Saltmarshes have gained recognition as blue carbon habitats with a high capacity to act as effective sinks of organic carbon (OC) and their protection and restoration helping slow down global warming. However, regional estimates of saltmarsh OC storage are often missing, including for the Nordic region. To address this knowledge gap, we assessed OC storage and accumulation rates in 17 saltmarshes distributed along the Danish coasts and investigated main drivers of sediment OC storage. Danish saltmarsh sediments store 10 kg OC m^-2 (range: 5.4-36.4) in the top meter and sequester 31.5 g OC m^-2 yr^-1 (range: 5-142), values at the lower end of global estimates. Grazed but also older and stable saltmarshes had higher OC stocks and accumulation rates, highlighting the significance of ecosystem stability in maximizing OC potential. Saltmarsh sediments in mesohaline settings with fine grain sizes, and high proportion of eelgrass organic material showed highest OC densities, pointing to a more efficient OC preservation under these conditions. However, the dominant source of organic matter across sites was terrestrial. Scaling up, Danish saltmarsh sediments, comprising about 1% of the country's area, have the potential to capture up to 0.13 ± 0.03% of Denmark’s annual consumption-based CO₂ emissions. Our research expands the baseline data needed to advance blue carbon research and management in the Nordic region but also highlights the need for a more comprehensive approach to saltmarsh management that considers the full range of benefits and services of these important ecosystems.

Primary Presenter: Carmen Leiva Dueñas, Aarhus University (carmenld92@hotmail.com)

Authors:

Carmen Leiva Dueñas, University of Aarhus  (cleiva@ecos.au.dk)

Anna Elizabeth Graversen, Aarhus University  (au513721@ecos.au.dk)

Gary Banta, University of Southern Denmark  (banta@biology.sdu.dk)

Jeppe Hansen, Aarhus University and University of Southern Denmark  (jeppenajbjerg@hotmail.com)

Marie Louise Schrøter, Roskilde University  (malokj@ruc.dk)

Pere Masqué, International Atomic Energy Agency & School of Science & Centre for Marine Ecosystems Research  (p.masque@ecu.edu.au)

Marianne Holmer, University of Southern Denmark  (holmer@sdu.dk)

Dorte Krause-Jensen, Aarhus University  (dkj@ecos.au.dk)