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Particle Size, Critical Shear Stress, and Benthic Invertebrate Distribution and Abundance in a Gravel-bed River of the Southern Appalachians

To determine the relationship between the abundance and density of benthic invertebrates, and the critical shear stress of individual grain sizes, a reach along Smith Creek, was divided into ten 2m x 2m quadrants. Within each quadrant, five randomly selected clasts for each grain size ranging from 2.26 to 25.6 cm were cleaned for benthic invertebrates. Wolman pebble counts for each quadrant were also conducted and used to determine the critical Shields stress per grain size fraction from the model given by Wiberg and Smith (1987) that explicitly accounts for particle hiding/sheltering effects in mixed-bed rivers. Particle entrainment values were then compared with estimated bankfull Shields stress values to determine sediment transport potential during bankfull flow. Invertebrate abundance was strongly positively correlated with critical Shields stress up to the 18.0 cm grain size, indicating a preference for certain grain sizes; while density was positively correlated with all grain sizes present. INDEX WORDS: Benthic invertebrates, Shear stress, Critical Shields stress, Invertebrate abundance, Embeddedness, Invertebrate diversity, Organism-substrate relationships, HEC-RAS. Particle Size, Critical Shear Stress, and Benthic Invertebrate Distribution and Abundance in a Gravel-bed River of the Southern Appalachians