Groundwater discharge and hydrologic partition of the lakes in desert environment: Insights from stable 18 O/2 H and radium isotopes

Studies of isotope characteristics of lake water in a desert can provide important information on groundwater discharge and hydrologic partition of the lakes in the desert. This paper presents the investigation of ¹⁸O and ²H stable isotopes and radiogenic radium of different water endmembers in three representative lakes of Badain-E, Badain-W and Sumujilin-S in the Badain Jaran Desert (BJD), the fourth largest desert in the world. A stable ¹⁸O and ²H isotopic buildup model is constructed to classify the hydrologic conditions of the desert lakes by estimating the ratio between groundwater discharge rate (Fin) and lake surface evaporation (E). Then the radium mass balance models are developed to quantify Fin. Based on the obtained Fin/E and Fin, Badain-E, Badain-W and Sumujilin-S are classified as flowing through, terminal and desiccating lakes, respectively, and their hydrologic partition is obtained. The groundwater discharge rate of Badain-E, Badain-W and Sumujilin-S, is estimated to be 8-10 mm d⁻¹, 4-5 mm d⁻¹, and 7-8 mm d⁻¹, respectively. The total groundwater discharge to the lake areas in the BJD is about 1.68 x 10⁵ m³ d⁻¹. The flow-through condition explains the existence of the fresh lakes, while the terminal and desiccating conditions lead to the lake salinization over time. This study represents the first attempt to couple both stable and radium isotopic approaches to investigate the groundwater discharge and hydrologic partition of desert lakes in the BJD and is instructional to lake studies in other deserts in the world