Hydrogeochemical and isotopic characteristics of surface water and groundwater in the Qinghai Lake catchment (China)

Qinghai Lake plays an important role in the study of climate change in the western China and Qinghai-Tibet Plateau uplift processes and environmental effects. This study focused on the hydrogeochemistry of different waters (river, lake, groundwater, and precipitation) around and within Qinghai Lake. We analyzed major chemical elements and stable isotopes to examine water-rock interactions and the hydrogeochemical evolution of lake. The geochemical characteristics of river, groundwater, and precipitation have direct effects on the chemical composition of lake. The hydrochemical type of the river was HCO3-Ca·Na or HCO3-Na·Ca; groundwater was HCO3-Na·Ca, Cl·HCO3-Na·Ca, or HCO3-Ca·Na; and lake was Cl-Na, which was different from Erhai (Cl·HCO3-Na). The different geological settings and amount of river and groundwater input between the Buha and Shaliu subcatchments led to fluctuation in the major chemical ions present in the Buha River. The supply to river and groundwater is different in the various areas and manifests as overlap in the ion concentrations in river and groundwater. The relationship of major ions showed that sulfate reduction, ion exchange, carbonate and silicate rock weathering, dissolution, and evaporation occurred in the evolution of the groundwater, river, and lake in the Qinghai Lake catchment. The evolution of Qinghai Lake may be towards poor calcium and potassium enrichment as well as the removal of carbonate and increasing chloride. The salinity of Qinghai Lake is likely to become much higher if the amount of river and groundwater input decreases or the climate continues to dry in the future.