Midwestern agriculture causes an oxygen-starved hypoxic zone, and challenges coastal economies by contributing most of the nitrogen in the Gulf of Mexico. State and federal policymakers have tried for decades to provide solutions and incentives, but the hypoxic zone keeps coming back. A study by University of Illinois researchers offers a new way to understand Midwestern nitrogen dynamics. It forecasts future nitrogen loads under various management scenarios.
The study is published in Water Research; the U.S. National Science Foundation provided support.
"The model explains what's going on across 83 watersheds in the Midwest, providing an understanding of why certain watersheds differ in terms of nutrient loss," said Kaiyu Guan of the U of Illinois, senior author on the study. "But the most important contribution is the scenario prediction, which hasn't been done before. If you increase tile drainage or the corn fraction, how much does the nitrogen load change? We can predict that."
Guan says a more detailed understanding of nitrogen and water flow dynamics, as well as the ability to forecast the impact of management changes, is a critical step in developing effective policies to reduce nutrient loss from field to watershed scales.
The research team analyzed the relationship between daily flow rate and nitrate concentration across the 83 Midwestern watersheds, finding a universal pattern throughout the region. Nitrate increases with flow before leveling off at a high flow threshold.
Guan says the more tile drainage is installed and the more crops are planted in a watershed, the greater the nitrate load in the water. That conclusion isn't new, but the ability to forecast the impacts of increased tile installation or changing levels of corn is.
"This model gives us a starting point for a meaningful discussion about ways to reduce nutrient loss," said study co-author Bin Peng. "These are key questions as we actively work toward nutrient loss reduction with farmers and policymakers."
Added Bruce Hamilton, an NSF program director, "Agricultural nitrogen run-off is a major pollution problem. Research like that reported here helps point to a path forward for reducing it."
