Abstract
Abstract. 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.
Highlights
Fresh lake water (FLW) L1, which was sampled from the freshwater lake recharged directly by river water in the low-lying depression (Zone 5), is slightly alkaline, with a pH value of 8.98
The Qaidam basin, a typical arid sedimentary closed basin formed with the uplift of the Tibetan plateau, has groundwater circulation patterns characterized by the complex tectonic activities, paleoclimate variation, arid climate characteristics, sedimentary lithology, and systematic evolution from fresh- to saltwater
Studies of this basin can enhance the understanding of groundwater origin, flow regime and hydrogeochemical evolution in such complex tectonic influenced arid sedimentary closed basins worldwide
Summary
Closed basins in arid and semiarid areas (e.g., the Great Artesian Basin and Murray Basin in Australia, Minqin Basin and Qaidam Basin in China, Death Valley in United States) have been the focus of attention due to their water scarcity, fragile ecology and rich mineral resources related to salt lakes (Edmunds et al, 2006; Lowenstein and Risacher, 2009; Love et al, 2013, 2017; Shand et al, 2013; Stone and Edmunds, 2014; He et al, 2015; Cartwright et al, 2017; Priestley et al, 2017a; Xiao et al, 2017). Several attempts have been made to understand the regional groundwater regimes (Tan et al, 2009; Gu et al, 2017; Xiao et al, 2017), but very little research reported the circulation and evolution of groundwater from the mountain pass area to the central terminal lake area due to the notable difficulties in moving through and access the swamps on the lacustrine plain. This would greatly limit the full understanding of the role of hydrogeological processes in the basin
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