CHARACTERIZATION OF ECOLOGICAL RISKS AT THE MILLTOWN RESERVOIR CLARK-FORK RIVER SEDIMENTS SUPERFUND SITE, MONTANA

A comprehensive field and laboratory approach to the ecological risk a ssessment for the Milltown Reservoir-Clark Fork River Sediments Site, a Superfund site in the Rocky Mountains of Montana, has been described in the preceding reports of this series. The risk assessment addresse s concerns over the ecological impacts of upstream releases of mining wastes to fisheries of the upper Clark Fork River (CFR) and the benthi c and terrestrial habitats further downstream in Milltown Reservoir. T he risk characterization component of the process integrated results f rom a triad of information sources: (a) chemistry studies of environme ntal media to identify and quantify exposures of terrestrial and aquat ic organisms to site-related contaminants; (b) ecological or populatio n studies of terrestrial vegetation, birds, benthic communities, and f ish; and (c) in situ and laboratory toxicity studies with terrestrial and aquatic invertebrates and plants, smalt mammals, amphibians,and fi sh exposed to contaminated surface water, sediments, wetland soils, an d food sources. Trophic transfer studies were performed on waterfowl, mammals, and predatory birds using field measurement data on metals co ncentrations in environmental media and lower trophic food sources. St udies with sediment exposures were incorporated into the Sediment Qual ity Triad approach to evaluate risks to benthic ecology. Overall resul ts of the wetland and terrestrial studies suggested that acute adverse biological effects were largely absent from the wetland; however, adv erse effects to reproductive, growth, and physiological end points of various terrestrial and aquatic species were related to metals exposur es in more highly contaminated depositional areas. Feeding studies wit h contaminated diet collected from the upper CFR indicated that trout are at high risk from elevated metals concentrations in surface water, sediment, and aquatic invertebrates. Integration of chemical analyses with toxicological and ecological evaluations of metal effects on the wetland and fishery has provided an important foundation for environm ental decisions at this site.