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

Impacts of Abandoned Mine Lands on Stream Ecosystems of the Upper Animas River Watershed, Colorado

By John M. Besser,¹ Del Wayne R. Nimmo,² Robert Milhous,³ and William Simon⁴

Recent surveys conducted by the State of Colorado suggested that abandoned mine lands may adversely affect the "ecological health" of streams in the upper Animas River watershed. Fish and invertebrate populations were reduced or virtually absent from stream reaches receiving heavy loadings of acidity and heavy metals from abandoned mines and natural acid drainage. The USGS, in cooperation with the Animas River Stakeholders Group (ARSG), initiated studies during 1997 to provide more detailed information on stream biological communities and to characterize the range of metal bioavailability, toxicity, and habitat quality at sites with a wide range of apparent mining impacts.

An ongoing biomonitoring study conducted by the ARSG will further characterize the abundance and taxonomic compositions of benthic invertebrate communities of the entire Animas River watershed, with an emphasis on the role of tributary inputs in the impact and recovery processes. Concentrations of heavy metals have been analyzed in tissues of stream biota (periphyton, invertebrates, and fish). Bioaccumulation and food-chain transfer of metals produce metal concentrations in invertebrates and fish which differ substantially from concentrations in water and sediment. Metal concentrations in the biota of the upper Animas River watershed are comparable to those associated with adverse effects on fish and invertebrates in other mining-impacted streams.

The toxicity of water and sediment from the Animas River and tributaries to fish and invertebrates has been evaluated in studies conducted onsite and in the laboratory. The toxicity of water differed substantially among sites, among habitats (stream water compared to interstitial water), and over time. The toxicity of water and sediment followed similar trends among sites, with greatest toxicity at sites where biotic communities are most affected.

Studies of the characteristics of stream substrata are intended to indicate whether physical impacts of mining (sedimentation or "cementation" of stream gravels) may degrade physical habitats required for fish reproduction. The results of these studies will be used to develop protocols for studying the mechanisms of impacts on stream biota and to identify target sites for monitoring the short- and long-term results of remediation.

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

²U.S. Geological Survey, Aylesworth Hall NW, Colorado State University, Ft. Collins, CO 80523 (del_nimmo@usgs.gov)

³U.S. Geological Survey, 4512 McMurry Avenue, Ft. Collins, CO 80525 (robert_milhous@usgs.gov)

⁴Animas River Stakeholders Group, 8181 County Road 203, Durango, CO 81301 (wsimon@frontier.net)

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