Quantifying Carbon Stocks and Carbon Sequestration Rates in Mangrove and Freshwater Wetlands of the Niger Delta Using Field and Remote Sensing Methods

This study quantifies above-ground and below-ground carbon stocks and annual carbon sequestration rates in intact mangrove and freshwater swamp forests of the Niger Delta, South South Nigeria, using an integrated field measurement and satellite remote sensing approach. The Niger Delta's wetland ecosystems contain substantial blue carbon stocks whose accurate quantification is essential for Nigeria's NDC accounting, REDD+ programme development, and voluntary carbon market engagement. Field plots were established at twelve representative sites across mangrove and freshwater swamp forest zones in Bayelsa and Delta States. Above-ground biomass was measured using allometric equations validated for West African mangrove species. Below-ground root biomass was measured by excavation and core sampling. Soil organic carbon stocks were determined from soil core profiles to one-metre depth. Sediment accretion rates were measured using feldspar marker horizons at selected sites. Remote sensing analysis used Sentinel-2 and ALOS PALSAR satellite data to estimate canopy biomass at the landscape scale and extrapolate field plot measurements. Results show that intact mangrove sites contain mean above-ground carbon stocks of 142 megagrams of carbon per hectare, with below-ground soil carbon stocks averaging 380 megagrams per hectare, substantially higher than temperate forest equivalents. Annual carbon sequestration in undisturbed sites averages 5.8 megagrams of carbon per hectare per year. Oil-impacted sites show 65 to 78 percent reductions in carbon stocks relative to intact reference sites. Landscape-scale carbon stock mapping reveals 218 megatonnes of carbon stored in the study area wetlands. Keywords: carbon sequestration, mangrove carbon, blue carbon, Niger Delta, remote sensing.