Spatial variability of organic carbon storage and sources in China’s subtropical Halophila beccarii seagrass meadow

Seagrass meadows are crucial in marine blue carbon storage. However, blue carbon storage of seagrass meadows in subtropical regions dominated by small-sized species may be overestimated, and the primary factors regulating organic carbon (C _org ) variability remain uncertain. Here we investigated spatial patterns in blue carbon storage and sediment C _org sources in China's subtropical estuarine meadows of the small seagrass, Halophila beccarii , and identified key environmental drivers influencing its spatial heterogeneity. The results revealed that these species may store less blue carbon than estimated, with low carbon stocks revealed in China’s estuarine meadows. Sediment carbon varied spatially, influenced by moisture, salinity, CaCO₃, and bulk density. Terrigenous sources contributed most sediment carbon, followed by seagrass, and phytoplankton, exhibiting distinct spatial variation along the transect. These findings highlight the need for refined blue carbon assessments in subtropical regions and suggest managing environmental factors to enhance seagrass carbon storage as a climate solution.