Habitat Conditions and Correlations of Sediment Quality Triad Indicators in Delaware Bay

Environmental Monitoring and Assessment (2006) 121: 181–212

DOI: 10.1007/s10661-005-9115-3 c© Springer 2006

HABITAT CONDITIONS AND CORRELATIONS OF SEDIMENTQUALITY TRIAD INDICATORS IN DELAWARE BAY

S. IAN HARTWELL∗ and M. JAWED HAMEEDINational Oceanic and Atmospheric Administration, National Centers for Coastal Ocean Science,Center for Coastal Monitoring and Assessment, 1305 East West Hwy., SSMC4, (N/SCI-1), Silver

Spring, MD, USA 20910(∗author for correspondence, e-mail: [email protected])

(Received 3 June 2005; accepted 4 November 2005)

Abstract. This paper summarizes sampling results from NOAA’s National Status and Trends (NS&T)

Program for marine environmental quality in Delaware Bay. A stratified-random design was used to

determine the spatial extent of sediment contamination and toxicity in Delaware Bay from offshore

stations in the coastal zone, the lower estuary, the upper estuary, the fresh/salt mixing zone, and tidal

fresh areas. Sediment samples were taken for chemical analyses of major classes of environmental

contaminants, a suite of toxicity bioassays, and benthic macrofaunal community assessment to identify

patterns of resident species. The tidal-fresh areas and portions of the mixing zone of the study area

were heavily contaminated. Contaminant concentrations were frequently above the 90th percentile of

EMAP Virginian Province levels. PAHs in the sediment were higher than previously documented, with

a major component of PAHs being pyrogenic in origin. Bioassay results were highly variable. Toxicity

and contaminant levels were correlated when aggregated into indices, but were only marginally

correlated with benthic community impacts. High and low abundance stations were found in all

zones. Most of the tidal fresh stations were dominated by pollution tolerant species. Species diversity

and abundance were generally lowest in the fresh/salt mixing zone.

Keywords: contamination, Delaware Bay, indicators, sediment quality triad, toxicity

1. Introduction

Sediment contamination in U.S. coastal areas is a major environmental issue be-cause of potential toxic effects on biological resources and often, indirectly, onhuman health. A large variety of contaminants from industrial, agricultural, urban,and maritime activities are associated with bottom sediments, including syntheticorganic chemicals, polycyclic aromatic hydrocarbons, and trace metals. Criticalhabitats and food chains supporting many commercial and recreational speciesinvolve the benthic environment. Thus, characterizing and delineating areas of sed-iment contamination and toxicity are viewed as important goals of coastal resourcemanagement. Distributions of benthic organisms are predictable along estuarinegradients and are characterized by similar groups of species over broad latitudinalranges. Information on changes in benthic population and community parametersdue to habitat characteristics can be useful for separating natural variation fromchanges associated with human activities.

182 S. I. HARTWELL AND M. J. HAMEEDI

Many authors have addressed the problem of how to assess the condition of bi-ological communities and how to represent their assessment(s) quantitatively. Thephysical setting of a given habitat has a profound effect on our ability to subdi-vide the habitat into statistically repeatable units and establish reference and testsites for this purpose. Basic biological measurements such as species richness orabundance, while informative, may be too simplistic. More complex indices (e.g.,diversity, evenness) are more robust, but are inherently flawed for use as predictivetools because distinctly different communities may be equivalent mathematically.A great deal of effort has gone into development of an Index of Biotic Integrity(IBI) for estuarine benthic communities (Hartwell, 1998). This approach has beensuccessfully applied to many habitats (Karr and Chu, 1997). Application of themethod includes scoring metrics in discernable cause-effect gradients. While gra-dients allow Karr’s original application to work well in streams and other habitats(Karr, 1981), the highly variable nature of the estuarine environment has renderedstrict application of the approach difficult thus far, because of the confounding pa-rameters such as salinity and grain size. Development of an estuarine IBI for themid-Atlantic region (Llanso et al., 2002) has partially addressed this problem byselecting different metrics from the pool of attributes in each of 5 salinity zones. Insome zones, notably the freshwater-oligotrophic zone, the IBI has relatively poorpredictive capability however.

Effects-based numerical sediment quality guidelines (SQGs) have been devel-oped by Federal and state agencies in the United States and other countries forassessing sediment quality. SQGs have been derived using both theoretical and em-pirical approaches (Di Toro et al., 1991; EPA, 1997; Long et al., 1995; MacDonaldet al., 1996; Barrick et al., 1989; Field et al., 1999). Each approach has its ownstrengths and weaknesses. Two major concerns with the use of SQGs are their levelof precision in predicting toxicity to organisms in the field, and the ecological rele-vance of SQGs developed for one endpoint (i.e., amphipod toxicity) to be predictiveof effects on the other organisms or the benthic community as a whole (Wenningand Ingersoll, 2002).

Since 1991, NOAA has performed sediment toxicity, contamination, and benthicmacrofaunal community studies in a number of coastal embayments and estuariesacross the United States as part of its National Status and Trends Program (Turgeonet al., 1998). The sediment toxicity component of this study is based on a suite ofsediment toxicity tests to assess different modes of contaminant exposure (bulk sed-iment, sediment porewater, and chemical extracts of contaminants from sediment)to a variety of species (invertebrates, bacteria, and vertebrate cells) and differentassessment end-points (i.e., reduced survival, impaired reproduction, physiologicalstress, and enzymatic response). Since the toxicity test results are not necessarilyaxiomatic and biological effects of contaminants occur at different levels of bio-logical organization, results from a suite of toxicity tests are used in the “weightof evidence” context to infer the incidence and severity of environmental toxic-ity (Chapman, 1996). A variety of analyses, including concordance among results

HABITAT CONDITIONS AND INDICATORS IN DELAWARE BAY 183

and correlations are used to elucidate the relationship(s) between bioassay resultsand contaminant concentrations. A risk ranking method was previously developed(Hartwell, 1997) to quantify ambient toxicological effects for statistical contrastswith biological community response parameters. Positive correlation of toxicolog-ical impact and depressed community metrics implies cause and effect, but doesnot require a demonstrable mechanism of toxic effect.

A fundamental issue with any of these approaches is whether or not the methodscan be used to distinguish between contaminated habitats and naturally occurringpoor habitats due to salinity stress, poor food availability, extreme physical envi-ronments (e.g. severe tidal currents, etc. If it is possible to eliminate/normalize forthose parameters, will a purely chemical response signal become apparent whichis different than impacts from naturally occurring stressors such as salinity transi-tions? One of the most variable and dynamic habitats, and therefore among the mostdifficult to assess, is an estuary. The estuarine habitat is a mosaic of various habitatsthat exist along physical and chemical gradients which change over time and space,and not necessarily in the same direction. Thus, trying to discern the fingerprint ofcontaminant effects is particularly difficult in estuaries. The questions addressed inthis study were: Do toxicity bioassay results correlate with chemical contaminantdata?; Do bioassays predict community impact?; Do chemical contaminant levelspredict community impact?

