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Assessment of Metal Bioavailability in a Watershed Affected by Abandoned Mine Lands

John Besser and William Brumbaugh
USGS Biological Resources Discipline
4200 New Haven road, Columbia, Missouri 65201

Stanley Church
USGS Biological Resources Discipline, Denver, Colorado and

Briant Kimball
USGS Water Resources Discipline, Salt Lake City, Utah

Abstract

The Upper Animas River watershed of Colorado has been mined extensively for gold and other metals. The water quality, habitats, and biota of streams in the watershed are affected by acid drainage and metal contamination, which originate from hundreds of abandoned mines and from weathering of rocks and soil. This study examined relationships among metal concentrations in water, suspended colloids, sediments, and biota; transfer of metals among trophic levels (attached algae or periphyton, benthic invertebrates and fish); and potential hazards of metal toxicity to fish. Tributaries draining mineralized areas contribute high loadings of dissolved and colloidal ions, iron, aluminun, zinc, and copper to the Animas near Silverton, resulting in reduced or eliminated fish and reduced invertebrate populations in downstream reaches. Periphyton contained metal concentrations similar to those in sediment, except for greater concentrations of iron and aluminum. Metal concentrations in invertebrates and fish reflected differences in metal loadins among sites, but were also affected by differences in metal uptake among taxa and differences in metal transfer between trophic levels. Cadmium and copper were transferred more readily between predators and prey than were zinc and lead. Concentrations of metals in invertebrates - the principal food source for stream strout - were similar to or greater than concentrations associated with adverse effects on trout in other metal-contaminated streams.

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