Saltmarshes are among the most efficient ecosystems at capturing and storing carbon. These coastal habitats trap organic carbon in their soils, playing a crucial role in fighting climate change. However, accurately determining how much carbon they accumulate over time is vital for their conservation and for integrating them into national climate policies.
Our study provided the first comprehensive assessment of how quickly saltmarshes across Great Britain accumulate organic carbon. By analysing soil cores from 21 marshes around England, Scotland, and Wales, we discovered that British saltmarshes accumulate carbon much more slowly than previously thought.
We found that, on average, saltmarshes in Britain accumulate about 111 grams of carbon per square metre each year – less than half the rate previously assumed from global averages. This slower rate translates to around 46,563 tonnes of carbon stored annually across all British saltmarshes, significantly lower than earlier global estimates.
Our study highlights that earlier global assessments, which suggested northern European saltmarshes were among the most carbon-rich globally, have overestimated their contribution. These inaccuracies arose from data biased towards regions with exceptionally high carbon accumulation rates, like North America.
The slower accumulation rates identified by our research do not diminish the importance of saltmarshes. Instead, they underline the critical need to protect the significant carbon stores already present in these ecosystems. British saltmarsh soils currently hold over 5 million tonnes of carbon, equivalent to the emissions of millions of cars. Losing these habitats would release vast amounts of carbon back into the atmosphere, exacerbating climate change.
Our findings emphasise the importance of conserving and restoring saltmarshes to maintain their carbon stores. With climate change and rising sea levels increasingly threatening these ecosystems, preserving the carbon already stored is more critical than ever. Furthermore, this new understanding should guide future policy, ensuring that saltmarshes are accurately valued in carbon markets and included in national emissions reports.
In summary, while British saltmarshes might not accumulate carbon as quickly as previously thought, protecting these coastal habitats remains essential. Their significant existing carbon stores make them valuable assets in climate change mitigation efforts, underscoring the urgency of conservation action.