2. Methods

2.1. SITE DESCRIPTION

Delaware Bay is one of the largest drowned river valley coastal plain estuarieson the US east coast. Dilution of sea water by fresh water flow is evident on thecontinental shelf beyond the mouth of the bay. Within the lower estuary, salinityis generally above 20 ppt up to the region where the bay begins to narrow nearMoney Island (Figure 1). Salinity steadily decreases in the upstream directiontoward Philadelphia, PA. The water column may exhibit salinity stratification butis generally well mixed to the bottom, even in the channel areas. From southernPhiladelphia upstream, the river is tidal fresh. Outside of three relict river channelsand actively dredged areas, most of the bay is less than 10 m deep. The ancientriver channels range from 10 to 46 m deep and run north-west from the mouthof the bay. At the mouth of the bay, Cape May shoals restrict the entrance to thebay on the north side, with characteristic flood tidal shoals behind it. Tidal flowvelocities are strongest in the channels, and net sediment flux is actually in theupstream direction in the lower estuary because ebb tidal velocities are relativelyweaker due to the shoreline configuration and Coriolis effects. Knebel (1989) hasfully described the sedimentary environments in Delaware Bay. Sediments in thecentral bay are characteristically coarser in grain size than on the flanks, and the


Figure 1. Sample stations and strata boundaries in Delaware Bay and coastal areas.

bathymetry exhibits distinct sand wave and sand ribbon patterns perpendicular tochannels and boundary shoals from prehistoric river levees. Broad flat shoals inthe south and the large north-east expanse of the bay are characteristically finegrained depositional zones with few gross bathymetric features. Further upstream,


the estuary narrows significantly and the influence of lateral water movement ondepositional patterns is reduced.

The major source of freshwater input is from the Delaware River. The watersheddrains portions of the states of New York, Pennsylvania, New Jersey and Delaware.Philadelphia is one of the oldest and largest urban centers on the US East Coastwith a metropolitan area population over 1.5 million. Philadelphia has numerousmunicipal point and non-point source releases, industrial and petrochemical dis-charges, and extensive commercial and naval ship traffic and port facilities. Trenton,NJ, Camden, NJ, and Wilmington, DE are also industrial centers with numerousmunicipal and industrial contaminant sources. Three of the basin’s States maintainfish consumption advisories due to PCBs and chlorinated pesticides.

2.2. SAMPLING DESIGN AND COLLECTION METHODS

A stratified-random design was used for selection of sampling sites. The study areawas divided into strata within which sampling sites were selected on a randombasis. This allows some control of spacing of samples in the study area. Strataboundaries were established in consultation with regional scientists and resourcemanagers based on bathymetric, hydrographic, regional environmental consider-ations, and results of previous studies. The minimum number of sampling siteswithin each stratum was three. The study area was divided into 20 strata (Figure 1)representing five zones. The upper six strata contained 18 sampling stations in thetidal fresh zone above and below Philadelphia. The next three strata encompassed9 stations in the saltwater/freshwater mixing zone. Three strata with 11 stationscomprised the upper estuarine zone. These sites exhibit steadily increasing salini-ties from 5 to 15 ppt in the downstream direction. Four strata containing 23 stationscomprise the wide portion of the lower estuarine zone. Four strata were located inthe coastal zone and contained 12 stations from north of Cape May to below CapeHenlopen, and beyond the Rehoboth and Indian River Bays. Sampling was con-ducted during the late summer period when the benthic community was at its peakdevelopment.

Sediment samples were collected at each site with a Young-modified Van Veengrab sampler. One 0.04 m2 sample was taken for benthic community analysis.Minimum sample depth was 5 cm. The entire sample was sieved on site through0.5 mm mesh. All organisms were retained and preserved in buffered formalincontaining Rose Bengal. Additional grab samples were taken and the top 3 cm ofsediment was collected and composited until sufficient volume (7–8 L) of sedimentfor all the toxicity bioassays and chemical analyses was collected. This compositesample was homogenized on site, and subdivided for distribution to various testinglaboratories. All subsamples were either stored on ice or frozen, as appropriate,prior to shipment. Basic water quality parameters (salinity, dissolved oxygen, etc.)were measured at the surface and bottom of the water column.


2.3. TOXICITY TESTS

All toxicity bioassay tests were based on standard methods promulgated by theEPA, ASTM, and/or APHA. Ten day amphipod (Ampelisca abdita) survival testswere conducted in accordance with ASTM (1992) and additional guidance devel-oped for testing four different amphipod species (EPA, 1994a). Based on statisticalanalyses of previous amphipod survival data, including power analysis, two criteriaare used to infer toxicity to amphipods: first, the t-test must show that the sam-ple survival is statistically lower than in a clean control sediment, and second, thesample’s mean survival must also be less than 20% of that in the control (Thursbyet al., 1997). In this paper, these results are described as having statistically lowersurvival, and demonstrating a toxic response, respectively. Since the inclusion ofminimum significant difference (MSD) limits as an acceptable criterion is a rela-tively new practice, our approach allows for comparison with older data sets basedon significant differences. Positive control tests with sodium dodecyl sulfate (SDS)in 96-hour water-only exposure bioassays were also run.

The sea urchin (Arbacia punctulata) fertilization impairment test was used totest the toxicity of pore water. Specific methods of the pore water extraction proce-dure and testing protocol are outlined in Carr (1998). Each porewater sample wastested in a dilution series (100%, 50% and 25%) with five replicates per treatment.A reference porewater sample collected from Redfish Bay, Texas was includedwith each test as a negative control. Redfish Bay sediments have been used as acontaminant free reference sediment in previous studies (Carr, 1998). The toxic-ity test exposes sea urchin sperm to pore water followed by the addition of eggs.At the tests’ conclusion, the fraction of successfully fertilized eggs is recorded.Reduction in mean fertilization success after exposure to pore water, in compar-ison with the negative control, is the experimental end-point. SDS was used as apositive control toxicant. Statistical treatments of data include analysis of varianceand Dunnett’s one-tailed t-test on the arcsine square root transformed data. Thetrimmed Spearman-Karber method with Abbott’s correction was used to calculateEC50 values based on dilution series tests. Statistical power establishing criticallevels of difference between test and control has been previously evaluated for thistest (Carr and Biedenbach, 1999).

