FANDOM


Donna Nook

Flooded salt marsh- from flickr

A salt marsh is an environment in the upper coastal intertidal zone between land and salt water or brackish water, it is dominated by dense stands of halophytic (salt-tolerant) plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments. Salt marshes play a large role in the aquatic food web and the exporting of nutrients to coastal waters. They also provide support to terrestrial animals such as migrating birds as well as providing coastal protection.


Basic information on Salt marshEdit

Formation

Salt marshes occur on low-energy shorelines in temperate and high-latitudes.[3], which can be stable or emerging, or submerging if the sedimentationrate exceeds the subsidence rate. Commonly these shorelines consist of mud or sand flats (known also as tidal flats or abbreviated to mudflats) which are nourished with sediment from inflowing rivers and streams. [4] These typically include sheltered environments such as embankments, estuaries and the leeward side of barrier islands and spits. In the tropics and sub-tropics they are replaced by mangroves; an area that differs to a salt marsh in that instead of herbaceous plants, they are dominated by salt-tolerant trees.[1] Most salt marshes have a low topography with low elevations but a vast wide area, making them hugely popular for human populations.[5] Salt marshes are located among different landforms based on their physical and geomorphological settings. Such marsh landforms include deltaic marshes, estuarine, back-barrier, open coast, embayments and drowned-valleymarshes. Deltaic marshes are associated with large rivers where many occur in Southern Europe such as the Camargue in the Rhone delta or the Ebrodelta. They are also highly extensive within the rivers of the Mississippi Delta.[2] In New Zealand, most salt marshes occur at the head of estuaries[6] in areas where there is little wave action and high sedimentation. Such marshes are located in Awhitu Regional Park in Auckland, the Manawatu Estuary and the Avon-Heathcote Estuary in Christchurch. Back-barrier marshes are sensitive to the reshaping of barriers in the landward side of which they have been formed.[2] They are common along much of the eastern coast of the United States and the Frisian Islands. Large, shallow coastal embayments can hold salt marshes with examples including Morecambe Bay and Portsmouth in Britain and the Bay of Fundy in North America.[2] Salt marshes are sometime included in lagoons, and the difference is not very marked: e.g. a major part of the Venetian Lagoon is made up of these sorts of animals and or living organisms belonging to this ecosystem.

[edit]Edit

Tidal flats gain elevation relative to sea level by sediment accretion, and subsequently the rate and duration of tidal flooding decreases so that vegetation can colonise on the exposed surface. [7]The arrival of propagules of pioneer species such as seeds or rhizome portions are combined with the development of suitable conditions for their germination and establishment in the process of colonisation. [8] When rivers and streams arrive at the low gradient of the tidal flats, the discharge rate reduces and suspended sediment settles onto the tidal flat surface, helped by the backwater effect of the rising tide. [4] Mats of filamentous blue-green algae can fix silt and clay sized sediment particles to their sticky sheaths on contact [9] which can also increase the erosion resistance of the sediments. [10] This assists the process of sediment accretion to allow colonising species (e.g. Salicornia spp.) to grow. These species retain sediment washed in from the rising tide around their stems and leaves and form low muddy mounds which eventually coalesce to form depositional terraces, whose upward growth is aided by a sub-surface root network which binds the sediment. [11] Once vegetation is established on depositional terraces further sediment trapping and accretion can allow rapid upward growth of the marsh surface such that there is an associated rapid decrease in the depth and duration of tidal flooding. As a result, competitive species that prefer higher elevations relative to sea level can inhabit the area and often a succession of plant communities develops. [7]

[edit]Tidal flooding and vegetation zonationEdit

Coastal salt marshes can be distinguished from terrestrial habitats by the daily tidal flow that occurs and continuously floods the area.[1] It is an important process in delivering sediments, nutrients and plant water supply to the marsh.[5] At higher elevations in the upper marshzone, there is much less tidal inflow, resulting in lower salinity levels.[1] Soil salinity in the lower marsh zone is fairly constant due to everyday annual tidal flow. However, in the upper marsh, variability in salinity is shown as a result of less frequent flooding and climate variations. Rainfall can reduce salinity and evapotranspiration can increase levels during dry periods.[1] As a result, there are microhabitatspopulated by different species of flora and fauna dependant on their physiological abilities. The flora of a salt marsh is differentiated into levels according to the plants' individual tolerance of salinity and water table levels. Vegetation found at the water must be able to survive high salt concentrations, periodical submersion, and a certain amount of water movement, while plants further inland in the marsh can sometimes experience dry, low-nutrient conditions. It has been found that the upper marsh zones limit species through competition and the lack of habitat protection, while lower marsh zones are determined through the ability of plants to tolerate physiological stresses such as salinity, water submergence and low oxygen levels.[12][13]

Plant species diversity is relatively low, since the flora must be tolerant of salt, complete or partial submersion, and anoxic mud substrate. The most common salt marsh plants are glassworts (Salicornia spp.) and the cordgrass (Spartina spp.), which have worldwide distribution. They are often the first plants to take hold in a mudflat and begin its ecological succession into a salt marsh. Their shoots lift the main flow of the tide above the mud surface while their roots spread into the substrate and stabilize the sticky mud and carry oxygen into it so that other plants can establish themselves as well. Plants such as sea lavenders (Limonium spp.), plantains (Plantago spp.), and varied sedges and rushes grow once the mud has been vegetated by thepioneer species.The New England salt marsh is subject to strong tidal influences and shows distinct patterns of zonation.[13] In low marsh areas with high tidal flooding, a monoculture of the smooth cordgrass, Spartina alterniflora dominate, then heading landwards, zones of the salt hay, Spartina patens, black rush,Juncus gerardii and the shrub Iva frutescens are seen respectively.[12] These species all have different tolerances that make the different zones along the marsh best suited for each individual.

Salt marshes are quite photosynthetically active and are extremely productive habitats. They serve as depositories for a large amount of organic matter and are full of decomposition, which feeds a broad food chain of organisms from bacteria to mammals. Many of the halophytic plants such as cordgrass are not grazed at all by higher animals but die off and decompose to become food for micro-organisms, which in turn become food for fish and birds.

What Native Species can you find Here?Edit

This habitat is jusat right for Naterjack toads. You may not be able to find any as they are increasingly rare in the UK, but if your looking to find them this would be one of the best places to look for them. Because it is salt water you won't usually find common frogs/toads but they should be around the area. Adders and grass snakes may be found basking. And common lizards may be found in the long grass in and around the marsh.