Comparison of groundwater hydrogeochemistry of karst areas in northern and southern China with emphasis on their performance in karst development

Carbonate Weathering in south and north China in Lihu underground river in south China (LHSC) in Nandan, Guangxi province and Dawu karst underground water source in north China (DWNC) of Zibo, Shandong province are different. Hydrochemical analysis and isotope analysis are used to analyze the differences of carbonate weathering in karst areas of north and south China. The results show that the hydrochemical type of Lihu underground river is HCO 3 –Ca, and the hydrochemical type of groundwater in Dawu karst water source area is mainly HCO 3 –Cl–Ca, which reflects that the material composition of regional groundwater are controlled by carbonate rocks weathering and dissolution. By analyzing the equivalent ratios of [Ca 2+ + Mg 2+ ]/[HCO 3 − ] and [Ca 2+ + Mg 2+ ]/[SO 4 2− + NO 3 − + HCO 3 − ] in the LHSC and DWNC. It shows that exogenous acids such as sulfuric acid and nitric acid also participate in the weathering of carbonate rocks, besides the dissolution of carbonate rocks by carbonation. And the research on the stable isotope of sulfur, the nitrogen and oxygen isotope of nitrate also suggest that there are carbonate rocks weathered by sulfuric acid and nitric acid. According to the δ 13 C–HCO 3 − value in the underground river of LHSC and DWNC, it is calculated that the proportion of carbonate rocks weathered by carbonic acid in the DWNC is relatively high (65~100%), and the proportion of LHSC is relatively low (52~66%). The proportion of sulfuric acid and nitric acid weathering carbonate rock is relatively high in the LHSC (34~47%) and relatively low in the DWNC (0~35%).