Identifying nitrogen sources in intensive livestock farming watershed with swine excreta treatment facility using dual ammonium (δ15NNH4) and nitrate (δ15NNO3) nitrogen isotope ratios axes.

We proposed a novel approach based on dual ammonium and nitrate nitrogen isotope ratios (δ15NNH4 and δ15NNO3, respectively) axes to identify nitrogen sources in intensive livestock farming watersheds, especially those with swine excreta treatment facilities. The δ15NNH4 and δ15NNO3 values in water samples were measured monthly in 2016-2017. Soil and mineral fertilizers, sewage, sewage effluent, manure, and swine effluents were the five sources considered to identify nitrogen sources. The results showed that nitrogen pollution from agricultural activities was well reflected by the seasonal δ15NNH4 and δ15NNO3 patterns in the river, and microbial nitrification was suggested as the dominant nitrogen transformation process in the river. This study revealed that δ15NNH4 and δ15NNO3 axes provided better results than the traditionally used nitrate oxygen (δ18ONO3) and δ15NNO3 axes for identifying nitrogen sources in agricultural watersheds with swine excreta treatment facilities. The mixing model results showed that stream water was severely contaminated with swine effluents (e.g., a mean minimum contribution of 31%), thus affecting the quality of the mainstream (p = 0.068 < 0.10). This study was the first successful application of dual δ15NNH4 and δ15NNO3 axes to better understand nitrogen sources in intensive livestock farming watersheds with swine excreta treatment facilities.

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 (δ15NNH4) and nitrate (δ15NNO3) 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 δ15NNH4 and NH4-N than that between δ15NNO3 and NO3-N for river water samples. Furthermore, the use of δ15NNH4 was more effective than that of δ15NNO3 in evaluating nitrogen variations between May and August in the Cheongmi River because the differences in δ15NNH4 between May and August were more remarkable compared to those in δ15NNO3. Finally, the simultaneous use of δ15NNH4 and δ15NNO3 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.