Hydrochemical characteristics and formation mechanism of groundwater in northern Taihu Lake Basin

In order to find out the hydrochemical characteristics and genetic mechanism of groundwater in northern Taihu Lake Basin, based on hydrogeological conditions, the groundwater chemical characteristics and the distribution of controlling factors in different aquifers are analyzed by using mathematical statistics, Piper three-line diagram and ion ratio method. The results are as follows:Firstly, the hydrochemical types of shallow groundwater in the study area are complex with the main cations including Ca·Na-HCO₃ and Ca·Na-HCO₃·SO₄. On the contrary, the hydrochemical types of confined water are relatively simple with HCO₃ as the main anion and Ca, Ca·Na and Na as the main cation. Secondly, hydrochemical formation of shallow groundwater is mainly affected by the weathering and dissolution of minerals, among which the dissolution of silicate rock plays a great role. With respect to the impact on phreatic water from human activities, the influence from industrial and mining activities is much greater than that from agriculture and domestic sewage. Cationic exchange occurred in the confined water, which reduced the concentrations of Ca²⁺ and Mg²⁺ and increased the concentration of Na ⁺. Thirdly, the ion characteristics of phreatic water and confined water have obvious stratification in vertical direction.