Integrated measures of ambient toxicity and fish community diversity in Chesapeake Bay tributaries

Abstract

The goals of this study were to assess the results of a suite of sediment and water column bioassays in the framework of a toxicological risk ranking model and evaluate correlations of model output with fish community metrics. The test sites were located in four tributaries of Chesapeake Bay that are impacted on by industrial, urban and agricultural land use (Curtis Creek, Rock Creek, Fishing Bay and Wicomico River). The mortality, reproduction and growth rates in the water column assays indicated low-level chemical contamination impacts in Curtis Creek and Rock Creek. The results from the Wicomico River and Fishing Bay did not indicate contaminant impacts, but some borderline effects were seen. The sediment bioassays demonstrated greater toxicological responses than the water column assays. The sediments in the Curtis Creek and Rock Creek sites were contaminated with heavy metals and PAHs. The heavy metal concentrations were an order of magnitude lower in the Fishing Bay sediments and below detection in the Wicomico River sediments, except for zinc. The acid-volatile sulphides:simultaneously extractable metals (AVS:SEM) ratios were below 1 in all cases. All four systems had detectable petroleum hydrocarbon contamination. Organic contaminants were below detection for all analyses in the Wicomico River and Fishing Bay samples. The risk ranking model ranked Curtis Creek as the most toxicologically impacted site, followed by Rock Creek, Fishing Bay and Wicomico River, which were essentially equal. The diversity index for fish communities sampled by bottom trawl was significantly correlated with the toxicological risk scores for sediment. The toxicological results indicate sediment contamination effects on the deep water fish community in Curtis Creek and indicate that contaminant impacts are not likely to be a contributing factor to disturbed fish communities in Fishing Bay