Low Climate Benefit of Nordic Coastal Marshes: Site Conditions Outweigh Grazing Effects and Shape Trade-Offs Between Carbon Storage and Its Stability.

C (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.