Ecological risk assessment in a large river-reservoir: 6. Bioindicators offish population health

Spatial distribution of contaminants in the sediments and biota of a large reservoir ecosystem were related to a variety of biological responses in fi sh populations and communities to determine possible relationships between contaminant loading in the environment and fish health. Much of the contami nant inventory in the Clinch River/Watts Bar Reservoir (CR/WBR) system has originated from three U.S. Department of Energy facilities on the Oak Ridge Reservation, which borders this system in its upper reaches. Fish sampled from areas of the CR/WBR system with the highest levels of contaminants in the sediments and biota, primarily mercury and PCBs, had the most dramatic bioindicator responses. The major changes observed were induction of detoxi fication enzymes, organ dysfunction, increased frequency of histopathologic al lesions, impaired reproduction, and reduced fish community integrity. Me rcury, the dominant contaminant, displayed a decreasing concentration gradi ent from the: upper reaches of Poplar Creek to the lower Clinch River, whic h was consistent with a downstream gradient in several of the biological re sponses. A multivariate analysis using all of the individual fish health re sponses at each sire in a discriminant analysis procedure also revealed a d ownstream gradient in integrated fish health. In Poplar Creek where contami nant concentrations were the highest, statistical correlations were observe d between individual bioindicator responses such as contaminant exposure in dicators. organ dysfunction, histopathological damage, and reproductive imp airment. Relationships between contaminant Loading and fish community indic es such as species richness and relative abundance, however, were more diff icult to establish in Poplar Creek because of the possible dominating influ ence of food and habitat availability on fish community dynamics. Using a s uite of bioindicators that encompass a range of levels of biological organi zation and response-sensitivity scales improves the probability of identify ing cause (contaminant) and effect (biological response) and helps in disti nguishing between natural and anthropogenic sources of stress in aquatic ec osystems.