Periphyton community responses to elevated metal concentrations in a Rocky Mountain stream

The effects of elevated metals on stream periphyton in the Eagle River, a mining impacted river in central Colorado, were assessed in 1991 and 1992 using assemblage information (taxa richness, community similarity) and non-taxonomic measures (biomass, chlorophyll α, autotrophic index). The number of periphyton genera collected ranged from 2 at a site adjacent to abandoned mining operations to 21 at a downstream site, but was not significantly correlated with dissolved metals concentrations. Fragilaria and Achnanthes were the dominant genera at all sites, with Fragilaria dominating the less impacted sites and Achnanthes dominating at the more impacted sites. Taxonomic similarity was greatest among those sites receiving the greatest inputs of metals from mining operations, where the coefficient of similarity ranged from 0.87 to 0.99. Cluster analyses revealed significant differences among sites adjacent to the mine and either the upstream or downstream sites. Chlorophyll a content of periphyton and the autotrophic index in both years showed significant downstream decreases associated with increasing dissolved metals concentrations. Overall, the periphyton community data were able to separate metal contaminated sites from reference or less impacted sites, and responded in predictable ways to increasing metal concentrations of Eagle River water.