Constructed Wetland: A shallow vegetated pool that helps filter nutrients, especially nitrate, control flooding and provide wildlife habitat.
Nutrient treatment wetlands are an important edge-of-field practice. They have been shown to improve water quality by reducing nitrogen by 52 percent on average. Actual nitrate removal depends on rainfall, with greater removal in drier years and lesser removal in wetter years. In addition to removing nutrients, wetlands provide habitat, recharge groundwater, reduce flooding downstream by storing runoff and can provide recreational opportunities.
More than 70 constructed wetlands have been installed in Iowa for water quality improvement as part of the Conservation Reserve Enhancement Program (CREP). It is estimated that Iowa needs about 7,000 CREP wetlands to fully implement the Iowa Nutrient Reduction Strategy. CREP is a major state/federal initiative of strategically located wetlands using advanced computer technology and designed to remove nitrate from tile-drainage water from cropland areas. These systems typically include a 5 to 10 acre wetland, surrounded by a 30 to 40 acre grass buffer. The typical system handles water from roughly 1,000 acres. One CREP wetland provides roughly the same amount of nitrate removal from 1,000 acres as converting 500 acres to permanent grass. The demand for the program greatly exceeds available funding and the waiting list extends at least 5 years.
The program is implemented by the Iowa Department of Agriculture and Land Stewardship in cooperation with the U.S. Department of Agriculture Farm Services Agency and is available in 37 counties in the tile-drained region of north central Iowa. Financial incentives are provided to private landowners to develop and restore wetlands that intercept tile drainage from agricultural watersheds. Landowners receive annual land payments for up to 15 years and reimbursement for costs of wetland and buffer establishment. Easements to maintain the wetlands and buffers are required for a minimum of 30 years, and permanent easements can also be developed. Nutrient treatment wetlands may also be installed outside of the CREP program, but financial incentives are not as significant.