Development of a wetland geospatial framework to support agricultural nutrient management across the conterminous United States

Wetlands provide numerous ecosystem functions within their connected landscapes that improve water quality, including nutrient removal. 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 identifying existing and potential wetlands for targeted management efforts (e.g., preservation and construction) as a strategy to buffer nonpoint source nutrient pollution within watersheds and improve water quality. We investigated the capacity of wetlands to intercept nutrients from agricultural runoff across the conterminous United States (CONUS) by identifying existing and potential wetlands lying on surface flow paths draining agricultural lands and developing a dataset of their delineated basins. We identified 2.3 million existing wetlands (256,360 km2) that intercept agricultural runoff and an additional 10.3 million parcels of potential wetland area (422,499 km2) that could be used to increase interception. These intercepting wetland areas, both potential and existing, lie on flow paths that drain 78% of all agricultural land cover, and their delineated basins drain 3,108,055 km2 (38%) of CONUS. Landscape characteristics of these delineated basins are being used to develop a framework to identify specific wetland areas that could support water quality management. Our framework will provide valuable insight for state and local managers to evaluate wetland implementation strategies to mitigate impacts of nonpoint source pollution across CONUS and improve water quality.

Impact/Purpose

Wetlands provide numerous critical functions, including nutrition cycling and water quality improvement, that have made them a critical component of many state and local stewardship programs. Broad-scale wetland loss has reduced the capacity of wetlands to buffer nutrient inputs in watersheds, making downstream water resources more susceptible to eutrophication. Wetland construction (e.g., either restoration of previous wetlands or creation of new wetlands) is a potential strategy for nutrient reduction to improve water quality within watersheds. However, implementation of water quality strategies including wetlands are often resource limited, creating the need for targeted prioritization among existing and potential wetland areas (PWA) to maximize effectiveness and efficiency of these efforts. In this talk, we describe development of a database containing delineated catchments of existing and potential wetlands that lay on surface flow paths of agricultural nonpoint source pollution entering water resources. We examined catchment characteristics (e.g., land cover) to quantify the amount of nutrients existing wetlands intercept within watershed landscapes and to identify PWA that intersects with high nutrient runoff and serve as candidates for conversion to meet water quality strategies across the conterminous United States. Of 456,128 km2 of individual existing wetlands and 934,208 km2 of PWA across CONUS, 56% of existing wetlands (256,360 km2) and 45% of PWA (422,499 km2) lie on surface flow paths of approximately 78% of all agricultural land cover across CONUS. The delineated basins of these intercepting wetlands, both existing and potential, drain 38% (3,108,055 km2) of the land cover of CONUS. Landscape nutrient data from EPA’s National Nutrient Inventory will be applied to these basins to quantify current nutrient interception by existing wetlands and quantify potential interception under different wetland implementation scenarios. This dataset will provide critical insights for the prioritization of wetland areas to help state and local managers and stakeholders meet their water quality goals. 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, S. Markley, M. Weber, J. Compton, M. Brehob, AND R. Sabo. Development of a wetland geospatial framework to support agricultural nutrient management across the conterminous United States. Oregon State University Clean Water Symposium, Corvallis, OR, April 17, 2025.