Use of wetlands to remediate gold mine effluent

Abstract

The effluent from Musselwhite Mine was examined to determine the improvement to water quality as it passed through a treatment wetland prior to final discharge to the receiving water body. Potential toxicity problems from the discharge of Al, Cu, Fe, Mn, Ni, Zn, As, Hg, and CN into the mine’s industrial treatment wetland were assessed by an examination of sediment/soil and uptake of these contaminants into vegetation. In total, five study sites were established along the entrance of wetland to the receiving environment. Two of the study sites were positioned within the treatment wetland and a final site in the receiving environment each with corresponding control sites. The treatment wetland was proven to reduced the loadings of Cu, Ni, As and Al by absorption into the sediment or uptake by plants. Concentrations of Fe, Mn and Zn were released by the wetland and were slightly elevated in the discharge water. The release of heavy metals from acid mine drainage from the tailings area of the closed Dona Lake Mine (5 C42' N 90°6' W) was examined in the second part of the study. Potential toxicity due to the release of Al, Cu, Fe, Mn, Ni, Zn, As, Hg, and CN from the mine’s tailings was assessed by an examination of sediment/soil sorption and uptake by vegetation. Four sites were established extending from the tailings impoundment to the receiving environment. Heavy metals released from acid mine drainage caused corresponding elevated metal concentrations in the sediment/soil present at the Dona Lake Mine. Total metal levels in the plant tissue were not elevated when all species were considered simultaneously at the various sites, but increases in metal concentrations in plant tissue did occur when only Typha latifolia was considered. Reclamation of gold mine tailings waste through the development of wetland vegetation covers to determine the control of heavy metal release was examined in the third part of the study. Using a microcosm approach, the potential toxicity of the release of Al, Cu, Fe, Mn, Ni, Zn, As, Hg, CN and SO4 from the mine’s tailings was assessed through an examination of changes in water and sediment/soil concentrations of these compounds, and uptake by vegetation. Four treatments were used consisting of: 1) a control treatment that consisted only of the tailings and water with no added vegetation, 2) a tailings only treatment with added vegetation, 3) a fertilized tailings treatment which included the addition of fertilizer pellets and vegetation and 4) an organic fertilized treatment (15 cm cap of organic soil plus fertilizer pellets) and vegetation. The ability of the vegetative cover to reduce concentrations of contaminants in the water column was most successful in the organic plus fertilizer treatment. The species considered most suitable in terms of survival and limited heavy metal uptake was Nuphar variegatum.