Temporal and spatial variability of invertebrate communities in potential reference headwater streams of the Georgia Piedmont

Standard bioassessment protocols compare macroinvertebrate communities in potentially impacted streams to communities in reference streams. However, in many landscapes ‘pristine’ reference streams may not exist and researchers may be forced to use the best available alternatives. The objective of this study was to evaluate macroinvertebrate communities in potential reference streams in the highly impacted Piedmont physiographic region of Georgia. We determined the influence of season, substrate, and reach-scale habitat type on macroinvertebrate assemblages in five forested, headwater streams that were minimally disturbed by current anthropogenic activities. The five streams represented three different reach-scale substrate compositions (gravel, sand, and bedrock). We predicted that macroinvertebrate communities in these streams would be influenced by season and by substrate composition. Streams were sampled in May, August, and November 2003, using a corer to sample riffles and a Hess sampler to sample runs and pools. Four of the five streams studied exhibited distinct seasonal variation, which exceeded spatial variation among those streams. Invertebrate community compositions among streams were not consistently predicted by reach-scale substrate in our study. The communities in the two sand streams were unique but generally dissimilar to each other. The two gravel streams supported similar communities across seasons. Riffle and wood habitats supported distinct invertebrate communities that were dissimilar to the run and pool habitats. Our data indicated that potential reference streams can vary widely in invertebrate community compositions and we cannot always predict that variability simply by substrate alone. Thus, selecting reference streams for bioassessment projects in the Georgia Piedmont may be complex.