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Strategic placement of wetlands mitigate surplus nutrient losses in tile-drained agricultural landscapes
Citation:
Evenson, G., H. Golden, J. Christensen, C. Lane, M. Kalcic, A. Rajib, Q. Wu, D. Mahoney, E. White, AND E. DAmico. Strategic placement of wetlands mitigate surplus nutrient losses in tile-drained agricultural landscapes. 2021 American Geophysical Union (AGU) Annual Meeting, New Orleans, LA, December 13 - 17, 2021.
Impact/Purpose:
Non-point source nutrient losses from agricultural landscapes cause harmful algal blooms and hypoxia. Conservation practices - including restored and constructed wetlands - have been widely implemented to reduce nutrient losses from these landscapes but many watersheds have failed to show improved water quality conditions. Extensive tile drainage may be one reason why water quality conditions have not improved as nutrient loss via tiles may bypass conservation practices such as wetlands. We used watershed-scale hydrologic models to evaluate the extent to which tile drains impact the nutrient reductive capacity of restored and constructed wetlands. Results indicate that tiles substantially reduce the capacity of wetlands to receive, store, and remove surplus nutrient. However, results also indicate that wetlands can be especially successful in reducing surplus nutrient losses if tile-effluent is routed directly to the wetlands. Region partners and managers responsible for the allocation of funds to support water quality conservation measures may be interested in these results. Extensive resources have been committed to mitigating surplus nutrient losses via a variety of conservation practices, including restored and constructed wetlands. Despite these efforts, some watersheds have failed to show substantial improvement in water quality conditions at the watershed outlet. This phenomenon may be partly attributed to landscape alterations including subsurface ‘tile’ drainage which, while advantageous for agricultural productivity, promotes transport of surplus nutrient to downgradient waters while often bypassing wetlands and other conservation practices. We apply previously constructed hydrologic models of the Upper Mississippi River Basin (~4.4 x 105 km2) and the Maumee River Basin (~1.7 x 104 km2) – two of the most expansively tile-drained landscapes in the United States – to ask: To what extent does tile drainage affect the capacity of wetland restoration and construction to mitigate surplus nutrient (nitrogen, phosphorus) export at the watershed scale? Our model simulations demonstrate that tile drains substantially reduce the ability of wetlands to receive, store, and remove surplus nutrients at the watershed scale. However, we additionally show that wetland restoration and construction can be especially advantageous in these landscapes if wetlands are strategically positioned to receive and treat tile-effluent. Our work demonstrates the potential of wetland restoration and construction in tile-drained landscapes to reduce downstream nutrient loads while highlighting the continued challenge of balancing the agricultural production benefits of tile drainage with large-scale water quality mitigation needs.
Description:
Extensive resources have been committed to mitigating surplus nutrient losses via a variety of conservation practices, including restored and constructed wetlands. Despite these efforts, some watersheds have failed to show substantial improvement in water quality conditions at the watershed outlet. This phenomenon may be partly attributed to landscape alterations including subsurface ‘tile’ drainage which, while advantageous for agricultural productivity, promotes transport of surplus nutrient to downgradient waters while often bypassing wetlands and other conservation practices. We apply previously constructed hydrologic models of the Upper Mississippi River Basin (~4.4 x 105 km2) and the Maumee River Basin (~1.7 x 104 km2) – two of the most expansively tile-drained landscapes in the United States – to ask: To what extent does tile drainage affect the capacity of wetland restoration and construction to mitigate surplus nutrient (nitrogen, phosphorus) export at the watershed scale? Our model simulations demonstrate that tile drains substantially reduce the ability of wetlands to receive, store, and remove surplus nutrients at the watershed scale. However, we additionally show that wetland restoration and construction can be especially advantageous in these landscapes if wetlands are strategically positioned to receive and treat tile-effluent. Our work demonstrates the potential of wetland restoration and construction in tile-drained landscapes to reduce downstream nutrient loads while highlighting the continued challenge of balancing the agricultural production benefits of tile drainage with large-scale water quality mitigation needs.
