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Science for Watershed Decisions on Abandoned Mine Lands: Review of Preliminary Results, Denver, Colorado, February 4-5, 1998

Metal Uptake, Transfer, and Hazards in the Stream Food Web of the Upper Animas River Watershed, Colorado

By John M.Besser,¹ William Brumbaugh,² S.E. Church,³ and B.A. Kimball⁴

Streams in the upper Animas River watershed of Colorado drain a highly mineralized basin which has been extensively mined for gold and other heavy metals. The water quality, aquatic habitats, and stream biota of these streams are affected by acid drainage and metal contamination from hundreds of abandoned mines and from natural weathering of rocks and soil. We conducted a survey of metal concentrations in water, suspended colloids, sediment, and stream biota from the upper Animas River watershed. The objectives of this study were to examine: (1) relationships among metal concentrations in water, suspended colloids, sediment, and biota (periphyton, benthic invertebrates, and fish); (2) transfer of metals among trophic levels; and (3) potential hazards of metal toxicity to fish.

Tributaries draining highly mineralized areas of the watershed (Cement Creek and Mineral Creek) contributed high concentrations of dissolved and colloidal iron, aluminum, zinc, and copper to the Animas River near Silverton. These metal loadings were associated with severe alterations of benthic invertebrate communities and reduction or elimination of brook trout populations.

Metal concentrations in periphyton samples (consisting of algae, other associated microorganisms, and mineral deposits) were strongly correlated with metal concentrations in fine sediment. Metal concentrations in invertebrates and fish reflected overall differences in metal loadings among sites, but also varied among taxa of invertebrates, with differences apparently related to body size and feeding mode. Livers of brook trout contained greater concentrations of copper and cadmium, and lesser concentrations of zinc and lead, than invertebrates.

Concentrations of copper in tissues of invertebrates and fish corresponded most closely to observed impacts on biota of the upper Animas River watershed. Concentrations of both copper and zinc in invertebrates from impacted sites in the watershed were similar to concentrations of these metals associated with adverse effects on invertebrates and fish in other streams draining abandoned mine lands.

These results indicate that exposure of predators such as brook trout to metals via metal-contaminated diets differs from waterborne exposure due to processing of metals through the stream food web. Chronic metal exposure of both fish and invertebrates of the upper Animas River watershed, which occurs via both water and diet, may result in impacts at sites where water is not acutely toxic.

¹U.S. Geological Survey, 4200 New Haven Road, Columbia, MO 65201 (john_besser@usgs.gov)

²U.S. Geological Survey, 4200 New Haven Road, Columbia, MO 65201 (william_brumbaugh@usgs.gov)

³U.S. Geological Survey, MS 973, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (schurch@usgs.gov)

⁴U.S. Geological Survey, 1745 West 1700 South, Salt Lake City, UT 84104 (bkimball@usgs.gov)

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