[Distribution Characteristics and Genetic Analysis of Fluorine in Groundwater in Middle Reaches of Heihe River]

Excess fluoride （F^-） in groundwater can be harmful to the health of local residents who depend on it. To study the distribution characteristics and genetic mechanism of high fluoride groundwater in the middle reaches of the main stream of Heihe River, 196 sets of shallow groundwater samples and 9 sets of middle and deep groundwater were collected. Mathematical statistics, Durov diagram, Gibbs diagram, and ion ratio relationship were comprehensively used to explore the distribution characteristics, sources, and influencing factors of fluoride in the groundwater. The results showed that ρ（F^-） of shallow groundwater in the study area ranged from n.d to 2.71 mg·L^-1, and ρ（F^-） in the middle and deep groundwater ranged from n.d to 0.69 mg·L^-1. The spatial distribution trend of F^- concentration in groundwater was high in the northeast and low in the southwest and the F^- concentration decreased with increasing depth. The main chemical type of the regional shallow high fluoride groundwater was SO₄·HCO₃-Na·Mg, which was mainly distributed in the groundwater discharge area of the piedmont plain of Heli Mountain. Hydrogeological environment and aquifer lithology were the main factors affecting the shallow high fluoride groundwater in the middle reaches of the Heihe River. Fluoride-rich minerals in mountainous areas were the source of F^- in groundwater. The alkaline groundwater environment, cation exchange adsorption, and evaporation further promoted the enrichment of F^-. This study aims to clarify the source of fluoride in regional groundwater and identify the hydrogeochemical processes and influencing factors of F^- enrichment in groundwater, which is essential to ensure the sustainable development of water resources in arid areas.