Which is the Most Accurate Predictor for Macroinvertebrate Communities: Impervious Surface vs. Streamside Land Use? Christopher H. Kodani, Biology Department, Clayton State University, Morrow, GA Introduction: This study examined the effects of land use type and impervious surface on the macroinvertebrate communities at 20 locations. Materials & Methods: Twenty different stream sites were sampled for macroinvertebrates to obtain Georgia Adopt-A-Stream’s Water Quality Index (WQI). Two ways of describing the study sites were compared. One method was a categorization of a site’s adjacent land use into 5 categories: forests, wetlands, suburban day-use parks, and parking lots. The other method was to quantify each watershed’s impervious surface area using Geographical Information System (GIS) analysis. Table I. Study sites arranged by average WQI. The WQI measures the macroinvertebrate species richness and sensitivity at each study site, with pollution sensitive species receiving 3 points, somewhat-tolerant species receiving 2 points, and tolerant species receiving 1 point. Rank Average WQI Site Visits Site Type Water Quality Rating 1 25.0 Forest Excellent > 22 2 22.0 Good 17-22 3 21.0 7 4 19.5 5 19.0 Suburban Park 6 18.6 17.0 Subdivision 8 9 16.6 Fair 11-16 10 16.3 Wetland 11 14.5 12 14.0 Parking Lot 13 13.0 14 12.0 15 11.0 16 9.0 Poor < 11 17 6.0 18 5.5 19 4.5 20 2.4 Results: Polynomial regression revealed that 64% of the variation in WQI was accounted for by imperviousness. Site type did not produce a consistent pattern with regards to WQI. Conclusions: A watershed’s impervious surface area was a more reliable predictor of a small stream’s macroinvertebrate community than a study site’s land use type. Acknowledgments: Georgia Adopt-A-Stream, Lake Spivey Rotary Club, Reynolds Nature Preserve, Henry Co. Storm Water, City of Griffin Storm Water, and Clayton State University for their cooperation and support.