Research focuses on Iowa as Mississippi River nitrate villain

Researchers found that Iowa contributes more than its share of nitrate pollution to the Mississippi River due largely to agriculture.


FILE – In this file photo, a grain silo on a farm in Johnson County. Approximately 30.6 million acres of land in the state of Iowa is used for farming. (File photo/The Daily Iowan)

University of Iowa researchers may have found that Iowa farms contribute nitrate pollution to the Mississippi River disproportionately compared with other states in the watershed in a study published April 12.

“Things over time are changing differently in Iowa than they are in the rest of these larger basins,” said UI research scientist/engineer Christopher Jones, the author of the study.

Nitrates, key soil nutrients often boosted with synthetic fertilizers, dissolve and drain from farm fields to streams and rivers.

The research focused on Iowa’s nitrate load into river basins draining into the Gulf of Mexico, using data collected at 23 sites in Iowa and publicly available data from states downstream. On average, Iowa contributes 29 percent of total nitrates in the rivers studied, though at times Iowa’s contributions were several times higher.

The findings suggest that nitrates in the non-Iowa area of the basins remained stable during the 18 years of the study, but Iowa’s contribution increased over time. Jones said Iowa’s landscape and management practices, as opposed to weather trends, are likely to blame.

“What farmers are doing here isn’t a whole lot different from what they’re doing elsewhere,” Jones said. “The difference we have is we just do so much of it.” He noted that 72 percent of Iowan land is used for growing crops.

The study provides the first detailed estimate of Iowa’s nitrate contribution into the Upper Mississippi and Missouri River Basins. Jones said conservationists have historically disregarded western Iowa’s Missouri River watershed as a major contributor because it is drier and hillier than the rest of the state and because it has less drainage tile than in the rest of the state.

Adam Schnieders, a water-quality resource coordinator for the Iowa Department of Natural Resources, said in a phone interview that data on nitrate load in that part of the state showed higher than expected levels. More research should be done in the area, he said.

The study aids the Mississippi River/Gulf of Mexico Hypoxia Task Force, a team of government officials from 12 states that uses monitoring, strategic support, and legislation to reduce nutrient runoff into the Gulf.

As of 2017, the Gulf’s Dead Zone, in which natural processes caused by excess nutrients have stripped the water of life, measured 22,720 square kilometers, according to the Environmental Protection Agency. The task force aims to reduce the zone to 5,000 square kilometers by reducing nitrogen pollution by 45 percent.

Schnieders said all states involved with the task force have put science-based nutrient-reduction strategies into action in an effort to achieve that goal. Despite the efforts, nitrates in the Mississippi have risen 40 percent since 2003, according to the study.

“Before we can see a change in the water, we need to see a change in the landscape,” said Schnieders, who works closely with the task force on a nutrient-reduction strategy. Before that can happen, he said, people and input must change.

The Iowa State University Extension and Outreach Water Quality Program works to implement the nutrient-reduction strategy on all those levels, through research and communication on nutrient-reduction practices.

“We take that great research and deliver it in a way that is useful to farmers, stakeholders, and policymakers,” said program manager Jamie Benning via phone.

The program uses social science to get information to farmers effectively, she said. Because farmers tend to trust certified crop advisers and other farmers most, she noted, ISU offers information and training to those individuals and models farmer-to-farmer learning at farm extension field days.

Managing nitrates added to fields through fertilizer would only reduce nitrate load by 10 percent, Benning said. The water-quality program focuses on managing the whole system, including naturally occurring nitrate loss from soil, she noted.

According to the Nutrient Reduction Strategy 2017 Annual Report, outreach and education efforts doubled from 2016 to 2017, reaching 54,478 people through 474 events. Such efforts resulted in a 9 percent increase in farmers’ knowledge on nutrient reduction over that in 2015.

Schnieders said water-friendly changes to farm landscapes, such as cover crops and natural buffers, are increasing, in part thanks to outreach and education. Government-sponsored incentives have also contributed, he said.

Schnieders called Senate File 512, passed in January, “encouraging.” The bill would increase funding for water-quality initiatives that reduce nitrate pollution.

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