Bioaccumulation of metals in the benthic food web of a Rocky Mountain stream ecosystem contaminated by acid mine drainage

The use of whole-body concentrations of metals in benthic insects as a biomonitoring tool to assess impacts of acid mine drainage on aquatic ecosystems gains greater ecological relevance when trophic function and life history traits affecting metal bioaccumulation are considered. To characterize spatio-temporal distributions of metals accumulated in the trophic web of a mine-impacted ecosystem of the Rocky Mountains, seasonal samples of water, sediment, aufwuchs, detritus, aquatic vegetation, and benthic insects were collected over 3 years from pool and riffle habitats at 8 stations within Haggarty Creek in southcentral Wyoming. To characterize the transport of metals by aquatic insects to the riparian food web and to fish, emergent adults of stream insects and benthos consumed in situ by native trout were also collected. Metals in non-insect components are reported in “Part I: The Foundation for Accumulation,” in which Cu was the sole metal accumulated in the benthic food web. Metal accumulation in benthic insect taxa is discussed in “Part II: Copper in Benthic Insects” with respect to trophic function and life histories. In “Part III: Implications for the Riparian Food Web and Colorado River Cutthroat Trout (Oncorhynchus clarki pleuriticus),” trophic exposure of insectivores to metal contaminants via consumption of Cu-laden aquatic insects is considered. Sediment Cu was a better predictor than aqueous Cu of spatio-temporal patterns of metal accumulation in benthic insects. Strong spatio-temporal correlations between Cu in aquatic insects and their food sources indicate the relevance of including trophic relationships in analyses of benthic bioaccumulation. Elevated levels of Cu in adult aquatic insects and terrestrial arthropods from stream margins suggest the trophic transfer of Cu into the riparian food web. A previously undescribed phenomenon was indicated in which native trout were shown to consume benthic insects containing lower whole-body metal concentrations than insects sampled from surrounding benthic habitats. Hypotheses are offered to explain this observation in contexts of selective feeding by trout and insect physiology, life history, and behavior, indicating the need for consideration of these organismal levels of biological organization in toxicological studies of metal bioaccumulation in aquatic ecosystems.