Use of fish communities to assess environmental impacts in South Carolina coastal plain streams

We developed an index of biotic integrity (IBI) and a biotic index based on fish species richness (FSBI) to assess the ecological health of streams on the Savannah River Site, a 780-km(2) U.S. Department of Energy facility located in the Sand Hills ecoregion on the upper coastal plain of South Carolina. To maintain the responsiveness of the IBI to a variety of impacts yet incorporate sufficient ecoregion specificity to achieve acceptable accuracy, we included metrics from each of six metric categories proven useful in other ecoregions (species number, species composition, trophic composition, local indicator species, fish abundance, and fish condition) but selected specific metrics within each category based on their ability to discriminate between disturbed and undisturbed sites in the Sand Hills ecoregion. We also developed a procedure based on species-area curves to remove the potentially confounding effects of site-specific differences in sample unit size and sampling effort from species number metrics. With these changes, the modified IBI was minimally affected by sample unit size and sampling effort and accurately discriminated undisturbed sites from sites affected by physical habitat alterations, thermal effluents, and chemical pollution. The FSBI, based on four species richness metrics (adjusted for the effects of sample unit size and sampling effort), discriminated between disturbed and undisturbed streams approximately as well as the modified IBI. The precision of both indices was affected by sample reach length, with samples from 50-m reaches exhibiting relatively low precision and samples from 150-m reaches high precision.