Carbon stocks of the mangrove forest in Mwache creek, Mombasa, Kenya

Abstract

It is generally accepted that escalating concentrations of atmospheric carbon dioxide (CO2) are driving changes in climate patterns. Policy mechanisms such as ‘Reducing Emissions from Deforestation and forest Degradation’ (or REDD+) aim to reduce CO2 levels in the atmosphere through compensating landowners to manage their land as carbon sinks. However, for such a scheme to succeed accurate quantification and reporting of the sequestered carbon must be conducted using verifiable methodology. Vegetated coastal habitats, such as mangrove forests, provide an opportunity to develop a carbon offset project.In Kenya, mangroves face a myriad of human and natural induced stresses ranging from over-exploitation of resources, conversion pressure, and sea level rise. The degradation presents an opportunity for engaging in carbon markets through rehabilitation, conservation and sustainable utilization of mangrove resources. This study at Mwache creek, in Mombasa, aimed at estimating total mangrove carbon stocks in the area; in order to provide baseline information in which future offset projects could be based. Systematic stratified sampling technique was used in the study. Three carbon pools were considered, viz: Above ground, below ground (root) and soil carbon pools. Soil cores were collected at the center of 10 x 10 m2 plots laid 100 m apart along transects. For each soil core, four sub-samples; viz., 0-15; 15-30; 30-50; and 50-100 cm were extracted for analysis of soil structure, bulk density and carbon concentration. Wet sieving was used to determine soil structure; whereas organic matter and carbon concentration were determined using loss on ignition (LOI) and the colorimetric methods. The study results indicate a statistical difference (p<0.05) in the vertical distribution of soil organic carbon but no statistical difference (p>0.05) in the horizontal distribution along the sea-land transects. A statistical difference (p<0.05) in the soil carbon was observed across degradation gradients with less degraded sites exhibiting higher concentrations. Above and below ground biomass was obtained using published allometric equations (230.6 and 82.7 Mg ha-1, respectively) and used to determine associated carbon. The derived above and below ground carbon was added to the soil carbon to obtain total mangrove carbon of the area. The total mangrove carbon in Mwache was estimated at 388.92 Mg C ha-1 of which 63% was soil carbon, 28% above ground carbon, and 9% below ground carbon. These findings provide a good baseline data for establishment of a small scale blue carbon project in the area.