How was Keyhaven salt marsh formed?
The Keyhaven Marshes are salt marshes formed in the lee of Hurst Castle Spit. The landform has been actively shaped by longshore drift for hundreds of years. Henry VIII built a castle near the tip of the spit to help defend England from possible invasions.
How do salt marshes form in estuaries?
Marshes are usually found in estuaries, which is where a river meets the sea and are rich in wildlife. Birds feed or roost on marshes and fish and crustaceans move in and out with the tide. When a mud/sand flat is stable enough and has enough nutrients, saltmarsh plants can begin to grow and a salt marsh is formed.
What causes coastal salt marshes?
A salt marsh begins when mud and silt are deposited along a sheltered part of the coastline. This is because rates of deposition are greater than transportation due to the lack of energy in the waves. The deposition builds up over time meaning that the mud breaks the surface to form mudflats.
How is a coastal marsh formed?
Flooding of coastal lowlands from rising sea levels has created broad coastal marshes that are protected from wave action by barrier islands or reefs. Coastal wetlands also form when rivers deposit sediment as they reach the ocean. Plants then take root and hold the soil firm against the forces of tides and waves.
How did Hurst Castle spit formed?
The spit formed from loose flint pebbles which had been eroded from the cliffs further west. This scheme rebuilt the shingle bank using dredged shingle, and saw the building of a new rock revetment utilising larvikite rocks shipped from Norway at the western end of the spit and near the castle.
How are spits formed?
A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end. Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift. An example of a spit is Spurn Head, found along the Holderness coast in Humberside.
Where do salt marshes develop?
coastal
Salt marshes generally form in coastal areas that are relatively sheltered from harsh ocean waves and where rivers or creeks deposit a special type of fine sediment. These areas of fine sediment are referred to as mud flats. As the sediment continues to collect, these flats grow in size and elevation.
What are salt marshes and how are they formed?
Salt marshes generally form in coastal areas that are relatively sheltered from harsh ocean waves and where rivers or creeks deposit a special type of fine sediment. These areas of fine sediment are referred to as mud flats. As the sediment continues to collect, these flats grow in size and elevation.
Is a salt marsh formed by erosion or deposition?
A salt marsh is a coastal marsh that forms on mud flats. They usually form in very sheltered inlets and estuaries, or behind spits (places where fine sediment accumulates). Salt marshes form as vegetation builds up on these mud flats . Sand dunes are created by strong winds and not by coastal erosion or deposition.
What is salt marsh made of?
Salt marshes are normally associated with mud flats but also occur on sand flats. These mud flats are sometimes dominated by algae and covered with algal mats.
What often forms behind a spit?
Spits. A spit is an extended stretch of sand or shingle jutting out into the sea from the land. Waves cannot get past a spit, therefore the water behind a spit is very sheltered. Silts are deposited here to form salt marshes or mud flats.
Where are the Keyhaven marshes in the UK?
Hurst Castle spit is a shingle spit located on the Hampshire coast close to the city of Southampton. The Keyhaven Marshes are salt marshes formed in the lee of Hurst Castle Spit. The landform has been actively shaped by longshore drift for hundreds of years.
Why are the Keyhaven marshes an SSI site?
Keyhaven Marshes has been nationally recognised as an important site for wildfowl and wading birds, so is an SSI, and parts are a nature reserve. This means that the area is carefully monitored to manage and maintain its rich biodiversity.
Why is the salt marsh being squeezed by the sea?
The salt marsh is retreating by up to 6m a year. The reasons for this aren’t fully understood, but further sea-level rise threatens a ‘squeeze’ of the salt marsh as it lies between a low sea wall built in the early 1990s and the encroaching sea. The salt marsh has been under threat from the breaching of Hurst Castle spit during severe storms.
How does a pioneer plant help a salt marsh?
The roots of pioneer plants will help consolidate the mud that has already built up by binding it together. Their upper parts will help trap more sediment. (It’s been estimated that Spartina can add 8-10cm of mud a year to a salt marsh). Primary producers will provide a source of food and places of refuge for animals.