Storage of CO2 by seagrass meadows
It was assumed that reclamation seagrass meadows on coasts is an effective natural means of storing large amounts of carbon dioxide from the atmosphere. A new study shows that the success of reclamation of seagrass meadows as a so-called blue carbon method depends on the location, since many chemical processes take place during the storage of CO2, which are decisive for the extent to which CO2 is stored or even released.
An international team of scientists led by Dr. Bryce Van Dam of the Hereon Institute for Carbon Cycles has combined 2 methods of measurement for the first time to create a complete carbon budget. The first method measured the direct exchange of CO2 between the water and the atmosphere. A second similar method determined the exchange of bicarbonate and other chemicals between the sediment and the water. Sampling was used to measure the interactions of geochemical processes in the sediments, which can be used to infer whether CO2 is being consumed or produced.
“Really, the novel aspect of this study is that we were able to combine all of these approaches together at the same place and at the same time,” says Bryce Van Dam. “By linking measurements in the sediment with related measurements in the water and in the air, we were able to track and account for the important processes that drive the ecosystem toward storing or releasing CO2.”
For more information, see the full Hereon press release:
==> Seagrass Is Not a Miracle Solution Against Climate Change
Van Dam, B.R., Zeller, M.A., Lopes, C., Smyth, A.R., Böttcher, M.E., Osburn, C.L., Zimmerman, T., Pröfrock, D., Fourqurean, J.W., & Thomas, H. (2021): Calcification-driven CO2 emissions exceed “Blue Carbon” sequestration in a carbonate seagrass meadow. Science Advances, Vol 7, Issue 51, doi:10.1126/sciadv.abj1372
Abstract:
Long-term “Blue Carbon” burial in seagrass meadows is complicated by other carbon and alkalinity exchanges that shape net carbon sequestration. We measured a suite of such processes, including denitrification, sulfur, and inorganic carbon cycling, and assessed their impact on air-water CO2 exchange in a typical seagrass meadow underlain by carbonate sediments. Eddy covariance measurements reveal a consistent source of CO2 to the atmosphere at an average rate of 610 ± 990 μmol m−2 hour−1 during our study and 700 ± 660 μmol m−2 hour−1 (6.1 mol m−2 year−1) over an annual cycle. Net alkalinity consumption by ecosystem calcification explains >95% of the observed CO2 emissions, far exceeding organic carbon burial and anaerobic alkalinity generation. We argue that the net carbon sequestration potential of seagrass meadows may be overestimated if calcification-induced CO2 emissions are not accounted for, especially in regions where calcification rates exceed net primary production and burial.
