Sheng Ting, Yang Ping-Heng, Xie Guo-Wen, Hong Ai-Hua, Cao Cong, Xie Shi-You, Shi Wei-Yu
Chongqing Key Laboratory of Karst Environment, School of Geographical Sciences, Southwest University, Chongqing 400715, China.
Field Scientific Observation & Research Base of Karst Eco-environments at Nanchuan in Chongqing, Ministry of Natural Resources, Chongqing 400715, China.
Huan Jing Ke Xue. 2018 Oct 8;39(10):4547-4555. doi: 10.13227/j.hjkx.201804046.
The objectives of this study were to reveal the sources of nitrate and the ratio of karst in an agricultural basin based on a N and O isotope technique and quantitative calculation of the IsoSource model. From May to October 2017, six sampling points in the Qingmuguan river basin, Chongqing, were monitored every 24 d. Results showed that there was a great risk of nitrate pollution in the underground river system, because most NO-N concentrations of the sampling points exceeded the threshold. Spatially, NO-N concentrations in the underground river increased from upstream to downstream. Temporally, NO-N concentrations of Fishpond and Yankou Ponor upstream and Jiangjia Spring downstream were impacted by agricultural fertilizer from May to June and fluctuated from June to September due to precipitation. With decreased agricultural activities, NO-N concentrations gradually decreased after September. NO-N concentrations were high in midstream soil water. Daluchi, in the middle and lower reaches, maintained relatively low NO-N concentrations with stable fluctuations. Dual N and O isotopic compositions suggested that the upstream nitrates were derived from soil organic nitrogen and a mixture of manure and sewage. The midstream nitrates originated from soil organic nitrogen and NH from fertilizer and rain. Nitrates in the middle and lower reaches were derived from the mixing of manure and sewage, soil organic nitrogen, and NH from fertilizer and rain. Jiangjia Spring, the outlet of the underground river, was seriously polluted by nitrates. It is believed that soil organic nitrogen, NH in fertilizer and rain, the mixing of manure and sewage, and NO in precipitation were the main nitrate sources in the outlet. Nitrate source contribution of the outlet was calculated with the IsoSource model. The calculation results showed that manure and sewage, soil organic nitrogen, NH in fertilizer and rain, and NO in precipitation contributed 46.4%, 32.6%, 18.6%, and 2.4%, respectively.
本研究的目的是基于氮和氧同位素技术以及IsoSource模型的定量计算，揭示农业流域硝酸盐的来源和岩溶比例。2017年5月至10月，对重庆青木关流域的6个采样点每24天进行一次监测。结果表明，地下河系统存在很大的硝酸盐污染风险，因为大多数采样点的NO₃-N浓度超过了阈值。在空间上，地下河中的NO₃-N浓度从上游到下游增加。在时间上，上游的鱼塘和堰口溶潭以及下游的江家泉的NO₃-N浓度在5月至6月受到农业肥料的影响，6月至9月因降水而波动。随着农业活动的减少，9月后NO₃-N浓度逐渐下降。中游土壤水中的NO₃-N浓度较高。中下游的大池NO₃-N浓度保持相对较低且波动稳定。氮和氧的双重同位素组成表明，上游硝酸盐来自土壤有机氮以及粪便和污水的混合物。中游硝酸盐源于土壤有机氮以及肥料和雨水的铵态氮。中下游的硝酸盐来自粪便和污水、土壤有机氮以及肥料和雨水的铵态氮的混合。地下河出口江家泉受到硝酸盐的严重污染。据信，土壤有机氮、肥料和雨水中的铵态氮、粪便和污水的混合以及降水中的硝酸盐是出口处主要的硝酸盐来源。利用IsoSource模型计算了出口处硝酸盐源的贡献率。计算结果表明，粪便和污水、土壤有机氮、肥料和雨水中的铵态氮以及降水中的硝酸盐分别贡献了46.4%、32.6%、18.6%和2.4%。
