The hydrochemical characteristics and evolution of groundwater and surface water in the Heihe River Basin, northwest China

A combination of isotopic and chemical indicators has been used to characterize rainfall, surface water and groundwater in the Heihe River Basin, China. Surface- vs. groundwater chemistry data enabled geographical zones and chemical types to be differentiated. The dissolution of halite, Glauber’s salt, gypsum, dolomite and calcite determine Na⁺, Cl⁻, Mg²⁺, Ca²⁺, \( {\text{SO}}^{{2 - }}_{4} \) and \( {\text{HCO}}^{ - }_{3} \) chemistry, but other processes such as evaporation, ion exchange, and deposition also influence the water composition. The majority of deep confined groundwaters are tritium-free and less mineralized than in the shallow aquifer. Radiocarbon values in the deeper groundwaters range from 18.8 to 38.9 pmc, and 80 pmc probably represents the upper limit of initial ¹⁴C activity; this yields ages of approximately 5,960–11,971 years BP, which is about 3,000 years older than those calculated by models in previous work. The shallow aquifer exhibits fairly high and variable tritium activities (4–75 TU), evidence of recent recharge and low residence time (<60 years), which is in line with estimates from previous work. Isotopic signatures indicate formation of deeper groundwaters in a colder and wetter climate during the late Pleistocene and Holocene. The results suggested that significant changes are urgently needed in water-use strategy to achieve sustainable development.