ScholarWorks at University of Montana

Metal-specific Effects on Stream Macroinvertebrates--physiological and ecological approaches

The success of remediation of mining wastes in the upper Clark Fork River (CFR) will be measured by mitigation of metal exposures and reduction of risk to biological communities. Dissolved Cu concentrations at most sites in the upper 90 km of the CFR have declined during the period 1993-2002. Annual trends in benthic macroinvertebrate assemblage data indicate that in-stream ecological conditions have improved, also. Despite the general similarity in those patterns, correlation in year-to-year Cu exposure and changes in the benthos within sites is weak. These simple relationships are probably confounded by other factors acting on the benthos. Additionally, interpretation of metal effects is hindered by a vague understanding of how species composition reflects differences in the metal sensitivity of individual species. To better understand the metal-specific responses of species within the assemblage, metal bioaccumulation and detoxification were compared among five resident species. From these results, we characterized two species as sensitive and three as tolerant. These characterizations of tolerance were similar to tolerance values derived from species distributions. Species most sensitive to Cu do not occur at sites in the upper river. This suggests where metals-specific effects are most likely occurring. The physiological studies may provide a mechanistic explanation for why some species tolerate metals and others do not. This information should be considered within the context of ecological factors that might affect species distributions. Physiological and ecological studies are complementary approaches that strengthen understanding of metal-specific effects on stream benthos.