Author Identifier (ORCID)
Pere Masque: https://orcid.org/0000-0002-1789-320X
Abstract
Coastal marshes, recognized as effective organic carbon (OC) sinks, have gained attention for their potential contribution to climate mitigation through protection and restoration. However, the climate mitigation potential of Nordic coastal marshes remains understudied, likely due to their heterogeneous and often non-tidal nature. To fill this gap, we examined soil OC storage and accumulation rates, and the effects of grazing, a common management practice, across eight Nordic coastal marsh areas spanning broad climate and environmental gradients. We also assessed soil methane emissions in selected areas. The Nordic marshes studied store a median of 7 kg OC m−2 (interquartile range, IQR: 6–8) in the top 15–35 cm of soil and accumulate 41 g OC m−2 yr.−1 (IQR: 32–47). Considering only the additional OC, attributed to the presence of the marsh habitat, these values drop to 4 kg OC m−2 (IQR: 2–6) and 21 g OC m−2 yr.−1 (IQR: 11–33). Globally, both rates are comparatively low. OC stocks and accumulation rates increased with marsh age, root: shoot ratio (stress adaptation), and δ15N (fast N cycling), but declined with soil δ13C (related to faster decomposition under warmer conditions and sandier soils). Danish marshes had the highest but also most vulnerable OC stocks due to faster turnover, labile compounds, and coarser soil grain sizes. Although grazing only weakly increased soil OC stocks and had no effect on OC accumulation rates, it significantly reduced methane fluxes compared to ungrazed marshes. In ungrazed areas, methane emissions weakened the carbon sink by 32% in Finland and 68% in Denmark. However, estimated greenhouse gas emissions from on-site cattle, even at low grazing intensity, largely outweighed the coastal marsh climate benefits. A comprehensive Nordic marsh management strategy is needed, extending beyond the focus on their limited, yet relevant, role in climate mitigation, and considering biodiversity, coastal protection and nutrient retention.
Keywords
Blue carbon, carbon burial, climate mitigation, grazing, greenhouse gases, Nordic coastal marshes
Document Type
Journal Article
Date of Publication
5-1-2026
Volume
32
Issue
5
PubMed ID
42068073
Publication Title
Global Change Biology
Publisher
Wiley
School
Centre for Marine Ecosystems Research / School of Science
Funders
We acknowledge funding from the 2019–2022 BiodivERsA/BiodivClim ERA-Net COFUND programme (“NordSalt – Climate Change Impacts and Biodiversity Interactions in Nordic Salt Marshes”, BiodivClim-845) in collaboration with national agencies: Innovation Fund Denmark (ID), The Academy of Finland (AKA), German Research Foundation (DFG), The Research Council of Norway (RCN), and the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS); and from the LIFE Programme COASTal LIFE project (LIFE21-NAT-DK-COASTal-LIFE/101074422).
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License
Comments
Leiva‐Dueñas, C., Banta, G. T., Boström, C., Eller, F., Eklöf, J., Andersen, L. H., Jensen, K., Lanari, M., Logemann, E., Masque, P., Ostertag, T., Reisdorff, C., Richard, A., Vehmaa, A., Alm, J., Von Numers, M., & Krause‐Jensen, D. (2026). Low climate benefit of nordic coastal marshes: Site conditions outweigh grazing effects and shape trade-offs between carbon storage and its stability. Global Change Biology, 32(5), e70889. https://doi.org/10.1111/gcb.70889