Nonpoint loads of nitrate-nitrogen in agricultural drainage to surface waters in the U.S. corn belt are among the highest in the country. These nitrogen loads can negatively effect human health where such water is used for drinking water supplies and are suspected to contribute to hypoxia in the Gulf of Mexico. Substantially reducing nitrate losses from these agricultural systems will require a combination of in-field best management practices and off-site landscape modifications.

Wetland restoration is one of the most promising off-site strategies for reducing surface water contamination, and research conducted at Iowa State University has demonstrated that wetlands have the potential to remove 40-90% of the nitrate in tile drainage from upper-lying croplands. The effect of wetlands on watershed scale nitrate reduction is largely determined by the fraction of the watershed's total nitrate load that the wetlands intercept. If not sited so as to intercept a significant fraction of the watershed load, restored wetlands have very little effect on either nitrate concentrations or exported nitrate.

The Iowa Conservation Reserve Enhancement Program (CREP) provides incentives to landowners to voluntarily establish wetlands strategically located and designed to remove nitrate from tile-drainage water from cropland areas. By placing the wetlands within existing or improved drainage networks, landowners can get the benefits of drainage and reduce nitrate losses to streams and rivers.

To date, nearly 900 sites have been identified that meet Iowa CREP criteria, with over 160 of these currently under landowner consideration. Six sites have been completed and landowners for 32 additional sites have requested their projects move forward through survey and engineering. These sites total nearly 1907 acres of wetland plus buffer and reduce nitrates for over 52,600 acres of tile drained cropland.

By restoring strategically placed and designed wetlands, Iowa CREP will reduce nitrate run-off.

Waterfowl also benefit from Iowa's restored wetlands.