Assessment of carbon budgets and potential blue carbon stores in Scotland's coastal and marine environment

Background

A three-tiered approach has been adopted to assess Scotland’s marine blue carbon stores. Information on habitat extent, or predicted habitat extent, has been collated into a GIS. The relevant scientific information on the primary habitats for carbon uptake and storage have been reviewed and quantitative rates of production and storage were obtained. Habitat specific reviews also include a brief assessment of the main threats to each habitat. Finally, the collected information has been assembled into an ecosystem-scale inventory of the key rates and ultimate sequestration capacity of each habitat. Habitats were reviewed by relevant experts (Michael Burrows, for kelp; Paul Tett, phytoplankton; David Hughes, benthic suspension feeders including reef-building species; Henrik Stahl, for fate of carbon in marine sediments; John Howe; postglacial geology of sediments; Nick Kamenos, maerl beds).

Main findings

• Coastal and offshore sediments are the main repositories for carbon in Scotland’s marine environment.
• An estimated 18 million tonnes (MtC) of organic carbon are stored in the top 10cm of sediments across the 470 000km2 area of Scotland’s seas.
• An estimated 1738 million tonnes (MtC) of inorganic carbon are similarly stored as nonliving shell material.
• Deposition of organic carbon amounts to 7.2 MtC/yr and inorganic carbon 0.5 MtC/yr in Scotland’s marine sediments.
• The main producer of carbon entering long-term storage in sediments is phytoplankton, 3.9 MtC/yr, with coastal plants (predominantly kelp) potentially contributing a further 1.8 MtC/yr.
• Habitat-forming species on the coast (seagrasses, saltmarsh, bivalve beds), are highly productive but their contribution to the overall carbon budget is very small because of the limited extent of each habitat.