For Microtox R© and P450 assays, sediment was extracted with organic solventsin accordance with the EPA Method 3550 (EPA,1996; Johnson and Long, 1998).The extracts were split for testing with the Microtox R© and P450 HRGS (HumanReporter Gene System) assays. The extraction procedure is well suited for extrac-tion of neutral, non-ionic organic compounds, such as aromatic and chlorinatedhydrocarbons. Extraction of other classes of toxicants, such as metals and polarorganic compounds, is not efficient with this technique.

In the Microtox R© test, a standard dose-response curve method was used todetermine EC50 values. Each sample was tested in triplicate. A negative control(extraction blank) was prepared using dimethyl sulfoxide. Sediment extract from


Redfish Bay, Texas were used as a reference. A phenol spiked Redfish Bay extractwas used as a negative control standard. Sample EC50 s were normalized to theRedfish Bay extract EC50. Any sample with an EC50 significantly (P ≤ 0.05)lower than the controls indicated marginal probability of toxicity. Samples withan EC50 significantly below the phenol-spiked standard were considered to have ahigh probability of toxicity.

The human reporter gene system (HRGS Cytochrome P450) response is used todetermine the presence of organic compounds that bind to the Ah (aryl hydrocar-bon) receptor and induce the CYP1A locus on the vertebrate chromosome. Underappropriate test conditions, induction of CYP1A is evidence that the cells have beenexposed to one or more xenobiotic organic compounds, including dioxins, furans,planar PCBs, and several polycyclic aromatic hydrocarbons. The details of this testare provided in Standard Method 4425 (EPA, 1999), the American Public HealthAssociation (APHA, 1998) and American Society of Testing and Material (ASTM,1999). The extract of sediment was applied to cell cultures for a 6 hr incubation.A solvent blank and a reference toxicant tetrachlorodibenzo-p-dioxin (TCDD) at aconcentration of 1 ng/mL) were used with each batch of samples. From a standardconcentration-response curve for benzo[a]pyrene (B[a]P), the HRGS response to1 ug/mL is approximately 60. Data were converted to μg of B[a]P equivalents perg of sediment using this factor. Quality control tests were run with control extractsspiked with (TCDD) and B[a]P. A 16 hr incubation period was run in addition tothe normal 6 hr period for selected stations. The longer incubation period allowsa contrast between PAH induction and TCDD/PCB induction. During the longerincubation, enzyme induction is reduced due to metabolism of PAH compounds;dioxins and PCBs continue to induce the CYP1A gene and the response signalremains static or increases depending on the relative amounts of PAHs, PCBs,dioxins, and other P450-inducing chemicals in the sample.

There are no clearly defined assessment end-points for P450 induction that sig-nify a threshold of biological damage. Statistical procedures have been used to gen-erate decision points. Based on analyses from 527 sampling points in the NOAA bio-logical effects database, HRGS induction values below 10 mg B[a]PEq/kg representbackground conditions in estuarine waters. HRGS values greater 60 mg B[a]PEq/kgare known to be associated with degraded benthic communities. (Anderson et al.,1999a, b; Fairey et al., 1996).

2.4. CHEMICAL ANALYSES

Chemical analyses followed procedures used in the NOAA NS&T program(Lauenstein and Cantillo, 1998). Strict QA/QC controls are required on all NS&Tanalyses to meet specified performance-based standards employing minimumquantitation limits, and blank, duplicate, matrix spike, duplicate spike, and SRM(Standard Reference Materials) analyses. A broad suite of chemicals were analyzedat each station (Hartwell et al., 2001). Sixteen elements (Ag, As, Al, Cd, Cr, Cu,


Fe, Hg, Mn, Ni, Pb, Sb, Se, Si, Sn, and Zn) were analyzed by atomic absorptionanalysis following extraction with HNO3, HF and, boric acid. For analysis ofHg, sediment samples were digested using a modified version of EPA method245.5. Butyl-tins were analyzed by high resolution, capillary gas chromatographyusing flame photometric detection (GC/FPD). Organic compounds (PAHs, PCBs,chlorinated pesticides, furans and dioxins) were extracted in a Soxhlet apparatus.Quantitation of PAHs and their alkylated homologues was performed by gaschromatography mass spectrometry (GC/MS). Chlorinated pesticides and PCBswere quantitatively determined by capillary gas chromatography with an electroncapture detector (ECD). Detection limits were at or below 1 ng/g dry weight forthe PAHs, PCBs and chlorinated pesticides.

2.5. BENTHIC ANALYSES

Benthic infauna samples were stored in 70% isopropanol solution until processing.All sorted macroinvertebrates were identified to the lowest practical identificationlevel, which in most cases was to species level unless the specimen was a juvenile,damaged, or otherwise unidentifiable. The number of individuals of each taxon,excluding fragments, was recorded. At a minimum, 10 percent of all samples wereresorted and recounted. The minimum acceptable sorting efficiency was 95%.

Quantitative benthic community characterizations included enumeration of den-sity, species richness, evenness, and diversity. Taxa diversity, was calculated withthe Shannon-Wiener Index (Shannon and Weaver, 1949). Evenness of taxa diversityfor a given station was calculated as Pielou’s Index “J” (Pielou, 1966).

2.6. STATISTICAL ANALYSES

Statistical analyses were performed to search for correlations between habitat vari-ables (e.g. contamination, physical parameters) and the observed toxicity and ben-thic community parameters. The P450 and Microtox data used were the log trans-formed inverse of the values. This maintains a consistent response direction with am-phipod survival and sea urchin fertilization data (high values = low response). Am-phipod and sea urchin proportional response data were normalized using an arc-sinetransformation. Contaminant concentration data were analyzed as log transformedvariables to reduce the impact of extreme values. Abundance data were also logtransformed for the same reason. The chemical data were grouped into broad classes(e.g. metals, PAHs, PCBs, etc.) and in subgroups including individual metals, lowand high weight PAHs, alkyl substituted and parent compound PAHs, DDT andmetabolites, chlordane and related cyclodiene compounds, Butyl Tins, hexachloro-hexane (HCH) and, hexachlorobenzene (HCB). Analyses were run on a matrix ofdata sets, including the entire data set and data subsets (e.g. fresh, estuarine).

Statistical analyses of the data were performed on two versions of the data.The first were the individual bioassay endpoints (e.g. P450), chemical classes


concentrations (e.g. PAHs, PCBs), and community measurements (e.g. diversity,number of taxa), arbitrarily termed metrics. Simple scatter plots were produced forall community metrics versus toxicity and chemical metrics, and between toxicityresults and contaminants to assess general patterns of correspondence. Stepwise lin-ear regression was used on benthic community, toxicity and transformed chemicalmetrics.

