ETC BE Working paper:Carbon accumulation rates and protected area networks for Europe’s saltmarshes and seagrasses meadows

Halting losses and supporting recovery of saltmarshes and seagrasses through protection and restoration offer benefits for biodiversity, coastal protection, and long-term retention of nutrients and carbon (blue carbon) in their sediments. However, the recent policy-driven attention on blue carbon of these habitats calls for a more articulated assessment of such benefits. We review the long-term organic carbon accumulation rates (CAR) of European saltmarsh- and seagrass sediments and quantify CAR associated with the saltmarsh /seagrass habitats included in the existing EU protected area network. Saltmarsh CAR was consistently higher than seagrass CAR, but with large regional and habitat-specific differences. Saltmarsh CAR was similar in the NE Atlantic and the Mediterranean (~88gC m-2 y-1) while Baltic saltmarsh CAR was only about half of that (47gC m-2 y-1). Seagrass CAR was highest in the Mediterranean (~30gC m-2 y-1), lower in the NE Atlantic (~25gCm-2 y-1), and very low in the Baltic (~1gCm-2 y-1). The seagrass Posidonia oceanica, which only grows in the Mediterranean, also had higher CAR (~31gCm-2 y-1) than other European seagrasses (~20gC m-2 y-1). Overall, CAR of non-Posidonia seagrasses and Baltic saltmarshes fall markedly below IPCC’s Tier 1 emission factors, implying a need to adjust those to avoid overestimation of the climate benefit of European blue carbon strategies. Currently established EU protected area networks cover most of Europe’s saltmarsh area and associated CAR (~74-99% across EU geographic regions), whereas seagrass meadows are less covered (~58-65%). Despite the spatial protection coverage, continued pressure on the land-sea interface including projected ecosystem loss scenarios due to climate change highlight the need for more efficient protection strategies of these ecosystems into the future.