Scientists are establishing the first network of greenhouse gas monitoring stations on saltmarshes around the UK coast to support national efforts to mitigate climate change.

The UK Centre for Ecology & Hydrology (UKCEH) has installed two flux systems in the Ribble Estuary with others to follow at Essex Marshes and The Wash in East Anglia over the coming months. The flux towers will measure how much carbon dioxide gas is captured from the atmosphere and stored as carbon within the saltmarsh ecosystem, which will provide evidence to help unlock investment in restoration schemes of these important coastal wetlands.

Some 85% of UK saltmarshes have been lost since the mid-19th century as land has been reclaimed from the sea for agriculture, development or coastal flood defences, degraded through pollution or eroded by rising sea levels. When the marsh destabilises and sediment begins to erode, greenhouse gases that are produced within the soil can be released to the atmosphere at enhanced rates. 
In addition to improving biodiversity and providing natural flood protection, the plants covering the marshes draw down CO2 through photosynthesis and can also trap carbon-rich sediments in their roots and stems on the incoming tide. 

It is estimated that UK saltmarshes accumulate between 3-14 tonnes of carbon dioxide equivalent* (or CO2e) per hectare per year, depending on the condition of each site. However, there is a lack of data on how much greenhouse gas different types of UK saltmarsh could remove from the atmosphere. UKCEH is therefore working with a range of partners including the Environment Agency, Defra, Natural England, World Wide Fund for Nature (WWF) and the Royal Society for the Protection of Birds (RSPB) to address this key knowledge gap.

UKCEH wetland scientist Annette Burden says: “Our new monitoring will provide much-needed evidence on how much greenhouse gas is currently being absorbed from the atmosphere by UK saltmarshes, and what could be removed if more sites were restored. This will then help pave the way for private investment in restoration projects through the voluntary carbon market.

“Restoring saltmarshes across the UK would support progress towards our net zero targets and provide vital habitat for wildlife, including overwintering migratory birds and commercially important fish species such as Seabass.”

The carbon benefits of saltmarshes could be traded in the same way that peatlands and woodlands are. This would enable companies to invest in restoration schemes in order to voluntarily offset their greenhouse gas emissions. UKCEH is currently developing a UK Saltmarsh Code which would assure buyers of carbon credits that the climate benefits being sold are real, quantifiable, additional and permanent.

Dr Ross Morrison, Biometeorologist at UKCEH added: “The new network of saltmarsh flux towers fills an important gap in the wider UK wide flux monitoring network. It will provide the evidence base for saltmarsh that has been so important in raising the profile of terrestrial habitats as solutions for mitigating climate change and biodiversity loss. By the end of next year, we will be able to provide the first directly measured carbon budgets for a range of different saltmarsh systems across the country and will have gained a much deeper scientific understanding of how these vital coastal ecosystems function now and into the future.”

The new flux systems are monitoring saltmarshes that are in a natural state as well as areas under restoration, on both the east and west coasts of the UK, which have different tidal dynamics. This will provide data on the carbon sequestration potential of habitat in different environments. This will provide data on the carbon sequestration potential of habitat in different environments, as well as information on how saltmarshes respond to tidal and seasonal patterns. 

The UK only has about 45,000 hectares of natural saltmarsh remaining, holding a total of around 2.3 million tonnes of carbon in the top 10cm of their soil. However, so far, there has been relatively limited restoration, with the majority of schemes to date creating compensatory habitat for damage to designated sites due to development. In England alone, the introduction of a carbon credit scheme with accompanying Saltmarsh Code could generate £1 billion of private investment over 25 years to support the restoration of 22,000 hectares of saltmarsh.

Additional information

Saltmarshes are habitats that are flooded by seawater and created when fine mud and silt are deposited along a sheltered part of the coastline. Atmospheric carbon is absorbed by saltmarshes’ vegetation via photosynthesis. Carbon-rich sediment and organic matter can also flow in on the tide, trapped by the roots and stems of saltmarsh plants. This carbon is then stored within sediment for potentially hundreds of years if the marsh remains stable. Learn more about saltmarshes in our saltmarsh factsheet [PDF].

UKCEH has installed a flux system on an historic saltmarsh in the Ribble Estuary, funded by a WWF and Aviva partnership, and another funded by Natural England at a nearby restored site. In a separate project with the Environment Agency and Defra, UKCEH will install flux systems at sites managed by RSPB in The Wash, the Essex Wildlife Trust in Essex, and another site to be confirmed.

UKCEH has been deploying flux systems to measure gas exchange between the land surface and the atmosphere for several decades. The institute now runs a UK network of around 40 flux systems, spanning different types of habitat and land use, including peat bogs, agriculture on mineral and peat soils and bioenergy crops.

*CO2e means “carbon dioxide equivalent”. CO2e is a measurement of the total greenhouse gases emitted, expressed in terms of the equivalent measurement of carbon dioxide.

In 2021, WWF and Aviva joined forces to call for a transformational shift in the UK financial sector to help slow climate change – a shift without which the UK will not be able to meet its net zero target. Together, WWF and Aviva are also working with communities in the UK and Canada to build more climate resilient ecosystems to help reduce the risk of climate-related natural disasters and create wider benefits for people. With this three-year partnership, Aviva is WWF’s lead partner in the insurance and pension sector.