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Ecological Condition of the Delaware and Maryland Coastal Bays
1996. U.S. Environmental Protection Agency, Office of Research and Development, Washington, D.C. 20460 EPA/620/R-96/004.
Executive Summary
The coastal bays of Delaware and Maryland are an important ecological and economic resource whose physical characteristics and location make them particularly vulnerable to the effects of pollutants. This project was undertaken as a collaborative effort between state and federal agencies to assess the ecological condition of this system and fill a data void identified in previous characterization studies. Two hundred sites were sampled in the summer of 1993 using a probability-based sampling design that was stratified to allow assessments of the coastal bays as a whole, each of four major subsystems within coastal bays (Rehoboth Bay, Indian River Bay, Assawoman Bay, and Chincoteague Bay) and four target areas of special interest to resource managers (upper Indian River, St. Martin River, Trappe Creek, and dead-end canals). Measures of biological response, sediment contaminants, and eutrophication were collected at each site using the same sampling methodologies and quality assurance/quality control procedures used by EPA's Environmental Monitoring and Assessment Program (EMAP). As an additional part of the study, trends in fish communities structure were assessed by collecting monthly beach seine and trawl measurements during the summer at about 70 sites where historic measurements of fish communities have been made.
Major portions of the coastal bays were found to have degraded environmental conditions. Twenty-eight percent of the area in the coastal bays had degraded benthic communities, as measured by EMAP's benthic index. More than 75% of the area in the coastal bays failed the Chesapeake Bay Program's Submerged Aquatic Vegetation (SAV) restoration goals, which are a combination of measures that integrate nutrient, chlorophyll and water clarity parameters. Most areas failed numerous SAV goal attributes. Sixty-eight percent of the area in the coastal bays had at least one sediment contaminant with concentrations exceeding published guidelines for protection of benthic organisms. Further study is needed to assess whether the biological effects observed were the direct result of contamination.
Within the coastal bays, Chincoteague Bay was in the best condition of the four major subsystems, while Indian River was the worst. Only 11% of the area in Chincoteague Bay had degraded benthos compared to 77% in Indian River. Less than 10% of the area in Indian River met the Chesapeake Bay SAV Restoration Goals. In comparison, almost 45% of the area in Chincoteague Bay met the Chesapeake Bay Program's SAV restoration goals, a figure which increased to almost 85% when only the most controllable components of the goals (nutrient and chlorophyll) were considered.
All of the target areas of special management interest were in poorer condition than the remainder of the coastal bays, with dead-end canals having the poorest condition. Chemical contaminants exceeded published guideline values in 91% of the area of the dead-end canals, and 57% of their area had dissolved oxygen concentrations less than the state standard of 5 ppm. Dead-end canals also were biologically depauperate, averaging only 4 benthic species per sample compared to 26 species per sample in the remaining portions of the coastal bays.
The consistency of the sampling design and methodologies between our study and EMAP allows unbiased comparison of conditions in the coastal bays with that in other major estuarine systems in EPA Region III that are sampled by EMAP. Based on comparison to EMAP data collected between 1990 and 1993, the coastal bays were found to have a similar or higher frequency of degraded benthic communities than in Chesapeake or Delaware Bays. Twenty-eight percent of the area in the coastal bays had degraded benthic communities as measured by EMAP's benthic index, which was significantly greater than the 16% EMAP estimated for Delaware Bay using the same methods and same index, and statistically indistinguishable from the 26% estimated for Chesapeake Bay. The coastal bays also had a prevalence of chemical contamination in the sediments that was higher than in either Chesapeake Bay or Delaware Bay. Sixty-eight percent of the area in the coastal bays exceeded published guideline values for at least one contaminant compared to 46% for Chesapeake Bay and 34% for Delaware Bay. While the percent of area having these concerns is higher in the coastal bays, the absolute amount of area having these concerns is greater in the Delaware and Chesapeake Bays because of their larger size.
The fish community structure in Maryland's coastal bays was found to have remained relatively unchanged during the past twenty years while that of similar systems in Delaware have changed substantially. Fish communities of the Maryland coastal bays are dominated by Atlantic silversides, bay anchovy, Atlantic menhaden and spot, which is similar to the community structure measured in the Delaware coastal bays 35 years ago. The fish fauna in Delaware's coastal bays has shifted toward species of the Family Cyprinodontidae (e.g., killifish and sheepshead minnow) which are more tolerant to low oxygen stress, and salinity and temperature extremes.