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Virginian Province 1990-1993
Statistical Summary 1990-1993
Strobel, C.J., H.W. Buffum, S.J. Benyi, E.A. Petrocelli, D.R. Reifsteck and D.J. Keith. 1995a.
U.S. Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, Narragansett, RI. EPA/620/R-94/026.
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Executive Summary
The Environmental Monitoring and Assessment Program (EMAP) is a nationwide program initiated by EPA's Office of Research and Development (ORD). EMAP was developed in response to the demand for information about the degree to which existing pollution control programs and policies protect the nation's ecological resources.
EMAP-Estuaries (EMAP-E) represents EMAP's efforts in near-coastal environments. These efforts are designed to provide a quantitative assessment of the regional extent of coastal environmental problems by measuring status and change in selected indicators of ecological condition. Specific environmental problems investigated include:
- hypoxia,
- sediment contamination,
- coastal eutrophication, and
- habitat loss.
In 1990 EMAP-E initiated a four-year demonstration project in the estuaries of the Virginian Province, which includes the coastal region of the Northeast United States from Cape Cod south to the mouth of Chesapeake Bay. It is composed of 23,574 km2 of estuarine resources including 11,469 km2 in Chesapeake Bay and 3,344 km2 in Long Island Sound.
Estuarine resources in the Virginian Province were stratified into classes by physical dimension for the purposes of sampling and analysis. Large estuaries in the Virginian Province were defined as those estuaries greater than 260 km2 in surface area and with aspect ratios (i.e., length/average width) of less than 18. The areal extent of large estuaries in the Province is 16,097 km2. Large tidal rivers were defined as that portion of the river that is tidally influenced (i.e., detectable tide > 2.5 cm), greater than 260 km2 in surface area, and with an aspect ratio of greater than 18. Approximately 2,602 km2 were classified as large tidal rivers. The third class was the small estuaries and small tidal rivers which includes those systems whose surface areas fall between 2.6 km2 and 260 km2. This class represents 4,875 km2 of the Virginian Province.
A total of 446 Base Sampling Sites (BSS: the probability-based sites used to characterize conditions in the Province) were identified for sampling over the four-year period (1990-1993). Of these 446 sites, 21 were deemed inaccessible due to inadequate water depth or other logistical constraints. The 425 sites sampled represent 94% of the estuarine surface area of the Province. All sites were sampled by three crews during the summer index period (late July through September).
The purpose of this report is to provide regional managers and administrators with estimates of the ecological condition of the estuarine resources of the Virginian Province for the first complete four-year cycle of sampling. A separate Assessment Report (Paul et al., in preparation) is currently being produced to evaluate associations between indicators as well as to evaluate the overall design of the Program. In addition, interim reports and Statistical Summaries have been produced describing the results of the 1990, 1991, and 1992 sampling efforts (Weisberg et al., 1993; Schimmel et al., 1994; Strobel et al., 1994).
All EMAP-VP data used in the generation of this report were subjected to rigorous quality assurance measures as described in the 1993 Quality Assurance Project Plan (Valente and Strobel, 1993).
Biotic Condition Indicators
Biotic condition indicators are characteristics of the environment that provide quantitative evidence of the status of ecological resources and biological integrity of a sample site from which they are collected (Messer, 1990). Ecosystems with a high degree of biotic integrity (i.e., healthy ecosystems) are composed of balanced populations of indigenous benthic and water column organisms with species compositions, diversity, and functional organization comparable to undisturbed habitats (Karr and Dudley, 1981; Karr et al., 1986).
A benthic index which uses measures of organism and community condition to evaluate the condition of the benthic assemblage was utilized in the assessment of biological resources of the Virginian Province. The index under development was constructed from the combined 1990 - 1993 data and was developed to represent a combination of ecological measurements that best discriminates between good and poor ecological conditions. This index represents EMAP-E's attempt to reduce many individual benthic indicators into a single value that has a high level of discriminatory power between good and poor environmental conditions.
A benthic index critical value of zero was determined from the combined 1990 - 1993 Virginian Province dataset. Twenty three (+- 3) percent of the bottom area of the Virginian Province had an index value of < 0, indicating likely impacts on the benthic community (Figure 1). The lowest incidence was found in the large estuaries (18 +- 4%).
A "standard" fish trawl (trawling at a specified speed for a specified time) was performed at each station to collect information on the distribution and abundance of fish. Because many factors influence fish abundance, poor catch may not be an indication of degraded conditions, but simply the natural habitat. Catches of <10 fish/trawl (catch per unit effort) occurred at stations representing approximately 36 +- 3% of the Province (Figure 2).
The incidence of gross external pathologies (growths, lumps, ulcers, and fin erosion) among fish collected in the Virginian Province was 0.3%. Of the over 16,000 fish examined, 55 were identified as having one or more of these conditions.
Abiotic Condition Indicators
Abiotic condition indicators historically have been the mainstay of environmental monitoring programs, because these indicators quantify the levels of stresses to which organisms are exposed.
One potential stress to aquatic organisms is a low concentration of dissolved oxygen (DO). Two and 5 mg/L are values employed by EMAP to define severe and moderate hypoxia, respectively. Approximately 25 +- 3% of the sampled area of the Province contains bottom waters with DO concentrations less than or equal to 5 mg/L (Figure 3). "Bottom" is defined as one meter above the sediment-water interface. Approximately 5 +- 2% of the sampled area exhibited bottom DO conditions <= 2.0 mg/L. Dissolved oxygen conditions <= 2.0 mg/l were evident in all three classes of estuaries (Figure 3).
