Lijun Wu

To better protect lacustrine ecologies and understand the evolutionary process of lake environments, it is critical to study the interacting mechanisms between lakes and the surrounding groundwater. The Wuliangsu Lake watershed is the largest wetland in the Yellow River basin and is the discharge area of the Hetao Irrigation District (HID), which is one of the three largest agricultural production areas in China. Due to the influence of human activities, the discharge water from the HID has led to the deterioration of the Wuliangsu Lake ecology and the degradation of the lake environment. Based on long-term observation data and water sampling data collected in 2021, a water–salt equilibrium model was used to analyze the recharge rate of groundwater to the lake. The contribution rate of groundwater to lake recharge in the study area was calculated with a Bayesian mixing model by combining D and ¹⁸O stable isotope data. Furthermore, the environmental evolutionary process of the lake was also analyzed using the collected water quality data. The results show that channel drainage was the main source of recharge to Wuliangsu Lake, accounting for more than 75%, while groundwater contributed less than 5% of lake recharge. After implementing the ecological water supplement plan, the concentration of various ions in the lake decreased, the concentration of the total dissolved solids (TDS) in the lake decreased from 1.7 g/L in 2016 to 1.28 g/L in 2021, and the ecological environment was improved. The contribution of groundwater to lake recharge was quantitatively analyzed. The results of this study can facilitate the development of vital strategies for preventing the further deterioration of lake water quality and for protecting wetland ecologies.

The concentrations of Cu, Zn, As, Pb, Cr, and Cd in soil were analyzed in a mining area in the Inner Mongolia Autonomous Region, China. The average metal concentrations in the soil samples were 204.07 mg/kg, 88.15 mg/kg, 14.47 mg/kg 88.52 mg/kg, 56.45 mg/kg, and 0.235 mg/kg, respectively. Based on the evaluation standards, background values of the soil heavy metals, multiple soil pollution assessment indices, such as the single factor index (P_i), the geological accumulation index (I_geo), the Nemerow index (P_n), the ecological risk index (ER), and the health risk index (HI) were applied to evaluate the soil environmental risks in the study area. It was found that in different soil layer depths (0–10 cm, 10–30 cm, and 30–50 cm), the evaluation result of each index showed that there were significant spatial differences in soil pollution levels, and the focus of different indices differed greatly from each other. The P_i put 18.14% of the area at high risk of soil contamination levels, due to the fact that this index highlights the Cu pollution factor more than other indices and relatively amplifies hazards in some high-risk areas. While the P_n indicated that 61.36% of the study area was at a safe level of soil contamination, it can underestimate the regional soil heavy metal pollution risk. In order to scientifically carry out soil-pollution-risk prevention and control, it is necessary to comprehensively compare and analyze the information disclosed by different indices.

Heavy metal pollution of soil restricts the sustainable use of land and poses risks to human health throughout the world. Changes in the physicochemical properties of soil may increase the mobility of heavy metals in the soil ecosystem and lead to groundwater pollution. In this study, the effects of different salt solutions (NaCl, CaCl₂, NaNO₃, MgCl₂, Na₂SO₄, and mixed salts) on the release of Cd from soil were investigated by batch desorption tests and the Freundlich isothermal sorption model. Increased concentrations of the salts, except for NaNO₃, significantly promoted Cd release (R² > 0.9, p < 0.01). Under the salt stress, Cd release from the test soils was promoted more by CaCl₂ and MgCl₂ than by the other salts, and the average desorption rates of eight soil samples at 3.5% salt concentration were 11.15% and 10.80%, respectively, which were much higher than those of NaCl (4.05%), Na₂SO₄ (0.41%), and NaNO₃ (0.33%). Ca²⁺ and Mg²⁺ showed better ion exchange capacity than Na⁺ to promote Cd release; for anions, Cl⁻ formed hydrophilic Cd chloride complexes with Cd in soil. In addition, principal component analysis results revealed that Cd release was mainly influenced by soil texture, cation exchange capacity, and iron–manganese oxide content of the soil. The Cd release level for different soil samples was most closely related to the proportion of fine particles in the soil. The higher the clay content was, the higher the Cd desorption rate.