TIDAL RIVER SEDIMENTS IN THE WASHINGTON, DC AREA .3. BIOLOGICAL EFFECTS ASSOCIATED WITH SEDIMENT CONTAMINATION

Sediment toxicity and benthic macroinvertebrate community structure we re measured as one component of a study conceived to determine the dis tribution and effect of sediment contamination in tidal freshwater por tions of the Potomac and Anacostia rivers in the Washington, D.C., are a. Samples were collected at 15 sites. Analyses included a partial lif e cycle (28 d) whole sediment test using the amphipod Hyalella azteca (Talitridae) and an assessment of benthic community structure. Surviva l and growth (as estimated by amphipod length) were experimental endpo ints for the toxicity test. Significant mortality was observed in 5 of 10 sites in the lower Anacostia River basin and at the main channel P otomac River site. Sublethal toxicity, as measured by inhibition of am phipod growth, was not observed. Toxicity test results were in general agreement with synoptically measured sediment contaminant concentrati ons. Porewater total ammonia (NH3 + NH4+) appears to be responsible fo r the toxicity of sediments from the Potomac River, while correlation analysis and simultaneously extracted metals:acid volatile sulfide (SE M:AVS) results suggest that the toxicity associated with Anacostia Riv er sediments was due to organic compounds. Twenty-eight macroinvertebr ate taxa were identified among all sites, with richness varying from 5 to 17 taxa per site. Groups of benthic assemblages identified by grou p-average cluster analysis exhibited variable agreement with sediment chemical and sediment toxicity results. Integration of toxicological, chemical, and ecological components suggests that adverse environmenta l effects manifest in the lower Anacostia River benthos result from ch emical contamination of sediment.