Assessing Multiple Carbon Fluxes in a Temperate, Pacific Seagrass Meadow

Conservation and restoration of submerged aquatic vegetation have been proposed as strategies for combatting the effects of increases in oceanic and atmospheric carbon dioxide (CO₂) concentrations. Seagrass meadows can act as carbon sinks by (1) drawing down atmospheric CO₂; (2) absorbing aqueous carbon in seawater; and (3) sequestering organic carbon in sediment. However, few studies consider multiple carbon fluxes or how they interact with one another within a given seagrass meadow, often leading to apparent discrepancies in the net carbon values assigned to meadows.Here, we analyzed three key carbon cycle components in a temperate seagrass meadow (Zostera marina). We specifically focused on atmospheric CO₂exchange, seawater carbonate chemistry, and carbon burial. Atmospheric exchange over the meadow, despite high temporal variability, served as a significant net annual sink for atmospheric CO₂, absorbing 491.47 ± 46.63 g C m^-2 y^-1. A first order estimate of seagrass metabolism indicated net absorption of 227 g C m^-2yr^-1in summer and 746 g C m^-2yr^-1in winter. Seagrass metabolism also increased temporal variability in pH and DO (dissolved oxygen). Variability in DO concentration correlated with overlying air-sea fluxes, suggesting that seagrass photosynthetic activity can influence atmospheric CO₂drawdown. Lastly, a substantial amount of carbon is buried and stored annually in meadow sediments, with a burial rate of 12.74 – 16.99 g C_orgm^-2yr^-1producingorganic carbon stocks of 4.1 ± 0.37 mg cm^-3. Together these data help elucidate the interdependencies of carbon fluxes in seagrass meadows and their role in climate change and OA mitigation.