Examination of wetland conservation and creation as nutrient interception strategies across the conterminous United States

Wetlands provide numerous ecosystem functions within their connected landscapes, including nutrient filtering that improves water quality. Broad-scale loss of wetlands has removed landscape buffers to sources of nonpoint source pollution, such as nutrient-laden agricultural runoff, making downstream connected waters more susceptible to eutrophication and decreasing watershed resiliency. Due to growing recognition of the role of wetlands in maintaining downstream water quality, there is an increasing emphasis on identification of potential wetland areas (PWA) for targeted wetland creation (e.g., construction or restoration) as a strategy to buffer nutrient pollution within watersheds and improve water quality. We investigated the capacity of existing wetlands identified by the National Land Cover Database and PWA identified by EPA’s EnviroAtlas for nutrient reduction across the conterminous United States (CONUS) by developing a dataset of delineated wetland basins and examining current land use to quantify interception of agricultural run-off. Of 456,128 km2 of individual existing wetlands and 1,390,336 km2 of PWA across CONUS, 56% of existing wetlands (256,360 km2) and 45% of PWA (422,499 km2) intercept agricultural run-off. Agricultural interception by wetland type varies regionally with highest density of intercepting existing wetlands in the US coastal plain and upper midwest regions but highest densities of intercepting PWA in the Missouri River Basin, upper Mississippi River Basin, and San Francisco Bay Delta watershed. Differences in proportional dominance of intercepting wetland types indicates that conservation of existing wetlands may be a more effective means of nutrient interception along the Gulf and East Coasts, whereas wetland creation on PWA may be more effective in the upper Mississippi River Basin, Ohio River Basin, and US West Coast regions. This dataset provides critical insights for the prioritization of wetlands to meet national water quality goals. Our study provides a valuable framework to evaluate watershed management strategies seeking to mitigate impacts of anthropogenic land use across CONUS and increase future watershed resiliency. 

Impact/Purpose

Wetlands provide numerous critical functions, including nutrition cycling and water quality improvement. Broad-scale wetland loss derived from climate change and human activities has reduced the capacity of wetlands to buffer nutrient inputs in watersheds, decreasing resiliency of downstream water resources that are susceptible to eutrophication. Wetland creation (e.g., either restoration of previous wetlands or construction of new sustainable wetlands) is a potential strategy for nutrient reduction within watersheds. However, effort to create wetlands are often resource limited, creating the need to prioritize among potential wetland areas (PWA) to ensure they intercept nutrient laden runoff and improve water quality. In this talk, we describe development of a database containing delineated catchments of existing and potential wetlands intercepting nonpoint source pollution from agriculture. We examined catchment characteristics (e.g., land cover) to quantify the amount of nutrients existing wetlands intercept on watershed landscapes and to identify PWA that intersects high nutrient runoff (e.g., from agricultural land use) that serve as candidates for conversion to meet water quality strategies across the conterminous United States. Of 456,128 km2 of individual existing wetlands and 1,390,336 km2 of PWA across CONUS, 56% of existing wetlands (256,360 km2) and 45% of PWA (422,499 km2) intercept agricultural run-off. Agricultural interception by wetland type varies regionally with highest density of intercepting existing wetlands in the US coastal plain and upper midwest regions but highest densities of intercepting PWA in the Missouri River Basin, upper Mississippi River Basin, and San Francisco Bay Delta watershed. Differences in proportional dominance of intercepting wetland types indicates that conservation of existing wetlands may be a more effective means of nutrient interception along the Gulf and East Coasts, whereas wetland creation on PWA may be more effective in the upper Mississippi River Basin, Ohio River Basin, and US West Coast regions. This dataset will provide critical insights for the prioritization of wetland areas to meet national water quality goals, including goals of more focused programs such as EPA’s Hypoxia Task Force.   The results of this work will support efforts to meet the goals of the Clean Water Act and contributes to StRAP Subproduct SSWR.405.4.1.1  – National mapping of nutrient interception by existing and potentially-restorable wetlands to prioritize restoration with additional connections to work under StRAP Product SSWR.405.1.1 – Novel applications of the nutrient Inventory (N, P, or both).  

Citation

Alford, S., R. Hill, J. Compton, AND M. Weber. Examination of wetland conservation and creation as nutrient interception strategies across the conterminous United States. 60th Anniversary Joint Water Resources Conference, St. Louis, MO, September 30 - October 02, 2024.