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

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 mu mol m(-2) hour(-1) during our study and 700 +/- 660 mu mol 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.

Automated summary

Long-term Blue Carbon burial in seagrass meadows is influenced by other carbon and alkalinity exchanges, with ecosystem calcification-induced CO2 emissions being the main contributor. Overestimation of net carbon sequestration potential may occur if these emissions are not taken into account.