Quantification of blue carbon in tropical salt marshes and their role in climate change mitigation.

Vegetated coastal ecosystems (VCE) display a promising potential to act as natural carbon sinks in climate change mitigation. Although growing interest in wetland carbon has intensified the global level carbon stock estimation studies, large knowledge gaps and uncertainties remain, particularly in tropical salt marshes in the South and Southeast Asian regions. Therefore, the current study aims to quantify the organic carbon stocks in the salt marsh habitats on the Northwest coast of Sri Lanka and to showcase the relevance of salt marsh carbon in local and regional contexts. Vegetation and soil up to a depth of 50 cm were sampled from four sites representing the Wedithalathive Nature Reserve (WNR). Species-specific allometric relationships developed for the major succulent halophytic species indicated a significant positive correlation between dry biomass and plant height. The loss-on-ignition (LOI) technique was applied in combination with a carbon conversion factor to calculate the soil organic carbon (SOC) content across 4 depth intervals. The study provided an average total organic carbon (TOC) storage of 73 ± 14.47 Mg C ha up to a depth of 50 cm, in which the aboveground vegetation accounted for ~2% share. Sri Lankan salt marshes hold 2.01 Tg of organic carbon and directly reflect their potential for inclusion in Nationally Determined Contributions (NDCs) under the Paris Agreement. This has been the first comprehensive study on salt marsh blue carbon stocks in Sri Lanka and the findings of this study will strengthen the knowledge base on regional and global saltmarsh carbon stocks and their potential role in climate change mitigation.