Blue carbon is the carbon stored in coastal and marine ecosystems. Coastal ecosystems such as mangroves, tidal marshes, and seagrass meadows sequester and store 4-5 times more carbon per unit area than terrestrial forests and are now being 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. Therefore, it is vital to conserve these ecosystems, but the inadequacy of data on the ecosystem services provided by them, including carbon sequestration and storage poses a great debacle. This study aimed to assess the carbon storage capacities of mangroves, seagrasses and salt marshes in Sri Lanka.
The study was conducted in mangrove, seagrass and salt marsh habitats in connection with the Puttalam Lagoon in Anawasala and Soththupitiya in Puttalam District, North Western Sri Lanka. Both natural mangroves and 15 years old planted mangroves were included in the study. Belt transects were taken from the shore towards the land. Nested circular plots having a 7m radius were established, large trees were sampled for diameter at breast height (DBH) and height. Small trees (<3 cm DBH) were sampled in 2m radius. Litter, pneumatophores and seedlings were sampled in 30 cm x 30cm area plots. Soil samples were taken at depths; 0-30cm, 30-60cm, 60-100 cm for the measurement of bulk density and carbon content. The biomass of the mangrove plants was measured using species-specific allometric equations.
In the seagrass beds and salt marshes, belt transects were set up parallel to the beach (along the coastline), and 1 x 1m plots were sampled along this. The carbon content of the aboveground components was analyzed using Walkey Black Method, while the soil carbon was measured by Loss on Ignition (LOI) method using a muffle furnace. The data were analyzed using MINITAB statistical software.
Rhizophora mucronata and Avicennia marina were abundant in the natural mangroves while the former was the only one in the planted mangrove site. Enhalus acoroides was observed in the sea grass beds. The species observed in salt marshes were Suedo varae and Salicornia Brachiata.
In all three ecosystems the organic carbon content was higher in the Soil compared with the tree components. Natural mangroves showed the highest soil organic carbon (382.72 t/ha), while the planted mangroves showed only 148.26 tC/ha. The soil organic carbon of sea grass beds was 236.76 tC/ha, and salt marshes was 199.30 tC/ha. With regards to the organic carbon in the vegetative matter, natural mangroves showed the highest (206.48 tC/ha) followed by planted mangroves (175.8 tC/ha).
The contribution from the sea grass beds and salt marshes were negligent. When the total organic carbon from the ecosystem is considered, natural mangroves showed the highest (589.20 tC/ha), followed by planted mangroves (324.06 tC/ha), seagrass beds (236.76 tC/ha) and then salt marshes (199.3 tC/ha).
30 Dec 2022.