Groundwater Recharge Mechanisms in the Lake Clusters of the Badain Jaran Desert and the Salinity of Confined Aquifers Based on the Electrical Conductivity Model of Pore-fluid Saturated Sandstone

The Badain Jaran Desert, located in the western part of the Inner Mongolia Autonomous Region in China, distinguishes itself from typical deserts by its abundance of lakes and rich groundwater reserves. At the Badain Jaran Desert, 153 magnetotelluric sounding stations have been explored to perform one-dimensional and three-dimensional inversion analyses of the collected magnetotelluric dataset. The results of one-dimensional inversion at each sounding station, where the top interface of the first underground low-resistivity layer is less than 400 meters, were used to build a map of the potentiometric surface level of the study area. This map aligns closely with the findings from hydrological surveys. The three-dimensional resistivity model indicates the existence of a conductive layer at the deep of 2-3 km, interpreted as a sandstone-confined aquifer, located between the mountain areas surrounding the Badain Jaran Desert and its clusters of lakes. 
Moreover, there is an almost vertical conductive zone underneath the lake cluster, which is interpreted as the discharge area of the confined aquifer. This zone is related to the upward flow of deep groundwater through fractures, replenishing both the lakes and the shallow groundwater, while the surrounding mountainous regions of the desert act as the recharge areas for this confined aquifer. Finally, an estimation of the volumetric percentage of saline fluid in the confined aquifer was derived based on the electrical conductivity model of pore-fluid saturated sandstone, yielding the saline fluid content that meets the resistivity/conductivity range conditions of the confined aquifer.