Geological and Anthropogenic Factors Jointly Influence Hydrochemical Interactions between Groundwater and Surface Water in the Middle and Lower Yellow River

Abstract

The interaction between groundwater and surface water plays a crucial role in regulating water resource availability and maintaining ecosystem stability, particularly through hydrochemical exchange processes. However, at the regional scale, the driving factors governing hydrochemical interactions between groundwater and surface water remain inadequately understood. This study aims to identify the dominant controlling factors and ion sources influencing hydrochemical interactions in the middle and lower reaches of the Yellow River. A comprehensive literature review was conducted on the hydrochemical characteristics of groundwater and surface water across China. Ultimately, 150 representative sampling sites located in the middle and lower Yellow River Basin were selected, encompassing 28,351 groundwater samples and 15,487 surface water samples. Sampling was conducted during both the rain and dry seasons, covering different hydrological periods. Hydrochemical characteristics were analyzed by using a combination of hydrogeochemical statistical methods, Piper diagrams, ion ratio relationships, Gibbs plots, and Principal Component Analysis (PCA). Furthermore, the Absolute Principal Component Scores–Multiple Linear Regression (APCS-MLR) model and PHREEQC geochemical simulations were applied to quantify the contributions of different ion sources and assess mineral dissolution and precipitation processes. The results show that the main ions in groundwater and surface water mainly come from rock weathering, evaporation, and human activities. The dissolution of carbonates and gypsum is the source of Ca²⁺, Mg²⁺ and HCO₃^– in groundwater and surface water. In addition, the discharge of industrial wastewater and domestic sewage contributed significantly to Cl^–, SO₄^2– and Na⁺. The K⁺ and NO₃^– ions might be due to the application of nitrogen and potassium fertilizers, although contributions from other sources (e.g., sewage, natural mineral dissolution) cannot be excluded. Moreover, the PCA and APCS-MLR analyses indicated that the hydrochemical interactions between groundwater and surface water were predominantly controlled by geological conditions (48.979%), followed by agricultural activities (16.773%), industrial influences (12.276%), and unidentified factors (21.972%). Among these, geological factors and mineral dissolution processes emerged as the most significant controls. Unidentified factors may include unmeasured variables such as atmospheric deposition, localized anthropogenic inputs, or complex groundwater–surface water exchange dynamics not fully captured by the model. These findings provide a comprehensive understanding of the mechanisms driving groundwater–surface water hydrochemical interactions and offer valuable insights for regional water resource management, sustainable utilization, and ecological environment conservation in the Yellow River Basin.