桂林甑皮岩岩溶地下水硝酸盐来源与转化

Sources and transformation of nitrate in karst groundwater of Zengpiyan site,Guilin

峰林平原是人类活动和居住的密集区,也是岩溶地下水系统的主要径流、排泄地段,地下水资源丰富。随着城市化的发展,地下水硝酸盐污染问题日渐突出。为研究桂林甑皮岩岩溶地下水硝酸盐来源与转化,分别于2018年10月、2019年2月、3月和4月采集地下水样,利用常规水化学及氮氧同位素技术识别硝酸盐来源与转化。结果表明:甑皮岩地下水中NO3-浓度在0~19.523 mg·L-1,δ15N-NO3-和δ18O-NO3-分别在-0.17‰~45.12‰和-5.82‰~16.47‰。硝酸盐氮氧同位素数据表明,甑皮岩地下水硝酸盐来源主要为粪便及污废水,少量来自降雨中的NH4+和土壤有机氮。受岩溶介质不均一性的控制,甑皮岩地下水中NO3-浓度、δ15N-NO3-和δ18O-NO3-均表现出明显的空间变异性。甑皮岩地下水硝酸盐的转化过程复杂,受控于季节和岩溶介质不均一性,表现为旱季以反硝化为主,雨季则以硝化过程为主。厘清硝酸盐来源与转化为治理甑皮岩地下水硝酸盐污染提供一定的科学依据。

The peak-forest plain is a concentration area of human activities and living,and also the main runoff and discharge section of karst groundwater systems,with rich groundwater resources.With the development of urbanization,the problem of groundwater nitrate pollution has becomes increasingly prominent.In order to study the source and transformation of nitrate in the karst groundwater of Zengpiyan site in Guilin,groundwater samples were collected in October 2018,February 2019,March 2019 and April 2019,respectively.By virtue of these samples,using conventional water chemistry and nitrogen and oxygen isotope techniques,this work identified groundwater nitrate sources and transformation process.The results show that the concentration of NO3-in the groundwater of Zengpiyan is 0-19.523 mg·L-1,and δ15N-NO3- and δ18O-NO3-are between-0.17‰-45.12‰ and -5.82‰-16.47‰,respectively.According to the data of nitrogen and oxygen isotopes of groundwater in the study area,the source of nitrate in groundwater is mainly feces and wastewater,a small amount of nitrate comes from NH4+ in rainfall and soil organic nitrogen.Controlled by the heterogeneity of karst medium,NO3-concentration,δ15N-NO3- and δ18O-NO3-in the groundwater of Zengpiyan show obvious spatial variability.The process of nitrate transformation of groundwater in Zengpiyan is complex,which is controlled by seasons and the heterogeneity of karst medium.Denitrification is the main process in dry seasons and nitrification in rainy seasons.Clarifying the source and transformation of nitrate can provide a scientific basis for the control of nitrate pollution in groundwater of the Zengpiyan site.