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Geography, Geology and the Environment


Dr. Eric Peterson

Mentor Department

Geography, Geology and the Environment


In the U.S. Midwest, where fertile soils with high water retention are prevalent, the installation of tile drainage networks have become a common practice to drain excess soil water, which enhances plant growth and increases crop productivity. However, tile drainage networks coupled with the use of inorganic fertilizers have significant implications on water quality, contributing to eutrophication, leading to harmful algal blooms, and resulting in hypoxic conditions in surface water bodies. To mitigate excess nutrient exports to surface water bodies, edge-of-field practices have been introduced. One such practice is the saturated riparian buffer (SRB), which utilizes a diversion system to redirect tile drainage water from an agricultural field into a riparian buffer rather than directly discharging into a stream. As a best management practice, SRBs have been shown to reduce nitrate loads delivered to surface water by increasing the travel time of nutrient- rich waters through soils and exposing the nutrients to soil processes. Examining six years (2015-2021) of data from a SRB, this research investigated trends in the nitrate as nitrogen (NO3-N) concentrations of the groundwater upgradient (independent) of the diversion system as compared to waters downgradient (dependent) of the diversion system during tile flow and examined the duration of time the tile water influences the SRB. A mixed effect model analysis of the data identified a positive relationship between NO3-N concentrations in the downgradient groundwater and the volume of diverted tile flow. However, the NO3-N concentrations in the upgradient groundwater decreased as the tile discharge increased. The difference in the response between the upgradient and downgradient waters highlighted the influence of the diverted tile water on the SRB. In the absence of flow, the concentration of NO3-N in the downgradient groundwater continued to increase up to two weeks before declining after three weeks. After five weeks, the concentration of NO3-N in the downgradient groundwater returned to its initial concentration before tile flow. On a year-to-year basis, NO3-N concentrations within the SRB remained stable, indicating that there was not a long-term accumulation within SRB.

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