Identification of geochemical processes by hydrogeochemical analysis in karst aquifers of a semi-arid region, Northern China

Understanding the groundwater evolution has always been a challenging work for geochemists and hydrogeologists. The purpose of this study is to reveal the evolution mechanism of groundwater quality in karst groundwater system from Liulin, northern China. Multiple hydrochemical indicators were used to differentiate the dominant geochemical processes of hydrogeochemical evolution. The results suggested that the dissolution of calcite and dolomite widely occurred in Liulin karst water system, especially in the recharge area, and the dissolution of halite, gypsum and mirabilite locally occurred in the runoff and discharge areas of the system. Dedolomitization driven by gypsum dissolution was found in the runoff areas of karst aquifers on the north and south of Liulin springs. Cation exchange between Ca2+, Mg2+ and Na+ was proved to take place in the runoff and discharge areas. Besides, the springs in the north of Sanchuan River were more saline than those in the south, which could be attributed to the common effect of geologic background and recharge sources. Eventually, an updated conceptual model of the geochemical processes in Liulin karst water system was developed, which illustrated the chemical evolution and geochemical processes of karst groundwater along the flow paths.