Carbon stocks in two temperate Zostera meadows in the Yellow Sea, North China

Seagrass meadows play a crucial role in carbon sequestration, but the control factors for their carbon storage efficiency and carbon sources remain unclear. In this study, we investigated carbon sequestration in two seagrass meadows characterised by similar geomorphic features but differing in sediment types and seagrass species composition—Zostera marina and Z. japonica. We collected sediment cores approximately one meter in length to assess carbon stocks and compositions. The results suggest that mud content of sediments has a greater impact on carbon stocks than seagrass species. We find that carbon buried in seagrass meadows of open gulfs are mainly sourced from phytoplankton rather than seagrass themselves, and the sediments under seagrass coverage exhibit an even higher phytoplanktonic contribution than bare sediments. Our study also suggests a general overestimation of carbon stocks from short sediment cores in areas with seagrass distribution, but an underestimation in bare sediments. Furthermore, the study highlighted a vital proportion of inorganic carbon in the temperate Z. japonica meadows, emphasizing the importance of analyzing inorganic carbon content in these ecosystems. Overall, these findings highlight the complexity of sediment carbon stocks in seagrass meadows and the urgent need to understand the underlying mechanisms of carbon sequestration dynamics.