Graduation Term

2022

Degree Name

Master of Science (MS)

Committee Chair

Eric Dr. Peterson

Abstract

The Upper Mississippi Basin (UMB), which includes Illinois, has highly fertile soils and therefore, experiences intensive agricultural practices. While fertile, the soils do not drain well, resulting in the installation of tile-drainage systems. Agricultural practices within the UMB involves the application of nitrogen (N)-rich fertilizers. The tile systems coupled with the application of N fertilizers have led to the excessive export of nitrates as nitrogen (NO3-N) from the agricultural fields into surface and subsurface waters through subsurface tile drainage systems. Excess NO3-N contributes to eutrophication and to development of hypoxic zones in aquatic environments. One method that has exhibited success in lowering NO3-N concentration is the diversion of tile drained waters from the agricultural fields into a saturated buffer zone (SBZ) before the water enters a stream. A SBZ is an area of perennial vegetation between agricultural fields and water ways where a tile-outlets drain. The SBZ serves as a sink where NO3-N is lost through natural processes such as plant uptake, denitrification, and dilution with groundwater. Previous works have shown a decrease in the NO3-N content in the SBZ, but the extent to which this removal occurs cannot be quantified without knowing the travel time of the water through the SBZ. Our goals were to use sodium bromide (Nar) and sodium chloride (NaCl) as tracers to determine the travel time of the tile waters in a SBZ at the T3 site in Hudson, Illinois and to quantify the amount of loss or dilution of the NO3-N in the SBZ using a mixing model. The travel times of NO3-N from diversion tiles to wells ranged from 7 days to 17 days. Results from the tracer test show an average groundwater velocity of 0.36 m/day with a standard deviation of 0.18 m/day, using the arrival time of the chloride tracer. The travel time from the SBZ to the stream is 27 days which corresponds to 43% NO3-N removal from the mixing model. This research further reinforces the effectiveness of using SBZ as NO3-N reduction strategy.

Access Type

Thesis-Open Access

DOI

https://doi.org/10.30707/ETD2022.20221020070313922344.999971

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