[Major Ionic Characteristics and Controlling Factors of Karst Groundwater at Xiangshui, Chongzuo]

To investigate the major ionic characteristics, seasonal variation, and controlling factors of karst groundwater at Xiangshui, Chongzuo, 210 groundwater samples were collected and measured in wet season, dry season, and flat season in 2016. The controlling factors of karst groundwater were analyzed by using multivariate statistical analysis method. The results showed that the groundwater samples were weakly alkaline fresh water and rich in Ca²⁺ and HCO₃^-, which accounted for more than 75% and 70% of total ion concentration. The average concentrations of K⁺, Na⁺, Cl^-, and NO₃^- decreased in the order of wet season > flat season > dry season. None of the concentrations of Ca²⁺, Mg²⁺, HCO₃^-, SO₄^2-, pH, TDS, TZ⁺, and TZ^- showed significant seasonal variation. The hydrochemical characteristics were found to be of HCO₃-Ca type and mainly determined by carbonate rock dissolution. Only a small proportion of them were of HCO₃·Cl-Ca and HCO₃·SO₄-Ca type in wet season and flat season, Cl·NO₃-Ca type appeared in flat season, and HCO₃-Ca·Mg type appeared in dry season, reflecting the influence of dolomite and ferric mudstone dissolution in the stratum, and of NO₃^- and Cl^- input from anthropogenic activities. Groundwater Ca²⁺ and HCO₃^- mainly came from limestone dissolution; Na⁺, Cl^-, K⁺, and NO₃^- came from atmospheric precipitation and human activities; while Mg²⁺ and SO₄^2- came from dolomite and ferric mudstone dissolution. The chemical composition of groundwater was controlled by water-rock interaction, the groundwater in the carbonate aquifer was controlled by carbonate rocks dissolution, and the groundwater in villages and densely populated areas was affected by atmospheric precipitation and human activity.