Summary

Description

This study evaluated the effects of arsenic and heavy metals on individual salmonids and the aquatic community within Gold Creek, Idaho. Gold Creek is a tributary to Lake Pend Oreille in northern Idaho, and has a long history of hardrock mining within its headwaters. Initial investigations measured concentrations up to 8500 mg Askg in mine tailings and up to 1200 mg Askg within stream sediments. Gold Creek is the second most productive stream in terms of spawning and rearing for threatened bull trout within the Lake Pend Oreille Basin. To determine metals effects on salmonids at the organism level we measured concentrations of As, Cd, Cu, Pb, and Zn in water, sediment, benthic macroinvertebrate tissues, and whole body fish tissues. Furthermore, we analyzed histopathology of major organs in fish to assess physiological impacts. Water concentrations were higher than those in reference areas, but only Cd and Zn in Chloride Gulch was above USEPA water quality criteria for protection of aquatic biota. Labile i.e. weak acid extracted sediment metals concentrations were 537 mg As kg, 3.56 mg Cd kg, 51 mg Cu kg, 304 mg Pb kg, 836 mg Zn kg in CG below Lakeview Mine. Benthic macroinvertebrate tissue concentrations for all analytes were significantly higher at all sites compared to the reference site. Fish tissues were significantly higher below mine sites in comparison to the reference site, but only Cd and Pb were higher as far down as the Gold Creek delta. The concentrations within sediments and biota were similar to other studies in which adverse effects to salmonids were documented. We observed histopathological changes in livers of bull trout within the study area including inflammation, necrosis, and pleomorphism. To evaluate effects of metals on the aquatic community we collected benthic macroinvertebrate diversity and abundance, fish assemblage, and habitat data. Benthic macroinvertebrate structure showed a graded response to sediment metals concentrations based on 13 metrics. Eleven of 13 metrics indicated adverse impacts to benthic communities and were statistically different below mine sites in comparison to reference conditions. The numbers of metal sensitive families were rare or absent in areas with elevated sediment metals concentrations in comparison to the reference site. The benthic macroinvertebrate metrics were correlated with sediment metals concentrations. Multivariate analysis showed CG and UGC were well separated and statistically different from the reference site based on benthic macroinvertebrate family structure. Fish density and biomass were lower in CG and LGC in comparison to the reference sites. Bull trout were not observed in areas below mine sites with elevated metals concentrations. Our habitat data suggests that habitat is not a major limiting factor within the drainage, and the changes we observed are most likely metals related. We conclude that metals may be impacting native salmonids within the study area after remediation of Lakeview Mine. Sediment concentrations have not decreased since remediation, although cleanup may have reduced metals loading. Considerable concentrations of metals still persist in stream sediments below mine sites and will likely persist for some time before attenuation within the Gold Creek Drainage.