The toxicity, contaminant, and community data were further condensed intoindices suitable for simple statistical correlations in the context of the sedimentquality triad approach (Chapman, 1996). The mean quotient of the numerical sedi-ment quality guideline Effects Range Median (ERM-Q) (Hyland et al., 1999; Longet al., 1995) and environmental levels were calculated for all 23 individual metalsand organic compounds, (excluding Ni), for each site. The sum of Effects RangeLow (ERL) exceedances were also tabulated for each site as a surrogate for levelsof contamination for testing purposes. Chemical data were normalized by divid-ing concentrations by the mean concentration by compound, and summed by site.To aggregate the bioassay data into a single value, a toxicity risk ranking index(Hartwell, 1997, 1999) was calculated. This consisted of a simple toxicity scorecalculated for each bioassay at each sediment site as the sum of the products ofendpoint severity and percent response (control corrected). Severity was arbitrarilyset to 3 for amphipod mortality 2 for sea urchin reproductive impairment and 1for the exposure endpoints (P450 and Microtox). A cumulative toxicity index foreach site was calculated as the sum of the scores, divided by

√N , where N is the

number of bioassays. A benthic IBI was developed by EPA for the Virginian EMAPprovince (Paul et al., 1999). This index is based on Gleason’s diversity index andindicator species abundance.

B IBI = [1.389(D − 51.5)/28.4] − [0.651(T − 28.2)/199.5]

−[0.375(S − 20)/45.4]

Where D = salinity normalized Gleason’s diversity based on infauna and epifauna;T = salinity normalized Tubificid abundance; S = Spionid abundance.

Part of EPA’s EMAP data base was derived from NOAA’s NS&T samplingprogram in a coordinated undertaking at all Delaware Bay stations and the benthicIBI values were calculated for all stations. Pearson correlation coefficients werecalculated between all the condensed indices and the community index metrics.

3. Results

Summary statistics for all parameters are available on a site by site basis andaveraged by stratum in the NS&T report available from NOAA (Hartwell et al.,2001) in tabular and location map form.


Figure 2. Grain size distribution at Delaware Bay sampling stations, expressed as percent of total.

3.1. HABITAT CONDITIONS

Sediment grain size data for the 73 sampling sites are shown in Figure 2. Sedimentcomposition varied considerably from 73% silt at site 3 to ≥99% sand at some sites.The coastal zone sites were primarily sand with some gravel, and the lower estuarinesites were predominantly sand or silty sand. Approximately half of the tidal freshand upper estuarine sites were dominated by silt/clay material. Site 56, near themouth of the Bay had an unusually large proportion of fine grained material. It is ina protected area behind Cape Henlopen, near a temporary anchorage for ships witha constructed breakwater. The total organic carbon (TOC) fraction of the sedimentsranged from 0.07% at site 64 to 3.28% at site 29 (Figure 3). Only 17 sites had TOCconcentrations above 2%. Site 5 had a TOC value of 2.12% despite being composedof 99% sand.

The water column was essentially fresh at stations 1–18. Salinity increasedsteadily up to 15 ppt through the upper estuary (stations 19–29), and to over 25ppt in the lower estuary. Stations at the Bay mouth and extending out into thecoastal zone sites were slightly diluted ocean water. Temperature was relativelyuniform throughout the system and stressful dissolved oxygen conditions were notobserved at any station, with the exception of borderline hypoxic conditions atstation 22 (3.2 mg/l). The weather during the sampling period was stormy, and the


Delaware Bay Sediment Total Organic Carbon

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73

Station

TO

C (

%)

Figure 3. Total organic carbon content at Delaware Bay sampling stations.

salinity, DO and temperature data all indicate a well mixed water column, typicalfor Delaware Bay.

3.2. CHEMICAL CONTAMINATION

The tidal fresh and mixing zones were heavily contaminated with metals, chlori-nated pesticides (ClPest) and DDTs, PCBs and PAHs. Some portions of the upperestuarine zone were also contaminated in the vicinity of the C&D canal. Contam-inant concentrations varied greatly from station to station. In general, the concen-trations of all chemical constituents were either relatively high or low at a givensite (Figure 4). TBT was the exception to this trend, and was found at elevated con-centrations at stations 17 and 57, and at low concentrations at other stations. Sandysites had generally lower concentrations of contaminants than sites with a signif-icant proportion of silt/clay. Chemical concentrations at the other lower estuaryand coastal zone stations outside of the bay proper, were basically uncontaminatedbeyond trace levels.

The concentration of DDT and breakdown products showed a similar distri-bution as PCBs, but elevated concentrations of DDT were not distributed as fardownstream. All but two samples from the tidal fresh zone exceeded the ERL forpp’ DDE. Seven samples exceeded the ERM for DDE. Twelve samples in the mix-ing and upper estuarine zones exceeded the ERL for DDE and/or total DDT, ofwhich two exceeded the ERM. The concentration of other chlorinated pesticides


Figure 4. Normalized contaminant concentrations at Delaware Bay sampling stations. Concentrations

are normalized to the mean for each chemical class.

was dominated by chlordane and related cyclodienes. These compounds were foundover a more widespread area than DDT.

Metals contamination followed the same pattern as organic contaminants. Sta-tions with elevated metals concentrations corresponded to the same locations ex-hibiting elevated organic contaminants (Figure 4). Concentrations were frequentlyabove ERLs in the tidal fresh, mixing, and upper estuarine zones, but ERM ex-ceedances were rare. Excluding aluminum, iron and manganese, the metal of high-est concentration was zinc, on both a mass and molar basis. There were high con-centrations of zinc throughout the tidal fresh zone, in contrast to the other metalswhich were concentrated in the sediments nearer to the mixing zone. Chromium,Cd, Cu, Hg, Ni, Pb, and Zn were all enriched above normalized levels (Schropp andWindom, 1988) from the tidal fresh through the upper estuarine zones. Butyl-tinswere detected at most of the tidal fresh, mixing, and upper estuarine stations. Othercontaminants showed a small but consistent increase in the vicinity of stations 57and 58, which are influenced by discharge from Dividing Creek and Maurice River.

For those chemicals for which ERLs and ERMs exist (Long et al., 1995) (Table I),most of the tidal fresh sites exceeded one or more ERLs (Table II). About half of thesites exceeded the ERL for individual high-weight PAHs. The ERM for aggregatelow-weight PAHs was exceeded at several stations, but the ERM was not derivedfor as large a set of compounds as are in the current data set (e.g. there are a largernumber of compounds in the data set contributing to the mass of low-weight PAHs).


