Hydrochemical Characteristics and Formation Mechanism of Groundwater in the Liulin Karst System

The Liulin karst system is typical of hydrogeological systems in northwestern China, with a group of springs as the dominant mechanism for regional groundwater discharge. To reveal the hydrochemical formation mechanism of the Liulin karst groundwater system, we studied the hydrogeochemical processes of karst groundwater in aquifers at the base of the hydrogeological investigation. Then starting from the chemical composition of karst groundwater together with the recharge-runoff - discharge process of groundwater systems, we analyzed the solutes origin and the dissolved mineral facies of the groundwater chemical composition. The results showed that the anionic and cationic compositions of karst water were different in recharge, runoff and discharge areas, with the main anions of HCO3- and SO42- in recharge areas, and HCO3- and Cl- in runoff and discharge areas, as well as the main cationic for Ca2+ and Na+, of which the molar concentrations of Ca2+ was greater than Na+ in recharge areas and contrary to the runoff and discharge areas. Karst water was influenced by carbonate and evaporite dissolution while flowing through the aquifers, of which carbonate rock dissolution dominated in recharge areas, and evaporite rock dissolution increased to be the dominate lithology in runoff and discharge areas. Based on analysis of water- rock interaction, the main dissolved mineral facies included dolomite, calcite, gypsum and halite. Dolomite is the most important dissolved mineral, followed by calcite and gypsum in recharge area, as well as calcite, gypsum and halite in runoff and discharge areas. Keywords: karst; hydrochemistry; solutes origin; mineral facies; Liuli