Scott Schrage, July 28, 2022
Team predicts climate impacts on herbicide runoff
POCKET SCIENCE: EXPLORING THE ‘WHAT,’ ‘SO WHAT’ AND ‘NOW WHAT’ OF HUSKER RESEARCH
Welcome to Pocket Science: a glimpse at recent research from Husker scientists and engineers. For those who want to quickly learn the “What,” “So what” and “Now what” of Husker research.
Atrazine’s ability to control weeds has made it a popular herbicide in the United States, where it helps maximize yields of corn and sorghum. But the herbicide also poses environmental and health risks, with research establishing that it can curb local plant diversity and disturb hormone production in wildlife and possibly humans.
In some cases, the risks are literal examples of downstream effects: Precipitation and irrigation can transport atrazine across landscapes to rivers and other bodies of water or draw it downward into soil. Mitigating those risks depends on knowing where atrazine will migrate, how far it will travel, and how much of it will accumulate. Predicting its fate has proven difficult, though, even before accounting for how climate will continue changing in the coming decades.
Nebraska’s Yusong Li, Chuyang Liu and Shannon Bartelt-Hunt approached the challenge with the help of supercomputers at the university’s Holland Computing Center. Informed by historical climate data from a cornfield-laden research site near Shelton, Nebraska, the team ran a total of 2,000 simulations — 100 for each of 20 different models — that projected the site’s climate in the years 2056 through 2059. The researchers also factored in projections of atrazine application and degradation, groundwater elevation and recharge, and other relevant variables.
Though the simulations projected the site’s average annual precipitation to increase 9% over the historical average, they also predicted that water lost to the atmosphere via evaporation and plant transpiration will jump by 19%. Consequently, the team reported that the yearly recharge of groundwater, which ranged from about 60-200 millimeters a decade ago, could average just 1-60 millimeters between 2056 and 2059.
The expected hike in precipitation will likely increase the transport and accumulation of atrazine, the researchers found. Still, the migration of atrazine plumes — pockets of high atrazine concentrations — seems to hang on precipitation patterns, requiring a year or two of reasonable rain followed by multiple years of heavy precipitation. Under that worst-case scenario, plumes could migrate as much as 16 feet downward in a three-year span, approaching the groundwater table in the process.
The team did conclude that climate variability will generally matter only if atrazine degrades slowly in soils, or if those soils are poor at clinging to and absorbing the herbicide.
Given the potential importance of atrazine degradation rates, future research should investigate the factors that influence those rates, the researchers said. Incorporating other locales and soil types into simulations, meanwhile, could yield insights across a broader swath of the Corn Belt.