Groundwater origin, flow regime and geochemical evolution in arid endorheic watersheds: a case study from the Qaidam Basin, northwestern China

Groundwater origin, flow and geochemical evolution in the Golmud River watershed of the Qaidam Basin was assessed using hydrogeochemical, isotopic and numerical approaches. The stable isotopic results show groundwater in the basin originates from precipitation and meltwater in the mountainous areas of the Tibetan Plateau. Modern water was found in the alluvial fan and shallow aquifers of the loess plain. Deep confined groundwater was recharged by paleowater during the late Pleistocene and Holocene under a cold climate. Groundwater in the low-lying depression of the central basin is composed of paleobrines migrated from the western part of the basin due to tectonic uplift in the geological past. Groundwater chemistry is controlled by mineral dissolution (halite, gypsum, anhydrite, mirabilite), silicate weathering, cation exchange, evaporation and mineral precipitation (halite, gypsum, anhydrite, aragonite, calcite, dolomite) and varies from fresh to brine with the water types evolving from HCO3 · Cl-Ca · Mg · Na to Cl-Na, Cl-K-Na and Cl-Mg type along the flow path. Groundwater flow patterns are closely related to stratigraphic control and lithological distribution. Three hierarchical groundwater flow systems, namely local, intermediate and regional, were identified using numerical modeling. The quantity of water discharge from these three systems accounts for approximately 83 %, 14 % and 3 %, respectively, of the total groundwater quantity of the watershed. This study can enhance the understanding of groundwater origin, circulation and evolution in the Qaidam Basin as well as other arid endorheic watersheds in northwestern China and elsewhere worldwide. © 2017 Copernicus Publications. All rights reserved.