Overlying water fluoride concentrations influence dissolved organic matter composition and migration from pore water in sediment via bacterial mechanisms

Fluoride (F^-) is widespread in aquatic environments; however, it is not clear whether the fluctuation of F^- concentrations in overlying lake water affects the composition and migration of dissolved organic matter (DOM) from sediment. A case study was presented in Sand Lake, China, and an experiment was conducted to analyze the influence of different F^- concentrations in overlying water on DOM characteristics. Diffusion resulted in similarities in DOM components between overlying and pore waters, and bacterial activities and enzyme variation resulted in differences between them. Higher F^- concentrations in overlying water resulted in a higher pH of pore water, which favored the enrichment of protein-like substances. Higher F^- concentrations caused lower DOM concentrations and lower maximum fluorescence intensities (F_max) of protein-like components in pore water. The F^- concentrations had significantly negative correlations with Shannon indexes (P < 0.05). Thiobacillus influenced the migration of tyrosine-like substances by decreasing the pH of pore water. Trichococcus and Fusibacter altered the F_max of protein-like, humic-like, and fulvic-like substances. The F^- concentrations affected the DOM composition and migration due to the response of functional bacterial communities, which were positively correlated with the relative abundance of Thiobacillus and negatively correlated with the relative abundances of Trichococcus and Fusibacter. The high F^- concentrations influenced the biosynthesis and degradation of protein-like substances by shifting the abundances of the relevant enzymes. The results of this study may provide ideas for investigating DOM cycling under the influence of F^-, especially in lakes with fluctuations in F^- concentrations.