SitS: Coupling High Frequency Soil Solute Signals and Scalable Simulations to Quantify Biogeochemical Mechanisms Governing Water Quality

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This award was made through the "Signals in the Soil (SitS)" solicitation, a collaborative partnership between the National Science Foundation and the United States Department of Agriculture National Institute of Food and Agriculture (USDA NIFA). Agricultural areas face a pervasive problem of poor water quality that is tied to inefficient use of fertilizer-provided nutrients by crops. Soils play a key role in regulating whether nutrients from fertilizers actually add value to the plant growth or if the nutrients are not absorbed and end up contaminating groundwaters and streams. The ability to understand how to promote the retention of nutrients in soils, reduce the potential for water resource contamination, and increase delivery of nutrients to crop production are collectively hampered by the inability to make direct observations of the activities of dissolved chemicals in soil water. This work will use new sensors embedded in soils to observe a suite of added nutrients, including the key nutrient and major water contaminant nitrate, over a range of experimental and field conditions. These buried sensors will transmit data electronically, and a soil model will be used to interpret the signals. The results of this work will identify conditions that balance water quality and sustainable plant production in model rain-irrigated systems of the Northern Great Plains. This project will also motivate activities supporting science, technology, engineering, and math (STEM) education and participation in underserved communities of the region. If successful, this project will strengthen the nation’s food security while preserving water resources by providing technology that makes the use of agricultural fertilizers more efficient and decreases the negative environmental impacts of these fertilizers.The movement of water through soils mediates both weathering reactions and biogeochemical cycles to drive solute loads delivered to groundwater and rivers. However, current sensor technologies and solute transport modeling approaches limit the efficacy of efforts to address critical questions about soil processes governing the consequences of land use for water quality. In soils, the highly soluble and mobile nitrate ion provides an indicator of nitrogen (N) availability and transformation, serving as a frequently studied yet under-observed signal molecule in disturbed and fertilized systems. Nitrate concentrations in soils are currently quantified using destructive soil sampling, a technique used for over a century. In-situ and real-time measurements of nitrate concentrations in soil waters are lacking. Two limitations hamper understanding of the nitrate signal: 1) lack of high-frequency observations of soil solution composition, and 2) lack of observations that differentiate dynamics in nitrate concentrations driven by variation in the pore structure of the soil fabric. This work will develop, test, and produce a coupled multi-scale sensor approach and solute transport modeling framework capable of scaling reaction dynamics from pore to profile scales. The team will undertake measurements of nitrate in parallel with measurements of general water quality (conductivity, pH, temperature), to address how variation in soil water biogeochemistry associated with variation in pore structure dictates nitrate fate and transport in agricultural soils. Results will include the establishment of new technologies for exploring mechanisms interrelating physical soil structure, hydrologic dynamics, and solute reaction regimes from pores to profiles. These fundamental insights about soil systems will benefit efforts to balance water quality protection with sustainable food production.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.