Assessment and identification of nitrogen pollution sources in the Cheongmi River with intensive livestock farming areas, Korea

This study aimed to develop methods for assessing and identifying nitrogen sources in the Cheongmi River, Korea, that has intensive livestock farming areas (ILFA) in its watershed. The assessment focused on the feasibility of the simultaneous use of stable isotopic compositions of ammonium (δ 15 N NH4 ) and nitrate (δ 15 N NO3 ) for identifying the main nitrogen pollution sources in the Cheongmi River watershed. Our results suggested that the organic nitrogen (Org-N) to total nitrogen (T-N) ratio could be used as an indicator for assessing the effect of livestock excreta on waterways in ILFA. We observed that the T-N concentration was much more strongly affected by livestock excreta than the T-P concentration in the mainstream of the Cheongmi River. The positive correlation was more significant between δ 15 N NH4 and NH 4 -N than that between δ 15 N NO3 and NO 3 -N for river water samples. Furthermore, the use of δ 15 N NH4 was more effective than that of δ 15 N NO3 in evaluating nitrogen variations between May and August in the Cheongmi River because the differences in δ 15 N NH4 between May and August were more remarkable compared to those in δ 15 N NO3 . Finally, the simultaneous use of δ 15 N NH4 and δ 15 N NO3 showed that the dominant nitrogen source at sites M3, M4, M5, and M6, specifically in May, was livestock excreta in the Cheongmi River. The results of this study could be used for sustainable water quality management in the Cheongmi River watershed.