EFFECTS OF CHANGING LAND USE ON MACROINVERTEBRATE INTEGRITY: IDENTIFYING INDICATORS OF WATER QUALITY IMPAIRMENT Allison Roy', Amy D. Rosemond2 , David S. Leigh', Michael J. Paul' and J. Bruce Wallace 2 AUTHORS: 'Graduate Student, 'Assistant Director, and 4 Post-Doctoral Associate, Institute of Ecology, University of Georgia, Athens, GA 30602; and 'Professor, Department of Geography, University of Georgia, Athens, GA 30602. REFERENCE: Proceedings of the 2001 Georgia Water Resources Conference, held March 26-27, 2001, at the University of Georgia. Kathryn J. Hatcher, editor, Institute of Ecology, the University of Georgia, Athens, Georgia. Abstract. We sampled macroinvertebrates in 30 streams (11-126 krn 2 watersheds) within the Piedmont of the Etowah River basin in northern Georgia to examine the relationships between urban land use, physical and chemical characteristics of streams, and biotic assemblages. Percent urban land cover in 1973, 1987, and 1997 was negatively correlated with macroinvertebrate integrity, with the recent land cover exhibiting the highest correlations. The Environmental Protection Agency's visual-based habitat assessment was the single, best overall variable correlated with macroinvertebrate integrity. Specific conductance, average riffle particle size, and standard deviation of stream bed particle size were also highly correlated with indices of macroinvertebrate integrity. Out of the macroinvertebrate indices we calculated, total richness, the Invertebrate Community Index (ICI), and riffle insect richness formed the strongest predictive models with environmental variables, suggesting their importance as water quality indicators in this system. These results demonstrate that macroinvertebrate integrity can be used to assess stream water quality impacts that occur due to changing land use and suggest that stream protection relies on minimizing the percent urban land cover in the catchment. INTRODUCTION Suburban growth around Atlanta is threatening the water quality of numerous streams by converting forested and agricultural land into commercial and residential uses. Urbanization impacts the chemical and physical characteristics of streams, which, in turn, affect stream biota (Richards et al. 1996, Benke et al. 1981). Although relationships between urban land cover and water quality degradation have been identified, more research is needed to quantitatively assess the effects of urbanization, determine mechanisms of the impacts of recent land use, and identify thresholds of biotic impairment. The purpose of this study was to (1) determine whether past land use, recent land use, or land use change was most related to macroinvertebrate integrity, (2) identify environmental indicators of biotic impairment, and (3) select good macroinvertebrate indices for detecting urban degradation. Understanding the influences of urbanization within the catchment on water quality, aquatic fauna, and stream processes is essential for determining how humans can live within the landscape without impacting aquatic ecosystems. METHODS Study Area This study took place in 30 streams (11-126 km 2 watersheds) within the Piedmont physiographic region of the Etowah River basin in northern Georgia. For a description of the sites, see Leigh et al. in this volume. Macroinvertebrate Sampling Benthic macroinvertebrates were collected in three riffle, three pool, and three bank habitats within a 100 m reach between 6 and 19 March 1999. Quantitative samples were collected using a surber sampler, dip net, and stove-pipe corer and filtered over a 500 gm sieve. Samples were preserved in the field in —8% formalin and returned to the laboratory for identification. Taxa were counted, identified to genus, and used to calculate multiple macroinvertebrate indices. Total richness and insect richness in the riffle habitats were calculated. The number of taxa in the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT richness) was also determined. Total densities were multiplied by the proportion of riffle, pool, and bank habitat present at each site to estimate habitat-weighted density and were log io(x) transformed. Macro- 229