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Restoring Wetlands for Nitrate Removal from Subsurface Drainage: Research Foundation and Program Elements of the Iowa Conservation Reserve Enhancement Program

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  701P0904,  . (doi: 10.13031/2013.17425)
Authors:   William G. Crumpton

Surface water nitrate loads in the Midwest Corn Belt are among the highest in the Mississippi River Basin, and in addition to local water quality impacts, are suspected as a major contributor to hypoxia in the Gulf of Mexico. Wetlands have the potential to significantly reduce nitrate loads, if wetlands can be sited and designed to intercept nitrate carried in subsurface drainage tile. For the past 10 years, Iowa State University and the Iowa Department of Agriculture and Land Stewardship have cooperated on a targeted research program addressing the hydrologic and water quality functions of wetlands in agricultural watersheds. This effort supported the development and application of performance forecast models for siting, design and assessment of wetland restorations in agricultural watersheds. This work elucidated the benefits and limitations of wetland restorations for nutrient reduction and provided the research foundation for the Iowa Conservation Reserve Enhancement Program (CREP). The Iowa CREP provides financial incentives to restore wetlands that are strategically located to intercept tile drainage and reduce nitrate export from agricultural watersheds of the Des Moines Lobe. A unique aspect of the Iowa CREP is that expected water quality benefits will not simply be assumed based on wetland acres enrolled, but in fact be calculated based on the measured performance of CREP wetlands. As an integral part of the Iowa CREP, the Agricultural Drainage & Wetlands Research Team at ISU is monitoring a representative subset of wetlands to document nitrate reduction. This will allow further refinement of modeling and analysis tools used in siting and design of CREP wetlands. Research at Iowa State University has shown that wetlands meeting CREP requirements will remove 40-90% of the nitrate received, which for sites currently constructed or under design equates to 36,900 tons of nitrate over the design life of the wetlands.

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