Comparison of Hydrochemical Characteristics of Groundwater in the Qihe River Alluvial Fan of North China over the Past 35 Years

Groundwater resources play a crucial role in socioeconomic development and domestic water use in piedmont alluvial plain areas. In this study, the Qihe River alluvial fan (QRAF) was selected as a representative area to investigate the evolutionary patterns of shallow groundwater chemistry in the North China Plain (NCP). Based on shallow groundwater monitoring data collected during the wet seasons of 1983 and 2017, the spatiotemporal trends in chemical characteristics and their influencing factors in shallow groundwater in the QRAF were studied using multi-hydrochemical and statistical methods. The results showed that the groundwater in the QRAF was generally weakly alkaline, and groundwater quality has generally deteriorated over time. In particular, the concentrations of Cl‒ and NO3‒, two important indicators of water quality and pollution, increased significantly in 2017 compared with 1983. Although the groundwater chemical types were still dominated by HCO3-Ca and HCO3-Ca·Mg types, significant changes occurred along the middle to outer edge of the fan between 1983 and 2017, especially in the low-lying areas along the Weihe River. In 1983, the groundwater chemical composition was primarily controlled by natural processes such as water-rock interaction, whereas in 2017 it was additionally affected by anthropogenic activities, resulting in a more complex hydrochemical driving mechanism. The research findings can provide a reference for groundwater safety and protection management in the QRAF and other similar areas in the world.