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(38-41) Particle size distribution analysis of a mining-impacted gravel-bed stream using a hybrid sediment sampling technique. Dalecky, Amanda1, Babendreier, Justin2, Gallagher, Daniel*,3, 1 Olver, Inc, Blacksburg, VA2 Ecosystems Research Division, Athens, GA3 Department of Civil and Environmental Engineering, Blacksburg, VA ABSTRACT- An ecological risk assessment study was conducted of the Leading Creek watershed in Ohio. The watershed, which is heavily impacted by mining and agricultural activities, suffers from low pH, high concentrations of metals and sediment in the water column, and excessively silted streambeds. As part of the study, a hybrid sediment sampling technique that integrates adhesive sampling for fine sediment with grid sampling for larger particles was assessed. The hybrid technique allows for separate sampling of the pavement layer, important for hydraulics, and the subpavement layer, critical to benthic macroinvertebrates. The efficacy of the technique as well as possible relationships between siltation and ecological health were evaluated. A correlation analysis among streambed texture, ecological quality (including taxon richness and abundance), and land-use was performed. Taxon richness and abundance data were negatively correlated with pavement particle size statistics, with r-values between -0.7 and -0.8. Overall, however, ecological and land-use trends were influenced more by landscape and water quality than by sediment texture. The hybrid sediment sampling technique consistently achieved an effective particle size sampling range of 0.05 mm to over 300 mm; this reduced the common problem of truncation in particle size analysis. However, the overlap of the clay adhesive and natural sediment distributions hindered the analysis of particles finer than 0.125 mm. Adhesive sample results had to be converted from an areal to a volumetric basis to integrate with grid samples. This proved problematic because of the amount of fines in the samples. Particle size results differed from other watershed studies because of atypical sediment loading from surrounding abandoned mine lands. In particular, downstream fining was not present, and the armor ratio (pavement to subpavement D50) was higher than typical. Key words: sediment, sampling, hybrid, mining |
