USING SEASONAL GROUNDWATER SHIFTS IN NITRATE ISOTOPES TO EXAMINE THE TRANSPORT AND FATE OF NITRATE WITHIN A SATURATED BUFFER ZONE

Surface water pollutants are progressively causing questionable water quality for human consumption and at-risk aquatic life. Determining the nonpoint source can be of extreme importance. Agricultural practices apply fertilizers with high concentrations of nitrates to the land surface. Runoff and infiltration may contaminate surface and groundwater. Identifying the pathway nitrates are removed from a system, through denitrification or plant uptake, will aid in remediation efforts to ensure these nitrates do not reach the major bodies of water. Nitrogen is necessary for the growth of aquatic systems; however, increased concentrations of nitrates entering surface waters can impact these systems negatively. The objective of this study is to determine if groundwater nitrates are removed through denitrification within a saturated buffer zone. Quantifying the isotopic composition of ¹⁵N and ¹⁸O will identify if enrichment is occurring through a steadily increased concentration of both isotopes. Temporal affects of ¹⁵N and ¹⁸O are also examined during growth and nongrowth season. Samples are being taken near a second order stream that sits within a riparian buffer zone; downgradient from a 65-acre agricultural farm with tile-drainage flowing directly to the stream. In July 2015, a tile-diversion system that redirects tile flow to three subsurface drainage tiles was installed. Between each diversion tile, wells were installed to monitor the groundwater at a depth of 2.3m. Samples from the wells, the diversion box, and the stream are being drawn on a monthly basis from May 2019 through November 2019. Preliminary data shows ¹⁵N and ¹⁸O plotted against one another has a steady increase of both isotopic values, suggesting that denitrification is occurring