Protection of saltmarshes is vital for climate change mitigation

The UK’s saltmarshes are under threat from climate change, coastal erosion and sea-level rise, according to a new study.

Saltmarshes cover more than 450km² of the UK coastline. They capture and store large quantities of carbon, providing a natural climate regulation service. This makes them one of the UK’s most important coastal ecosystems. 

Year by year, thin layers of carbon-rich sediments build on saltmarshes from plants, rivers and the sea. As this organic carbon is buried in the waterlogged soils, decomposition is slowed, keeping carbon out of the atmosphere. 

The new study, published in Science of the Total Environment, follows an assessment of the amount of saltmarsh carbon in the UK in 2023. 

Researchers looked at the density of organic carbon in 21 saltmarshes around the UK. They used specialist dating techniques to work out when and how quickly the sediments accumulated. 

They found that although UK saltmarshes store 5.2 million tonnes of carbon, rates of new carbon accumulation are much slower than expected. These findings emphasise the value of these expansive carbon reserves, especially because they take so long to form. 

While the annual accumulation rate of carbon in UK saltmarshes may be lower than previously thought, this study shows how critical these ecosystems are in storing large amounts of carbon. 

It highlights the pressure they are under from the changing climate, sea-level rise and disturbance by humans activity. 

There must be a significant focus by UK, and others, on protecting the existing carbon stored in these environments

Professor Natasha Barlow, School of Earth and Environment

Dr Craig Smeaton, Lecturer in Geography & Sustainable Development at the University of St Andrews and the lead author of the study said: “Understanding the true carbon storage capacity of saltmarshes at the scale of the UK has been a major technical challenge, involving a large multidisciplinary team of researchers. We are excited to have published the first national organic carbon accumulation assessment for Great Britain.”

The work is the result of the NERC-funded C-SIDE project and involves researchers from the Universities of Leeds, St Andrews, York and five other UK institutions.  

Professor Natasha Barlow, Professor of Environmental Change within the School of Earth and Environment and a researcher on the project, added, “Salt marshes are important coastal environments for biodiversity, coastal protection and people. However, our results show that there is a low rate of carbon accumulation in UK salt marshes. This means there must be a significant focus by UK, and others, on protecting the existing carbon stored in these environments, since the climate benefits of any new carbon accumulating in saltmarshes is much smaller.” 

Dr Ed Garrett, Assistant Professor at the University of York and joint lead author of the new study, said: “We found the accumulation of organic carbon was far lower than global estimates, which means the contribution of northern European saltmarshes, such as those in the Humber Estuary, has likely been significantly overestimated.” 

The project’s principal scientist, Professor William Austin at the University of St Andrews, noted, “While restoring and creating new saltmarshes offers a potential boost for climate, people and biodiversity and may be valuable to counteract habitat loss, there has never been a more important time to protect the vulnerable organic carbon already stored in existing saltmarshes.

“This must be a priority for the UK and elsewhere because the protection of existing habitats (and carbon stores) offers climate benefits from avoided greenhouse gas emissions which are several times more significant than those gained from new accumulation of organic carbon in these ecosystems.” 

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