基于水化学和氮氧双同位素的地下水硝酸盐源解析

为定性及定量识别地下水中氮的污染来源，比例及迁移转化特征，对河北省张家口市宣化区洋河北岸主要供水区的地下水进行取样分析.基于土地利用类型，综合利用水化学分析方法耦合δ¹⁵N-NO₃^-，δ¹⁸O-NO₃^-双同位素示踪技术对研究区地下水硝酸盐污染来源，贡献率及迁移转化规律进行判断.研究结果表明：研究区氮污染以NO₃^-为主，12处采样点4次采样过程中约77%超出世界卫生组织标准（10mg/L）的限值，其污染在2018年8月（夏季）较为严重，空间浓度插值结果显示硝酸盐呈现出沿河及远岸点位浓度相对较低，中间较为稳定区域浓度较高的空间特征，并表现出不同土地利用类型上污染程度的差异性：旱地浓度最高，城镇次之.稳定同位素模型（SIAR）显示地下水硝氮污染来源中粪肥及生活污水占45.37%，土壤氮来源为41.39%，降水和化肥中NH₄⁺来源占13.24%，与研究区以城镇和耕地为主的土地利用现状较为一致.此外，同位素特征值结果显示氮的迁移转化过程以硝化作用为主.文可为地下水氮的污染来源解析提供更加精准，全面的分析方法进而为污染的防治提供优先治理建议.

Source of nitrate in groundwater based on hydrochemical and dual stable isotopes

The groundwater samples of the north bank of Yanghe, Xuanhua District, Zhangjiakou City, Hebei Province were selected, to identify the pollution source, ratio, migration and transformation characteristics of nitrogen in groundwater by qualitative and quantitative methods. Land type analysis, hydrogeochemistry analysis, and isotope tracer technique of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- were used in the study. The results showed that the main contaminant of nitrogen pollution was NO₃^- in the study area, and 77% samples during four sampling sessions at 12 sampling points exceeded World Health Organization standard value 10mg/L. The serious pollution period was in August 2018. According to spatial concentration interpolation results, the lower nitrate concentration was along the river and the offshore area, and the higher was in the middle area. Different land use type had different concentration, dry land had highest and urban system had higher concentration. The results of stable isotope model (SIAR) showed that the proportion of groundwater nitrate pollution sources were 45.37%, 41.39%, and 13.24% for manure and domestic sewage, soil nitrogen, and NH₄⁺ in rainfall and fertilizers. The result was consistent with the land use types. Besides, nitrification was dominated migration and transformation process of nitrogen. The study can provide more accurate and comprehensive analysis method for groundwater nitrogen pollution sources analysis, and recommendation for groundwater pollution control.