Anthropogenic metal storage in wetland soils across the conterminous United States

Wetlands provide many ecosystem services, such as mitigating pollution, attenuating flooding and drought extremes, and providing habitat for many species. However, studies quantifying potential wetland sequestration of heavy metals as an ecosystem service, particularly across large spatial extents, are sparse. We utilized data from the United States Environmental Protection Agency’s National Wetland Condition Assessment to estimate anthropogenic metal (Pb, Cu, Cr) storage in the upper 40 centimeters of wetland soils across the conterminous United States (CONUS). Large amounts of anthropogenic Cu and Cr are stored in wetland soil across the CONUS, at 299.5 ± 73.2 (95% confidence interval) and 483.4 ± 132.1 thousand metric tons (MT), respectively. Anthropogenic Pb totaled 394.3 ± 265.2 thousand MT, an amount roughly equivalent to 7% of lead-based gasoline additives used in the U.S. between 1927–1994, the largest widespread anthropogenic source of Pb across the landscape. Between 15–22% of Cu, Cr, and Pb mass stored within the upper 40 cm of wetland soils across the CONUS is anthropogenic. We also estimated wetland anthropogenic metal loading to normalize mass by area. Anthropogenic metal loading is related to the complex interaction of landscape features. However, national-scale variations obscure which features are dominant in metal loading and retention processes. In most cases, estimated wetland redox state, tidal influence, the wetland hydrologic regime, and the geographical region do not substantially impact estimates of anthropogenic metal loading within wetland soils. More detailed regional research may help disentangle these complex relationships to further support wetland ecosystem management.