Calcification-driven CO2 emissions exceed “Blue Carbon” sequestration in a carbonate seagrass meadow

Coastal management actions aimed at protecting or restoring seagrass meadows are often assumed to have the collateral benefit of removing large amounts of carbon dioxide from the atmosphere to combat climate change. Be aware, however: not all seagrass meadows are alike, and under certain conditions some release more carbon dioxide than they absorb, and are in fact net carbon sources to the atmosphere. This is now shown in a new study by an international team of researchers led by biogeochemist Bryce Van Dam from Helmholtz-Zentrum Hereon, published in the scientific journal Science Advances. This study combined direct eddy covariance measurements of air-water gas exchange with geochemical approaches to build a comprehensive carbon budget for a tropical seagrass meadow in south Florida. Revealed is that the process of ecosystem calcification released far more CO2 to the atmosphere than was buried in sediments as “Blue Carbon”. This study calls into question the reliability of Blue Carbon approaches towards net CO2 sequestration in tropical waters. But still unclear is how applicable these results are to the global scale, and what fraction of tropical seagrass meadows are net sources, rather than sinks, of CO2 to the atmosphere.

Reference: Bryce, R. V., Mary, A. Z., Christian, L., et al., (2021). Calcification-driven CO2 emissions exceed “Blue Carbon” sequestration in a carbonate seagrass meadow. Sci. Adv., 7(51). https://doi.org/10.1126/sciadv.abj1372.