Origin of Water and Hydrochemical Components of Lakes: Example From the Mu Us Desert, Northwest China

Abstract

Desert lakes are sparsely distributed in arid/semi-arid regions of the world and are crucial to desert hydro-ecosystem. However, the sources of water and dissolved components in desert lakes, especially the inputs from anthropogenic activities, remain to be fully understood. This study used water stable isotopes, self-organizing maps, and principal component analysis to explore the origins of lake water in the Mu Us desert, northwest China, where intensive coal mining activities exist. Results show that all desert lakes were distinguished into two types: (a) Type A, dominated by Ca-HCO₃ type with a relatively low TDS (192–405 mg/L) and the highest concentration of NO₃⁻ (1.14–5.94 mg/L); (b) Type B, characterized by Na-HCO₃ type with a highest content of SO₄^2– and TDS up to 159 and 1,207 mg/L, respectively. The water stable isotopic compositions in lake water of Type B are depleted compared to those of the lake water of Type A. A combined analysis of hydrochemistry of lake water, groundwater, and mine water suggest that the desert lakes have different sources: lake water of Type A originated from Quaternary groundwater discharge, while lake water of Type B was derived from the treated mine drainage (TMD) which led to higher TDS and SO₄^2–. The hydrochemistry of Type A lakes was influenced by agricultural activities (fertilizer use and livestock manure), whereas the hydrochemistry in Type B lakes were mainly controlled by the infiltrated TMD nearby. This hydrochemical characterization approach may be helpful to understand the hydrology of desert lakes elsewhere.