Peatland rewetting with freshwater reduces carbon dioxide (CO 2 ) emissions but often increases methane (CH 4 ), undermining its climate benefits. Brackish water, rich in sulfate (SO 4 2– ), offers a potential alternative for CH 4 mitigation. However, its effectiveness and dominant mechanisms across different coastal land uses remain unclear, hindering broader application. Here, we conducted a four-month incubation experiment using intact soil cores from eight drained coastal peatlands representing four land-use types: grass-cut, grass-graze, arable, and unmanaged. We assessed CH 4 emissions from soils rewetted with either natural brackish water (SO 4 2– = 392 ± 2 mg L –1 ) or synthetic water containing 0% (simulating freshwater), 50%, or 100% of the natural SO 4 2– concentration. Results showed that natural brackish water significantly suppressed CH 4 emissions by ∼90% compared to freshwater, with stronger suppression in grass-cut, arable, and unmanaged soils, but limited effects in grass-graze sites. Such differences were attributed to land-use-induced soil variations, where higher pH and lower methanogen relative abundance enhanced suppression. Mechanistically, natural brackish water primarily suppressed CH 4 via physiological inhibition of methanogens (likely through salt stress and hydrogen sulfide toxicity). This effect persisted after SO 4 2– reduction inhibition (day 90) and lasted until the end of incubation, reflecting resilience to short-term SO 4 2– depletion. Our study advances understanding of CH 4 dynamics and informs targeted use of brackish water rewetting for CH 4 mitigation in coastal peatlands.
Guo et al. (Fri,) studied this question.