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Examining the impacts of increased corn production on groundwater quality using a coupled modeling system
Garcia, V., E. Cooter, J. Crooks, B. Hinckley, M. Murphy, AND X. Xing. Examining the impacts of increased corn production on groundwater quality using a coupled modeling system. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 586:16-24, (2017). https://doi.org/10.1016/j.scitotenv.2017.02.009
Excess nutrients (i.e., nitrogen) in the environment don’t just come from one source. For example, water quality can be affected by agricultural surface runoff, atmospheric deposition, percolation of nitrogen into ground water, as well as many other sources. Thus, the impacts of excess nutrients cross traditional media-specific management boundaries. EPA scientists have developed and applied a unified modeling system to study the ways that excess nutrients move through the biosphere and affect the environment, ecosystems and public health. EPA’s One Biosphere Modeling System is a multi-media modeling system linking air quality, land use, agricultural land management, meteorology, hydrology, and ecosystem models. Seven manuscripts documenting the approach and results of EPA’s "One Biosphere Modeling System” are planned for journal submission in fiscal year 2016, with the first paper expected to be submitted in February.
This study demonstrates the value of a coupled chemical transport modeling system for investigating groundwater nitrate contamination responses associated with nitrogen (N) fertilizer application and increased corn production. The coupled Community Multiscale Air Quality Bidirectional and Environmental Policy Integrated Climate modeling system incorporates agricultural management practices and N exchange processes between the soil and atmosphere to estimate levels of N that may volatilize into the atmosphere, re-deposit, and seep or flow into surface and groundwater. Simulated values from this modeling system were used in a land-use regression model to examine associations between groundwater nitrate-N measurements and a suite of factors related to N fertilizer and groundwater nitrate contamination. Multi-variable modeling analysis revealed that the N-fertilizer rate (versus total) applied to irrigated (versus rainfed) grain corn (versus other crops) was the strongest N-related predictor variable of groundwater nitrate-N concentrations. Application of this multi-variable model considered groundwater nitrate-N concentration responses under two corn production scenarios. Findings suggest that increased corn production between 2002 and 2022 could result in 56% to 79% increase in areas vulnerable to groundwater nitrate-N concentrations ≥ 5 mg/L. These above-threshold areas occur on soils with a hydraulic conductivity 13% higher than the rest of the domain. Additionally, the average number of animal feeding operations (AFOs) for these areas was nearly 5 times higher, and the mean N-fertilizer rate was 4 times higher. Finally, we found that areas prone to high groundwater nitrate-N concentrations attributable to the expansion scenario did not occur in new grid cells of irrigated grain-corn croplands, but were clustered around areas of existing corn crops. This application demonstrates the value of the coupled modeling system in developing spatially refined multi-variable models to provide information for geographic locations lacking complete observational data; and in projecting possible groundwater nitrate-N concentration outcomes under alternative future crop production scenarios.