By MARK BUTZOW
Associate Editor 

URBANA, Ill. — As methods of reducing nitrate runoff go, a constructed wetland is one of the best ways. But it’s also one of the hardest sells.

A University of Illinois research project may make it a little easier to convince farmers – at least those whose land abuts a river, stream or drainage ditch – that turning some of their frontage into a wetland would be a worthwhile stewardship step.

The new data come from measurements collected in the past two years at wetlands along the Embarras River in southern Champaign County, Ill.

Biogeochemist Mark David was involved when the wetlands were created in the 1990s to "scrub" runoff water as it left a farmer’s 190 acres of crop land. More recently, graduate student Tyler Groh joined David and faculty researcher Lowell Gentry to revisit the Embarras wetlands to measure their effectiveness.

What they found is an overall 62 percent nitrate removal rate. In addition, they documented that little nitrous oxide, a potent greenhouse gas, is being released into the air. "Slowing down the rate of flow of the water by intercepting it in the wetland is what helps to remove the nitrate," said Professor David, a faculty member in the College of Agricultural, Consumer and Environmental Sciences.

"It’s just about slowing the water down and allowing the microbes in the sediment to eliminate the nitrate. It goes back into the air as harmless nitrogen gas."

Groh is lead author, along with David and Gentry, of Nitrogen removal and greenhouse gas emissions from constructed wetlands receiving tile drainage water, which was published in the May/June issue of Journal of Environmental Quality. The research was partially funded by the USDA National Institute of Food and Agriculture.

Wetlands do work, but again, getting people to put them on their farm is a different story.

The government will share the cost of a lot of nitrate-removal projects, but the farmer still may be losing some tillable ground for the long haul and the revenue that would have come from crops on that land going forward.

"We found people willing to add bioreactors, but no one wanted wetlands. And we were paying for it," David said.

Agricultural applications of fertilizers and pesticides have increased dramatically since the middle 1960s, and the impact of agrochemicals on water quality has become a serious environmental concern, according to information from the Iowa Conservation Reserve Enhancement Program. Nitrate is a particular concern:

•Because of the potential adverse impacts on both public health and ecosystem function

•Because of the high mobility of nitrate in surface and groundwater

•Because of the widespread use of nitrogen in modern agriculture

Annual application of fertilizer-N in the United States has grown from a negligible amount prior to World War II to approximately 10 million metric tons of N per year.

Agricultural nutrient losses to streams are a special concern in the Corn Belt, a region characterized by intensive row-crop agriculture and by correspondingly intensive use of commercial fertilizer. Corn and soybeans are the two largest acreage crops in the region and account for the vast majority of fertilizer use.

Since 1950, total acreage of these two crops has increased by about 50 percent, primarily because of increases in soybean acreage. Over this same period, commercial fertilizer use has increased dramatically to approximately 10 million metric tons per year.

Nutrient loads to Corn Belt streams are among the highest in the country and are reflected by significantly elevated stream nutrient concentrations.

Nitrate nitrogen concentrations in agricultural streams frequently exceed the drinking water standard of 10 mg N L-1, and concentrations in tile drainage water are commonly more than double the drinking water.

In addition to impacts on water quality within the region, agricultural nutrient loads to Corn Belt streams are considered a major cause of the hypoxia in the Gulf of Mexico.

The EPA in 2011 directed 12 Midwest, Plains and Delta states to create "nutrient reduction strategies," but most have not developed those goals and action steps. The 12 states (Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Ohio, Tennessee and Wisconsin) together are referred to as the Hypoxia Task Force.

"The USDA requested proposals on the effectiveness of wetlands and woodchip bioreactors to reduce nitrate losses from fields, but was also concerned about greenhouse gas emissions. On the Embarras River wetlands, we found the greenhouse gas emissions were really quite low. Nitrous oxide was not a problem."

Along with fertilizer management, cover crops and bioreactors, David said wetlands will be an integral part of the Illinois Nutrient Reduction Strategy. A September 2014 progress report on federal efforts to improve the Gulf of Mexico hypoxic zone concluded that state nutrient reduction strategies "have been slow to develop and are missing essential components."

Only two states, Iowa and Ohio, have a final strategy. To date, only three states – Iowa, Minnesota and Wisconsin – had set nutrient reduction goals. Of these three states, only Minnesota has a timeframe for meeting these goals.

The report also said those state strategies’ "emphasis on local waterways needs to be augmented with a focus on the larger (Mississippi-Atchafalaya) watershed."

As a result, the EPA’s Office of Water will work with the states to put more emphasis on monitoring results. "We recommend that the Assistant Administrator for Water work with state and federal Task Force members in the Mississippi River Watershed to develop and enhance monitoring and assessment systems that will track the environmental results of state nutrient reduction activities, including their contribution to reducing the size of the Gulf of Mexico hypoxic zone," said the EPA report.

The full report is available online at www.epa.gov/oig/reports/2014/20140902-14-P-0348.pdf