典型岩溶地下河流域水体中硝酸盐源解析

Identifying Nitrate Sources in a Typical Karst Underground River Basin

地下河是岩溶地区地下水赋存运动的主要场所和重要水源,近年来,硝酸盐污染严重.为解析典型岩溶地下河流域水体中硝酸盐的来源,利用δ15N-NO3^-、δ18O-NO3^-和δ18O-H2O稳定同位素示踪技术开展研究,并通过SIAR稳定同位素模型,对不同污染源的贡献率进行了定量识别,同时阐明了土地利用类型对流域水体硝酸盐分布及来源的影响.结果表明:①降雨/化肥中的氨盐、土壤有机氮和粪肥污水是流域内水体硝酸盐的主要来源;②流域内水体硝酸盐的转化过程主要以硝化作用为主导,水体硝酸盐氮氧同位素初始值未受分馏影响;③基于SIAR模型,不同端元对流域内水体硝酸盐的贡献比例呈季节性差异,化肥、土壤有机氮和粪便污水对丰水期流域内水体硝酸盐的贡献比例分别为57.07%、34.06%和8.87%;对流域内枯水期水体硝酸盐的贡献比例分别为34.14%、33.02%和32.84%.

Underground rivers are an important source of groundwater in karst area.Recently,nitrate pollution of underground rivers has become a serious issue.To identify the sources of nitrate in Guancun typical karst underground river basin,stable isotope techniques(δ15N-NO3^-,δ18O-NO3^-,andδ18O-H2O)were applied in this study.The contribution rates of different nitrate sources in groundwater were quantitatively identified based on the stable isotope analysis in R(SIAR)model,and the influence of land use type on nitrate distribution and source in watershed water was clarified.The results showed that①nitrate mainly came from fertilizers,soil organic nitrogen,and manure/sewage based to the isotopic composition of nitrate nitrogen and oxygen isotopes.It was revealed that non-point sources significantly contributed to nitrate in waters of the Guancun underground river basin.②Nitrification dominated the formation process of nitrate in groundwater,and the initial values of nitrogen and oxygen isotopes were not affected by fractionation.③Based on SIAR,the contribution of different sources to nitrate in water in the basin varied seasonally,and the contributions of fertilizer,soil organic nitrogen,and manure/sewage to nitrate were 57.07%,34.06%,and 8.87%in the wet season and 34.14%,33.02%,and 32.84%in the dry season,respectively.Overall,the present study quantitatively evaluated the temporal variations of nitrate sources in a typical karst groundwater river basin and provided a theoretical foundation for prevention and control management of non-point source pollution and watershed management in karst areas.