Vegetated coastlines, including seagrass, mangroves, and salt marshes, are valued for their capacity to sequester and store large amounts of organic carbon in their soils.

However, coastal habitats are degrading globally, raising fears that blue carbon habitats could largely disappear by the end of this century unless significant protection and restoration efforts are enacted.

The widespread conversion of Scotland’s saltmarshes to agricultural and development land, especially during the 18th and 19th centuries, together with more recent acceleration of sea-level rise, places this important coastal habitat under extreme pressures.

Key findings

• There is significant potential for managed realignment in Scotland.
• However, the rates at which additional carbon stores are accumulating are not clear at these sites nor is their potential to contribute GHG emissions back to the atmosphere.
• We found evidence supporting a perceived growing threat of rising sea-levels, particularly associated with the potential loss of saltmarsh area, and associated soil carbon.
• Managed realignment and the creation of new saltmarsh offers a net gain at most sites over the existing saltmarsh area.
• The lower saltmarsh edge only extends down to the mean high water neap level in a few cases. This means local monitoring of vegetation in relation to tidal variation prior to restoration is needed to model future marsh extent.
• To fully assess marsh vulnerability to relative sea-level rise, evidence suggests inclusion of high-tide levels.

It is still not possible to estimate the time taken for a managed realignment site to reach a stable state with natural rates of carbon sequestration. The approach taken in this study to estimate potential blue carbon gains assumes that the realigned saltmarsh will reach a state where it buries and stores organic carbon in a similar way to a natural saltmarsh but does not include this time-dependent process.

Detailed monitoring of existing restored sites across Scotland would improve our understanding of the additional blue carbon gains in soil profiles at these sites, and to also understand the extent of any losses, including GHG emissions, over periods of time.

Blog

Read a blog about a conference poster developed as part of this project 

Academic posters are a valuable way to communicate research clearly and compellingly. CXC researcher Alex Houston describes creating a prize-winning conference poster, drawing on findings from our blue carbon project.

I was excited to present a poster at November’s ‘Blue Carbon: Beyond the Inventory’ conference – and even happier when it won the ‘best poster’ competition. The event – my first in-person conference, having only started my PhD two months ago – was organised by the Scottish Blue Carbon Forum, Marine Scotland and the University of St. Andrews and hosted by the Royal Society of Edinburgh.

Designed to be accessible to non-experts, the poster was developed as a summary of the literature review which I carried out for an ongoing CXC project – ‘Blue carbon potential of Scottish intertidal wetlands and the implications of sea-level rise: policy brief’. The project’s first output, it reviews the evidence for implementing ‘managed realignment’ in Scotland to create more blue carbon stores.

Managed realignment is the process of either removing all or part of a sea wall to allow tidal flows to enter a previously restricted area. This can allow intertidal habitats such as saltmarshes to be (re)created. Saltmarshes are valuable habitats which form in sheltered coastal environments, supporting unique biodiversity, and reducing coastal flood risk. They can sequester carbon at rates much faster than terrestrial forests, and for much longer periods.

It was a challenge to sift through the research material and decide what to include – to get over the key points without overcrowding the poster. I also had to use accessible language and to describe sometimes complex processes with non-technical terms. The judges liked how it looked visually, said it had a good flow and that it was clear for non-experts such as policy makers – great to hear.

As for presenting the poster, it was a challenge to get into the mindset that I was the expert on the subject area (as I had spent time working on it) when speaking to more experienced researchers and professionals about it. I was quite nervous initially as it was my first time presenting a poster in person – it feels much more exposed than presenting online.

Emissions reductions

The conference was a fantastic learning experience, also giving me the opportunity to hear about many aspects of marine and coastal science, from a range of perspectives, and to identify the next steps for blue carbon research. I particularly enjoyed the keynote presentation given by Prof. Patrick Megonigal, ‘Blue Methane: Challenges and Opportunities Posed by Methane Emissions for Blue Carbon Accounting’. It highlighted how the emissions aspect of blue carbon research is often neglected despite the importance of avoiding over-accounting of emissions reductions.

While our CXC research comes at a time of increasing interest, from both public and private bodies, in using carbon credits from saltmarshes to offset emissions, it is important to acknowledge that increasing blue carbon stores cannot replace significant and rapid emissions reductions. Rather, they can offset any remaining emissions from sectors such as agriculture.

Contributing to the CXC project and attending the conference have provided an excellent start to my PhD journey. I am looking forward to seeing where it takes me!