岩溶流域不同水体硝酸盐的来源解析

Analysis of Nitrate Sources in Different Waters of a Karst Basin

为解析岩溶流域不同水体中硝酸盐的来源和转化过程,运用δ15N-NO-3、δ18O-NO-3和δ18O-H2O多同位素示踪技术和水化学分析方法,对地表水和地下水的硝酸盐时空分布特征、来源及转化过程进行分析,并利用SIAR模型,计算不同端元对水体硝酸盐的贡献比例.结果表明,研究区水体溶解性无机氮以NO-3-N和NH+4-N两种形态为主,地下水样品中的NO-3-N浓度在平水期和枯水期的超标率分别为7.89%和16.67%.时间上,枯水期水体硝酸盐平均浓度高于平水期.空间上,旱地集中区(凯伦河至松柏山水库坝前区域)地下水硝酸盐浓度明显高于水田集中区(干河区域),旱地和建设用地集中区(凯伦河区域)地表水硝酸盐浓度普遍较高.水体硝酸盐转化过程以硝化作用为主,土壤有机氮、粪便污水和化肥为水体硝酸盐的主要来源,对地表水硝酸盐的贡献比例分别为36.7%、 34.7%和28.6%,对地下水硝酸盐的贡献比例分别为39.9%、 34.9%和25.2%.

To identify the sources and transformation processes of nitrate in surface water and groundwater in a karst basin,water samples were collected in the Songbai Mountain Reservoir basin during the normal and dry seasons.The spatio-temporal distribution,sources,and transformation processes of nitrate in the waters were analyed using a hydrochemical and stable isotopic(δ15N-NO3-,δ18O-NO3-,andδ18O-H2O)multi-tracing approach.The contribution rates of different nitrate sources in surface and groundwater were estimated based on the SIAR model.The results showed that NO3--N and NH4+-N were the main species of dissolved inorganic nitrogen in the waters.The over standard rate of NO3--N in groundwater was 7.89%in the normal season and 16.67%in the dry season.Temporally,the nitrate concentrations of waters in the dry season were higher than those in the normal season.Spatially,the nitrate concentrations of groundwater around dryland areas(from the Kailun River to the Songbai Mountain Reservoir)were higher than those of paddy fields(Ganhe River),and the nitrate concentrations of surface water in dryland and construction sites(Kailun River)were generally high.Nitrification was the dominant process in the waters.The nitrate in the waters mainly came from soil organic nitrogen,manure/sewage,and chemical fertilizers;their contribution rates to nitrate were 36.7%,34.7%,and 28.6%for surface water and 39.9%,34.9%,and 25.2%for groundwater,respectively.Nitrate pollution in the waters was mainly affected by agricultural activities and the discharge of sewage;appropriate control measures such as water and fertilizer regulation for farmland and treatment of rural sewage should be strengthened.