Impact of restoration on reducing carbon emissions from different blue carbon ecosystems

Abstract

Blue carbon ecosystems (BCEs) are natural climate solutions. There is uncertainty regarding the impact of different restoration strategies on carbon emissions of BCEs, with greenhouse gas fluxes potentially offsetting part of carbon sequestration. Field surveys were performed to measure carbon emissions, sediment δ13C and gas isotopes of restored and natural BCEs in subtropical China, and identified the controlling factors and sources of carbon emissions. CO2and CH4emissions at the sediment-air interface were influenced by abiotic and biotic factors. The emissions at the water-air interface were controlled by abiotic factors, explaining 86.8 % and 93.8 % of the variance in CO2and CH4, respectively. Carbon dioxide emissions from mangroves restored with alien species (14.5 ± 2.9 to 22.1 ± 4.8 mmol m−2d−1) were significantly higher than those restored with native mangrove species and invasive marsh species (1.3 ± 0.6 to 1.9 ± 1.0 mmol m−2d−1). CO2fluxes from mangroves and seagrass beds restored with native species were lower than those at natural sites. CO2fluxes from large estuaries were significantly lower than those from small estuaries. Methane emissions at the sediment-air and water-air interfaces are mainly due to carbonate reduction and acetate fermentation, respectively. Methane flux offsets 11.0 % and 3.5 % of carbon accumulation in mangrove and seagrass sediments, respectively, lower than global estimates of 20.50 % and 28.85 %. Our results highlight that BCEs restored with native species are effective in reducing carbon emissions compared with those restored with alien species, and the use of alien mangrove species to control the invasive species of tidal marshes enhances carbon emissions.