CORRELATION OF MEASURES OF AMBIENT TOXICITY AND FISH COMMUNITY DIVERSITY IN CHESAPEAKE BAY, USA, TRIBUTARIES - URBANIZING WATERSHEDS

This study was performed to evaluate ambient toxicity conditions in Ch esapeake Bay tidal tributaries whose watersheds are impacted by urban development and to further evaluate an existing toxicological risk ran king model. A battery of water-column and sediment bioassays were empl oyed with animals and plants. The study was conducted in coordination with a fish community sampling program. Tests were conducted monthly f rom April through August 1994 at five sample sites in each of four tid al tributaries. Mortality, reproduction, and growth rates in the water -column assays did not consistently indicate chemical contamination in any system. Chemical analyses did not indicate elevated levels of con taminants in the water column. Sediment bioassays demonstrated greater responses than water-column assays. Sediment in the upstream reaches of the South River demonstrated significant toxicity. Toxicity was als o observed at the uppermost Severn River station and the middle Patuxe nt River station. Chemical analyses of composite sediment samples indi cated elevated metals levels in the South River. Some metals were abov e threshold values in the Patuxent and Wicomico rivers. The AVS/SEM ra tios in pore water were below 1 in all cases. Organic analyses demonst rated low level polycyclicaromatic hydrocarbon contamination in all fo ur systems. The toxicological risk ranking model ranked the South Rive r as the most contaminant-impacted site. The Patuxent and Severn river s were ranked below the South River; however, the ranking model identi fied specific locations in the Severn and Patuxent rivers that indicat e sediment contamination. The Wicomico River had the lowest overall ri sk score. The Patuxent River requires more intense sampling due to its relatively larger size. The toxicological risk ranking results for se diment were significantly correlated with species diversity for fish c ommunities sampled by bottom trawl. Results were consistent with data from previous years. Regression analysis of 2 years of data indicate t hat fish community impairment can be predicted with ambient toxicity r esults.