The spatiotemporal variations and controls on the hydrochemistry of different aquifers under groundwater level fluctuations

Groundwater is an important water resource, systematically clarifying the geochemical characteristics, water quality status, and dominant controlling factors of groundwater in different aquifers is crucial for the sustainable management of water resources. However, the seasonal geochemical evolution and driving mechanisms of different aquifers under the influence of fluctuations in groundwater levels remain insufficient. To address this issue, this study proposed a comprehensive framework of hydrochemical characteristic analysis, self-organizing map (SOM), entropy weight quality index (EWQI) and structural equation modeling (SEM) to explore and quantify geochemical evolution processes and driving mechanisms of different aquifers during groundwater level fluctuations and evaluate its water quality suitability. Based on 32 groundwater samples collected from agricultural irrigation wells in June and October 2024, the framework aims to explore and quantify the geochemical evolution process and driving mechanisms of different aquifers in the Shijin Irrigation District (SID) during groundwater level fluctuations. With the rise of the groundwater level and seasonal changes, the improvement proportions of groundwater quality in shallow aquifers and deep groundwater are 62.5% and 50%, respectively. In terms of identifying the relationship between key control factors and water quality response, SEM reveals that groundwater quality is positively regulated by mineral dissolution and environmental factors, while negatively affected by ion exchange and evaporation effects. This study reveals the geochemical driving mechanism of groundwater, significantly improving the capability to identify key control factors in groundwater quality, and provides scientific support for sustainable groundwater management in similar hydrogeological backgrounds areas.