Sediment deposits and organic carbon sequestration along mangrove coasts of the Leizhou Peninsula, southern China

Mangroves are an important affecter of atmospheric CO2 level via sequestrating carbon and trapping sediments. However, their sequestrating effectiveness varies with vegetation development and sedimentation processes under site-specific hydrogeomorphic settings. In order to detect the determinants of organic carbon sequestration, this study investigated four mangrove fringing locations along the coast of the Leizhou Peninsula. Surface and core sediment samples were collected from these sites and analyzed for grain-size distribution, sedimentary organic carbon content (SOCC) and stable isotope signature (δ13Corg). It is found that a significantly higher concentration and density of organic carbon were preserved in the interior surface sediments regardless of location or surface grain size distribution. The sedimentary environments, as indicated by core sediment analysis, are controlled under low-to moderately low-energy conditions. Fluvial action on these sedimentary environments decreases from the river dominated site to the tide dominated site. The more stable energy condition favored both sediment and organic carbon accumulation in the mudflat subzone. However, as revealed by δ13C signature, sedimentary organic carbon of the core samples from the four sites was dominantly derived from suspended particulate matter except the tide-dominated offshore core. Whereby, we conclude that vegetation provided control on the surface sedimentary organic carbon distribution via its influence onmangrove debris input and fluid energy condition over the intertidal surface, while hydrogeomorphology determined the long-term organic carbon burial via its impact on the local sedimentation accretion rate and the proportion of autogenous organic carbon sequestration.