Citation:

Evenson, G., H. Golden, J. Christensen, C. Lane, M. Kalcic, A. Rajib, Q. Wu, T. Mahoney, E. White, AND E. DAmico. Bounded scenarios depicting basin-scale wetland restoration and construction impacts on surplus nitrogen. Joint Aquatic Sciences Meeting (JASM), Grand Rapids, MI, May 14 - 20, 2022.

Impact/Purpose:

This study addresses water quality problems (e.g., harmful algal blooms) attributable to surplus nitrogen losses from agricultural landscapes. Wetland restoration and construction are management-action that can remove surplus nitrogen but the magnitude of their potential impact is uncertain at large river-basin scales. We used a model to project wetland restoration and construction impacts on river basin yields and loads under varying conditions. We found that projections can vary substantially under varying conditions and that these conditions should be managed so that constructed and restored wetland intercept greater quantities of surplus nitrogen. Projections can help program and regional partners guide wetland restoration and construction efforts

Description:

Wetland restoration and construction are primary management options for reducing surplus nitrogen at river-basin scales. Yet the magnitude of change these management actions affect upon river-basin scale nitrogen losses is contingent, in part, on several factors: (1) the quantity of restored or constructed wetlands, (2) their location within the basin, (3) the size of the catchments they drain, (4) the efficiency of their denitrification processes, and (5) the quantity of tile-effluent that they intercept. We used a process-based model of the Upper Mississippi River Basin (UMRB) (~440,000 km2) to simulate basin-scale wetland restoration and construction impacts on surplus nitrate under a range of factor conditions. We assessed the relative influence of these factors on restoration and construction success, as measured by decreased nitrate yields and loads at the subbasin and the river basin outlets. Our results indicated that the magnitude of surplus nitrate reduction from wetland restoration and construction will vary widely with different factor conditions – e.g., if ~4,400 km2 of wetland were restored or constructed, mean annual UMRB nitrate loads could decrease by 6 to 67%, with larger load reductions requiring unlikely factor conditions. Wetlands will provide greater nitrate reductions when these factors are considered and managed in concert to intercept greater quantity of surplus nitrogen. Our analysis provides novel insights into a more nuanced understanding of how wetland restoration and construction impact river-basin scale nitrogen dynamics. 

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