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On the Trail of Nitrates

by John Riehl
Office of Postdoctoral Scholars
University of Iowa Graduate College
IIHR Postdoctoral Associate Carrie Davis shows visiting Chinese students instruments used to test water quality.

IIHR Postdoctoral Associate Carrie Davis shows visiting Chinese students instruments used to test water quality.

The Mississippi River—one of the defining physical features in North America—serves as a vital transportation corridor for much of the United States and provides drinking water for those who live along its banks.

Significant changes in the river jeopardize its future. Excess plant nutrients and sediment reach the river and travel to the Gulf of Mexico, resulting in algae and other plant overgrowth that can choke delicate ecosystems. Other problems include invasive species such as Asian carp and zebra mussels.

Over time, these problems have begun to alter the river’s navigation routes and drinking water quality. To save the largest river on the continent, researchers must learn more about the Mississippi River’s complex ecosystems and our human impact on them.

To study these problems, researchers gather at the UI’s Lucille A. Carver Mississippi Riverside Environmental Research Station (LACMRERS), located near Muscatine, Iowa. This facility provides access to the Upper Mississippi River, stretching from St. Paul, Minn., to Cairo, Ill.

IIHR—Hydroscience & Engineering, a unit of the University of Iowa’s College of Engineering, operates the research station.

IIHR Assistant Research Scientist Caroline Davis, a Cedar Rapids native, is based at LACMRERS (

“There is so much work to be done research-wise on the Mississippi,” says Davis, who works for Doug Schnoebelen, director of LACMRERS. “The fact that we’re able to operate a state-of-the-art station with all kinds of water-quality equipment, sediment analysis equipment, and research space, is so important because we can bring University of Iowa researchers and students to do collaborative research on-site at the Mississippi.”

Davis operates real-time water quality sensors in the Lower Iowa River and Lake Odessa. The Iowa River joins the Mississippi River near Wapello, Iowa, while Lake Odessa is a backwater lake in Louisa (Iowa) County with water levels that fluctuate with the Mississippi.

The sensors continually measure nitrate, turbidity, dissolved oxygen, pH, temperature, and specific conductance.  Nitrate, a naturally occurring form of nitrogen found in soil, is of particular interest. Nitrogen is essential to all life, and most crop plants require large quantities to sustain high yields.

“Carrie has been doing the heavy lifting in getting 12 real-time water quality sensors out in the Lower Iowa/Cedar River, Mississippi River, and Lake Odessa,” Schnoebelen says. “The sensors will give us a unique opportunity to study the Mississippi River and tributary streams in a new way for water quality fate and nutrient transport. This research has many practical applications for agricultural stewardship and sustainability in Iowa and the Upper Mississippi River.”

The sensors at Lake Odessa collect data every 20 minutes, and researchers take water samples periodically to measure nitrate levels in the lab. Communication technology transmits this data to researchers at IIHR and the research station.

Caroline Davis operates real-time water-quality sensors in the Lower Iowa River and Lake Odessa.

Caroline Davis operates real-time water-quality sensors in the Lower Iowa River and Lake Odessa.

Initial results suggest that nitrate and water quality at Lake Odessa are less dependent on water level variations and more directly related to flow-through conditions from the river source due to inlet gate position.

“We have real-time monitors set up throughout Lake Odessa and we see as water goes from the Mississippi into the lake that the nitrate levels go from pretty high to nothing,” Davis says. “We’re able to say that this backwater system processes nitrate very well, so we’re able to take this information and suggest that this type of system be put in different environments along other sections of the Mississippi River.”

The formation of nitrates is an integral part of our environment’s nitrogen cycle. In moderate amounts, nitrate is a harmless constituent of food and water. If people or animals drink water high in nitrate, it may cause methemoglobinemia—an unusual and potentially fatal blood disorder in which an abnormal amount of methemoglobin, a form of hemoglobin, is produced. Hemoglobin is the molecule in red blood cells that distributes oxygen to the body. Methemoglobin binds with and carries oxygen, but cannot release the oxygen.

“With our sensors in the lower Iowa River watershed, we’re looking at how nitrate and nutrients are transported from the site where the farmer applies the fertilizer to the surface water stream and onto the Mississippi,” Davis says. “That’s what we’re trying to figure out right now, fate and transport of nitrate.”

The lack of rain, however, has caused Davis and her colleagues to play a waiting game in their search for answers.

“We have essentially very low nitrate in Clear Creek, the Iowa River, and even the Mississippi River,” Davis says. “What happens when we get that rainfall? We’re looking for that pulse that is going to come through and pretty much shoot the nitrate levels through the roof. Nitrate is just sitting there in the ground waiting to be washed into the surface water system and out to the Mississippi and then to the Gulf of Mexico.

“How is that going to happen? How can we start taking some of this data and evaluate nutrient management practices in certain parts of the watershed? We’re sitting and waiting right now. We have the sensors out in the network. We’re waiting to see this pulse.”

Davis says her position at LACMRERS is the perfect next step in her career. Previously, she was a contract geologist for the Iowa Geological and Water Survey at the UI’s Oakdale Campus. Davis also earned a master’s degree in geology at Fort Hays State and a Ph.D. in geophysics at Missouri-Rolla. She also served as a postdoctoral research scholar at LACMRERS.

“At the Iowa Geological and Water Survey, I started learning more about nitrates, water quality, and nutrient monitoring,” Davis says. “When that contract ended, I found the postdoc position at LACMRERS. It was a perfect opportunity to continue with water quality and environmental research in Iowa.”

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Last modified on June 29th, 2015
Posted on September 11th, 2013

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