Use of an Index of Biotic Integrity to Detect Effects of Land Uses on Stream Fish Communities in West-Central Georgia

Abstract

An index of biotic integrity (IBI) was developed for use in the lower piedmont and upper coastal plain physiographic regions of west-central Georgia to investigate the relation between stream fish communities and land use. Fish samples and habitat data were collected at 507 sites in 340 first- to fifth-order tributary streams in the Chattahoochee, Flint, Ocmulgee, and Oconee river drainages during 1990–1993. Watershed cutouts upstream of sample sites were made from raster digital files based on LANDSAT thematic mapper satellite imagery from land use and land cover data collected during the winters of 1988–1990. Six of the 12 original IBI metrics were modified to take into account regional ichthyological differences between Georgia and the midwestern United States while maintaining the basic underlying ecological assumptions. The number of darter species metric was expanded to include madtoms (Noturus spp.) and sculpins (Cottus spp.), number of intolerant species metric was expanded to include moderately intolerant species, proportion piscivores was modified for small streams where proportion pioneer species was substituted, proportion hybrid metric was deleted and proportion of lithophilic spawners was substituted, proportion green sunfish Lepomis cyanellus was replaced with proportion tolerant species, and the proportion of diseased fish metric was replaced with proportion of individuals in a sample with deformities, eroded fins, lesions, or tumors. Nonpoint and point source runoff from low-density urban areas negatively influenced the number of fish species, number of darter species, number of individuals, proportion of insectivorous cyprinids, and proportion of lithophilic spawners. Proportions of tolerant species and proportions of species with deformities, eroded fins, lesions, or tumors were positively related to increased levels of turbidity–suspended solids. In addition, higher levels of turbidity–suspended solids generally had a negative influence on the number of sensitive species, number of individuals, proportion of lithophilic spawners, and proportion of omnivores. The relationship between IBI site scores and measures of relative habitat quality suggested that the derived IBI was effective in differentiating stream quality.