Definition and characteristics
An area of vegetated tidal mudflats located within an estuary or on the landward side of a sand spit. They tend to have a well developed series of creeks through which the tide rises and ebbs.
Salt marshes support a range of habitats including grassland, scrub, salt marsh and reed beds, accounting for a wide diversity of wildlife.
Examples of species found in salt marshes:
Cordgrass spiky, untidy-looking grass that grows fast on mudflats
Sea Lavender attractive, colourful flowers attract wildlife
Oystercatcher feeds and nests in salt marshes. Long beak and legs. Black with white underbelly
Ringed Plover feeds inter-tidally and nests on the salt marsh. Fawn, short beak & legs. Dark brown neck and white underbelly
Wold Spider clings for hours to submerged stems of cordgrass waiting for low tide and food. Grayish-brown.
Why are salt marshes important?
- Important habitats for a variety of plant and animal species allowing a diverse ecosystem to develop.
- They attract people to visit them, therefore providing an economic benefit to the local area.
- In some locations, the salt is extracted for commercial usage.
- Salt marshes can provide an important soft management tool when used as part of managed retreat. They're effective barriers against the sea and a cheap option compared to hard strategies.
Formation of salt marshes
Stage 1: Mud and silt accumulates in a sheltered coastal area, for example in the lee of a spit. Over time the mud builds up and breaks the surface to form mudflats.
Stage 2: Salt-tolerant plants (cordgrass) colonise the mudflats. These pioneer plants have long roots to stop them being swept away and stabilizes the mud.
Stage 3: The more the mud rises, it's less covered by water. The conditions are less harsh as rainwater washes out some of the salt and decomposing plant matter creating new soil. Sea lavenders and sea asters dominate.
Stage 4: The marsh uplands (oaks and shrubs) dominate so the smaller plants and species die out. This is known as vegetation succession. This area is rarely covered in water.
Case Study: Keyhaven Salt Marshes, Hampshire
- Located behind Hurst Castle spit
- Supports a range of habitats accounts for a rich diversity of wildlife in the area
But they are at risk:
- Retreating up to 6 metres a year, which threatens a squeeze of the salt marsh.
- Human activities such as trampling, parking and pollution wear away the salt marshes.
- With sea levels expected to rise by 6 mm a year, the big issue is the "squeeze" between the low sea wall and the rising sea.
- Under threat from the severe storm breaching Hurst Castle Spit. In 1989, it was eroded in less than 3 months.
What has been done to manage the salt marshes?
- In 1996, rock armour and beach nourishment helped increase the height and width of the spit, in attempt to help the creation of the salt marshes.Since the £5 million defences, Keyhaven salt marshes have not been breached.
- The area is officially a site of special scientific interest (SSSI) and partly a National Nature Reserve. Access and development have been limited.