Coupling stable isotopes to evaluate sources and transformations of nitrate in groundwater and inflowing rivers around the Caohai karst wetland, Southwest China
Coupling stable isotopes to evaluate sources and transformations of nitrate in groundwater and inflowing rivers around the Caohai karst wetland, Southwest China
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耦合稳定同位素评估中国西南部草海喀斯特湿地周边地下水和入流河流中硝酸盐的来源和转化
DOI：
10.1007/s11356-021-13827-4
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发表时间：
2021-04
影响因子：
5.8
通讯作者：
Liao Jiahao
中科院分区：
文献类型：
--
作者：
Cao Xingxing;Yang Shidi;Wu Pan;Liu Shan;Liao Jiahao
硝酸盐是水生生态系统中最常见的污染物之一，特别是在高度脆弱的岩溶含水层中。草海是我国西南地区重要的岩溶湿地，岩溶地表水和地下水是重要的补给水源，硝酸盐随地表水和地下水沿着流入湿地，使湿地水质恶化。因此，弄清草海流域地表水和地下水中硝酸盐的来源，对湿地水环境保护具有重要意义。本研究采用硝酸盐浓度、水化学和多种稳定同位素比值（δ 18 O-H2O、δD-H2O、δ 15 N-NO3 −和δ 18 O-NO3 −）分析草海湿地地下水和入流河流中NO3−的来源和去向。结果表明，在雨季，南部地下水样本中的NO3−浓度超过了世界卫生组织的限值，而其他样本则没有超过限值。地下水中NO3-的平均浓度高于流入河水中NO3-的平均浓度，地下水和流入河水中NO3-的浓度均表现为丰水期>枯水期>平水期。水化学和多种同位素比值表明，硝酸盐的转化是由硝化过程占主导地位，而反硝化作用对NO3-（如同位素证明）在旱季地下水中的转化有影响。根据R（SIAR）稳定同位素分析，污水和粪便是地下水中NO3-的主要来源，而污水、粪便和化肥是流入河水中NO3-的主要来源，因此，应加强农田化肥的科学使用和生活污水的处理，以保障地下水水质，控制河流中NO3-的浓度。
Nitrate is one of the most common pollutants in aquatic ecosystems, particularly in highly vulnerable karst aquifers. In Caohai Lake, an important karst wetland in southwestern China, karst surface water and groundwater are important recharge water sources, and nitrates flow into the wetland along with the surface water and groundwater, degrading the wetland water quality. Therefore, identifying the sources of nitrate in the surface water and groundwater in the Caohai catchment is of great significance to the protection of the wetland water environment. In this study, the nitrate concentrations, hydrochemistry and multiple stable isotope ratios (δ18O-H2O, δD-H2O, δ15N-NO3−and δ18O-NO3−) were used to identify the sources and fate of the NO3−in the groundwater and inflowing rivers around the Caohai wetland. The results showed that the NO3−concentrations in the groundwater samples from the southern side exceeded the WHO limit during the wet season, while other samples did not exceed the limit. The mean concentrations of NO3−in groundwater were higher than those in the inflowing river water, and NO3−concentrations decreased in the order of wet season>dry season>normal season in the groundwater and inflowing rivers. The hydrochemistry and multiple isotope ratios suggest that the nitrate transformation was dominated by nitrification processes, while denitrification had an influence on the transformation of NO3−(as evidenced by isotopes) in groundwater during the dry season. According to the analyses based on a stable isotope analysis in R (SIAR), sewage and manure were the main sources of NO3−in the groundwater, while sewage, manure and chemical fertilizer were the major sources of NO3−in the inflowing river water; therefore, the scientific use of farmland fertilizers and the treatment of domestic sewage should be strengthened to safeguard groundwater quality and control the NO3−concentrations in rivers.
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