Arsenic mobility and microbial community composition in the sediments of coastal wetlands driven by tidal action

Arsenic (As) pollution in coastal wetlands has been receiving growing attention. However, the exact mechanism of As mobility driven by tidal action is still not completely understood. The results reveal that lower total As concentrations in solution were observed in the flood-ebb treatment (FE), with the highest concentration being 7.1 µg/L, and As(V) was the predominant species. However, elevated levels of total As in solution were found in the flooded treatment (FL), with a maximum value of 14.5 µg/L after 30 days, and As(III) was the predominant form. The results of dissolved organic matter (DOM) suggest that in the early to mid-stages of the incubation, fulvic acid-like substances might be utilized by microorganisms as electron donors or shuttle bodies, facilitating the reductive release of As/Fe from sediments. Both flood-ebb and flooded treatments promoted the transformation of crystalline iron hydrous oxides-bound As into residual forms. However, prolonged flooded conditions more readily facilitated the formation of specific adsorption forms of As and the reduction of crystalline iron hydrous oxides-bound As, increasing As mobility. In addition, the flood-ebb tides have been found to increase the diversity of microbial populations. The main microbial genera in the flood-ebb treatment included Salinimicrobium, Erythrobacter, Yangia, Sulfitobacter, and Marinobacter. Bacillus, Psychrobacter, and Yangia showed a significant correlation with As(V). In flooded treatment, Bacillus, Pseudomonas, and Geothermobacter played a major role in the reduction and release of As. This study significantly contributes to the current understanding of how As behaves in diverse natural environments.