Methane emissions partially offset “blue carbon” burial in mangroves

Organic matter burial in mangrove forests results in the removal and long-term storage of atmospheric CO(2), so-called “blue carbon.” However, some of this organic matter is metabolized and returned to the atmosphere as CH(4). Because CH(4) has a higher global warming potential than the CO(2) fixed in the organic matter, it can offset the CO(2) removed via carbon burial. We provide the first estimate of the global magnitude of this offset. Our results show that high CH(4) evasion rates have the potential to partially offset blue carbon burial rates in mangrove sediments on average by 20% (sensitivity analysis offset range, 18 to 22%) using the 20-year global warming potential. Hence, mangrove sediment and water CH(4) emissions should be accounted for in future blue carbon assessments.