South China Sea Annual Meeting 2023 (SCSAM)

105 / 2023-07-30 22:05:15

Variations of surface water pCO2 in different seagrass ecosystems, China

Seagrass ecosystems, pCO2, physical-biogeochemical processes

Seagrass ecosystems are important wetland systems that are recognized as major blue carbon sinks. Although in general it is believed that complex biogeochemical processes influence the exchange of CO₂ between the seagrass water column and the atmosphere, there has been limited research on the carbon aquatic chemistry in seagrass meadows ecosystems. To address this gap, we conducted a time-series study in various typical seagrass ecosystems in China to investigate diurnal variations of surface seawater partial pressure of CO₂ (pCO₂). The surveys were carried out in autumn 2022, covering inshore regions such as Swan Lake in Shandong Province, Maowei Sea in Guangxi Zhuang Autonomous Region, and Li’an Port in Hainan Province. Our results showed significant diurnal changes of surface pCO₂ in all three locations, ranging from 444.2 - 862.6 μatm in the Zostera marina regions in Swan Lake, 687.0 - 1237.8 μatm in the Halophila beccarii regions in Maowei Sea, and 275.6 - 547.4 μatm in the Enhalus acoroides regions in Li’an Port. We further analyzed the influence of different physical-biogeochemical processes on surface water pCO₂. Tidal mixing appeared to be a major factor regulating surface water pCO₂ in the Maowei Sea, whereas biological processes largely modulated the pCO₂ variations in the Swan Lake and Li’an port. Results of this study demonstrate that different physical-biogeochemical processes may play important but different roles in regulating surface water pCO₂ in seagrass meadows, and thereby modulating CO₂ sink/source patterns.