Assessment of the Blue Carbon Stocks Including Mangroves, Seagrasses, Salt Marshes and Algae in Selected Locations in Northern Province, Sri Lanka

Blue carbon is carbon stored in coastal and marine ecosystems. Coastal ecosystems such as mangroves, tidal marshes, seagrass meadows and algae sequester and store more carbon per unit area than terrestrial forests and are now recognized for their role in mitigating climate change. However, most of these coastal ecosystems are not under protection; hence, their potential as carbon sinks could be threatened. This study aimed to assess the carbon storage capacities of mangroves, seagrasses, salt marshes and algae in selected locations in Northern Province, Sri Lanka. The study was conducted in Vidathalathivu in Mannar, Kiranchi in Kilinochchi and Pooneryn. With regard to For mangrove sampling, belt transects were taken from the shore toward the land. Nested circular plots with a 7m radius were established. Large trees were sampled for diameter and height. Small trees (<3 cm DBH) were sampled in a 2m radius. Litter, pneumatophores and seedlings were sampled in plots of 30 cm x 30cm area. Soil samples were taken at depths; 0-30cm, 30-60cm, 60-100 cm for the measurement of bulk density and carbon content. In the salt marshes and sea grasses, 1 x 1m plots were sampled. 22m x 7m plots were used for planted algae in the sea. In all the ecosystems studied, soil contributed to the highest organic carbon. Mangroves recorded the highest carbon content (695.03 Mg/ha), followed by seagrasses (266.55 Mg/ha), salt marshes (203.95 Mg/ha), and algae (0.38 Mg/ha). The carbon sequestration rate of mangroves was 6.52 Mg/ha/yr. These blue carbon stocks could offset approximately 1.2% of Sri Lanka's annual carbon emissions if properly protected. However, these ecosystems face significant threats from coastal development, aquaculture expansion, and climate change impacts like sea-level rise. The study highlights the significance of conserving and restoring blue carbon ecosystems in mitigating climate change, and provides baseline data for potential carbon offset initiatives that could be valued at US$126-378 per hectare annually, based on current carbon market prices.