Groundwater circulation and hydrogeochemical evolution in Nomhon of Qaidam Basin,northwest China

In this study, analysis of hydrogeological conditions, as well as hydrochemistry and isotopic tools were used to get an insight into the processes controlling mineralization, recharge conditions, and flow pattern of groundwater in a typical arid alluvial-lacustrine plain in Qaidam Basin, northwest China. Analysis of the dissolved constituents reveals that groundwater evolves from fresh water (TDS =300–1000 mg/l) to saline water (TDS ≥5000 mg/l) along the flow paths, with the water type transiting from HCO ₃?Cl–Na ?Mg to HCO ₃?Cl–Na, and eventually to Cl–Na. Groundwater chemical evolution is mainly controlled by water–rock interaction and the evaporation–crystallization process. Deuterium and oxygen-18 isotopes in groundwater samples indicate that the recharge of groundwater is happened by meteoric water and glacier melt-water in the Kunlun Mountains, and in three different recharge conditions. Groundwater ages, estimated by the radiogenic (³H and ¹⁴C) isotope data, range from present to Holocene (～28 ka). Based on groundwater residence time, hydrogeochemical characteristics, field investigation, and geological structure distribution, a conceptual groundwater flow pattern affected by uplift structure is proposed, indicating that shallow phreatic water is blocked by the uplift structure and the flow direction is turned to the northwest, while high pressure artesian water is formed in the confined aquifers at the axis of the uplift structure.