TABLE I

Chemicals and chemical groups for which ERLs and ERMs

have been derived (ppb, dry wt. for organic compounds and

ppm, dry wt. for elements)

Chemical ERL ERM

Total DDT 1.58 46.1

pp’-DDE 2.2 27

Total PCBs 22.7 180

Total PAHs 4022 44792

High weight PAHs (≥4 rings) 1700 9600

Low weight PAHs (≤3 rings) 552 3160

Acenaphthene 16 500

Acenaphthylene 44 640

Anthracene 85.3 1100

Flourene 19 540

2-Methyl Naphthalene 70 670

Naphthalene 160 2100

Phenanthrene 240 1500

Benzo-a-anthracene 261 1600

Benzo-a-pyrene 430 1600

Chrysene 384 2800

Dibenzo(a,h)anthracene 63.4 260

Fluoranthene 600 5100

Pyrene 665 2600

As 8.2 70

Cd 1.2 9.6

Cr 81 370

Cu 34 270

Pb 46.7 218

Hg 0.15 0.71

Ni 20.9 51.6

Ag 1.0 3.7

Zn 150 410

Individual and total high weight PAH concentrations exceeded the respective ERLsat 4–12 of the stations in the tidal fresh zone, and at 1–4 stations in the mixing andupper estuarine zones in the vicinity of south Philadelphia and below the C&D canal.

3.3. SEDIMENT TOXICITY

Amphipod bioassay results were highly variable. Toxic responses were observed atonly 3 stations (13, 20, and 29, Figure 5). Seven stations had statistically reduced


TABLE II

Number of ERL/ERM exceedances and total ERMq val-

ues at Delaware Bay sampling stations

Sum

Station #>ERL #>ERM ERMq

1 25 3 7.25

2 17 3.46

3 26 3 9.03

4 26 5 11.68

5 2 0.92

6 14 3.26

7 26 4 11.04

8 26 4 9.24

9 10 2.55

10 13 2 5.05

11 16 1 5.13

12 1 1.02

13 28 5 17.88

14 9 2.00

16 19 4 10.12

17 4 1.92

18 6 2.02

19 19 1 6.26

20 26 5 13.52

21 13 4.63

22 2 1.77

23 16 4.40

24 8 2.75

25 9 3.20

26 8 2.78

27 4 1.84

28 2 1.63

29 21 2 7.77

30 11 3.25

31 2 1 1.70

32 2 1.59

33 2 1.37

34 4 1.96

35 3 1 2.53

36 4 2.02

37 3 1.87

38 2 1.53

57 6 2.36

69 1 0.40

Stations without exceedances are not listed.


Figure 5. Combined toxicity scores for Delaware Bay sediment bioassay results. (P450 results from

Station 11 not shown.)

survival (8, 11, 41, 42, 43, 46, and 48). Reduced survival was observed at stations40, 47, 52 and 57, but results were not statistically significant. Significant toxicityin the sea urchin fertilization test was limited to saline stations. Sediment fromstations which were toxic to amphipods were different than the stations that ex-hibited toxicity in the sea urchin bioassays. The highest response in the sea urchinfertilization bioassay was at station 56, behind Cape Henlopen. A total of 6 stationsdemonstrated statistically significant fertilization reductions at the 100% pore watertests. Pore water from station 56 also resulted in significant reduction at the 50%dilution level.

The Microtox R© results were the most variable of the toxicity bioassays both interms of response level and distribution of significant responses. Several stationsin the tidal fresh zone showed significant responses. The most extreme values wereseen in the vicinity of the C&D canal where observed EC50s were as low as 0.3%of the reference. A similar result was seen at station 56. A total of 58 stationsdemonstrated marginal depression of EC50s. A total of 40 stations demonstratedstatistically significant depression relative to the phenol-spiked reference standard.

The P-450 results indicated significant toxicity potential primarily in the tidalfresh and mixing zones. With the exception of station 11 this bioassay tracked veryclosely with PAH concentrations (Figure 4), regardless of salinity. Twelve stationsexhibited B[a]P equivalency factors above 60 ug/g. The response from station 11was over 1,500 ug/g, while the next highest value was 344 ug/g B[a]P equivalents


Figure 6. Fold induction (relative increase in P450 activity) results for selected Delaware Bay samples

diluted by 1:100 and measured after 6 and 16 hrs.

at station 13. In the 6 and 16 hrs timed sequence of experiments, performed todistinguish between PAHs and chlorinated compounds, stations 2, 10, 17, and 19indicated contribution of chlorinated dioxins, furans, and/or PCBs to the observedresults. Results from stations 11, 16 and 20 indicated the response was predomi-nantly to chlorinated contaminants. Station 11 was notable in that results showed asignificant contribution of chlorinated compounds even at a 1:100 dilution, whicheffectively diluted the other samples to concentrations below induction thresholds(Figure 6). Stations 13 16 and 20 had the highest measured PCB concentrations.Also, station 13 had a high concentration of planar PCBs, specifically PCB77.

3.4. BENTHIC COMMUNITY CHARACTERIZATION

A total of 231 taxa were enumerated from the benthic infauna samples. Of these 131were identified to species level. Among all taxa, 81 were found to be unique to onestation. Forty three taxa were rare, which were defined as being found at only twostations. Eight stations had 25 or more taxa (72, 67, 66, 58, 44, 43, 42). Unique andrare taxa were major contributors to the high taxa counts at these stations (Table III).

Polychaetes were the most numerous taxa present representing 34.7% of the to-tal number of species, followed by malacostracans (31.4%) and gastropods (9.6%).In terms of abundance, malacostracans represented 36.1% of the total number ofindividuals, followed by polychaetes (28.0%), oligochaetes (25.5%), and bivalves


TABLE III

Number of unique (occurring at only one station) and

rare (occurring at only 2 stations) species from Delaware

Bay sampling sites

Total Total rare

Station taxa # Unique # Rare & unique

1 17 1 3 4

3 15 3 1 4

4 16 0 1 1

5 6 1 0 1

7 18 2 3 5

8 7 1 1 2

12 12 0 1 1

15 7 1 0 1

16 13 0 2 2

19 8 2 0 2

20 7 1 1 2

27 4 0 1 1

28 11 0 2 2

30 14 2 1 3

32 10 1 1 2

36 15 0 2 2

38 15 1 0 1

39 7 1 0 1

40 16 1 1 2

41 19 1 1 2

42 27 1 1 2

43 31 2 4 6

44 42 5 5 10

45 15 0 1 1

47 13 2 0 2

48 14 2 1 3

49 10 0 1 1

50 23 2 1 3

51 9 2 0 2

52 16 0 1 1

53 10 2 0 2

55 18 3 1 4

56 15 1 0 1

58 29 1 3 4

59 15 2 1 3

(Continued on next page)


TABLE III

(Continued)

Total rare

Station Total taxa #Unique # Rare & unique

60 21 0 3 3

61 9 1 0 1

62 20 5 2 7

63 32 4 5 9

64 4 2 1 3

66 41 9 12 21

67 34 6 10 16

68 18 0 1 1

69 14 0 2 2

70 9 0 1 1

71 16 1 0 1

72 30 8 5 13

73 24 1 2 3

(4.6%). The dominant taxon collected from the samples was the amphipod, Am-pelisca abdita which accounted for 19.38% of all individuals, but occurred at only24.7% of the sites. Oligochaetes (Family Tubificidae) were the next most abundanttaxon representing 17.88% of all individuals identified. This taxon was also the mostwidespread, occurring at 61.7% of the sites. Total number of taxa, organism abun-dance, diversity and evenness are shown for individual stations in Figures 7 and 8.

