[Chemical Characteristics of Groundwater and Material Sources Analysis in Shiqi River Basin]

To investigate the chemical characteristics of groundwater and material sources in a typical karst hill (valley) depression, 41 groundwater samples were systematically collected in the Shiqi River basin. The statistical analysis of the conventional ion content in the groundwater shows that pH of the groundwater in the study area is between 6.06-8.07, the total solid solubility is between 18.21 mg ·L^-1 and 336.28 mg ·L^-1, and the charges of anions and cations in the water body are balanced. Ca²⁺, Mg²⁺, and HCO₃^- are the main ions in groundwater, with concentrations of 2.61-108.7 mg ·L^-1, 0.54-27.61 mg ·L^-1, and 8.1-370.74 mg ·L^-1, respectively. The groundwater characteristics in the study area are consistent with the high calcium and weak alkalinity characteristics of karst water. By using the Gibbs diagram, piper diagram, end-member analysis, and ion proportional coefficient, hydrochemical characteristics and material sources of groundwater were further analyzed. The results show that Ca²⁺ and Mg²⁺ are mainly controlled by the weathering of limestone and dolomite in which carbonic acid is involved. Na⁺ mainly comes from the dissolution of silicate rocks. At the same time, Ca²⁺ and Na⁺ undergo cationic exchange adsorption in the groundwater flow process. K⁺, Cl^-, and NO₃^- are mainly affected by agricultural fertilizer application and domestic wastewater discharge. The hydrogen and oxygen isotope analysis of groundwater shows that atmospheric precipitation is the main recharge source of groundwater in this region, which impacts the chemical characteristics and material sources of local groundwater. The results of this study show that the geological background of groundwater is the main factor that affects its hydrochemical characteristics and material sources in areas with relatively little anthropogenic activity.