Assessment of Carbon Stock in Mangrove Forests of Akwa Ibom State Using Allometric Methods

Mangrove forests in the coastal zone of Akwa Ibom State store substantial quantities of organic carbon across above-ground biomass, below-ground roots, and sediment pools, yet this carbon stock remains unquantified, limiting the state's contribution to Nigeria's nationally determined contributions under the Paris Agreement. This study estimates the above-ground and below-ground carbon stocks of mangrove forests in three creek systems in Akwa Ibom State using field-based allometric methods. Circular inventory plots were established at thirty locations across Rhizophora-dominated and mixed species stands. Tree diameter at breast height, height, and species identity were recorded for all stems within plots. Above-ground biomass was estimated using mangrove-specific allometric equations, and below-ground biomass was calculated using a root-to-shoot ratio derived from regional literature. Soil carbon was assessed through sediment core sampling to 100-centimetre depth, with organic carbon determined by loss on ignition. Above-ground carbon stock averaged 112 tonnes of carbon per hectare in intact stands, while degraded stands averaged 43 tonnes. Below-ground carbon exceeded above-ground stocks by approximately 2.3-fold, consistent with published global averages. Total ecosystem carbon was estimated at 487 tonnes of carbon per hectare for intact mangrove. Spatial heterogeneity was high, driven by tidal inundation frequency and proximity to oil spill sites. Inclusion of Akwa Ibom mangrove in formal blue carbon accounting frameworks is strongly recommended. Keywords: carbon stock, mangrove, blue carbon, Akwa Ibom State, allometric equations