Description:
Precipitation infiltration is the unique recharge source of groundwater in most arid areas. In this paper, we focus on the desert area of the Ordos Plateau by assessing the capability of water stable isotope analysis (δD–δ18O) to refine the understanding of groundwater recharge mechanism. In situ profile monitoring of temperature, moisture content, and isotopic sampling in unsaturated and saturated zones was conducted at the Bulanghe station located in the middle of the Ordos Plateau to identify the detailed infiltration process. It was found that the capillary zone has the most depleted heavy O and H isotopes in the profile. The analysis of δD–δ18O relationships of local precipitation explains the isotopic variability and indicates the following processes: (1) Liquid water evaporated at hotter layer near the surface; 2) Part of vapor moves downward and condensates at the deeper layer where it becomes cooler. The isotopic fractionation that occurs in this process makes the condensation zone the most depleted heavy O and H isotopes zone. Temperature and moisture content in the profile also supported the capillary zone as vapor moves downward. The isotopic evidence indicates that, except for direct infiltration, the newly found secondary infiltration pattern, vapor–liquid flow, makes it possible that the low intensity precipitation event contributes to groundwater recharge. The results from this study may provide useful insights into the identification of infiltration mechanism in arid areas in the world.