73 / 2023-07-27 18:12:56

Rising Sea-Level Reduces CO2 and N2O Flux while promoting CH4 Emissions from Mangroves: Evidence from Multi-latitudinal Simulations

mangrove,GHGs,sea level rise,marsh oragn

Sea-level rise (SLR) may offset gains made by enhancing mangrove carbon sequestration through greater greenhouse gas emissions. However, accurate prediction of greenhouse gas (GHG_s) fluxes under future SLR is still relatively uncertain. In this study, we implemented a series of “marsh-organs” (experimental platforms at different elevations) along a latitudinal gradient in China, simulating four sea-level scenarios. We investigated the factors driving and the patterns observed in ecosystem respiration (R_eco), methane (CH₄) and nitrous oxide (N₂O) fluxes from mangroves and adjacent mudflats. We examined environmental factors, soil properties, net primary productivity (NEP), and used structural equation models to map functional process impacts on GHG fluxes. Our findings revealed that SLR reduced NEP, R_eco, and N₂O fluxes while increasing CH₄ emissions in both mudflat and mangroves. SLR and latitudinal distribution significantly altered biological and abiotic factors that influenced GHG fluxes. The present R_eco for mudflat and mangroves ranged from 0.23 to 1.64 kg m^-2 year^-1, with 0.32 to 0.88 g m^-2 year^-1 in CH₄ emissions and 17.64 to 286.15 mg m^-2 year^-1 in N₂O emissions. The net global warming potential (GWP) from current mangrove GHG emissions is -10,897 to -1093 gCO₂ m^-2 year^-1 at Yunxiao (YX), followed by -4113 to -246 gCO₂ m^-2 year^-1 at Haikou (HK) and -987 to -83 gCO₂ m^-2 year^-1 at Aojiang (AJ). SLR stimulated CH₄ emissions in mangroves, increasing the CH₄ emissions by 20% and 12% under RCP 4.5 and RCP 8.5 scenarios, respectively. In contrast, SLR markedly inhibited R_eco emission by 42% and 56%, N₂O emissions by 23% and 32%, under RCP 4.5 and RCP 8.5 respectively. Moreover, NEP experienced a decrease from 27% to 50%, indicating a projected 24% to 51% reduction in the capacity for mangroves to mitigate climate change through reduced GHG emissions in the future. Moreover, CH₄ and N₂O can even contribute over 55% and 66% for GWP of mangroves at their northern limits. This serves as a reminder that we should give more attention to non-CO₂ emissions from mangroves.