Assessment of Heavy Metal and Metalloid Concentrations at Horicon National Wildlife Refuge

Anthropogenic inputs of heavy metals and metalloids pose a risk to wetland ecosystems due to their long retention time in sediment, high toxicity at low concentrations, and ability to biomagnify in the food chain. Our study involved an extensive monitoring effort for seven heavy metals (cadmium:Cd, chromium:Cr, copper:Cu, mercury:Hg, nickel:Ni, lead:Pb, zinc:Zn) and one metalloid (arsenic:As) in sediment, roots of the invasive hybrid cattail ( Typha x glauca ), and livers from muskrats ( Ondatra zibethicus ) at Horicon National Wildlife Refuge, a wetland of international importance in southeastern Wisconsin, United States. Overall, our comparison to literature values and thresholds led us to conclude that heavy metals and metalloids pose a low risk to the refuge. The highest concentrations were found in the sediment, followed by T. x glauca roots, and with negligible concentrations in muskrat liver tissue for all but the essential metals Cu, Ni and Zn, indicating low biomagnification in this food chain. A spatial analysis using GIS revealed hotspots for Cd, Cr, Cu, Ni, and Zn in sediment in one particular subplot, which we hypothesize may be from runoff of agricultural amendments. However, since concentrations in sediment were similar to or lower than concentrations found in a prior survey from 1990, there may have been improvement over the last three decades. Overall, while anthropogenic influences are present, we recommend that our relatively low concentrations be used as healthy points of comparison regarding risk to plants and mammals for others conducting metal and metalloid surveys on wetlands.