ScholarWorks at University of Montana

Copper exposure-response relationships and their use in risk management of the Clark Fork River, MT

Remediation of river systems contaminated with mine waste, such as the Clark Fork, is concerned with reducing metal inputs from sources, thereby mitigating exposures to resident species and permitting ecological recovery. This process implies the presence of an exposure and biological response relationship. Identification this relationship within the context of multiple stressors could have utility in critically evaluating risk management plans. We analyzed the response of the benthic macroinvertebrate assemblage to Cu by merging data collected by monitoring programs within the Clark Fork Basin. A correlation matrix identified environmental gradients within the entire dataset (space and time) and these were correlated against taxa richness, a measure of biodiversity. Results indicated that Cu exposure was the most important explanatory variable for observed richness patterns. Analysis of site-specific temporal changes suggested that a gradual decline in Cu exposure corresponded with increased taxa richness at sites immediately downstream of the Warm Springs Treatment Ponds. At sites further downstream, however, the influence of Cu was confounded with annual fluctuations in discharge, which reduced richness during years of above average discharge. When paired Cu exposure and richness data for all sites and years were regressed, strong statistical relationships emerged, suggestive of exposure-response relationships. Further study is aimed at establishing the accuracy of these relationships and in evaluating their utility to risk management.