Saltmarshes might appear as humble grassy wetlands along the coast, yet they play an outsized role in tackling climate change. These ecosystems, regularly flooded by tidal waters, are incredibly efficient at capturing and storing carbon – so-called “blue carbon”. Despite their importance, Britain’s saltmarshes had never been thoroughly mapped to understand how much carbon they actually hold.
Our latest research undertook the first comprehensive mapping of organic carbon stored within the soils and vegetation of saltmarshes across Great Britain. By analysing almost 5,000 samples from 26 saltmarshes, we produced detailed estimates and maps of carbon stocks across the country’s 448 marshes.
The results were remarkable. We found that Great Britain’s saltmarshes contain about 5.2 million tonnes of carbon – equivalent to the emissions of millions of cars. Most of this carbon (93%) is stored in the marsh soils, hidden beneath the surface. On average, each square metre of marsh stores around 11.5 kilograms of carbon, though this varied widely depending on local environmental conditions.
Saltmarshes in northern Scotland emerged as particularly effective carbon reservoirs, storing up to 40 kilograms per square metre. These high storage levels were linked to rich organic matter from surrounding peatlands and stable sea-level conditions, allowing soils to build up carbon over thousands of years. In contrast, marshes in the southeast of England generally held less carbon, often due to their younger age.
Our study also showed how differences in local geography, vegetation types, sediment supply, and historical sea-level changes significantly affect carbon storage capabilities. By categorising marshes into distinct groups based on these factors, we identified key “hotspots” for carbon storage, helping prioritise areas for conservation and management.
Understanding these hidden carbon stores is crucial. Globally, saltmarshes are under threat from development, pollution, and climate change itself. When disturbed, the carbon trapped within these soils can be released back into the atmosphere, exacerbating climate change. Protecting and restoring these ecosystems thus becomes critical in national climate strategies.
Our findings provide a foundational step for incorporating saltmarshes into Britain’s national carbon accounting. By highlighting their climate importance, we hope to guide policymakers in safeguarding these coastal treasures. Effective management and conservation efforts will ensure that saltmarshes continue to support climate mitigation well into the future.
In short, Britain’s coastal marshes are more than scenic habitats. They’re essential allies in our fight against climate change, deserving urgent protection and recognition.