Organism density was highly skewed (Figure 9), ranging from 59,700organisms/m2 at station 58, to 75 organisms/m2 at station 24. Mean abundance forall stations was 451/m2. The high density stations were generally dominated byvery large numbers of an individual taxon. The density of Ampelisca abdita wasalmost 42,000/m2 at station 58, which accounted for 70% of the organisms countedthere, and Mediomastus sp. accounted for an additional 21%. Mean density of ben-thic macrofauna for tidal fresh, mixing, combined estuarine, and the coastal zonestations was 588, 430, 531 and 184/m2, respectively (Table IV). Excluding the top10th percentile of stations (66, 60, 58, 57, 50, 44, 42, 4) the mean density for tidalfresh, mixing, combined estuarine and, coastal zone stations was 530, 430, 190,and 135/m2, respectively. Organism densities at sites which did not exhibit toxicitywere 409, 365, 429 and 184/m2 for tidal fresh, mixing, combined estuarine, andcoastal zone stations respectively. Mean density at stations exhibiting significanttoxicity was 873/m2 (759, 480 and 1152/m2 at tidal fresh, mixing and estuarinestations, respectively including data from stations of 57 and 60). Without the highcount stations, the mean density was 541/m2. Excluding Tubificids and Limnodrilushoffmeisteri from all toxic stations, the mean density value for the tidal fresh


Figure 7. Abundance and number of species of macroinvertebrate organisms found in Delaware Bay

sediment samples.

Figure 8. Macroinvertebrate species diversity and evenness in Delaware Bay sampling stations.


TABLE IV

Mean densities of Delaware Bay stations with and without various extreme values (≥90 percentile)

of stations and/or taxa

All taxa All taxa Non-toxic Non-toxic Toxic Toxic All toxic All toxic

all 90% all 90% all 90% W/O∗ W/O

Zone sites sites sites sites sites sites species∗ species#

All 451 265 345 201 873 541 632 347

Fresh 588 530 409 397 759 673 338 338

Mix 430 430 365 365 480 501 48 48

Estuarine 531 190 429 179 1152 276 1107 424

Ocean 184 135 184 135 / / / /

∗Excluding Tubificidae and Limnodrilus hoffmeisteri.# Excluding Tubificidae and Limnodrilus hoffmeisteri plus Ampelisca abdita from #60 and Leuconamericanus from # 57.

Figure 9. Abundance of macroinvertebrate organisms in Delaware Bay sediment samples plotted in

order from highest to lowest.

stations falls to 338. Without the two extreme values for A. abdita at station 60 andL. americanus at station 57, the mean density at toxic estuarine stations was 424/m2.

The details of the number of species and abundance are important to understand-ing the derived values of diversity and evenness. Species diversity was generallylowest in the upper estuarine and mixing zones as a consequence of low numberof species. Mean diversity was higher in the coastal zone and lower estuarine sites,


but individual station values were highly variable in all zones. Diversity and even-ness were low at stations 8 and 26. These stations had relatively low numbers ofspecies and abundance and, were dominated by Tubificids. In contrast, station 60had low diversity and evenness in spite of high species richness and density, due tothe enormous number of Ampelisca abdita (over 29,000/m2) found at that site.

3.5. STATISTICAL ANALYSES

3.5.1. MetricsStepwise regressions showed several statistically significant associations betweenthe individual variables, but correlation coefficients were generally low. The regres-sion coefficients were also small, indicating little direct affect between variables.Examination of the data from within the tidal fresh and estuarine stations did notreveal consistent relationships between contaminant concentrations and toxicity re-sponses (Tables V and VI). Since most of the contaminant concentrations co-variedtogether, identifying specific relationships would be difficult under any circum-stances, even for bioassays that are reasonably chemical specific, such as the P450

TABLE V

Stepwise regression results including regression coefficients and R2 coefficients of community in-

dices and toxicity results on contaminant concentrations and log transformed concentrations for

stations in the freshwater zone

Contaminant Log[]Contaminant

Variable Class (Coefficient) R2 Class (Coefficient) R2

Total taxa Chlordane∗∗ (0.69) 38.2 Chlordane∗ (1.94) 32.1

HCB∗ (−6.38) 15.5

Diversity HCB∗∗ (−0.11) 41.2 /

Log abundance Chlordane∗∗ (0.10) 50.6 Chlordane∗∗ (0.41) 46.8

Evenness HCB∗∗ (−0.05) 56.9 HCB∗∗ (−0.05) 37.3

PAHs∗ (−0.05) 14.0

Metals∗ (−0.14) 9.6

Amphipod survival PCBs∗ (−0.001) 68.9 Chlordane∗∗ (0.33) 31.0

Chlordane∗∗ (0.03) 11.3 PCBs∗∗ (−0.18) 29.9

Metals∗ (−0.001) 7.5 Metals∗∗ (−0.40) 22.9

Log 1/Microtox DDT∗∗ (−0.01) 36.61 DDT∗∗ (−0.36) 43.1

Sea urchin fertilization HCH∗∗ (−0.12) 17.9 Chlordane∗∗ (−0.03) 35.5

HCH∗ (−0.01) 21.83

Log 1/P450 Metals∗ (−0.004) 34.5 / /

Significance levels ∗∗ = P ≤ 0.01, ∗ = P ≤ 0.05.

/ = No chemical variable regression was statistically significant.

N = 18.


TABLE VI

Stepwise regression results of community indices and toxicity results on contaminant concentrations

and log transformed concentrations for stations in the estuarine zone

Contaminant Log[]Contaminant

Variable Class (Coefficient) Partial R2 Class (Coefficient) Partial R2

Total taxa Metals∗∗ (−0.01) 15.3 Metals∗ (−3.895) 30.98

TBT∗ (1.507) 5.5

Diversity Metals∗∗ (−0.001) 16.6 PAHs∗∗ (−0.147) 20.7

Log abundance / DDT∗ (−0.456) 12.1

TBT∗∗ (0.452) 9.0

Evenness / /

Amphipod survival PAHs∗∗ (−0.0001) 52.0 DDT∗∗ (0.189) 15.6

Chlordane∗∗ (0.04) 16.7 PCBs∗ (−0.193) 9.3

PCBs∗ (0.002) 3.5

Log 1/Microtox / / PAHs∗∗ (−0.494) 23.8

HCB∗ (−0.348) 7.5

TBT∗∗ (−0.348) 5.2

Sea Urchin fertilization TBT∗∗ (−0.02) 16.5 TBT∗ (−0.028) 9.5

Log 1/P450 PAHs∗∗ (−0.0003) 63.53 PAHs∗∗ (−0.766) 79.7

Chlordane∗ (−0.465) 7.2


/ = No chemical variable regression was statistically significant.

