New National Science Foundation (NSF) funding will help a UNL research team investigate an understudied reservoir of organic nitrogen that may shape groundwater quality long after nitrogen management strategies are in place. A separate award from the Nebraska Corn Board will help them evaluate approaches that may proactively reduce nitrate risk before it reaches groundwater.
By Ann Briggs, Nebraska Water Center Communications and Program Specialist
Clean groundwater is vital to drinking water supplies, agriculture, and rural communities, but nitrogen contamination remains a persistent challenge. Roughly four out of five Nebraskans drink groundwater. Much of it sits beneath some of the most productive agricultural land in the world. Nitrogen fertilizer is a critical crop nutrient, however when it leaves the root zone it becomes a loss to the farmer and a concern for drinking water.
The puzzling part is what happens when nitrogen management practices are improved. Nitrate levels in some Nebraska wells continue to rise, even years after modern nutrient strategies to reduce excess nitrogen use have been implemented. A University of Nebraska–Lincoln (UNL) research team based at the Nebraska Water Center thinks the explanation lies in historical nitrogen stores buried in the deep vadose zone between the surface and the water table. Two new awards, one federal and one from Nebraska's corn producers, will support collaborative efforts to better understand these underground processes and evaluate proactive solutions.
Nebraska Water Center researchers have been studying the vadose zone for four decades to understand how nutrients, including nitrogen, move from the land surface to the groundwater. The vadose zone is a critical region for storage, transport, and transformation of chemicals that can affect groundwater quality.
Nitrogen is an essential nutrient present in many forms and is also applied as a fertilizer to crops like corn. While these plants then take up the nutrients they need, any remaining nitrogen can convert into mobile nitrate. However, the process of particular interest to the UNL research team is if this mobile nitrate may react with soil carbon through microbes to become bound as organic nitrogen in the deeper soil layers. This reaction could potentially act as a slow-release reservoir that gradually breaks down and generates new nitrate years later in the deep vadose zone, moving towards the groundwater.
Nebraska Water Center researchers have found that organic nitrogen accounts for the large majority of total nitrogen stored in Nebraska's deep vadose zone. While most studies of that underground nitrogen reservoir measure nitrate, the UNL research team measures everything else too – and that is where the story gets interesting.
“Most of the nitrogen down there isn’t nitrate at all,” said Arindam Malakar, assistant research professor at the Nebraska Water Center and the Daugherty Water for Food Global Institute, who leads the new project and has his academic home in UNL’s School of Natural Resources. “It’s organic nitrogen, locked in forms nobody has been counting. It can break down slowly, and may keep making new nitrate long after the fertilizer is gone.”
Building on previous USDA funding
New National Science Foundation (NSF) funding will allow the research team to build on a 2022 project funded by the U.S. Department of Agriculture's National Institute of Food and Agriculture (USDA NIFA). Awarded by the Agriculture and Food Research Initiative (AFRI), the project titled "Identifying Reactive Nitrogen Dynamics in the Deep Vadose Zone to Protect Groundwater Quality” established a statewide baseline for the new work. With this USDA NIFA funding, vadose zone cores were collected from 18 of Nebraska’s 23 Natural Resources Districts to characterize nitrogen transformation in different soil types and environments throughout Nebraska. Led by Malakar, the team also collected cores from prairie sites to examine nitrogen transformations in comparatively undisturbed ecosystems. The USDA NIFA funding increased the overall number of vadose zone cores that have been collected in Nebraska, building a larger sample pool that will be used as test environments for the project funded by NSF.
NSF award to investigate organic nitrogen's role in groundwater quality
Through the NSF's Water, Landscape, and Critical Zone Processes (WaLCZ) program, the UNL research team was awarded $496,722 over three years for their project titled “Collaborative Research: Impacts of organic nitrogen dynamics in the vadose zone on groundwater quality” (Award #2612620). UNL is serving as the lead on the project, with Arindam Malakar as the project's principal investigator, and Daniel Snow and David Hage as co-principal investigators. South Dakota Mines is a partner institution, awarded $397,098 over three years (Award #2612621), with Rajesh Sani as the principal investigator and Dipayan Samanta as co-principal investigator.
The research team will investigate how organic nitrogen moves and transforms in the vadose zone beneath agricultural and native prairie landscapes across Nebraska. Most vadose zone studies focus on inorganic nitrogen and nitrate transport without considering the organic nitrogen present in the soil. By focusing on how organic nitrogen moves and transforms, this project seeks to fill a knowledge gap that will be crucial to understanding the full picture of nitrogen present in different forms.
The project will combine field sampling, advanced chemical analyses, microbial studies, and computer modeling to better understand how underground organic nitrogen sources affect groundwater quality. The findings could improve nitrogen management strategies and provide farmers, water managers, and policymakers with new tools to protect water resources while supporting agricultural production. The project will also engage K-12 students, educators, and future STEM professionals through research, training, and outreach opportunities.
Nebraska Corn Board funding supports development of novel nitrogen management technology
In conjunction with the NSF funding, the research team is also investigating a novel nitrate remediation approach currently under development. The end goal of the technology is reducing the amount of nitrate in the vadose zone that becomes a groundwater contaminant, entering drinking water sources, and creating challenges for communities and individual well owners. The Nebraska Corn Board, through corn checkoff funds, has supported the project titled “Remediation of nitrate plume within the vadose zone, being proactive to protect groundwater quality,” with more than $570,000 across five years subject to the Board's annual proposal review and approval.
“The primary reason why we want to do it is to reduce the cost of treating water,” Malakar said. Rather than treating water after it reaches the aquifer, the work focuses on nitrate while it is still held in the vadose zone above the water table, which is expected to be more efficient and economical. Preliminary estimates suggest the approach could be less expensive than current water treatment processes that cities and communities need to use to treat groundwater to safe levels for drinking water.
Initial controlled laboratory studies have shown promising results. Researchers will next evaluate the approach across soil conditions representative of different landscapes across Nebraska and assess effectiveness, repeatability, environmental safety, feasibility and regulatory considerations before any potential field deployment.
Malakar said the appeal of the approach is timing. "By the time you see nitrate in a well, the decision that put it there was made a long time ago. Once it's in the aquifer, you're paying to take it back out."
Malakar envisions a future where the technology is deployed across Nebraska, reducing the amount of nitrate in the vadose zone that becomes a contaminant in the groundwater. That is several years out and contingent on results at every stage, from laboratory experiments to controlled field testing. But if it works, this project’s success could reduce the treatment burden on communities that rely on groundwater.
Multi-agency investment reflects value of Nebraska's groundwater quality
These awards from NSF and the Nebraska Corn Board show the commitment to understanding Nebraska's groundwater quality. The investment has the potential to pave the way for high-impact solutions that could positively impact groundwater quality for the benefit of all Nebraskans.
To meet the research team and learn more about the Nebraska Water Center team’s vadose zone research, visit go.unl.edu/VadoseStory.