Scientists at the University of Illinois Urbana-Champaign can now differentiate between human-derived and hydrological contributions of riverine nitrogen pollution in the Upper Mississippi River Basin. The advancement, published in Environmental Science and Technology, sets the stage for more nuanced policy and management of nitrate and nitrite, the nutrients that degrade drinking water quality and cause oxygen-starved “dead zones” in the Gulf each year.
“This is the first study that distinguishes changes in nitrogen loss attributable to human activities, such as fertilizer application and farm conservation practices, from hydrological variability, such as extreme rainfall and changes in streamflow. It also shows us where the hotspots of nutrient loss are and which driver — human activity or hydrological variability — is more influential in each sub-watershed location,” said Bin Peng, assistant professor in the Department of Crop Sciences, part of the College of Agricultural, Consumer and Environmental Sciences at Illinois. “Our goal in segregating these drivers is to further tailor policy and management to reduce nitrogen loss.”
Peng and his co-authors obtained 20 years of water quality data from U.S. Geological Survey monitoring sites across the Upper Mississippi River Basin and calculated annual nitrate and nitrite loads at each location. The team then used observational data to calibrate a modified version of the USGS’s SPARROW model, which relates stream nutrient loads to watershed characteristics, including nutrient sources, land-to-water delivery factors, and in-stream processes. Finally, the team conducted a factorial scenario analysis to attribute the changes to human-derived and hydrological drivers.