Long-term exposure to fly ash leachate enhances the bioavailability of potentially toxic metals and decreases bacterial community diversity in sediments.

The interaction between microorganisms and the physicochemical properties of sediments is the key to maintaining the stability of the ecological environment. However, the effect of fly ash stockpiling on the relationship between sediment bacterial communities and their physicochemical properties remains unclear. In this study, the interactions between geophysical and chemical factors, morphological distribution of potentially toxic metals (PTMs), and bacterial community diversity in sediments affected by long-term ash water seepage were examined. The results showed that (1) Ash water seepage markedly lowered the pH and elevated the electrical conductance; available potassium, available phosphorus, organic carbon contents; small particle size (<0.25 mm), and concentrations of eight PTMs, including nickel (P < 0.05); (2) Ash water seepage considerably raised the relative abundance of Proteobacteria in the sediments, reduced bacterial community α-diversity, and altered the community structure; (3) Bacterial communities in sediments were strongly correlated with the contents of available potassium organic carbon, selenium, arsenic (oxidizable and reducible), antimony (extractable with weak acids), and chromium (extractable with weak acids); and (4) Fly ash perturbation reduced the connectivity and cohesion in the molecular ecological network of sediment bacteria and increased the abundance of pollution-degrading metabolic pathways, such as low-toxicity and organic classes, as well as coupled stimulus-response and chemotaxis-avoidance defense mechanisms. In summary, the results of this study reveal the changes in bacterial communities, major physicochemical factors, and the morphological distribution of PTMs in sediments affected by long-term ash water leakage of fly ash landfills and provides a theoretical basis for ecological environmental management.