Abstract: With the underground river at Litang county of Guangxi province as a research object, we revealed the hydrochemical compositions of Yaocun underground river and discussed its temporal and spatial distribution by analyzing groundwater samples collected in wet season (June), normal flow season (September), and dry season (December). Results showed that 1) in space scale, the conductivity and the concentrations of Ca²⁺ and Mg²⁺ gradually increased from the upstream to the downstream, and in particular, the conductivity of the underground river’s outlet (point No.3) was higher than that of other positions, reaching 589 μS/cm in wet season, 634 μS/cm in normal flow season, and 614 μS/cm in dry season; 2) while in time scale, the concentrations of pH, SO₄^2-, NO₃^- varied with season, and NO₃^- concentration at underground river’s outlet in dry season was higher than that in other seasons; 3) the hydrochemical characteristics of the research area are influenced by karst degree and agricultural activities.

Key words: karst water, underground river system, hydrochemistry characteristics, karstification, agriculture activities, Yaocun at Litang county of Guangxi Province