Examination of wetland restoration and creation as a nutrient interception strategy within watersheds of US estuaries

Freshwater inflow drives environmental conditions and subsequently ecological function of estuaries. The quantity, quality, and timing of freshwater inputs are derived from the interaction of climatic drivers occurring over a mosaic of different land uses within watersheds feeding estuaries. 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 area (PWA) for targeted wetland creation or restoration as a means to buffer nutrient pollution within watersheds and improve water quality. We developed a dataset of delineated basins of 413,211 km2 of individual existing wetlands and 201,129 km2 of PWA on current croplands across the conterminous United States. We use basin characteristics (e.g., land use) to examine the potential benefit of converting PWA to wetlands on nutrient interception across landscapes feeding estuaries. Wetland creation has the highest potential nutrient reduction to estuaries along the Texas coast, within the Upper Mississippi River Basin, and the San Francisco Bay Delta Watershed due to relatively high concentrations of both PWA and agricultural land use. PWA within these regions primarily fall on current agricultural land, making federal incentive programs a viable strategy for wetland creation and water quality improvement. This dataset provides critical insights for the prioritization of wetland areas to meet national water quality goals.

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, such as estuaries. 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. We examined catchment characteristics (e.g., land cover) to quantify the amount of nutrients existing wetlands intercept on watershed landscapes feeding estuaries 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. We found that the Texas Gulf Coast, Upper Mississippi River Basin, and San Francisco Bay Delta Watershed contain relatively high concentrations of both PWA and agricultural land use and have the highest potential of nutrient reduction to estuaries from wetland creation. 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 Subproduct SSWR.405.1.1.4 – Quantification of nutrient inputs to conterminous US stream and lake watersheds via accumulation of nutrient inventories in StreamCat and LakeCat.

Citation

Alford, S., R. Hill, J. Compton, AND M. Weber. Examination of wetland restoration and creation as a nutrient interception strategy within watersheds of US estuaries. 2024 Coastal and Estuarine Summit, Washington D.C., DC, October 06 - 10, 2024.