Study on Hydrochemical Characteristics and Interactions between Groundwater and Surface Water in the Dongting Lake Plain
The Piper trilinear diagram is a common method for analyzing changes in water chemistry and water chemistry types and is not controlled by human factors [42]. As shown in Figure 3a, the distribution of groundwater and surface water samples in “the Three Inlets” water system area is mostly close to the Ca2+-Mg2+ end of the distribution, and part of the groundwater is close to the Na+ +K+ end of the distribution. The cations are mainly Ca2+ and Mg2+, while some groundwater is mainly Na+ and Ca2+, and the anions are mainly close to the HCO3− end of the distribution, while the anions are basically HCO3−. According to Sukharev’s classification, the hydrochemical types of surface water are mainly HCO3-Ca-Mg, and the hydrochemical types of groundwater are mainly HCO3 -Ca-Mg, followed by HCO3-Na-Ca-Mg and HCO3-Na-Ca. The groundwater and surface water exhibit the same hydrochemical types and distribution patterns, implying the same source. Figure 3b shows that the distribution of surface water samples from “the Four Rivers“ water system area is close to the Ca2+-Mg2+ end of the distribution, with Ca2+ and Mg2+ as the main cations; additionally, the anions are close to the HCO3− end of the distribution, and the anions are mainly HCO3−. In addition, the distribution of the groundwater samples is at the Ca2+, Mg2+, and Na+ +K+ ends of the distribution, and the majority of the anions are close to the HCO3− end of the distribution, while the anions are mainly HCO3−. The hydrochemical types of surface water are HCO3-Ca-Mg and HCO3-Ca, and the hydrochemical types of groundwater are mainly HCO3-Ca, HCO3-Ca-Mg, and HCO3-Na-Ca-Mg. Groundwater originates from “the Four Rivers” basins, and the stratigraphy is characterized by diverse lithologies and different degrees of human activity. The groundwater types are diverse, with HCO3-Cl, HCO3-SO4, and other water types sporadically distributed in local areas. As shown in Figure 3c, the distribution of the Dongting Lake water samples is close to the Ca2+-Mg2+ end of the distribution, with Ca2+ and Mg2+ as the major cations; additionally, the anions are close to the HCO3− end of the distribution. Moreover, the anions are all HCO3−, and the water chemistry types are HCO3-Ca-Mg and HCO3-Ca. Generally, the anions of groundwater and surface water in the Dongting Lake Plain are mainly HCO3−, and the cations are mainly Ca2+ and Mg2+. The relatively high content of Na+ at some of the sample points is related to the lithological differences in water-bearing rock groups and the interactions between water and rock.
