Globally, there is an increasing effort to incorporate seagrasses into blue carbon projects through meadow conservation or restoration. Here, we assessed the return of carbon sequestration and avoided emissions linked to the restoration of Amphibolis and Posidonia meadows in South Australia. Comparisons of organic carbon (C_org) stocks among undisturbed and restored A. antarctica (0.6±0.04 and 1.2±0.4 kg C_org m^-2, respectively) and P. sinuosa (1.5±0.4 and 0.5±0.3 kg C_org m^-2, respectively) meadows did not clearly show a return of C_org stocks and sequestration within 10-yrs recovery. The mixing and lack of excess ²¹⁰Pb radioisotopes precluded comparing stocks over the same period of accumulation, reflecting the high hydrodynamic nature of the sites. The comparison of C_org stocks between undisturbed and lost P. sinuosa meadows showed the likely erosion of 1.58 kg C_org m^-2, which could have been mitigated through restoration. Overall, the inability to robustly demonstrate C_org accumulation rats or erosion, and therefore, additionality linked to enhanced sequestration and avoided emissions, poses a major barrier to the inclusion of seagrass restoration efforts in verified carbon crediting schemes. We conclude that the selection of a depositional site known to accumulate sediment will likely be key to the success of seagrass blue carbon projects. Challenges with existing approaches for retrospectively demonstrating carbon accumulation calls for new methods to be developed to robustly demonstrate carbon abatement in seagrass restoration and recovery projects for carbon crediting.

Primary Presenter: Jack Robinson, Edith Cowan University (jack.robinson@ecu.edu.au)

Authors:

Jack Robinson, Centre for Marine Ecosystems Research, School of Science, Edith Cowan University, 270 Joondalup Drive, Western Australia 6027, Australia  (jack.robinson@ecu.edu.au)

Oscar Serrano, Centre d´Estudis Avançats de Blanes, Carrer Accés Cala Sant Francesc, 14, 17300 Blanes, Girona, Spain; Centre for Marine Ecosystems Research, School of Science, Edith Cowan University, 270 Joondalup Drive, Western Australia 6027, Australia.  (o.serranogras@ecu.edu.au)

Pere Masqué, Centre for Marine Ecosystems Research, School of Science, Edith Cowan University, 270 Joondalup Drive, Western Australia 6027, Australia; International Atomic Energy Agency, Marine Environment Laboratories, 4a Quai Antoine ler, 98000 Principality of Monaco, Monaco; Institute of Environmental Science and Technology (ICTA) and Physics Department, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain  (p.masque@ecu.edu.au)

Jason Tanner, South Australian Research and Development Institute, Aquatic Sciences, PO Box 120, Henley Beach, South Australia 5022, Australia; School of Biological Sciences, The University of Adelaide, Adelaide, Australia.  (Jason.Tanner@sa.gov.au)

Alison Turner, South Australian Department of Environment, Heritage and Sustainability, Climate Change, Coast and Marine Branch, GPO Box 1047, Adelaide, SA, 5001, Australia.  (Alison.Turner@sa.gov.au)

Milena Fernandes, South Australian Water Corporation, GPO Box 1751, Adelaide, SA 5001, Australia; College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia.  (Milena.Fernandes@sawater.com.au)