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Identification of Distribution of Nitrogen Pollutants Based on Nitrogen and Oxygen Stable Isotope Ration in Nitrate from Water in North Hangang River, Korea

To identify the origin of major pollutants, we determined the distribution of stable isotopes of δ15N and δ18O in nitrate extracted from water samples and sediments collected at two-month intervals during 2019-2020 from the North Hangang River, Korea. Stable isotope ratios were measured to investigate nitrogen contamination sources in the water system. This study determined that the North Hangang River was affected by soil organic matter, livestock manure, and domestic sewage, and that the streams and rivers flowing into the main stream of the North Hangang River were affected by domestic sewage or livestock manure, resulting in relatively heavy nitrogen isotope ratios. Generally, the concentration of nitrate nitrogen was higher in the inflowing streams (Geumsan, Hongcheon, Mukhyeon, and Gyeongan district) than at the main stream. Nitrogen pollution due to chemical fertilizers and soil organic matter were different in 2019 and 2020, and the ratio of stable nitrogen isotopes decreased owing to the influence of rainfall. Sediment in the North Hangang River has been affected by agricultural soil organic matter and livestock manure, showing the necessity to nitrogen pollutant management, particularly with pollutants such as soil organic matter and livestock manure.