Salt Marsh Study

In November 2022, under the auspices of Natural England, we set up three salt marsh study areas on Portbury Wharf Salt Marsh. The study areas are sited in places where high footfall has killed off some or all of the salt marsh plants.

The aim is to record:

1. which species of salt marsh plants recover quickest
2. how long it takes before damaged areas of salt marsh are restored

We have no answer to the question “How long will it take for the salt marsh to regrow?”   So the data recorded here could help with the restoration of other salt marshes.

But why does it matter?

Salt marshes and their plants may not necessarily look spectacular but they behave spectacularly!

As well as providing food and shelter for wildlife they also prevent flooding and bury carbon. Sequestering carbon helps to protect our climate. That is quite an achievement for this small but specialised group of plants. These halophytes are unusual plants able to tolerate life in, and at times under, salt water.

Once the study is underway we will post the progress of the study areas here.

Study area 1

This is one of two study areas located at the west (marina) end of the salt marsh. Study area 1 is closest to the sea wall along one of the informal “COVID lockdown” tracks. It has never been a public right of way. Indeed there are no public footpaths across this Site of Special Scientific Interest.

The track has been worn down by many feet so is currently lower than the surrounding salt marsh.  Now the sea flows faster along this track with no salt marsh plants to slow it down and dissipate the power of the waves.   It is likely that erosion will quicken here with the tide scouring out the path further.  If this track which is close to the edge of the salt marsh continues to expand and deepen it could break off this section of the salt marsh completely. If that happens restoration would be impossible.

However, if allowed to thrive, the salt marsh plants could regenerate and slow down the erosion. It does depend on local support and the community is rallying to the cause. Most visitors are happy to keep to the path by the sea wall especially once they know they can make such a positive difference.

The path was once pristine salt marsh but now is just mud holding standing rain water.

Study area 2

The next study area is also close to the west end of the salt marsh along a track heading out into the middle of the salt marsh. There is greater risk of wildlife disturbance here, especially on high tides. The shoreline birds, some of which are becoming increasingly rare, feed on the edge of the tide. As the tide rises the birds are pushed towards the top of the salt marsh.  By staying on the landward side of the posts by the sea wall we can protect the birds and allow them to feed and rest undisturbed whatever the tide.

The width of the damaged area has expanded significantly with use and very few of the unusual salt marsh plants remain. It will be interesting to compare how this mid marsh area recovers compared to higher sections of the marsh. The lower marsh spends more time underwater so the plants which grow here will vary in species and quantity. Plants like spartina and sea scurvy grass don’t mind having their feet in salt water for longer so will grow towards the bottom of the salt marsh. Others like sea lavender and thrift tend to grow higher up the marsh.

Below are a couple of higher tide views. The tide in these photos was 13.42 m high. When the tide is over 14 m the entire salt marsh will be underwater.

Study Area 3

Study Area 3 is in the middle of the salt marsh by the entrance from Portbury Wharf Nature Reserve.

Like Study Area 1 it is quite high up on the salt marsh but of course the path beyond will also be able to recover if left undisturbed. This will allow a whole range of salt marsh plants to regrow and do the job of protecting and feeding wildlife as well as sequestering carbon. So we will keep track of the whole path during the project with before and after photos.

Further Reading

Read more about salt marsh plants