Estimation of groundwater recharge from precipitation by using tritium and chloride concentrations in the Chinese loess unsaturated zone in Inner Mongolia, China

Groundwater recharge estimation is important for groundwater resource management especially in arid and semiarid areas, such as Loess Plateau, China. Here, loess deposits form regionally important aquifers, typified by a thick unsaturated zone, facilitating the application of environmental tracers to estimate groundwater recharge rates. In this study, the chloride mass balance (CMB) method was used to estimate groundwater recharge from precipitation for two sites in Inner Mongolia, China. Due to the uncertainty in determining the prerequisite chloride input flux for the CMB method, three different techniques (artificial 3H tracer method, the measured chloride concentration in precipitation, and 1963 tritium peak method) were used to determine the chloride input flux to increase the reliability of the calculated groundwater recharge rates. The different chloride input flux results obtained from the different techniques were found to be consistent. The average groundwater recharge rate calculated from the chloride mass balance method is 0.038 m/year. The groundwater recharge rate obtained in this study was found to be consistent with groundwater recharge rates derived from similar studies in the Loess Plateau.