[Major Ionic Characteristics and Factors of Karst Groundwater at Huixian Karst Wetland, China].

To investigate the major ionic chemical characteristics and seasonal variations, 27 groundwater samples were collected from the wet season, flat season, and dry season during 2018-2019 in the Huixian Karst wetland, which is the largest low-altitude karst wetland in China. The single pollution standard index was applied to evaluate the groundwater pollution during different periods, and the major ionic factors of the karst groundwater were analyzed using the statistical analysis method, Gibbs diagram, and ion ratio. The results revealed that the groundwater samples were a weakly alkaline fresh water that were rich in Ca and HCO. The average concentrations of the primary ions followed the order of flat season > wet season > dry season; meanwhile, the water quality in the dry season was better than that in the wet and flat seasons. The K and NO in the karst groundwater were mostly affected by the spatial distributions of the aquifers, and the Mg, SO, NO, NH, and TDS were related to the space-season scale. Na, Ca, HCO, and Cl were relatively stable ions in the karst groundwater. The hydrochemical characteristics were primarily determined by carbonate rock dissolution and were found to be the HCO-Ca type, which accounted for 77.78%, 77.78%, and 88.89% in the wet season, flat season, and dry season, respectively. The karst groundwater was predominantly polluted by SO, NO, and NO; particularly, NO exhibited serious pollution points, and SO had heavy pollution points in the wet and flat seasons. The chemical composition of the karst groundwater was controlled mostly by water-rock interactions. Ca and HCO primarily came from calcite dissolution, and the high concentrations of Mg and SO in a few number of points were controlled by dolomite, dolomitic limestone, and pyrite. K, Na, SO, NO, and Cl partly came from atmospheric precipitation, and Na and Cl partly came from human activities; K was related to potash fertilizer, and the main source of NO was chemical fertilizer.