Hydrochemical and isotopic characteristics of groundwater in the Jiuquan East Basin, China

To investigate the hydrochemical characteristics and evolution of groundwater in the Jiuquan East Basin, 133 groundwater samples were collected and tested. Statistical analysis, Piper diagram, Gibbs plot, ion ratio and isotope techniques were used to analyse the samples. Our results suggest that both shallow and deep groundwater generally consist of weakly alkaline freshwater, with SO42− and HCO3− as the main anions, and Mg2+ and Na+ as the cations. The shallow groundwater has gradually evolved from the HCO3·SO4–Mg·Ca type in the southern part of the basin (the groundwater recharge runoff area) to the SO4·Cl–Na·Mg type in the northern part of the basin (the groundwater discharge area). Similarly, deep groundwater has progressively evolved from the HCO3·SO4–Mg·Ca type to the SO4·HCO3–Na·Mg type. In the groundwater recharge-runoff area, the chemical components in the shallow and the deep groundwater are mainly originated from the silicate rock weathering, the evaporite rock dissolution and the carbonate weathering. From the groundwater recharge-runoff area to the discharge area, the evaporation concentration, the cation exchange and the adsorption gradually become the main controlling factors of the shallow groundwater hydrochemical composition. The deep groundwater mainly undergoes the leaching, the cation exchange and the adsorption, during the runoff. Furthermore, based on isotope analysis, ice-snow melt water and atmospheric precipitation are identified as the main recharge sources of the shallow and deep groundwater in the area. This paper is great significance for the further protection of water resources and ecological environment, in the area.