See the original article here and download PDF of the peer-reviewed journal article here.
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 and faculty extension specialist 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.
The researchers focused on two time periods — 2001–2005 and 2016–2020 — showing that nitrogen loss increased by nearly 10 kilograms per hectare per year on average during that 20-year span. About half of the increase was attributable to human activity, while the other half was due to hydrological changes. But that was for the entire region. When the team drilled down to the sub-watershed scale, they could tell which drivers were most important in each location.
“The northwestern part of the Upper Mississippi River Basin shows high contributions from both anthropogenic activities and hydrological changes, whereas the southeastern part of the basin has a higher contribution from hydrological change,” said Qianyu Zhao, first author of the study and a doctoral student in the Department of Natural Resources and Environmental Sciences (NRES) in ACES.
Tailoring solutions based on the prevalent drivers — an approach that could improve outcomes for state and federal nutrient loss reduction strategies — will look different in each location. For example, Peng says, the northwestern part of the region should focus on reducing fertilizer and manure inputs while simultaneously controlling losses from increased precipitation. The southeastern part of the basin may need to focus more on the impacts from hydrological variability.
The research team is now expanding their focus to the entire Mississippi River Basin, with the goal of reducing nutrient loss to benefit farmers’ bottom lines and prevent environmental impacts.
“Expanding this analysis to the whole Mississippi Basin will also help us build our new science-based and data-driven conservation prioritization framework, which will be of many practical uses to all stakeholders, including farmers, watershed managers, state and federal policy makers,” Peng said.
“This is a good example of how deeper scientific research at the Agroecosystem Sustainability Center (ASC) at Illinois can inform practices on the ground and environmental policies,” said Kaiyu Guan, Levenick Endowed Professor for Sustainability in NRES and Founding Director of the ASC. “Improving nutrient management and conservation planning for cleaner water has been one of our focuses since the very beginning."
The study, “How do hydrological variability and human activities control the spatiotemporal changes of riverine nitrogen export in the Upper Mississippi River Basin?” is published in Environmental Science and Technology [DOI: 10.1021/acs.est.5c06476]. Bin Peng and Kaiyu Guan are co-corresponding authors on the study. Doctoral student Qianyu Zhao, co-supervised by Peng and Guan, is the first author.
Research in the College of ACES is made possible in part by Hatch funding from USDA’s National Institute of Food and Agriculture. This study was also supported by the National Science Foundation, the Illinois Nutrient Research and Education Council (NREC), the U.S. Department of Energy’s Center for Advanced Bioenergy and Bioproducts Innovation, competitive funding from USDA NIFA, and the Dudley Smith Initiative in the College of ACES at Illinois. Members of the research team engage with statewide nutrient reduction efforts such as the Illinois Nutrient Loss Reduction Strategy.
Peng and Guan are also affiliated with the Agroecosystm Sustainability Center, the Institute for Sustainability, Energy, and Environment, the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI), and the National Center for Supercomputing Applications at U. of I.
