中文摘要：

全球变化背景下海岸带地区面临多种环境压力,快速城镇化和人类活动导致河流与海湾营养盐污染和富营养化问题加重,污染溯源是水体达标方案编制与实施的重要环节.兼顾科学性与操作性,本文基于综合溯源思路,以厦门湾河流为例,于水质较差的枯水期开展水系沿程梯度调查,进行氮的生物地球化学过程解析,结合硝酸盐氮氧双位素及土地利用统计分析,探明氮污染关键源区和氨氮超标成因.结果表明,研究区63%的站位水中氨氮占无机氮的50%以上,沿下游方向氨氮污染加重,且与城镇与农村宅基地、渔塘的面积占比均呈正相关.土壤氮、粪肥及污水和化肥贡献了硝酸盐89%～91%的来源.最后,提出了污染减排（控源）、生态修复（增容）、以海定陆（统筹）的水体达标策略,为我国水污染防治与管理提供方法示范.

英文摘要：

Global change has imposed multiple environment stresses on coastal waters. Rapid urbanization and increasing human perturbation resulted in severe nutrient loadings followed by eutrophication in coastal waters. Therefore source identification and tracking become critical for water quality management. Based on its feasibility, here we conducted a case study for Xiamen coastal river, in order to track possible nitrogen pollution sources. Water quality was measured in the whole river during dry season, in order to explore the biogeochemical processes of nitrogen. With dual isotopic techniques （δ15N and δ18O） and statistical information of land uses, we identified the key source of nitrogen pollutants, and clarified the causes leading to ammonium levels of exceeding standards. Current results show that ammonium was the dominant form （〉50%） of dissolved inorganic nitrogen at 63% sampling sites. Ammonium concentration increased along river downward and significantly correlated with the areal proportion of built/residence lands and aquaculture ponds in associate catchment. Soil organic nitrogen, manure and sewage, and synthetic fertilizer contribute 89%～91% of nitrate sources. Therefore, we proposed that nitrogen emission abatement, ecological restoration and integrated sea-land management should be considered together for improving water quality management. This study provides an important reference for national water pollution control and management.