. Concentrations range from undetectable amounts to 15,000 spores/g dry sediment and are above background levels in the upper 30 cm at nearly all core locations. Sediment focusing strongly impacts the accumulation of Clostridium perfringens spores. Inventories in the cores range from 28 to 70,000 spores/cm2, and elevated concentrations can extend to depths of 50 cm. The steep gradients in Clostridium perfringens profiles in muddier cores contrast with concentrations that are generally constant with depth in sandier cores. Clostridium perfringens concentrations rarely decrease in the uppermost sediment, unlike those reported for metal contaminants. Concentrations in surface sediments are highest in the western end of the Sound, very low in the eastern region, and intermediate in the central part. This pattern reflects winnowing and focusing of Clostridium perfringens spores and fine-grained sediment by the hydrodynamic regime; however, the proximity of sewage sources to the westernmost Sound locally enhances the Clostridium perfringens signals.

Connecticut, Massachusetts, New Hampshire, New Jer↗