混合土地利用下长河流域硝酸盐污染源解析

Analysis of nitrate pollution sources in Changhe River Basin under mixed land use

水环境中硝酸盐含量持续增加引发的环境问题已受到全球关注.为弄清混合土地利用下长河流域硝酸盐污染问题,本研究通过探究溶解态无机氮(DIN)各指标及氮氧同位素的时空变化特征,利用水化学与双稳定同位素示踪技术识别了硝酸盐的来源和转化,并结合贝叶斯稳定同位素混合模型(SIAR)量化了其主要来源,同时研究了土地利用对流域硝酸盐源时空分配的影响.结果表明:硝态氮是研究区水体中DIN存在的主要形式.同位素证据表明,氮的迁移和转化过程以水体中硝化作用为主,反硝化与同化作用对其组成并未造成显著影响.源解析结果显示,枯、丰两个水期水体硝酸盐污染源均以粪便和污水为主,且土壤氮和化肥贡献率在丰水期显著升高.此外,研究区土地利用对硝酸盐源分配在时间上影响显著,而空间上影响较弱.研究显示,人类密集活动对流域水环境影响显著,控制粪便和污水排放的同时减少氮肥的过度使用对于控制区域硝酸盐污染至关重要.

Environmental problems caused by the increasing nitrate content in aquatic environments have received global attention.To clarify nitrate pollution in the Changhe River Basin under mixed land use pattern,this study explored the spatio-temporal variation characteristics of dissolved inorganic nitrogen(DIN)indices and nitrogen and oxygen isotopes,identified the sources and transformations of nitrate via hydrochemistry and the double stable isotope trace technique,and determined the primary nitrate via Stable Isotope Analysis in R(SIAR).Additionally,the effects of land use on the spatio-temporal distribution of nitrate sources in the basin were discussed.Results showed that nitrate nitrogen was the main DIN present in the water bodies of the study area.Isotopic evidence indicated that nitrogen transportation and transformation were dominated by nitrification in a water column,and denitrification and assimilation showed no significant effect on DIN composition.The results of source analysis showed that manure and sewage were the main sources of nitrate during the dry and wet seasons,and the contribution rates of soil nitrogen and fertilizer increased remarkably during the wet season.Moreover,land use pattern in the study area showed a considerable temporal effect but a weak spatial effect on nitrate source allocation.Intensive human activities have a significant impact on the aquatic environment in the watershed.Controlling manure and sewage discharge and reducing the excessive use of nitrogen fertilizers are crucial to regulate regional nitrate pollution.