By Harshanee Jayasekera, DWFI Post-doctoral Research Associate
Nitrogen is an essential element for plant growth and therefore, agricultural economies. However, when nitrogen leaves the crop root zone it becomes a liability for groundwater, surface water, and air quality.
Once nitrate enters groundwater, removing it can be difficult. This is a particular challenge in agricultural states like Nebraska. Balancing the economic importance of agriculture with the need to protect drinking water requires long-term planning and effective resource management. Nebraska has substantial water resources and established institutions to help manage them, but protecting groundwater quality remains an ongoing challenge.
Our recent research shows how agricultural policies can support these efforts. We examined one policy option and found that continued enrollment in the USDA Conservation Reserve Program (CRP), which retires agricultural land from crop production, is associated with lower groundwater nitrate levels. Perhaps most importantly, our findings highlight a key lesson: improvements in groundwater quality can take a long time to emerge.
What does the research tell us?
In our 2026 study, Long-term impacts of land retirement on groundwater nitrate concentrations, Richard Melstrom (Loyola University Chicago), DWFI Faculty Fellow Taro Mieno (University of Nebraska–Lincoln) and I examine the relationship between agricultural land-retirement policies and groundwater nitrate concentrations. The study is published in the Journal of Environmental Research: Water. Our study uses an extensive Nebraska groundwater dataset covering 1996–2019, with more than two million nitrate observations from approximately 33,000 wells. This allows us to examine how groundwater quality changes over time in relation to policies that reduce agricultural activity and nitrogen inputs.
The findings suggest that land retirement can be one of the options that contribute to lower groundwater nitrate levels, but the benefits may not appear immediately. Nitrate from past agricultural activity can remain in the subsurface and continue moving toward groundwater long after land management practices change. As a result, improvements may unfold over years or even decades.
Why does this matter for decisionmakers?
Water managers and policymakers need realistic expectations about how long it may take for groundwater quality to improve following policy interventions. Groundwater dating studies provide useful insights into how water moves through groundwater systems and how contaminants may be transported over time. Long-term water-quality monitoring data complement these studies by providing evidence of how groundwater quality responds to policy changes over time. These real-world observations can be helpful when engaging with stakeholders beyond academic settings.
Our study adds to this evidence by documenting changes in groundwater nitrate levels over an extended period. These findings can help inform longer-term water-quality goals and support policies that account for the slow response of groundwater systems.
Protecting groundwater before it becomes contaminated
Nitrate pollution is not just about how much nitrogen enters the environment. It is also about when contamination becomes visible and how long its effects persist.
Reducing excess nitrogen inputs today can help prevent groundwater contamination that future generations would otherwise inherit. Waiting until groundwater quality declines may leave communities facing years of monitoring, treatment and remediation while natural recovery takes its course. While we cannot easily speed up groundwater movement or the natural processes that remove nitrate, we can reduce the amount of nitrogen entering the system in the first place.
When groundwater recovery can take decades, prevention is a long-term investment in reliable drinking water, healthier ecosystems and potentially lower future remediation costs.
Why this matters beyond Nebraska
We focused on Nebraska because its groundwater data allowed us to study these changes over an extended period. However, the implications extend to other agricultural regions where fertilizer use, manure management, and groundwater vulnerability create similar challenges.
The findings also underscore the importance of long-term planning and effective institutions, particularly in regions with limited technical or institutional capacity to manage groundwater recharge and protect water quality.
Acknowledgment
This research was supported by the State of Nebraska and the Pediatric Cancer Research Group, part of the Child Health Research Institute.
We acknowledge the support and contributions of the Claire M. Hubbard Foundation; the Water, Climate, and Health Program at the University of Nebraska Medical Center; and the Daugherty Water for Food Global Institute at the University of Nebraska.
We extend our thanks to the Nebraska Department of Water, Energy, and Environment for granting access to the restricted data from the Nebraska Groundwater Quality Clearinghouse and for permitting the University of Nebraska–Lincoln to host the unrestricted portion of the data.