北京西山岩溶地下水化学特征及成因分析

Chemical Characteristics and Genetic Analysis of Karst Groundwater in the Beijing Xishan Area

岩溶地下水是北京市重要的供水水源,西山岩溶水系统地处北京西部上游地区,绝大多数属于生态涵养区,区内分布有多个集中供水水源地,在城市供水安全和生态环境保护中发挥着难以替代的作用.以西山岩溶水系统为研究对象,开展系统地下水水化学组分调查,综合运用统计分析法、离子比例法以及主成分分析法(PCA)等方法,对研究区120件岩溶地下水样品进行了分析研究,探讨了地下水水化学空间分布特征及其形成机制.结果表明:①西山系统地下水水质整体状况较好,属中性、低盐度的优质淡水,84.17%水样属于硬水,地下水化学类型以HCO_(3)-Ca·Mg为主;②地下水化学组分主要受到水-岩石相互作用控制,岩石风化源类型由蒸发岩、硅酸盐和碳酸盐共同控制,以碳酸盐风化为主要控制因素.③主成分分析结果表明,系统地下水化学形成的34.41%归因于碳酸盐岩的溶解,27.33%来源于岩盐、蒸发岩溶解,11.76%来自于含水层沉积物的溶解,10.30%来自于人类活动生活污水的排放.由补给区到径流区再到排泄区,地下水TH、TDS逐渐升高.采煤活动和人类活动是引起山前地带地下水劣变和水化学类型多变的主要因素.未来应进一步加强环境治理,做好点源和面源污染治理,对重点部位持续监测,为生态环境保护提供科学支撑.

As an important water supply source in Beijing,karst groundwater has played an irreplaceable role in the security of urban water supply and ecological environment protection in the past 70 years.The Xishan karst groundwater system,located in the upper reaches of western Beijing,belongs to ecological conservation areas.There are several centralized water supply fields in this area.In this study,the Xishan karst groundwater system was taken as the research object.A total of 120 karst groundwater samples in this area were investigated by using statistical analysis,ion ratio,and principal component analysis(PCA)methods to explore the spatial distribution characteristics and formation mechanism of groundwater hydrochemistry.The research results showed that:①the groundwater quality of the Xishan system was generally good,with the characteristics of neutral pH and low salinity.A total of 84.17% of the water samples were classified as hard water.The chemical type of groundwater was mainly HCO_(3)-Ca·Mg.②The chemical composition of groundwater was mainly affected by the water-rock interaction,and the weathering source of rock was mainly the dissolution of carbonate.③The results of principal component analysis showed that 34.41% of the chemistry formation of groundwater could be explained by carbonate dissolution,27.33% by rock salt and evaporate dissolution,11.76% by aquifer sediment dissolution,and 10.30% by domestic sewage discharge.From the recharge area to the runoff area and then to the discharge area,the TH and TDS gradually increased.Coal mining drainage and human activities were the main factors that caused groundwater degradation and variable hydrochemical types in the piedmont.In the future,it is necessary to further strengthen environmental governance,control point and non-point source pollution,and continuously monitor key areas to provide scientific support for ecological and environmental protection.