Macroinvertebrate Forage in the Smith River Tailwater

Benthic macroinvertebrates were sampled in July 2000 and April 2001 at 12 sites in the Smith River below Philpott Dam in southwestern Virginia. One riffle in each site was stratified into upstream, middle, and downstream transects and Surber samples were collected at 2 randomly-selected locations on each transect. Macroinvertebrates were identified to family and each sample was measured for wet weight. Family richness was calculated and simple linear regression was used to evaluate longitudinal trends in mean abundance and wet weight with increasing distance from the dam. We found low values of family richness near the dam but richness more than doubled by 4.2 km downstream. Mean wet weight and abundance of macroinvertebrates were higher in April than in July and Ephemerellidae proportionately dominated the samples in April. Overall, abundance of aquatic invertebrates in this tailwater was lower than expected for a stream of this size in Virginia. No strong pattern was found between distance from the dam and macroinvertebrate abundance. However, isolated peaks in abundance of macroinvertebrates at spatially discrete locations suggest that localized channel characteristics improved some areas for macroinvertebrate colonization downstream of Philpott Dam.

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