Effects of Mining on Water Quality in Upper Colorado River Basin
By Nancy E. Driver
Acid mine drainage is a critical water-quality issue in the Upper Colorado River Basin. Twenty-seven streams in the basin have been identified as having substantial amounts of metals contributed by mines from complex ore metal deposits. Precipitation of hydrous metal oxides in two stream reaches greatly decreased the abundance of periphyton and benthic invertebrates. Concentrations of cadmium and lead exceeded Colorado State aquatic-life standards in 23 of the identified streams, and zinc and copper concentrations exceeded aquatic-life standards in 17 streams. Mercury, silver, manganese, nickel, gold, aluminum, and iron exceeded aquatic-life standards in three streams. The effect of mines on fisheries ranged from no noticeable effect to complete depletion of fish populations. Generally, fish populations were minimal in mine-affected stream reaches, and the species distribution, number, and size of fish were limited by metals concentrations. Manganese concentrations exceeded agricultural and drinking-water standards in 7 streams, and concentrations of cadmium, copper, zinc, lead, and iron exceeded these standards in three streams. Further investigations on the status, trend, fate, and transport of metals in these streams and their effect on biota are needed.