Wetland restoration yields dynamic nitrate responses across the Upper Mississippi river basin.
Grey R Evenson, Heather E Golden, Jay R Christensen, Charles R Lane, Adnan Rajib, Ellen D'Amico, David Tyler Mahoney, Elaheh White, Qiusheng Wu
Author Information
Grey R Evenson: U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Measurement and Modeling, Cincinnati, OH, United States of America. ORCID
Heather E Golden: U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Measurement and Modeling, Cincinnati, OH, United States of America. ORCID
Jay R Christensen: U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Measurement and Modeling, Cincinnati, OH, United States of America. ORCID
Charles R Lane: U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Measurement and Modeling, Athens, GA, United States of America. ORCID
Adnan Rajib: Department of Environmental Engineering, Frank H. Dotterweich College of Engineering, Texas A&M University, Kingsville, TX, United States of America. ORCID
Ellen D'Amico: Pegasus Corporation c/o U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, OH, United States of America. ORCID
David Tyler Mahoney: Civil and Environmental Engineering Department, University of Louisville, Louisville, KY, United States of America. ORCID
Elaheh White: Oak Ridge Institute for Science and Education c/o U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, OH, United States of America. ORCID
Qiusheng Wu: Department of Geography, University of Tennessee, Knoxville, TN, United States of America. ORCID
Wetland restoration is a primary management option for removing surplus nitrogen draining from agricultural landscapes. However, wetland capacity to mitigate nitrogen losses at large river-basin scales remains uncertain. This is largely due to a limited number of studies that address the cumulative and dynamic effects of restored wetlands across the landscape on downstream nutrient conditions. We analyzed wetland restoration impacts on modeled nitrate dynamics across 279 subbasins comprising the ∼0.5 million km Upper Mississippi River Basin (UMRB), USA, which covers eight states and houses ∼30 million people. Restoring ∼8,000 km of wetlands will reduce mean annual nitrate loads to the UMRB outlet by 12%, a substantial improvement over existing conditions but markedly less than widely cited estimates. Our lower wetland efficacy estimates are partly attributed to improved representation of processes not considered by preceding empirical studies - namely the potential for nitrate to bypass wetlands (i.e., via subsurface tile drainage) and be stored or transformed within the river network itself. Our novel findings reveal that wetlands mitigate surplus nitrogen basin-wide, yet they may not be as universally effective in tiled landscapes and because of river network processing.
