Hydrochemical Characteristics and Driving Factors of Groundwater in the Wet Season: A Case Study of the Henan Section of the Lower Yellow River

Shallow groundwater in the lower Yellow River alluvial plain is influenced by river seepage and multiple human activities, yet its hydrochemical evolution mechanisms remain unexplored. To bridge this gap, our study integrates hydrochemical analysis, ion ratio plots, and multivariate statistical techniques to reveal the hydrochemical characteristics, controlling factors, and anthropogenic influence mechanisms on groundwater chemistry in the Henan section of the lower Yellow River during the wet season. The results indicate that groundwater chemistry in the lower Yellow River is strongly influenced by rock weathering and human activities. When compared with the Class III limits of GB/T 14848-2017, 42.6%, 25.7%, 20.8%, 17.8%, and 17.8% of the samples exceed the limits for TH, TDS, Na+, Cl−, and SO42−, respectively. The dominant hydrochemical facies is HCO3-Na·Ca, accounting for 28.7% of all samples, and rock weathering constitutes the fundamental control on groundwater hydrochemistry. Within this framework, silicate weathering serves as the principal natural source for dissolved ions, while domestic sewage, industrial effluents and agricultural non-point pollution represent anthropogenic contributors to groundwater chemical composition. Principal component analysis results indicate that a mixed factor jointly influenced by evaporite–silicate weathering, evaporation–crystallization processes, and sewage discharge (44.1% contribution) is the main driving mechanism of groundwater hydrochemical variation in the wet season, while carbonate weathering (19.0%) and agricultural fertilization (13.4%) exert a comparatively minor driving influence. This study provides an in-depth understanding of the evolutionary mechanisms of groundwater chemical constituents in the lower Yellow River, offering a scientific basis for groundwater protection in this region and similar intensely human-disturbed areas.