Hydrochemical Variation and Its Influencing Factors in Typical Karst Subterranean River in SW China

Groundwater was monitored to investigate its hydrochemical variation and possible influencing factors from April, 2007 to May, 2009 at the inlet (D1) and outlet (S2) of Qingmuguan subterranean river in Chongqing, China. The response of the subterranean river discharge to rainfall events was very fast and dramatic, as the water level rising suddenly and dropping sharply with rainfall amount in the months with more rainfall. The water temperature, electrical conductivity, sodium, magnesium, calcium, bicarbonate, nitrate and chloride concentrations of S2 were higher than that of D1, while pH value, potassium and sulfate concentrations of S2 were lower than that of D1. The pH value, electrical conductivity, sodium, calcium, magnesium and bicarbonate concentrations were lower in May and June, and potassium concentration was higher in September and October, and nitrate and phosphate concentrations showed rising-falling variation obviously in May and June. Hydrochemical variation of the subterranean river was influenced by geological background and karstification intensity, flushing eluviation and dilution effects of rainfall, land use and seasonal farmland fertilization and other anthropogenic inputs. The karst groundwater dynamics are highly sensitive to the changes in the external environment, and the water of subterranean river is bad for drinking directly during the rising-dropping process of water level.