Why are saltmarshes such effective carbon sinks?

The invisible yet lethal threat of radioactive pollution is an ever-present risk to the Blackwater. Even a small leakage of nuclear material from the decommissioned Bradwell reactor cores or radioactive waste stores could negatively affect the role that the estuary’s marshlands play in trapping carbon, known as carbon sequestration. In short, radioactive leakage may erode the amount of carbon that can be sequestered in future. This risk alone should be enough to deter any further development of new nuclear power at the Bradwell site.

2 September 2025

David Humphreys explains the role of saltmarshes in the struggle against our heating climate in the August 2025 column for Regional Life

The saltmarshes and mudflats of the Blackwater Estuary are an important yet fragile environment rich in birds, flora, invertebrates, fish and oysters. But saltmarshes are also highly effective in storing carbon, thereby acting as carbon sinks with a vital role to play in tackling increases to the global temperature.

Like all forms of plant life, the vegetation that thrives in marshlands absorbs carbon from the atmosphere through photosynthesis to create food for the plants.

Carbon sinks may release their carbon back into the atmosphere in two ways. First, combustion generates carbon dioxide emissions, for example during forest fires. Second, carbon dioxide is realised when living organisms respire. Respiration is how life forms, including plants, obtain energy. If plants are in an oxygen-rich (aerobic) environment they create more carbon dioxide when breathing than if their environment is lacking in oxygen (anaerobic).

Why are saltmarshes such effective carbon sinks?

2 September 2025

David Humphreys explains the role of saltmarshes in the struggle against our heating climate in the August 2025 column for Regional Life

The saltmarshes and mudflats of the Blackwater Estuary are an important yet fragile environment rich in birds, flora, invertebrates, fish and oysters. But saltmarshes are also highly effective in storing carbon, thereby acting as carbon sinks with a vital role to play in tackling increases to the global temperature.

Like all forms of plant life, the vegetation that thrives in marshlands absorbs carbon from the atmosphere through photosynthesis to create food for the plants.

Carbon sinks may release their carbon back into the atmosphere in two ways. First, combustion generates carbon dioxide emissions, for example during forest fires. Second, carbon dioxide is realised when living organisms respire. Respiration is how life forms, including plants, obtain energy. If plants are in an oxygen-rich (aerobic) environment they create more carbon dioxide when breathing than if their environment is lacking in oxygen (anaerobic).

And here’s why saltmarshes are such effective sinks: they are anaerobic, so plants breathe without oxygen. Anaerobic respiration generates less energy than aerobic respiration and produces less carbon dioxide. This enables carbon stocks to build up. Coastal marshlands also receive a constant influx of tide-borne sediment, which buries organic matter in sediment layers, a further factor that enables carbon to accumulate. The result is that coastal marshlands are more effective at carbon storage per hectare than any other ecosystem, including tropical forests.

The Blackwater Estuary forms part of a broader category of carbon sink known as ‘blue carbon’. This is carbon that has been captured and stored by living coastal ecosystems such as saltmarshes, mangrove forests and seagrass beds. Blue carbon ecosystems also provide other environmental services such as protection against sea-level rise and storm surges. Given the global sea-level increases projected for this century, the importance of blue carbon ecosystems cannot be overstated, both for coastal protection and trapping carbon.

The saltmarshes of Essex, then, are a vital asset in the fight against global heating. At the same time, they are threatened by the impacts of climate change, in particular coastal retreat from sea-level rise.

Marshland ecosystems are also at the mercy of pollution, which can reduce their carbon storage capacity. The invisible yet lethal threat of radioactive pollution is an ever-present risk to the Blackwater. Even a small leakage of nuclear material from the decommissioned Bradwell reactor cores or radioactive waste stores could negatively affect the role that the estuary’s marshlands play in trapping carbon, known as carbon sequestration. In short, radioactive leakage may erode the amount of carbon that can be sequestered in future. This risk alone should be enough to deter any further development of new nuclear power at the Bradwell site.

This is a further reason to ‘BANNG the drum’ against new nuclear at Bradwell and to resist further nuclear power construction in the United Kingdom.

David Humphreys is Emeritus Professor of Environmental Policy at the Open University.

September 5, 2025 - Posted by Christina Macpherson | environment, UK