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Saltmarsh at Northey Island

A view across the saltmarsh at Northey Island, Essex
A view across the saltmarsh at Northey Island | © National Trust Images/Justin Minns

Saltmarshes are a truly special habitat. Discover the role that Northey Island’s saltmarsh plays in increasing biodiversity, offering spawning and nurseries for fish, as well as food and shelter for birds. Find out how it also locks up carbon dioxide to reduce the effects of climate change and provides natural flood defences by reducing the power of the waves.

Biodiversity of saltmarshes

The sea water in the Blackwater Estuary around Northey Island is made slightly less salty by fresh water from the River Blackwater. The concentration of salt at any given time depends on the amount of rainfall, which changes from season to season. Only a limited range of specialist plants and animals can survive this changing environment, making Northey Island a unique place.

The species found in the lowest areas of saltmarsh can withstand hours under the salty water as the tide comes in and out. Meanwhile, the species in the upper marsh – where the land and sea meet – are more like land-based species and can only live for a limited time under the salt water.

Saltmarsh plants

Many commercial crops such as carrots, beetroot, sugar beet, celery and asparagus originated on the upper parts of saltmarshes. Many plants still found on saltmarshes today are used in cooking, such as saltmarsh herbs and samphire.

Birds of Northey Island

Birds are drawn to Northey Island all year round but dark bellied brent geese are particularly special winter visitors. They seek the protection of Northey’s fields as they wait out high tides. It’s a fantastic spectacle when they fly out into the estuary to feed when the tide recedes.

Beneath the mud

Lots of interesting creatures live hidden in the saltmarsh but they are a vital source of food for birds, fish and other wildlife. One such creature found in the mud surrounding Northey is the harbour ragworm. This predator spins a mucus net at the entrance to its burrow to trap smaller creatures. It is an important food for many other species including the curlew, bar-tailed godwit and common sole.

A channel running through mudflats at Northey Island, Essex
Mudflats at Northey Island | © National Trust Images/Justin Minns

How saltmarshes take the power out of the waves

When powerful waves driven by tides and wind hit man-made sea walls, the waves bounce back, and the energy stays in the estuary. This makes flooding and erosion far more likely – sometimes further along the estuary. When the same tides hit saltmarsh, the marsh slows down the water and reduces the height of the waves. This takes the energy out of the waves and helps to reduce the risk of flooding and erosion elsewhere.

Studies we've carried out alongside researchers at Cambridge University have shown that it’s the vegetation and physical features of creeks and sediment surfaces of saltmarshes that make them so effective at reducing wave and tidal energy. This is true both for regular spring tides (which bring less than a metre of water above the surface) and for storm surges, where tide levels can be a few metres above the saltmarsh surface.

Carbon storage in saltmarsh habitats

Healthy saltmarshes lock up carbon from the atmosphere, which helps to reduce the effects of climate change. The natural accumulation of sediment – known as accretion – locks in the carbon and makes salt marshes an effective carbon sink. The saltmarsh vegetation also takes in carbon dioxide and releases oxygen into the environment.

The amount of carbon a saltmarsh can store depends on several factors, including how healthy the saltmarsh is and whether it was formed naturally, by active intervention, or as a result of sea wall failure. Managing the saltmarsh is important both to reduce erosion and to make it healthy, functional, and sustainable into the future.

We’ve calculated that between 2018 and 2020 the saltmarsh at Northey Island locked up the same amount of carbon dioxide as would be emitted by driving a standard family car 28,885 miles – the equivalent of driving all the way around the Earth 1.16 times.

A view across the salt-marsh at Northey Island, Essex

Discover more at Northey Island

Find out how to get to Northey Island, where to park, things to see and do and more.

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