A hydrochemistry and multi-isotopic study of groundwater origin and hydrochemical evolution in the middle reaches of the Kuye River basin

The Kuye River basin lays in an economically and ecologically important area, therefore, the groundwater quality issues are of growing concern in this semi-arid region. In the present study, the combination of techniques (i.e. piper diagram, ionic ratios, Gibbs diagrams, multiple isotopic analyses etc.) provided an efficient way for analyzing the groundwater origin and hydrochemical processes that affected water chemistry. The groundwater type was Ca-HCO3 in low TDS values and Na-Cl/SO4 in high TDS values in both shallow un-confined and deep Cretaceous-Jurassic semi-confined aquifer. And, furthermore, Na+, Cl-, SO42- and F- were the dominated parameters deteriorating the groundwater quality. In general, groundwater was of meteoric origin and the more depleted delta O-18 and dD features of CJY groundwater samples indicated that the groundwater was formed during the wetter and colder climate. The rock weathering in conjunction with the cation exchange absolutely predominated in geochemical evolution and deuterium excess method quantified that mineral dissolution contributed most of the salinity (67-92%) of the groundwater. The SO42- of the groundwater was primary from the dissolution of sulfate minerals, next was the atmospheric precipitation. In addition, bacterial sulfate reduction was an important reaction affecting the SO42- concentration in the groundwater from CJY aquifer. The hydrochemical type of high fluoride groundwater in the study area was Na-HCO3 or Na-Cl/SO4 and it was mainly from the dissolution of fluoride bearing minerals. Na-HC3 water was favorable for Fenrichment due to CaF2 solubility and Na-Cl/S-4 type water may favor the F- enrichment by lower its activity in groundwater. The results of this study will facilitate understanding of groundwater origin and quality status to enable effective management and utilization of groundwater.