Enhancing phosphorus mobilization from sediments toward recovery via carbon-stimulated sulfate reduction under anaerobic conditions

Mobilization of sedimentary phosphorus (P) for subsequent recovery is a promising strategy to mitigate long-term eutrophication and alleviate global P resource shortages, yet the coupled biogeochemical mechanisms controlling this process remain poorly understood. In this study, anaerobic batch reactors were used to examine the individual and combined effects of glucose (1 g/L) and sulfate (up to 8 mM) addition on P release from the Baltic Sea sediments. Combined glucose and sulfate addition markedly enhanced dissolved P release compared with single-factor treatments and controls. Early-stage enhancement (Day 12 of a 36-day incubation) was dominated by inorganic P (IP) release (~10%), likely driven by sulfate reduction and sulfide-mediated Fe-P dissolution. In the later stage (Day 36), IP removal in the 8 mM sulfate treatment decreased to 1.4%, suggesting P re-retention in the sediments, whereas organic P (OP) mobilization increased to 18%, indicating a shift towards OP mineralization as the main release pathway. Microbial community analysis revealed that sulfate addition under glucose-rich conditions had limited effects on overall taxonomic composition, but induced functional shifts associated with P cycling, particularly genes related to P mineralization during glucose depletion and increasingly reducing conditions. Sulfate may appear to promote the conversion of butyrate to acetate/propionate, potentially enhancing energy availability for microbial OP mineralization. Overall, this study provides mechanistic insights into carbon-sulfur-P coupling in brackish sediments, offering a scientific basis for designing strategies to enhance sediment P mobilization toward downstream recovery and internal P loading control. • Integrated carbon-sulfur-P metabolism facilitated sediment P release • Glucose and sulfate synergistically enhance P mobilization • Organic P mineralization dominated P release at Day 36 under anaerobic conditions • Fermentation shifts stimulate sulfate reduction and sulfide-mediated Fe-P dissolution • Functional microbial changes dominate over taxonomic shifts in P release dynamics