By Scott V. Mize

Abstract

Intensive mining activity and highly mineralized rock formations have affected surface-water quality and aquatic biology within the upper reaches of the Uncompahgre River. The purpose of the study was to assess current (1995-98) chemical, biological, and habitat conditions at selected sites along the upper Uncompahgre River, to determine effects of mining land use on water and sediment quality and aquatic life, and determine relations among benthic macroinvertebrates and concentrations and distributions of trace elements in water, streambed sediment, and transplanted bryophytes. Water, streambed sediments, and benthic macroinvertebrates were collected at five mining sites on the upper Uncompahgre River and three nonmining sites in other drainage basins during low-flow conditions in July 1995-98. Nonmining sites were selected in other, non-impacted drainage basins for comparing results to sites in the Uncompahgre River basin. Bryophytes were transplanted at all sites for 15 days during which physical and chemical water-quality and benthic macroinvertebrate samples were collected. Stream habitat characteristics also were documented at each site.

Water chemistry was significantly different (p < 0.05) between site groups (nonmining and mining). Concentrations of copper, lead, zinc, iron, and aluminum in the water column were significantly different (p < 0.05) between site groups for all total concentrations and most dissolved concentrations, except lead and iron. Concentrations of copper, lead, and zinc in streambed sediments were significantly different (p < 0.05) between site groups. Concentrations of arsenic, copper, lead, and iron in transplanted bryophytes were significantly different
(p < 0.05) between site groups. In general, concentrations of trace elements in transplanted bryophytes and streambed sediments were more closely correlated than concentrations of trace elements in the water column and transplanted bryophytes and in the water column and streambed sediments.

All study sites were rated as optimal instream habitat, except two mining sites that were rated as suboptimal habitat for macroinvertebrate communities due to channelized banks, disturbed riparian vegetation, and erosion observed at the sites. Mining sites generally contained a larger percentage of tolerant macroinvertebrate species, such as Diptera (true flies) and more tolerant species of Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) (EPT). Total abundance, taxa richness, and EPT taxa richness were significantly different
(p < 0.05) between site groups. The predominance of Baetis sp., Hydropsychidae, and percent Orthocladiinae chironomids at mining sites indicated that these macroinvertebrates may be tolerant to elevated trace-element concentrations. The absences of Heptageniidae, Chloroperlidae, and Rhyacophila sp. at mining sites indicated that these macroinvertebrates may be sensitive to elevated trace-element concentrations. Mayfly, stonefly, and caddisfly abundances, as well as percent Chironomidae, seem to be good indicators of mining effects at sites in the study area. Benthic macroinvertebrates provided a measure of stream ecosystem health, which was compared between nonmining and mining sites.