New Target Tackles Question of Nutrient Source in Watershed

Graduate student Brian Breaker, with Erik Pollock, Brian Haggard of the Arkansas Water Resources Center and professor Phil Hays of the geosciences department and the U.S. Geological Survey, reported their preliminary findings at a recent meeting of the American Geophysical Union.

The Illinois River Watershed is the site of a mystery – high nutrient loads that have muddied the waters between Arkansas and Oklahoma. The nutrient loads themselves are not contested, but the source of these high amounts of nitrogen and phosphates are, and currently the sources of the nutrients are not explicitly identified.

Breaker and his colleagues are looking at oxygen isotopes of dissolved phosphates to try to identify the sources of the nutrients found in the watershed. Isotopes, or atoms of the same type but with slightly different weights, are found in plants, animals and organic matter. Different types of organic material have different isotope signatures, or unique proportions of a particular atom at a particular atomic weight. The researchers wanted to see if they could see a signature that varied between sources. If so, those signatures also might be seen in the nutrient loads downstream.

The researchers examined five different sources of potential nutrient loads in the watershed – soil derived phosphorus, septic system effluent, wastewater treatment plant effluent, poultry litter and commercial fertilizers. They collected water samples from the source and examined the oxygen isotopes of the phosphates contained in each one.

“We went straight to the point where we had a firm handle on the source,” Hays said. The researchers then took the samples to the laboratory, where they examined the oxygen isotope ratios found in the phosphates.

“We do indeed see a recognizable distinction between these sources,” Hays said.
The researchers continue to work in the watershed and plan to expand the project for further testing, collecting more environmental samples across a broader realm of ecosystems in the area.

“This could be a strong and effective method for managing nutrients,” Hays said. “It’s not a silver bullet. But it is another tool in the toolbox that can help clarify things.”

Phil Hays, professor, geosciences
J. William Fulbright College of Arts and Sciences
479-575-7343, pdhays@uark.edu