South China Sea Annual Meeting 2023 (SCSAM)

8 / 2023-07-22 15:38:26

Dissolved Organic Carbon in Water Bodies of Typical Seagrass Meadow Ecosystems in China

Blue carbon,Seagrass meadow ecosystem,Carbon reservoir,Dissolved organic carbon,Bioavailability

Seagrass meadow ecosystems, along with mangrove ecosystems and salt marsh ecosystems, are significant blue carbon ecosystems recognized for their considerable potential in carbon sequestration. Of these, seagrass meadow ecosystems globally occupy less than 0.2 % of the ocean area but contribute to ~10 % of the yearly organic carbon burial in the ocean.

Previous studies addressing organic carbon in seagrass ecosystems have primarily focused on the sediment reservoir, leaving the investigation of another large carbon reservoir, i.e., dissolved organic carbon (DOC) in the water columns, relatively understudied. DOC in natural aquatic systems constitutes a large carbon pool composed of numerous bio-resistant and long-lived molecules, offering significant potential for carbon sequestration. As part of the Blue Carbon Ecosystems Assessment, Restoration and Accounting (BLUE-CARE) project, we conducted large-scale and time-series surveys of DOC in three typical Chinese seagrass meadow ecosystems spanned from temperate to tropical zones (Shandong, Guangxi, and Hainan). Results of our study revealed large spatio-temporal variability in distribution, composition, and reservoirs size of DOC in the water column of seagrass ecosystems. Regions dominated by seagrass often exhibited higher DOC concentrations compared to those with limited seagrass. Bioassay experiments suggested that a large portion of DOC in seagrass-dominated areas was resistant to microbial degradation. Reservoir size of DOC estimated in the water columns was strongly influenced by tidal changes, and it overall exhibited a net export of DOC. This finding implies a potentially important contribution of seagrass DOC export to carbon sequestration.