Geochemical Processes And Evolution Mechanism Of Karst Water In The Liulin Karst System,Shanxi Province

As one of the top ten karst springs in Shanxi Province,Liulin spring is an important local source for water supply.It is of vital significance to the development of industry and agriculture,urban water supply and ecological protection.In recent years,the contradiction between supply and demand in Liulin spring,located in arid-semiarid climatic region,causes a series of problems on water environment,such as water pollution,land subsidence,and so on,which seriously affects the sustainable utilization and comprehensive planning of groundwater resources,and then constraints the social and economic development.Liulin karst system has long been divided based on the controls of geologic structure on the water flow in natural conditions.However,does the development and utilization of karst water change the water flow system or affect the decline of spring flows?What brought about the differences on hydrochemistry of springs?These questions may affect the sustainable utilization of water resources.So,we will provide some proves for the decline of spring flows based on the division of karst water flow paths and the geochemical processes,and scientific evidences for planning on the sustainable utilization of karst water.The purpose of this study is to reveal the evolution mechanism of groundwater quality in karst groundwater system from Liulin,northern China.Based on the comprehensive analyses of landform,geologic structures and hydrogeological conditions,multiple methods including hydrochemical data,stable isotope and geochemical modeling were used to discern the karst water flow path,clarify the geochemical processes,propose the conceptual model of geochemical processes,then give interpretations on the differences of hydrochemistry of springs located at the both sides of Sanchuan River,and eventually reveal the evolution mechanism of groundwater quality.There is of important theoretical significance for knowing Liulin karst system and hydrochemical evolution processes,and of important practical significance for the continuable utilization and protection of karst water resources in a semi-arid region.The major conclusions of the study are as follows:(1)The karst groundwater flow system was obviously controlled by geologic structure and exploitation and utilization of groundwater.Two local flow systems,the northwestern flow system(flow path I)and eastern flow system(flow path ?),were developed due to the occurrences of Wangjiahui-Zaolin anticline.The former one obtained the recharge in the recharge area,and then moved towards the Liulin spring zone through narrow passage and discharged by springs at the north of Sanchuan River.The latter flowed towards the west after receiving the recharge,and was blocked due to the barrier of Lishi syncline and discharged by well exploitation for drinking water.In addition,the local flow system(flow path ?)in the south of Sanchuan River moved towards the Liulin spring zone and discharged by springs at the south of the River.(2)The dominant geochemical processes were the dissolution of soluble minerals which controlled the chemistry of karst water in Liulin.The dissolution of carbonates occurred in the whole aquifer,but it was the dominated process in the recharge area.In the runoff area,the additional processes were the dissolution of gypsum,halite and mirabilite,cation exchange and dedolomitization.In the discharge area,the process of mixing/dilution with surface water was added.In the stagnant area,the process of sulfate reduction was added except for the dissolution of gypsum and halite,dedolomitization and cation exchange,since it was a kind of strong reducing environment.(3)The characteristics of more saline of the springs in the north than those in the south of Sanchuan River could be attributed to the effect of geologic setting and recharge sources.Controlled by the folds and faults,the springs in the north of Sanchuan River were recharge from the local flow system in the north with slow runoff and long-time water-rock interaction,while the ones located in the south,were recharged from the local flow system in the south,showing faster runoff and short-time water-rock interaction.