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Wetland soil storage of anthropogenic metals throughout the conterminous United States
Citation:
Dietrich, M., M. Dumelle, A. Nahlik, H. Golden, J. Christensen, AND C. Lane. Wetland soil storage of anthropogenic metals throughout the conterminous United States. American Geophysical Union Fall Meeting 2024, Washington, DC, December 09 - 13, 2024.
Impact/Purpose:
Heavy metals that have been deposited on the landscape over decades may find their way to waterways. This presentation identifies the estimated amounts of lead, chromium, and copper that are sequestrated in vary types of wetlands in the US and explores how wetland position in the landscape, surrounding land cover, and wetland water regime might influence heavy metal sequestration.
Description:
Wetlands provide many ecosystem services, such as mitigating pollution, attenuating flooding, and habitat provisioning for many species. However, efforts quantifying the ecosystem services of wetlands, particularly at large spatial extents, are sparse. We utilized comprehensive data from the U.S. EPA’s National Wetland Condition Assessment (NWCA) to provide estimates of anthropogenic metal (Pb, Cu, Cr) storage in wetland soils, applicable to over 36 million hectares of wetlands found throughout the conterminous United States (CONUS). Estimates of anthropogenic metals were calculated based on background wetland soil concentrations established at regional levels across the CONUS. Significant amounts of anthropogenic Cu and Cr are estimated to be stored in the upper 40 centimeters of wetland soils across the CONUS, at 299.5 ± 37.3 and 483.4 ± 67.4 thousand metric tons (MT), respectively. Anthropogenic Pb in the upper 40 centimeters of wetland soils totaled an estimated 394.3 ± 135.3 thousand MT, an amount roughly equivalent to 7% of lead-based gasoline additives used between 1927-1994 in the U.S., the largest widespread anthropogenic source of Pb across the landscape. Because the wetland study area constitutes ~4.5% of the total CONUS land area, these estimates suggest that wetlands disproportionately sequester anthropogenic Pb relative to the amount of land area they represent. Variations in metal storage in wetland soils are related to landscape factors such as land use and wetland type. Specifically, mean loadings of excess metals are greatest in hydrogeomorphic wetland classes of slope, riverine, and depression, versus tidal, lacustrine fringe, and flats. Wetlands that are classified as a semi-permanent/permanent water regime contain less total anthropogenic metals and lower mean anthropogenic metal loads in soil than seasonal or temporary wetlands. Wetlands in highly urban watersheds tend to have more anthropogenic wetland soil Pb and Cu, while this trend is not evident for Cr, signifying potentially different sourcing. The NWCA dataset illustrates that wetlands are important contributors to landscape-scale metal sequestration and provides insight into which wetlands are more likely to store anthropogenic metals, which is important for wetland management.