What do we know about the ‘Blue Carbon’ value of managed realignment projects, and what do we find when we compare 10 very different UK case examples?

For more than two decades, there has been growing recognition about the role that coastal habitats (especially marshes, seagrass and mangroves) can play in trapping and storing ‘blue’ carbon. Today, as COP26 comes to a close in Glasgow and a major new Blue Carbon conference is underway in Edinburgh, the level of interest in, and advocacy for, this subject is huge. 

There are now many organisations and research institutions exploring this issue. They are seeking to better understand how the protection and creation of habitats (nature-based solutions) can play a more significant role in contributing to Nationally Determined Contributions (NDCs) for mitigating climate change under the 2015 Paris Agreement. 

To contribute to ongoing discussions in this field, our latest White Paper summarises what we know about the Blue Carbon value of carrying out intertidal wetland restoration though the managed realignment of coastal defences.

It includes the findings of a review that applied a simple but standardised approach to calculating Blue Carbon to 10 very different wetland restoration projects completed in the UK. It then offers some recommendations for future project delivery and research.

Blue carbon: the current situation

We know that although saltmarshes cover a small proportion of the Earth’s surface, they can outperform other marine and terrestrial habitats as carbon sinks. Thus, they can be ‘hot spots’ for carbon burial. However, in many areas, UK saltmarshes are eroding, and thus may be releasing carbon to the marine environment.  

This means that protecting and creating coastal habitat can provide a climate change mitigation function. This is in addition to all the other benefits they can achieve (including coastal adaptation/protection, biodiversity enhancement, nutrient assimilation, fish production, improved land/seascapes and areas of recreational and health value). 

The creation of saltmarshes is most effectively done through the realignment of coastal defences. The resulting habitats are often sheltered by old and new sea walls and are on low-lying land historically claimed from the sea. As such, they are naturally a bit different to more exposed and older habitats. They often exhibit comparatively rapid sediment accretion. This is best understood as a natural function of these environments ‘bouncing back’ and reversing the damage wrought by previous generations having isolated the land from the tide (leading to sediment starvation and land compaction).

As most of the carbon in wetland habitats is in the soil, this rapid accretion can facilitate rapid and substantial carbon accumulation. Thus, realignments could be the hottest carbon burial spots of all.

This view has been expressed for years but evidence has been needed from completed restoration sites to verify it. That evidence is now emerging, though the methods and results of the studies are variable.

To look at this further, we compared how habitats have developed at 10 completed managed realignments over the first decade of their lives. Using a simple Blue Carbon Calculator, we found that they can sequester double the carbon quoted for mature marshes. We then explored how differences between sites influence the amount of carbon they store. We hope that this information can be used to help gauge the value of future ‘Blue Carbon Projects’ in different estuarine and coastal situations in advance of them being implemented.

Download the full White Paper, Blue Carbon in Managed Realignments.

ABPmer is a recognised specialist in marine and coastal habitat creation, restoration and protection. We work with clients from initial conception through planning and consent to scheme implementation.