A study of the characteristics of karst groundwater circulation based on multi-isotope approach in the Liulin spring area, North China

Due to the significance of karst groundwater for water supply in arid and semi-arid regions, the characteristics of the karst groundwater flow system in the Liulin spring area, North China, are analysed through isotopic tracing (δ2H, δ18O, δ13C and 3H) and dating approaches (14C). The results show that the primary recharge source of karst groundwater is precipitation. Evaporation during dropping and infiltration of rainfall results in a certain offset in the values of δ2H and δ18O in groundwater samples from the global meteoric water line (GMWL) and the local meteoric water line (LMWL). The altitudes of the recharge region calculated by δ18O range from 1280 to 2020 m above sea level, which is consistent with the altitudes of the recharge area. The Liulin spring groups could be regarded as the mixing of groundwater with long and short flow paths at a ratio of 4:1. In the upgradient of the Liulin spring, the groundwater represents modern groundwater features and its is mainly derived from dissolution of soil CO2, while in the downgradient of the Liulin spring, the 14C age of dissolved inorganic carbon (DIC) in groundwater shows an apparent increase and is mainly derived from the dissolution of carbonate rocks. The mean flow rate calculated by 14C ages of DIC between IS10 and IS12 is 1.23 m/year.