N = 43.

assay. The regression of P450 bioassay results on log-PAH concentration achieveda maximum R2 of 79.7% in the estuarine zones. Regression results between am-phipod survival and a combination of contaminants in the tidal fresh zone werelargely driven by extreme values. Similar results were seen with metals concen-trations, where correlation coefficients for individual metals were seldom above20% for toxicity bioassay or community indices. The relationships between ben-thic community indices and toxicity results were equally unclear (Table VII). Onlythree correlation coefficients for a community index/individual bioassay result wereabove 20%.

3.5.2. IndicesPearson correlation coefficients revealed strong positive relationships between thetoxicity score and each of the contaminant indices (Table VIII). The toxicity scorewas most strongly correlated to the ERM-Q. Correlations were negative with theB IBI and all the community parameters except abundance. The correlation be-tween ERM-Q and B IBI, diversity, number of taxa, and evenness are negative,and correlations with evenness and abundance were not significant. The B IBI was


TABLE VII

Stepwise regression results including regression coefficients and R2 coefficients of community indices

on transformed toxicity results for stations in the freshwater and estuarine zones

Variable Freshwater (coefficient) Partial R2 Estuarine (Coefficient) Partial R2

Total taxa P450∗ (−0.94) 23.5 P450∗∗ (3.38) 22.0

Amphipod∗∗ (10.02) 15.6 Microtox∗∗ (−2.90) 9.6

Diversity / / P450∗∗ (0.28) 16.2

Microtox∗∗ (−0.15) 10.2

Amphipod∗ (−0.76) 8.3

Log abundance Microtox∗∗ (−0.43) 21.5 Microtox∗ (−0.34) 15.0

Amphipod∗ (1.75) 18.0

Fertilization∗ (−7.11) 16.6

Evenness / / / /


/ = No bioassay regression was statistically significant.

N = 18 and 42.

negatively correlated with the chemical parameters, and positively correlated withall community parameters except log abundance.

Salinity and grain size were confounding factors. Areas with fine grained sedi-ments were more prevalent in the tidal fresh zone where contaminant concentrationswere also generally higher and community parameters tended to be depressed. Thedistribution of community types in the Delaware Bay system has been addressedby Hartwell and Claflin (2005).

4. Discussion

The fact that chemical concentrations tended to be either high or low for all con-stituents at a given station makes interpretation of benthic community and toxi-cological results with respect to cause and effect difficult, even in the absence ofother modifying parameters such as salinity or grain size gradients. Direct statis-tical correlations between toxicity and individual chemical constituents were onlydiscernable where contaminant concentrations were at the extremes of observedranges (Figure 10). The same was true for relationships between benthic com-munity indices and chemical concentration. This is interpreted as an indicationthat organisms can tolerate chemical contamination up to a certain threshold level,beyond which effects are observable. Below these levels, the relationships are in-fluenced by a myriad of other factors. Also, because contaminated sites containedall the major contaminant classes, as opposed to just one or two, trying to arriveat what the relative impacts of various contaminant classes are, and being able toassess potential contaminant interactions is impossible using these data. Anothercomplication is that salinity adjustment to standard laboratory bioassay conditions


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alters the chemical availability of contaminants in the bioassays. Neither individualchemical constituents nor individual bioassays successfully predicted communityimpacts. Ferraro and Cole (2002) noted they could correlate PAH concentrationswith toxicity results and community indicators, only after the confounding effectsof grain size, TOC, redox (Eh), and depth were statistically accounted for.

The P-450 bioassay, which is essentially a chemical specific response test,tracked PAHs well at all stations. The high value at station 11 is likely drivenby chlorinated compounds (Figure 6). Dioxins and furans were detected at station11, but planar PCBs were not analyzed in this sample. The station is located adja-cent to an industrial zone in southern Philadelphia. It is immediately downstreamfrom the confluence of the Schuylkill River, which is a known source area for PCBs(DRBC, 1998; Kiddon et al., 2003) .

Significantly elevated contaminant concentrations and/or overt toxicity does notappear to adversely impact benthic species abundance in this study. The ability ofopportunistic, chemically tolerant species to reproduce in high numbers, particu-larly in the absence of competitors and potential predators enables the so-called‘weed species’ to proliferate in contaminated habitats. Indirect effects of contami-nants have also been shown to have potentially significant impacts on communitydynamics (Carman et al., 1997; Fleeger et al., 2003). The prevalence of Capitellacapitata near outfalls is the classic example of this phenomenon (Reish, 1979).The distribution of Tubificids and Limnodrilus hoffmeisteri as dominant species inDelaware Bay throughout the tidal fresh and mixing zones illustrate this situation.


It has also been shown in numerous places that organisms can adapt, at a cost, tobadly contaminated habitats (Klerks and Levinton, 1989; Martinez and Levinton,1996; Millward and Grant, 2000; Nacci et al., 2002). The presence of what are con-sidered to be sensitive species (e.g. Cyathura polita, Ferrissia sp.) in neighboringChesapeake Bay (Llanso et al., 2002; R. Diaz, personal communication) in someof the most contaminated stretches of the Delaware River may be an example ofthis. Similarly, the number of species in a sample may be as much a product ofsalinity gradients and grain size as pollution gradients in Delaware Bay. This isalso a well known phenomenon (SCBW, 1959). The salinity transition zone is aphysiologically difficult habitat in which to survive. The number of species (as wellas abundance) declines from tidal fresh areas into the mixing and upper estuarinezones, and rises again to high levels in the lower estuarine habitat.

Because of the inability to draw firm conclusions about relationships betweenspecific metrics due to the influence (interference) of physicochemical habitat fea-tures that govern species’ distributions and bioavailability of contaminants, morebroad-based indicators that condense individual chemical, biological, and commu-nity parameters into more general indices of condition proved to be more useful inthis situation. Aggregated parameters may be more useful than simple indicatorsas they integrate values from a range of measurable responses. The cost is loss ofdetailed information, but the advantage is the ability to make realistic predictiveforecasts with a greater assurance of being correct, at least on a broad scale. Thisis consistent with the Sediment Quality Triad approach advocated by Chapman(1996) and others.

