Groundwater acidification in shallow aquifers in Pearl River Delta, China: Distribution, factors, and effects

The improper discharge has brought many environment problems in Pearl River Delta, China. As important reserve resources, groundwater resources have been affected by acidification. It is urgent to clarify the mechanism of groundwater acidification and take measures to alleviate this situation. The purposes of this study were to determine the main factor causing groundwater acidification in shallow aquifers, to quantify and analyze the hazard of acid precipitation on groundwater, and to analyze the characteristics of groundwater chemistry under acid precipitation. Acid rain hazard index (AHI) was defined and introduced to characterize the effects of the actual input of hydrogen ion on groundwater. The techniques of geographic information system (GIS) and principal components analysis (PCA) were used in this new analysis method. By analyzing the groundwater chemical data of 407 samples and meteorological data, the results showed that acid rain was the dominant factor leading to groundwater acidification rather than pyrite oxidation. Four principle components were derived. PC1 represented seawater intrusion effect and was consisted of Cl-, Na+, Mg2+ and TDS. PC2 demonstrated the water-rock interactions occurred in acidic groundwater environment, which was consisting of pH, Ca2+, HCO3-, PO43- and SO42-. PC3 represented agricultural activities with the variables of K+ and NO3-. PC4 was associated with Mn2+, Al and AHI and represented the directly influence resulting from the input of acid deposition. Therefore, to strengthen supervision of discharge and improve the industrial desulfurization technology could alleviate the deterioration of acidification.