Abstract：
Miyun Reservoir plays a vital role as a source of drinking water for Beijing, however it grapples with nitrogen contamination issues that have been poorly understood in terms of their distribution, source, and associated health risks. This study addresses this knowledge gap by employing data on nitrate nitrogen (NO3--N), chloride (Cl-), dual isotopic compositions of NO3- (δ15N-NO3- and δ18O-NO3-) data in water ecosystems, systematically exploring the distribution, source and health risk of nitrogen contaminants in Miyun reservoir watersheds. The results showed that over the past 30 years, surface water runoff has exhibited a notable decrease and periodic fluctuations due to the combined influence of climate and anthropogenic activities, while the total nitrogen (TN) concentration in aquatic ecosystems presented an annual fluctuating upward trend. The TN concentration in the wet season was predominantly elevated because a large amount of nitrogen contaminants migrated into water ecosystems through heavy rainfall or river erosion. The concentration of NO3--N, the main contaminant of the water ecosystems, showed distinct variations across different watersheds, followed as rivers over the Miyun reservoir. Moreover, NO3--N levels gradually increased from upstream to downstream in different basins. NO3--N in surface water was mainly derived from the mixture of agricultural ammonia fertilizer and sewage and manure, with a minority of samples potentially undergoing denitrification. Comparatively, the main sources of NO3--N in groundwater were soil N and sewage and manure, while the denitrification process was inactive. The carcinogenic risks caused by NO3--N in groundwater were deemed either nonexistent or minimal, while the focus should predominantly be on potential non-carcinogenic risks, particularly for infants and children. Therefore, it is crucial to perform proactive measures aimed at safeguarding water ecosystems, guided by an understanding of the distribution, sources, and associated risks of nitrogen contamination.
摘要：
密云水库作为北京的饮用水来源起着至关重要的作用,然而，它与氮污染问题作斗争，这些问题在其分布方面知之甚少，来源,和相关的健康风险。本研究通过使用硝酸盐氮(NO3--N)的数据来解决这一知识差距，氯化物(Cl-),水生态系统中NO3-（δ15N-NO3-和δ18O-NO3-）数据的双同位素组成，系统地探索分布，密云水库流域氮污染物来源及健康风险分析.结果显示，在过去的30年里，由于气候和人为活动的共同影响，地表水径流显着减少和周期性波动，而水生生态系统中的总氮（TN）浓度呈现年度波动上升趋势。雨季的TN浓度主要升高，因为大量的氮污染物通过大雨或河流侵蚀迁移到水生态系统中。NO3--N的浓度,水生态系统的主要污染物，在不同的流域表现出明显的差异，随后是密云水库上空的河流。此外，不同盆地NO3--N水平由上游向下游逐渐升高。地表水中NO3--N主要来源于农业用氨肥与污水、粪肥的混合物,少数样品可能会经历反硝化。相对而言,地下水中NO3--N的主要来源是土壤氮、污水和粪便，而反硝化过程不活跃。地下水中NO3--N引起的致癌风险被认为不存在或极小，虽然重点应主要放在潜在的非致癌风险上，特别是对于婴儿和儿童。因此,采取旨在保护水生态系统的积极措施至关重要，在对分布的理解的指导下，来源,以及相关的氮污染风险。
