The eastern Guanzhong Basin, a typical endemic fluorosis area in China, exhibit pronounced geomorphological differentiation characteristics in fluoride enrichment mechanisms within its shallow groundwater. However, existing studies have been predominantly limited to single geomorphic units, with insufficient understanding of multi-scale geomorphic controls and the spatiotemporal heterogeneity of hydrogeochemical processes.

Objective From a comparative study perspective across multiple geomorphological units, this research reveals the hydrochemical characteristics of shallow fluoride-containing groundwater and the variations in dominant fluoride enrichment mechanisms.

Methods In this study, 94 groundwater samples were collected from the Loess Plateau, Beiluo River valley, and Weihe River terrace, with fluorine and major ions in these samples were measured. The hydrochemical characteristics, distribution characteristics, and genesis differences of shallow high-fluoride groundwater across different geomorphological units were analyzed using mathematical statistics, Gibbs diagram, and Piper diagram.

Results The results show that the shallow groundwater is weakly alkaline, with high fluorine, total dissolved solids and sodium ions, and the hydrochemistry type is relatively complex. Fluorine concentrations are lower in the Beiluo River valley and higher in the Weihe River terrace and Loess Plateau. The vertical distribution of fluorine concentration in the groundwater of the Loess Plateau and Weihe River terrace exhibited a declining trend with increasing burial depth. The fluorine concentration in the groundwater of the Beiluohe terrace demonstrates an increase with increasing depth of burial. From the Loess Plateau in Sunzhen to the Beiluo River valley, fluorine concentrations gradually decreased with the extension of the groundwater discharge pathway. In the direction from the Loess Plateau in Weizhuang to the Weihe River terrace, fluorine concentrations gradually increased upward.

Conclusions The results demonstrate significant differences in the dominant fluoride enrichment mechanisms across various geomorphological units. In the Loess Plateau area, fluoride enrichment is primarily controlled by the synergistic effects of silicate weathering and ion exchange-driven leaching processes. In contrast, the secondary and tertiary terraces of the Weihe River exhibit notable evaporation-concentration effects, where intensive evapotranspiration leads to secondary enrichment of fluoride ions. The first-level terrace of the Beiluo River shows distinct dilution effects due to close hydraulic connectivity between surface water and groundwater through their active interactions. These study provide a spatial differentiation theoretical basis for risk zoning of high-fluoride groundwater and targeted prevention strategies for endemic fluorosis control.