Estimating Embeddedness From Bankfull Shear Velocity in Gravel Streambeds to Assess Sediment Impacts on Aquatic Biota

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Virginia Tech

Previous research efforts have shown that fish and macroinvertebrates are responsive to fine sediment in streambeds. Excess fine sediment (<2mm in diameter) impairs over 40,000 miles of streams in the U.S., degrading habitat quality for many aquatic species. Embeddedness (emb, %), a measure of fine sediment in gravel bed streams, is negatively correlated with bankfull shear velocity (u*, m/s). This relationship can be modeled by emb = au*b, with baseline coefficient values of a = 10 and b = –1. The purpose of this thesis was to investigate the applicability of this relationship across the U.S., to begin to quantify the variation of embeddedness in time, and to determine the applicability of embeddedness as a habitat metric for lotic biota. The areas that were studied included Stroubles Creek at the Virginia Tech Stream Lab, the Upper Roanoke River Basin in southwest Virginia, and Level II and III ecoregions nationwide with the U.S. EPA National Rivers and Streams Assessment dataset. Nationally, measurements of embeddedness were higher than modeled in areas with higher sediment supply, and lower than modeled in regions with low fine sediment supply. By calculating shear velocity through remotely sensed channel geometry metrics, embeddedness may be predicted throughout a stream network. Various biotic metrics were found to be correlated to embeddedness, with regional variation. Burrowing macroinvertebrate taxa, which may use increased sand to escape predation, increased with increasing embeddedness while the number of Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa, the number of lithophilic spawning fish, and the number of salmonid taxa decreased with increasing embeddedness. Highly embedded substrate is generally considered poor habitat, which was supported by a trend of decreasing intolerant fish taxa with increasing embeddedness. Richness (total number of taxa) did not show a significant correlation, indicating that embeddedness, and fine sediment in general, is not necessarily an impairment to all stream habitat, but is impactful for particular taxa.

embeddedness, fine sediment, shear velocity, remote sensing