The Saltmarsh at Northey Island
Increasing the extent and health of the saltmarsh area improves biodiversity and provides a range of other ‘ecosystem services’ (things that saltmarsh delivers for society) such as natural flood alleviation, reductions in wave energy, spawning and nurseries for fish, providing food and shelter for birds, and locking up carbon dioxide to reduce the effects of climate change.
Located in the Blackwater Estuary, the sea water at Northey Island is made slightly less salty by freshwater from the Blackwater river. The degree of alteration changes dependant on rainfall and so season; this is typical of many of our estuaries. Only a limited range of specialist plants and animals can survive this changing environment. The saltmarsh plant and animal species span different conditions, with the species in the lowest areas of saltmarsh able to withstand hours under the salty water as the tide comes in and out. Those species in the upper marsh link into terrestrial (land based) species and can only live for a limited time under the saltwater. This is where the land and the sea meet.
When powerful tide and wind driven waves hit sea walls, the wave bounces back and the energy stays in the estuary making flooding and erosion a far more likely outcome, possibly further along the estuary. When the same tides hit saltmarsh the marsh slows the water and reduces the height of waves; this takes the energy out of it and helps reduce the risk of flooding and erosion elsewhere.
We’ve been working with researchers from Cambridge University to study this further and gain a greater understanding of just how effective saltmarsh environments are at taking the power out of the waves. Cambridge University has found that not only is the vegetation an important element in reducing wave and tidal energy, but also the geomorphology of creeks and rough saltmarsh (sediment) surfaces are important too. This is not only true for Spring tides, where less than a meter depth of water is above the saltmarsh surface, but also under storm surges where tide levels can be raised by more than a meter above that, so a few meters above the saltmarsh surface.
Healthy saltmarshes are effective at locking up carbon and helping to reduce the effects of climate change. 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. The process of accreting sediment is important as this locks in the carbon and makes saltmarshes an effective carbon sink. The vegetation also fixes carbon dioxide and liberates oxygen to the environment. It is also important to bear in mind that if the saltmarsh is eroding this can lead to release of carbon that has been locked up historically and a reduction in the fixing of CO2, so managing the saltmarsh is important both to reduce erosion and to make it healthy, functional, and sustainable into the future. We’re working with others to understand more about how saltmarshes store carbon, which will help with the design of future saltmarsh habitat projects across the National Trust.
The management techniques we’ve implemented at Northey Island between 2018 and 2020 have locked up the same amount of carbon dioxide as would be emitted by driving a standard family car 28,885 miles – that’s the equivalent of driving all the way around the Earth 1.16 times or between central London and Edinburgh 73 times! Our on-going coastal adaptation work will add to this important tally.
We are grateful for various contributions to the work to date, including from Essex and Suffolk Water and from Defra's Natural Flood Management Fund. From 2021, much of our work to protect the saltmarsh at Northey Island is made possible thanks to EU funding under the LIFE on the Edge Project. We are working in partnership with the RSPB across several sites to create more and better coastal habitat to benefit breeding, wintering and migratory water birds, as well as other wildlife.
This video was made in April 2021 as part of the LIFE on the Edge Project, providing a flyover of the island before we commence work under the LIFE project to protect and enhance the saltmarsh habitat at Northey Island.