Formations of groundwater hydrogeochemistry in a karst system during storm events as revealed by PCA

High-frequency samples have been collected at Jiangjia Spring, the outlet of Qingmuguan underground river system (QURS) in Chongqing in late April, 2008. The variations of hydrogeochemical compositions are found responding rapidly to storm events. Principal component analysis (PCA) of the 20 variables is employed to interpret the relationships with specific processes that control the groundwater hydrogeochemical formations. Through PCA, 84.961% of the total amount information is extracted to indicate the formations of groundwater hydrogeochemical features in QURS during storm events. The first component separates the soil erosion (i.e., increases in turbidity and concentrations of Al3+, TFe, TMn, Ba2+ and NO2?), and dilution effect (i.e., decreases in specific conductance and concentrations of HCO3?, Ca2+ and Sr2+), accounting for 41.495% of the variability in the data. The second component indicates residual fertilizers and duck’s waste from farmlands (i.e., increases in specific conductance and concentrations of Na+, NO3-, PO43-,K+and Cl-), contributing to 37.449%. The dissolution of dolomite and dolomitic limestone makes up 6.017%. During the first rainfall event, the groundwater quality is mainly affected by residual fertilizers and duck’s waste from farmlands, whereas in the second rainfall event, it is mainly affected by increased turbidity and ionic concentrations caused by soil erosion.

High-frequency samples have been collected at Jiangjia Spring, the outlet of Qingmuguan underground fiver system （QURS） in Chongqing in late April, 2008. The variations of hydrogeochemical compositions are found responding rapidly to storm events. Principal component analysis （PCA） of the 20 variables is employed to interpret the relationships with specific processes that control the groundwater hydrogeochemical formations. Through PCA, 84.961% of the total amount information is extracted to indicate the formations of groundwater hydrogeochemical features in QURS during storm events. The first component separates the soil erosion （i.e., increases in turbidity and concentrations of A13~, TFe, TMn, Ba2＋ and NO2 ）, and dilution effect （i.e., decreases in specific conductance and concentrations of HCO3-, Ca2＋ and Sr2＋）, accounting for 41.495% of the variability in the data. The second component indicates residual fertilizers and duck＇s waste from farmlands （i.e., increases in specific conductance and concentrations of Na＋, NO3 , PO43-, K＋and Cl-）, contributing to 37.449%. The dissolution of dolomite and dolomitic limestone makes up 6.017%. During the first rainfall event, the groundwater quality is mainly affected by residual fertilizers and duck＇s waste from farmlands, whereas in the second rainfall event, it is mainly affected by increased turbidity and ionic concentrations caused by soil erosion.