U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Metal Concentrations in Sedges in a Wetland Receiving Acidic Mine Drainage from St. Kevin Gulch, Leadville, Colorado

Abstract

As of the 1989 growing season, there were no visible signs of metal stress on the wetland vegetation receiving the acid mine drainage (AMD) from of St. Kevin Gulch, Colorado. However, the AMD has affected the metal concentrations of the sedges growing on the wetland. Sedge concentrations of cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), and zinc (Zn), known to be high in the AMD waters, are higher in the area of direct inflow than the sedge baseline geometric means (GM) reported for the wetland. Concentrations higher than the GM in other areas of the wetland are evidence for other sources of contamination to the wetland. Maximum cattle dietary levels reported in the literature for Cd (0.5 milligrams per kilogram (mg/kg)) and Zn (500 mg/kg) are exceeded in some areas of the wetland and could present a nutritional problem for the cattle grazing this wetland each year. Vegetation toxicity levels for Cu (20-100 mg/kg) and Pb (30-300 mg/kg) are not exceeded, but Pb concentrations are higher in the inflow area and may indicate accumulation is occurring. Fe deficiency, common in vegetation and foodstuffs, was not detected in the sedges of this wetland. Mn concentrations above the 500 mg/kg level reported in the literature as resulting in signs of visible stress in vegetation are exceeded in most areas of the wetland. The Fe/Mn ratio necessary for healthy vegetation (1.5-2.5), occurs only in the areas with the higher Fe concentrations. Presently the only element being removed from the AMD waters by the wetlands is Fe.

If the sedges accumulated higher levels of Fe, the ratio of Fe/Mn would not necessarily be improved. Fe and Mn are physiological antagonists, and at toxic Mn levels, the absorption of Fe process could reverse resulting in more stress and eventual loss of biomass.