Integrative assessment of benthic macroinvertebrate community impairment from metal-contaminated waters in tributaries of the Upper Powell River, Virginia, USA.

Benthic macroinvertebrate communities of the North Fork Powell River (NFP), southwest Virginia, USA, appear to be impacted by aluminum (Al) and iron (Fe) from acid mine drainage (AMD) beyond the zone of pH depression. As part of a watershed restoration project, we used integrative techniques, including water column, sediment, and in situ toxicity tests; sediment and water column chemistry; and habitat assessments, to detect AMD impacts. An analysis of variance, least significant difference post hoc test, and Spearman correlations were used to test the sensitivity of these integrative techniques to detect various (acidic or neutralized) levels of AMD input and to determine the mode of impairment (metal-contaminated sediments or water) to the benthic macroinvertebrate community. Benthic macroinvertebrate indices were the most sensitive endpoint to AMD inputs and were significantly correlated (p < or = 0.05) with water column metal concentrations in in situ and water column toxicity tests. Sediment chemistry and toxicity did not detect AMD impacts and were not significantly correlated with benthic macroinvertebrate indices. These results suggest that the primary mode of impairment to the benthic macroinvertebrate communities beyond the zone of pH depression were waterborne Al and Fe.