Rising sea level reduces carbon sequestration and CO2 and N2O fluxes while promoting CH4 flux from mangroves

Sea-level rise (SLR) may reduce mangrove carbon sequestration by increasing greenhouse gas (GHG) emissions—a key factor in forecasting the trajectory of blue carbon reserves. Nonetheless, predictions of future GHG fluxes under SLR remain uncertain. Unlike prior studies limited to controlled or single-site settings, we deploy cross-latitude “marsh-organ” designs in China to access GHG fluxes in mangroves and neighboring mudflats. Our findings show that SLR-stimulated CH₄ emissions in mangroves could increase by 10% under RCP 4.5 and by 22% under RCP 8.5, relative to current sea level by 2100. Conversely, SLR decreases ecosystem respiration and N₂O emissions by 35%–51% and 28%–36%, respectively, while net ecosystem productivity decreases by 12%–28% as SLR increases. Overall, our results forecast a 17%–30% decline in mangroves’ climate mitigation efficiency. We recommend focusing on non-CO₂ GHG emissions from mangroves, as they may significantly offset climate mitigation capacity under climate change.