Growing Wetlands for Clean Water

Using small farm-based wetlands to naturally reduce nutrient runoff

Nutrient pollution is one of the biggest issues for the Mississippi River system, and the Illinois River Watershed is a huge contributor to it. Illinois contributes more nutrients to the Gulf of Mexico’s “dead zone” than any other single state. Meanwhile, as recent events like the contamination of Toledo's drinking water from Lake Erie have shown, excessive nitrogen and phosphorus are also degrading water quality in local and regional water bodies throughout the Midwest.

The largest source of Midwestern nutrient pollution is runoff of agricultural fertilizers. Excessive nitrogen primarily leaves farm fields via underground drain tiles—buried pipes that move water off farmland quickly. The Wetlands Initiative is advancing the use of farm-based constructed wetlands as a practical solution to help address this urgent issue. 

TWI has found that small, precisely positioned "in-line" wetlands can intercept and naturally remove nitrogen from drain-tile flows before they enter a major stream. These wetlands are placed along ditches or small streams on a farm without taking large amounts of prime farmland out of production. Not only do these in-line wetlands remove nitrogen from runoff more efficiently and cost-effectively than almost any other method, they do it within the typical Midwest farm landscape full of drain tiles.

In heavily agricultural north-central Illinois, TWI is partnering with landowners and ag-sector groups to construct wetlands on farmers' properties. The first TWI-designed wetland was installed in August 2015 and the second in 2016, and TWI staff are preparing wetland designs for more farmers who have appropriate sites. Ultimately, these farm-based wetlands could be replicated in similar watersheds throughout the Midwest to improve water quality.

Jill Kostel, TWI's senior environmental engineer, takes a water sample in the field.

TWI’s early outreach in north-central Illinois revealed that unfamiliarity with the wetland practice and insufficient local proof of its effectiveness are barriers to implementation. Consequently, TWI is partnering with a professor of environmental engineering at the University of Illinois at Chicago to conduct water quality testing on the first two wetlands to directly quantify their nutrient removal.

Research has shown that wetlands are a highly effective nutrient-removal practice when carefully designed and strategically positioned within the agricultural landscape. The natural physical, biological, and chemical processes in a wetland capture and retain nutrients and, in the case of nitrogen, transform it into a harmless gas. The key is to site the wetlands in locations where they can most effectively reduce nitrogen loads.

TWI's first in-line wetland designed for nutrient removal was installed on a farmer’s property in Bureau County, Illinois, in August 2015.

These scattered, small farm-based wetlands also provide wildlife habitat, some flood storage, and some sediment retention.

Funding for the Growing Wetlands for Clean Water project in 2015–16 has been provided by Clif Bar Family Foundation, Drive Current, Inc., Illinois Corn Growers Association, Illinois Nutrient Research & Education Council, The McKnight Foundation, New Belgium Brewing Company, Patagonia Chicago Magnificent Mile, The Siragusa Foundation, Walton Family Foundation, Winnetka Garden Club, Zea Mays Foundation, and individual donors to TWI.

Learn more:

Growing Wetlands for Clean Water: Farmers now putting wetlands in the ground (TWI Fact Sheet PDF)

Ask the Scientist: How do wetlands remove nutrients? 

Feasibility Assessment of a Nutrient Trading Market in the Big Bureau Creek Watershed (TWI Targeted Watershed Grant Technical Report to the U.S. EPA)