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大连大魏家水源地位于中国北方典型滨海岩溶地区。近30年来,地下淡水的不合理开采造成的地下水位降落漏斗引发了严重的海水入侵。以大魏家水源地为研究对象,通过大量的水文地质调查和水化学及同位素采样测试分析,探讨海水入侵形成的水动力条件,通过分析滨海岩溶含水层中地下水主要水化学和多种同位素(δ2H-δ18O,δ34S,δ13C)组成特征,识别了海水入侵过程中发生的主要水文地球化学作用,并对其进行了定量模拟,从而阐明了岩溶含水层中的海水入侵机理。研究结果表明:大连大魏家海水入侵主要通道为大魏家地区存在的导水断裂、岩溶裂隙以及第四系松散地层。对δ2H-δ18O同位素的组成分析表明,研究区地下水主要来自大气降水补给,结合Cl-浓度分布,认为除海水入侵淡水含水层后增加了地下水中的盐分外,浅层地下水的蒸发也对地下水中盐分的累积起到了重要作用。根据不同水体中δ34SSO4,δ13CHCO3等同位素特征,结合水化学成分(如SO2-4,Cl-)分析认为,研究区微咸水和咸水并不是地下水淡水和海水简单混合而成。利用反向水文地球化学模拟揭示了控制滨海岩溶含水层中水化学演化的主要水文地球化学反应有方解石、蒙脱石和石膏的溶解作用,伊利石的沉淀作用以及Ca-Na离子交换作用,伴随着CO2的释放。
Dalian Wei source of water in northern China typical coastal karst area. In the past 30 years, groundwater level dropping funnel caused by unreasonable exploitation of underground fresh water triggered serious seawater intrusion. Based on a large number of hydrogeological surveys, hydrochemical and isotopic sampling tests, the hydrodynamic conditions for the formation of seawater intrusion were discussed. Based on the analysis of the main hydrochemical and isotope compositions of groundwater in coastal karst aquifers, δ2H-δ18O, δ34S and δ13C). The major hydrogeochemical processes that occurred during the seawater intrusion were identified and quantitatively simulated to illustrate the mechanism of seawater intrusion in karst aquifers. The results show that the main channel of seawater intrusion in the Dayewei Formation in Dalian is the water-bearing faults, karst fissures and quaternary loose strata in the Wei-Wei area. The compositional analysis of δ2H-δ18O isotope shows that groundwater in the study area mainly comes from atmospheric precipitation recharge. Combined with the distribution of Cl-concentration, it is considered that the evaporation of shallow groundwater is also harmful to groundwater in addition to the increase of salt in groundwater after seawater invades freshwater aquifer Salt accumulation has played an important role. According to isotope characteristics of δ34SSO4, δ13CHCO3 and other isotopes in different water bodies and combined with chemical composition (such as SO2-4, Cl-), it is considered that brackish and brackish water in the study area is not a simple mixture of groundwater freshwater and seawater. The use of reverse hydrogeochemistry simulations revealed that the major hydrogeochemical reactions that control the chemical evolution of water in the coastal karst aquifers are the dissolution of calcite, montmorillonite and gypsum, the sedimentation of illites, and the Ca-Na ion exchange, with CO2 release.