[Hydrochemical Characteristics and Formation Mechanism of Groundwater in the Western Region of Hepu Basin, Beihai City].

Beihai City is a typical coastal city where groundwater provides a strong support for social and economic development. Studies on the hydrochemical characteristics and formation mechanism in Beihai City play an important role in the scientific management of water resources and coastal ecological environment protection. In this study, we revealed the main hydrogeochemical processes controlling groundwater quality by means of groundwater survey and water sample collection in the western region of Hepu Basin, Beihai City, combined with hydrochemistry and isotope theories and methods. The results showed that groundwater had the remarkable features of low pH value and low mineralization degree. For pore water, hydrochemistry type by primarily NO3 type water and concentrations of Na+ and Cl- were modestly increased along the flow path. Ca-HCO3 , Ca-Cl·HCO3 , Ca·Na-HCO3 , and Na-Cl·HCO3 types were predominant in fissure water. The groundwater was of meteoric origin, hydrogeochemical evolutions were mainly affected by water-rock interactions, cation exchange, and anthropogenic activities. Na+ , K+ , and Cl- were mainly derived from evaporite and silicate rocks; Ca2+ , Mg2+ , HCO3 - , and SO4 2- were from carbonatite and evaporite; and NO3 - principally arose from anthropogenic activities. This study suggests that the groundwater pollution prevention and control should be carried out as soon as possible in the area where the NO3 type water occurs to avoid the further deterioration of water quality.