Using Indicators of Wetland Condition to Predict Metals Changes in Natural and Treatment Wetlands in the Tar Creek Watershed

Abstract

Natural and treatment wetlands have been shown to improve water quality on mining impacted lands using biogeochemical and microbiological processes, as well as providing ancillary ecosystem services. Wetlands are evaluated through indicators of condition such as hydrology, water quality, hydrophytic vegetation, and hydric soils. In the Tar Creek Superfund Site, part of the historic Tri-State Lead-Zinc Mining District in Oklahoma, Kansas, and Missouri, treatment wetlands have been successfully incorporated into holistic multi-cell passive treatment systems to remove trace metals from net-alkaline, artesian flowing mine drainage. Incidental wetlands have also developed adjacent to the creek and near untreated mine drainage seeps throughout this watershed, due to mining-related landscape disturbances. This study compares the effectiveness of treatment wetlands and incidental wetlands in removing metals from surface water, determines which indicators of wetland condition correlate with effective removal of metals in mining-impacted wetlands, and determines which indicators of wetland condition correlate with a greater wetland vegetative structure in mining-impacted wetlands in order to develop site-specific recommendations for water quality improvement. Ten wetlands in the Tar Creek watershed were included, which represent various hydrologic regimes, water quality characteristics, vegetative communities, and substrate compositions. Treatment wetlands were determined to have greater removal efficiencies for Fe, Pb, Zn, and Cd; however, these trends were more closely related to influent water quality than hydrologic parameters. Vegetative cover was not more representative of metal removal efficiency than richness or diversity indices, and organic matter content in wetland substrate was not correlated with removal efficiency. Finally, excessive Fe concentrations in the substrate were shown to decrease vegetative diversity.