Comment on bg-2021-359

Among many ecosystem services, macro-climate regulation via the storage of large amounts of organic carbon (OC) in marine sediments (also known as ‘blue carbon’) has given mangroves enormous global attention due to their role in climate change mitigation. While there are many studies on blue carbon potential of intact mangroves (i.e. naturally growing), there have been very few on restored mangroves (i.e. planted). This study aims to address this knowledge gap by examining sediment development process during early colonization (rehabilitation) of mangroves in an OC-poor estuary in the Panay Island, Philippines. Based on endmember source apportionment in sedimentary organic matter, the contribution of mangrove plant material was higher at the older sites compared to the younger settings or bare sediment where there is more contribution of riverine input. A clear increasing gradient according to mangrove development was observed for bulk OC (0.06 to 3.4 µmol g−1), porewater OC (292 to 2150 µmol L−1), sedimentary OC stock (3.13 to 77.4 Mg C ha−1) and OC loading per surface area (7 to 223 µmol m−2). The estimate of carbon accumulation rates (6 to 33 mol m−2 yr−1) based on chrono-sequence are within the global ranges and show an increasing pattern with mangrove age. Although a differential yet systematic pattern of increasing OC sink based on short-term chrono-sequence can define the role of a mangrove rehabilitation program, there is a need for long-term monitoring to verify the consistently elevated OC with mangrove growth.