Assessing Blue Carbon Storage in an Urbanized Coastal Region: Insights from Hong Kong's Seagrass Ecosystems

Seagrass meadows are globally important blue carbon sinks, accumulating organic carbon within their beds from both seagrass and the burial of non-seagrass organic matter. To date, substantial attention has been attracted on this nature-based carbon offsetting solution, especially for countries with large blue carbon resources (e.g., Australia, Indonesia, and USA). However, the carbon sink potential of small coastal regions characterized by high carbon densities of blue carbon ecosystems and its contribution to regional climate change mitigation efforts remain largely unclear. This study focusses on the quantification of seagrass carbon stock in an urbanized coastal area, Hong Kong. We collect 1-meter sediment cores from four sites (i.e., San Tau, Yam O, Sheung Pak Nai and Ha Pak Nai) covering two seagrass species (i.e., Halophila beccarii and Halophila ovalis). Our investigation encompasses the analysis of total organic carbon (OC%), organic carbon sources (δ13C and δ15N), labile and recalcitrant organic carbon pools, and organic carbon accumulation rates (Pb210) at various depths within the sediment cores. The results of this study will shed light on the extent to which seagrass ecosystems can contribute to Hong Kong's Nationally Determined Contributions, as assessed under the IPCC Tier-II framework.