Hydrochemical Characteristics of Groundwater and Its Influencing Factors in Yuanzi River Basin, Shuozhou, Shanxi, China

The Yuanzi River flows through the alluvial plain of Pinglu District, Shuozhou City, Shanxi Province, which belongs to the upper Sanggan Valley of Yongding River in the Haihe River Basin. The regional topography is representative of the Loess Plateau, where the loess layer has a high degree of homogeneity and depth of thickness. To study the changing rules of groundwater hydrochemistry and its influencing factors, we collected a total of 42 groups of groundwater samples in Pinglu District during the abundant and dry seasons. We used descriptive statistics, Piper diagrams and Gibbs diagrams, hydrogen and oxygen isotopes, and correlation analyses to investigate the hydrochemistry of the groundwater in the study area, as well as the main sources of ions and their influencing factors. The results show that: (1) The groundwater in the study area is neutral to weakly alkaline, and SO₄·Cl-Ca·Mg controls the water chemistry of the groundwater in both the abundant and dry periods; the water quality in the abundant period is better than that in the dry period; (2) the groundwater undergoes water-rock interaction and cation adsorption alternatively in the flow path, and the water chemistry is mainly affected by the weathering of the rock and the precipitation from the atmosphere; (3) in the study area, there are gypsum, rock salt, and nitrate dissolution, and the groundwater is affected by the weathering and dissolution of carbonate minerals and silicate minerals; the weathering and dissolution of carbonate minerals are stronger than that of silicate minerals; (4) the recharge of the groundwater is dominated by atmospheric precipitation, and the groundwater is affected by evaporation during the dry season when the groundwater receives atmospheric precipitation. In addition to the impact of the water rock interaction and atmospheric precipitation recharge, the surface water and the wastewater discharged by human activities also have a certain influence on the groundwater. This study reveals the hydrochemical characteristics and influencing factors of groundwater in the Yuanzi River Basin, and the results are of great significance to the formation and evolution of groundwater in the Loess Plateau, and to the development, utilization, and protection of water resources.