In addition to measuring contaminants in sediments, acute toxicity tests were performed on sediments collected at each site to determine if they were toxic to the tube-dwelling amphipod, Ampelisca abdita. Sediments were classified as toxic if amphipod survival in the test sediment was less than 80% of that in the control sediment and statistically different from control survival. Approximately 10 +- 2% of the sampled area of the Virginian Province contained sediments which were toxic to the amphipod during 10-day exposures (Figure 4). Sediments were highly toxic (i.e., survival < 60% of control) in 2 +- 1% of the area of the Province.
Sediments collected at each station were analyzed for both organic contaminants and metals. Because of the complex nature of sediment geochemistry, the ecological impact of elevated contaminant levels is not well understood. Although no definitive statement can be made estimating the overall aerial extent of sediment contamination in the Virginian Province, the results of several different approaches are presented and discussed.
Figure 5 shows the distribution of the sum of measured polycyclic aromatic hydrocarbons (PAHs) in the Virginian Province. The complete list of analytes included in this summation can be found in Section 3. The 75th percentile for total PAHs was approximately 1,200 ng/g (i.e., 75% of the area of the Province contained sediments with concentrations of PAHs <= 1,200 ng/g), with a maximum measured concentration at any station of 80,100 ng/g.
Draft EPA Sediment Quality Criteria (SQC) are currently available for the PAHs acenaphthene, phenanthrene, and fluoranthene; and the pesticide dieldrin. Draft PAH SQC were exceeded at only one small estuary station within the Province (ca. 0.07% of the area).
Stations representing only 1 +- 1% of the area of the Province exceeded any ER-M (Effects Range-Median from Long et al., 1995) value for PAHs.
The extent to which polluting activities have affected concentrations of metals in sediments is complicated by the natural variation of metals in sediments. Crustal aluminum concentrations are generally many orders of magnitude higher than anthropogenic inputs; therefore, aluminum can be used to "normalize" for differing crustal abundances of trace metals. The process utilized was inefficient for several metals (i.e., r2 for the regression < 0.4), but performed well for As, Cr, Fe, Hg, Mn, Ni, Sb, and Zn. The percent area of the Virginian Province with sediments enriched by metals pertains only to the metals mentioned above. Figure 6 presents the results of this normalization. The metal exhibiting the greatest extent of enrichment is manganese. Approximately 46 +- 5% of the area of the Province showed enrichment of sediments with at least one metal. Thirty seven (+- 7), 64 +- 3, and 69 +- 16 percent of the large estuary, small estuary, and large tidal river class areas sampled contained sediments with metals concentrations exceeding predicted background levels. This only shows the percent of the Province with elevated concentrations of metals, and does not indicate the magnitude of enrichment; therefore, this does not imply concentrations are elevated to the point where biological effects might be expected. As shown below, sediment from only a fraction of this area contains concentrations of metals high enough to result in ecological effects.
Stations representing only 4 +- 2% of the area of the Province exceeded any ER-M (Effects Range-Median from Long et al., 1995) value for metals. It should be noted that earlier EMAP-E documents utilized the Long and Morgan (1990) values. ER-M and ER-L values have subsequently been updated (Long et al., 1995) and it is these newer values that are used in this report. The major difference is an increase in the ER-M values for metals, resulting in a significant reduction in the percent area of the Province in exceedence.
Presence of marine debris in fish trawls was documented by field crews as being encountered at stations representing 20 +- 3% of the Virginian Province area (Figure 7). The small estuary class had the largest percent area (35 +- 9%) where trash was found.
Habitat Characterization
Habitat indicators describe the natural physical and chemical conditions of the sites sampled. These parameters are important modifying factors controlling both abiotic and biotic condition indicators.
Figure 8 shows the distribution of water depth in the Virginian Province. The area shallower than 2 m is underestimated because this was the minimum depth sampled.
Based on the sampling design where a single station represents a statistical area (e.g., 70 km2 for large estuary sites), 6% of the area of the Province could not be sampled due to inadequate water depth or inaccessibility.
Bottom water temperatures in the Virginian Province ranged from 12 C to 30 C during the summer sampling season.
Vertical density differences (a function of both salinity and temperature) in the waters of the Virginian Province can be large enough to result in a reduction in mixing between surface and bottom waters, potentially allowing the bottom waters to become hypoxic. Degree of stratification in the Virginian Province was measured as the delta sigma-t which is the difference in sigma-t (sigma-t, a density measurement) between surface and bottom waters. Approximately 72 +- 3% of the Province area had a delta sigma-t of <1 unit; thus the majority of the water in the Virginian Province was well-mixed (Figure 10). Only 13 +- 3% of the Province area was strongly stratified ( delta sigma-t >2).
Water clarity was determined from light extinction coefficients, which describe the attenuation of light as it passes vertically through the water column. We are defining low water quality as water in which a diver would not be able to see his/her hand when held at arms length (i.e., only 10% of incident sunlight reaches a depth of one meter; light attenuation coefficient <= 2.303). Moderate water clarity, in terms of human vision, is defined as water in which a wader would not be able to see his/her feet in waist-deep water (i.e., only 25% of incident sunlight reaches a depth of one meter; light attenuation coefficient <= 1.387). Water clarity was good in 81 +- 3% of the area of the Virginian Province (Figure 11). Water of low clarity was found in 6 +- 2% of the Province and an additional 13 +- 2% had water of moderate clarity.
The silt-clay (mud) content of sediments (the fraction <63 particle diameter) is an important factor determining the composition of the biological community at a site, and is therefore important in the assessment of the benthic community. The distribution of mud (>= 80% silt-clay) vs sand (<= 20% silt-clay) is illustrated in Figure 12.