Factors influencing organic carbon accumulation in mangrove ecosystems

There is growing interest in the capacity of mangrove ecosystems to sequester and store 'blue carbon'. Here, we provide a synthesis of 66 dated sediment cores with previously calculated carbon accumulation rates in mangrove ecosystems to assess the effects of environmental and anthropogenic pressures. Conserved sedimentary environments were found to be within the range of the current global average for sediment accretion (approx. 2.5 mm yr^-1) and carbon accumulation (approx. 160 g m²² yr²¹). Moreover, similar sediment accretion and carbon accumulation rates were found between mixed and monotypic mangrove forests, however higher mean and median values were noted from within the forest as compared to adjacent areas such as mudflats. The carbon accumulation within conserved environments was up to fourfold higher than in degraded or deforested environments but threefold lower than those impacted by domestic or aquaculture effluents (more than 900 g m²² yr²¹) and twofold lower than those impacted by storms and flooding (more than 500 g m²² yr²¹). These results suggest that depending on the type of impact, the blue carbon accumulation capacity of mangrove ecosystems may become substantially modified.