Seagrass meadows is a typical coastal blue carbon ecosystem, is subject to complex biogeochemical processes. Depending on the aquatic environment, an ecosystem featuring seagrass beds can either a source or sink of atmospheric carbon dioxide (CO₂). This study takes an ecosystem approach and investigates the spatial and temporal variations of surface seawater pCO₂ (partial pressure of CO₂) in a shallow and semi-enclosed wetland system featuring seagrass beds (primarily Enhalus acoroides) located in the Li’an Port of Hainan Island. There were significant diurnal variations in surface water FCO₂ (CO₂ fluxes) and during our surveys in different seasons, spring is carbon weak carbon sink and summer and fall are weak carbon source in the Enhalus acoroides dominated ecosystem. With a semi-analytical framework by assessing the consumption of dissolved inorganic carbon relative to nutrients, we analyzed the influence of different processes on pCO₂ in the seagrass bed ecosystems under study. We reveal that temperature was not a major driver of the pCO₂ variability in the seagrass ecosystem, and its inter-seasonal changes are substantially regulated by non-thermal factors such as water mass mixing, net primary production and net primary calcification.

Seagrass bed ecosystem, pCO2, CO2 fluxes, non-thermal factors