Hydrogeochemical Characteristics And Evolution Of Karst Groundwater In Lancun Spring Basin,Taiyuan

The flow field and hydrochemistry field of the karst groundwater in Lancun spring area of Taiyuan city are destroyed for over exploitation.At present,the changing characteristics and laws of the hydrochemistry field of the karst groundwater are not clear.For the problem,this paper analyzes the hydrochemical characteristics,circulation mode and renewal rate of karst groundwater in Lancun spring basin by hydrochemical isotope diagram,correlation,principal component analysis,groundwater dating and ion proportion analysis,determines the formation mechanism and control factors of hydrochemical components of karst groundwater,and carries out reverse hydrogeochemical model by PHREEQC.The results show that:In Dongshan karst groundwater system,the karst groundwater located to the east of Fanzhuang fault is mainly supplied by atmospheric precipitation,which is the mixture of5-10-year-old groundwater and more than 50-year-old groundwater,with rapid renewal rate.The hydrochemical types are HCO₃-Ca·Mg,and the hydrochemical composition is mainly affected by the dissolution of Calcite and dolomite in the groundwater bearing medium;The age of karst groundwater in Dayu basin is 2145-6552 years,and the renewal rate is slow.The hydrochemical type is HCO₃-Ca·Mg,and the hydrochemical component comes from the dissolution of carbonate rocks;The age of karst water in Yangqu basin is 2799-9764 years,with slow renewal rat.The hydrochemical type is mainly HCO₃-Ca·Mg.The hydrochemical composition is affected by the dissolution of carbonate rock.The distribution characteristics of Sr elements in the karst groundwater of Dayu basin and Yangqu basin are quite different,so the Dongshan karst groundwater system can be divided into yangxinghe karst groundwater subsystem and Wuhe karst groundwater subsystem according to the hydrochemical characteristics.The age of karst groundwater in the west of Nitun basin is 5-10 years,and the renewal rate is fast.The hydrochemical types are HCO₃-Ca and HCO₃-Ca·Mg.The hydrochemical components are controlled by the dissolution of carbonate rock;The age of karst groundwater in Nitun basin is 419-5149 years,the hydrochemical type is HCO₃-Ca·Mg,and the hydrochemical components are mainly controlled by the dissolution of carbonate rocks;The age of karst groundwater is 1942-2128.The hydrochemical types are HCO₃-Ca·Mg and HCO₃·SO₄-Ca·Mg.The hydrochemical components are controlled by the dissolution of carbonate rocks and mixing.The simulation results of PHREEQC show that the water rock interaction in Karst Groundwater in spring basin is mainly the dissolution and sedimentation of dolomite,calcite and gypsum.In Dongshan karst groundwater system,the supply runoff area is located to the east of Fanzhuang fault.The runoff condition of karst groundwater is good,which mainly occurs dolomite,calcite and gypsum dissolution.In the catchment of the basin to the west of Fanzhuang fault,All minerals are precipitated,and the precipitation amount of the two fault basins is different for the difference of ion concentration of karst groundwater;In the Xishan karst groundwater system,all minerals in the recharge runoff area to the west of Nitun basin are dissolved,indicating that the runoff condition of karst groundwater in this area is good,which is conducive to the occurrence of water rock interaction.In the catchment of Nitun basin,all minerals are deposited,which indicates that the runoff condition of karst groundwater in this area is poor,and the concentration of ions is increased,which is not conducive to the water rock interaction;In the catchment of Lancun spring,the karst groundwater receives the supplement of Fenhe River water and atmospheric precipitation,at the same time,supplies the corrosive CO2（g）lost by the karst water in the runoff process.In addition,the karst groundwater is exploited frequently and the hydrodynamic conditions are good,so the dissolution occurs.The simulation results are consistent with it.All minerals are dissolved and CO2（g）is consumed.