Diversity and species richness do not show universally declining trends withincreasing ERM-Q and Toxicity Scores, but rather a general lack of high valuesat stations with high Toxicity Scores (Figure 11). That is, at locations with low

Figure 11. Toxicity index vs diversity and species richness.


Figure 12. Relationship between the toxicity index and mean ERM quotient for Delaware Bay sedi-

ment stations.

contaminant levels, high and low community parameter values were observed,depending on salinity and grain size. At locations with high contaminant concen-trations, high values of community parameters were absent, regardless of physicalsetting. This is due to more than just salinity stress, as some of the highest contam-inant and toxicity values were found well above the mixing zone in strictly tidalfresh areas.

While the Toxicity Score and the ERM-Q are only marginally correlated withcommunity impacts they are robust in predicting each other (Figure 12). Thereis clearly a threshold of contamination, above which toxicological impacts areseen. The ERM-Q and the toxicity score were highly correlated parameters, andcoefficient values were reasonably high for field measurements, particularly inlight of the fact that the ERMs were derived from empirical data unrelated to theDelaware Bay data set. Broad integration of empirically based information doesresult in useful relationships if properly applied.

In terms of the spatial extent of sediment contamination, more than 90% of theVirginian EMAP Province were below the ERL for total PCBs (EPA, 1994b),whereas 55% of the freshwater stations in the Delaware River exceeded theERL. Sediment quality guidelines for freshwater habitats have not been refinedto the extent that ERLs and ERMs have. MacDonald et al. (2000) did produceconsensus-based SQGs for inland Florida waters. These values are generally (butnot all) lower than ERLs and ERMs. Similarly, concentrations of chlorinated


pesticides in the tidal fresh reaches of the Delaware were routinely above the90th percentile of observed concentrations. Several locations in the mixing andupper estuarine zones of Delaware Bay are enriched with As, Cd, Cu, Hg, Pb, Sn,and Zn, compared to the Virginian Province database (EPA, 1994b). Chromiumand Ni showed borderline enrichment levels. Riedel and Sanders (1998) con-cluded that seston (phytoplankton and other suspended particulate material and/ormicroorganisms) were substantially enriched with Pb and Zn and moderatelyenriched with As, Se and Cd in Delaware Bay. The DRBC (1994) identifiedmultiple sources for metals contamination, and concluded that for Cd, Cu, Pb,Ag, and Zn, natural sources are unlikely to account for the observed distribu-tion of these metals. They also concluded the Delaware and Schuylkill Rivers arenot necessarily the predominant source, but that point sources on the mainstemand smaller tributaries, and non-point sources were the major sources of metalscontamination.

Low molecular weight (≤3 rings) and high molecular weight (≥4 rings) PAHswere generally present in equal concentrations on a mass basis. Alkyl-substitutedPAHs were much more prevalent in the low weight category than in the high weightcategory. This indicates a pyrogenic source for the high weight PAHs, whereas thelow weight PAHs are likely a mixture of pyrogenic sources and petrogenic (e.g. fuelspills) (NRC, 1985). The mass of PAHs in the sediment are higher than previouslydocumented, and it is certain that concentrations would be shown to be even higherif all forms of substituted compounds were considered.

At station 56 sediment grain size is finer than the surrounding area, and theTOC was relatively high. Clearly this is a consequence of the physical constraintson current velocity imposed by the natural shoals behind Cape Henlopen and theartificial breakwater constructed to provide protected anchorage for ships in transit.The actual sampling site was adjacent to, but not in the anchorage area. Contaminantconcentrations were elevated above other stations in the area, but only slightly, andall concentrations were generally low. However, both the Microtox R© and sea urchinfertilization bioassays showed significant responses. No explanation for the resultsis readily apparent, but this area may warrant further investigation.

5. Summary

The tidal fresh portion of the Delaware Bay Study area is heavily contaminated.Portions of the salinity mixing zone between Philadelphia, and the C&D canalwere also contaminated. Contaminant concentrations varied greatly from station tostation, depending on exact location and sediment texture. Sediment compositionvaried from >90% silt/clay to ≥99% sand. Shallow sites in the tidal fresh zonehave fine grained sediments. In the channels and dredged areas, sediments wereeither sandy or silt/clay basement layers. Sediments in the lower estuary were ei-ther fine grained depositional deposits or sandy sediments typical of higher energy


environments. Sandier sites had generally lower concentrations of contaminantsthan sites with a significant proportion of silt/clay. Chemical concentrations in thelower estuary, and coastal zone stations outside of the bay proper were basicallyuncontaminated beyond trace levels. Species diversity and abundance were gener-ally lowest in the salinity mixing zone. Mean diversity was higher in the coastalzone and lower estuarine sites, but individual station values were highly variablein all zones. The presence of unique and rare taxa were major contributors to thehigh taxa counts at the lower estuary and coastal zone sites. Significant toxicityresults were primarily limited to the tidal fresh and mixing zones. Diversity andspecies richness do not show declining trends with increasing contamination ortoxicity, but rather a general lack of high values above threshold values. At lo-cations with low contaminant levels, the community parameters were either highor low, depending on salinity and grain size. While toxicity and the contaminantlevels are only marginally correlated with community impacts due to confoundingparameters, they are strongly correlated with each other. Aggregated indices maybe more useful than simple parameters as they integrate values over a wider range ofmeasurement responses. The cost is loss of detailed information, but the advantageis the ability to make realistic predictive forecasts with a greater assurance of beingcorrect, at least on a general scale.

Acknowledgments

This study part of NOAA’s contribution to the Mid-Atlantic Integrated Assess-ment (MAIA) program, a demonstration project for an inter-disciplinary, multi-agency approach to provide integrated scientific information on the current condi-tions, stressors, and vulnerabilities of the region’s estuaries. The study benefittedfrom cooperation and information exchange with US Environmental ProtectionAgency, State of Delaware, the Delaware River Basin Commission (DRBC), theDelaware Estuary Program, regional port authorities, and a number of citizensgroups. We are pleased to acknowledge assistance by a number of organizationsas well as contractors and cooperating laboratories, including the Geochemical &Environmental Research Group and Trace Element Research Laboratory at TexasA&M University, USGS/BRD Marine Ecotoxicity Research Station, ColumbiaAnalytical Services Inc., Science Applications International Corp., Barry A. VittorAssoc. Inc., and USGS/BRD Environmental and Contaminants Research Center,Columbia, Mo. The Department of Natural Resources and Environmental Control,State of Delaware, provided considerable information on areas of particular envi-ronmental concern to the state and assisted in field operations. DRBC, providedbackground information and reports on previous studies. The officers and crewof the NOAA ship Ferrel provided excellent ship support, including small vesseloperations.


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Documents

Habitat Conditions and Correlations of Sediment Quality Triad Indicators in Delaware Bay