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Surface water nitrogen contamination is a pervasive issue in Nebraska, and agricultural practices are the main source of nitrogen input to streams (Spalding and Exner, 1993). Nitrate can come from inorganic fertilizers such as anhydrous ammonia, or animal waste. Studies have been conducted on nitrates dating back to 1947 (Addleman, 1985). The Bazile Groundwater Management Area (BGMA) located in northeast Nebraska has historically had high nitrate contamination. This qualitative study assesses the seasonal sources of nitrogen to stream water. It is predicted that the source of input is from commercial synthetic fertilizers. By using nitrogen- oxygen isotope methods, the source of nitrogen input to streams can be determined by isotopic ratios. 14 nitrogen-oxygen isotope samples were taken at 7 different locations in the BGMA during fall and winter to assess the seasonal variability of nitrogen pollution. Results showed that in the fall, nitrate was being derived from a mixture of anhydrous ammonia and manure, whereas in the winter the source of nitrate was primarily anhydrous ammonia. Nitrate contamination levels were also recorded at each site location and most were found to be above 10 mg/L. When 88% of rural Nebraskans utilize groundwater for drinking water (Nebraska Groundwater Quality Report, 2017), it is important to know how much nitrate is entering streams, and where the nitrate is coming from.