基于多环境介质氮素和同位素的滦平盆地地下水硝酸盐来源示踪

Source of Groundwater Nitrate in Luanping Basin Based on Multi-environment Media Nitrogen Cycle and Isotopes

选择密云水库上游承德市滦平盆地为研究区,通过不同土地利用类型地下水"三氮"含量、土壤全氮含量和包气带可溶硝态氮含量,结合水体硝酸盐氮氧双同位素、硫酸盐硫氧双同位素多种环境同位素特征和地下水放射性碳同位素测年示踪硝酸盐来源.结果表明,滦平盆地水体氮形态以硝态氮为主,地下水NO^-3质量浓度与居民用地、旱地土地利用类型显著相关,硝酸盐污染主要集中于居民建设用地和农用地区域浅层地下水中.13.79%地下水样品NO^-3质量浓度超过国标(GB/T 14848-2017)地下水硝酸盐限值Ⅲ类标准,超标范围为1.04~3.86倍;37.93%地下水样品NO^-3质量浓度超WHO饮用水硝酸盐浓度限值,超标范围为1.08~6.83倍.地下水NO^-3质量浓度、土壤全氮和浅层土壤可溶硝态氮空间变异受结构性因素和人为因素共同作用影响.地下水硝酸盐来源主要为家畜粪尿和生活污水混合污染,其次为化学肥料淋滤;盆地山前地下水径流区包气带-地下水氮循环主导过程为硝化作用.以盆地系统作为独立单元研究水环境硝酸盐污染来源和归趋规律,对流域整体地下水污染防治和修复具有重要意义.

The multi-environment media of water,surface soil and vadose zone soil samples were collected in the upstream of Miyun Reservoir,in the Luanping Basin of Chengde City,Hebei Province.The aim was to identify the pollution source,ratio,spatial distribution,migration,and transformation characteristics of nitrogen in groundwater.Hydrogeochemistry,soil total nitrogen,and dissolved nitrate nitrogen of vadose zone soil analysis and a multi isotope tracer technique ofδ15N-NO3 andδ18O-NO3,δ34S-SO4 andδ18O-SO4,δ14C,combined with land-use type analysis and geostatistics,were used in the study.The results showed that nitrate was the main form of nitrogen in the groundwater of the Luanping Basin.The NO^-3 concentration of groundwater was significantly correlated with the land-use types of residential land and cultivated land where the nitrate pollution of shallow groundwater was mainly distributed.Of the groundwater samples,13.79%exceeded the National StandardⅢfor Groundwater(GB/T 14848-2017)of NO^-3 concentration value,while the excess multiple was 1.04-3.86,and 37.93%of the groundwater samples exceeded the World Health Organization NO^-3 concentration standard value.The excess multiple was 1.08-6.83.The spatial variation of groundwater NO^-3 concentration,soil total nitrogen and surface soil dissolved nitrate nitrogen of vadose zone was affected by the combination of natural structural factors and anthropogenic factors.The source of groundwater nitrate was mainly from livestock manure and domestic sewage,followed by chemical fertilizer leaching.The nitrogen cycle in the aeration zone-groundwater-dominated nitrogen circulation in the groundwater runoff area of the piedmont basin was nitrification.These findings are highly significant for the prevention and remediation of groundwater pollution when viewing the basin system as an independent unit,and for studying the sources and fate of nitrate pollution in the water environment.