[Hydrochemical Characteristics and Controlling Factors of Groundwater in the Angulinao Basin]

To study the hydrochemical characteristics and controlling factors of groundwater from the quaternary aquifer， basalt aquifer， and other bedrock aquifer in the Angulinao Basin， 175 water samples from groundwater， surface water， and rain were collected. Comprehensive methods such as mathematical statistics， Piper trilinear diagram， Gibbs plot， ion ratio， and factor analysis were used to analyze and explore the hydrochemical characteristics and controlling factors of the groundwater in the study area. The results showed that the groundwater was characterized by a generally low alkalinity， with average TDS values of the three types of groundwater， from highest to lowest， shown as follows： 929.7 mg·L^-1 （other bedrock groundwater） > 863.4 mg·L^-1 （quaternary groundwater） > 657.4 mg·L^-1 （basalt groundwater）. Additionally， the contents of Na⁺， Cl^-， NO₃^-， and F^- were lower in basalt groundwater than in other types of groundwater. The hydrochemical types of basalt groundwater and quaternary groundwater were mainly HCO₃-Ca·Mg type， while the other bedrock groundwaters were HCO₃-Ca·Mg and Cl·SO₄-Ca·Mg type. The chemical evolution of groundwater was primarily influenced by a combination of factors， including rock weathering， evaporation， crystallization， cation exchange， and human activities in the study area. There was little difference in the main ion sources of the three types of groundwater； weathering and dissolution of silicate minerals had the greatest influence on the quality of the groundwater， while carbonate and evaporite rocks also provided part of the source of groundwater composition. The principal control factors were leaching and concentration processes as well as the impact of human activities and inherent geological factor， whose cumulative contribution rates were 81.32%， 84.83%， and 77.39% separately for the quaternary aquifer， basalt aquifer， and other bedrock aquifer， respectively. Finally， suggestions on the exploitation of groundwater resources and crop cultivation were put forward based on the analysis of hydrochemical characteristics.