IDENTIFYING SALINITY SOURCES AND RECHARGE MECHANISMS WITH STABLE ISOTOPES: THE BADAIN JARAN DESERT, CHINA

In this application the stable isotopes of water δ²H and δ¹⁸O feature as the centerpiece of a multi-tracer investigation to establish a conceptual model of shallow groundwater flow and salinity in a remote cold desert region in northwestern China. Groundwater TDS in the area is characterized by high spatial variability and a general trend of decreasing salinity along a flowpath from the margin towards the center of the desert. Samples were drawn from shallow wells, oasis lakes, unsaturated zone profiles and precipitation events. It is found that much of the spatial variability commented upon in previous studies can be explained by 1) evaporation within exposed wells prior to sampling and 2) reflux of highly evaporated saline lake water to groundwater. Detailed characterization of regional δ²H/δ¹⁸O relationships allows for estimation of unmeasured parameters in lake/groundwater interaction modeling. Direct recharge is shown to be negligible and therefore of little impact to groundwater salinity. The trend of decreasing TDS with distance along a flowpath is attributed to climate aridification over the late Holocene. While stable isotopes are of great value to help conceptualize flow systems in the absence of detailed physical data, it is emphasized that analysis of multiple tracers vastly enhances isotope interpretation, and that stable isotopes should not be viewed as a sufficient alternative to traditional hydrogeological characterization in most cases.