Blue carbon refers to carbon stored long-term (>100 years) in vegetated coastal and marine ecosystems, which constitutes an important sink for atmospheric carbon dioxide. However, during organic matter diagenesis methane and nitrous oxide can be produced or consumed. Methane and nitrous oxide have a global warming potential that is, depending on the 20-year or 100-year time-horizon, 81 to 28 for methane or 273 for nitrous oxide times respectively more powerful than carbon dioxide. As such, the production and release of methane and nitrous oxide from seagrass sediments has the potential to reduce the climatic benefit of carbon sequestered as blue carbon. Similarly, an uptake of methane and nitrous oxide  has the potential to enhance the climate benefit of seagrass communities. In this presentation we will present a synthesis of seagrass methane and nitrous oxide fluxes and organic carbon burial rates, and use these data to estimate the reduced climate benefit (offsets) of seagrass blue carbon. Three upscaling approaches will be presented (1) offsets for individual seagrass species, (2) a globally offset and (3) an offset for the Australian region. This presentation will highlight the importance of using long-term organic carbon burial rates and accounting for both methane and nitrous oxide fluxes in future seagrass blue carbon assessments.

Primary Presenter: Bradley Eyre, Southern Cross University (bradley.eyre@scu.edu.au)

Authors:

Bradley Eyre, Southern Cross University  (bradley.eyre@scu.edu.au)

Nicola Camillini, Alfred-Wegener-Institute  (Nicola.Camillini@awi.de)

Ronnie Glud, University of Southern Denmark  (rnglud@biology.sdu.dk)

Judith Rosentreter, Southern Cross University  (judith.rosentreter@scu.edu.au)