[Major Ionic Features and Possible Controls in the Groundwater in the Hamatong River Basin]

In order to study the major ion chemistry and controls of groundwater, 59 groundwater samples were collected and their major ions measured in the Hamatong River Basin. The hydrogeochemical characteristics of groundwater in this basin were analyzed by means of mathematical statistics, Piper triangular diagrams, Gibbs figures, and ionic relations, and the water chemical evolution and ion sources of the Hamatong River Basin were determined. The results showed that Ca²⁺ was the main cation in the groundwater, accounting for 22.1% to 72.4% of the total cations, with an average value of 48.7%. HCO₃^- was the main anion, accounting for 35.3% to 97.5% of the total anions, and with an average value of 80%. Total dissolved solids concentration ranged from 93.3 mg·L^-1 to 521.1 mg·L^-1 with a median value of 219.1 mg·L^-1. The hydrochemical types of groundwater are HCO₃-Ca, HCO₃-Ca·Mg, and HCO₃-Ca·Na. Chemical weathering rates of carbonates and silicates were estimated, and the chemical composition of groundwater samples located in the middle of Gibbs model indicated that the major chemical process of groundwater was controlled by rock weathering. Silicate weathering is believed to significantly contribute to dissolved solute compositions, and carbonate weathering played an important role as the source of dissolved ions.