THe Clarence Plains Saltmarsh is an Important Urban Wetland
What is a Saltmarsh ?
Salt marshes form when mudflats are raised to the level of the average high tide. The accumulation of mud is most common in estuaries where the river brings fine-grained sediment to slack water but where wave action cannot rework the settled mud. Grasses tolerant of salt water then slowly take hold and spread, stabilizing the land through the growth of root systems and trapping more sediment.
The diagram is from : The SoundBook Online which is published by Soundkeeper, which works to protect Long Island Sound in the USA and to keep it viable
Topography of a salt marsh. 1. Normal low water 2. Normal high water 3. High water springs
The ebb and flood of daily tides creates process and vegetation zones:
the tidal flat remains under water for long periods and so terrestrial vegetation cannot establish itself
the low marsh is often submerged under salt water but emerges at low to mid tide. At Aberlady, these mudflats are colonised by glasswort or samphire, a pioneer plant tolerant of high salinity and waterlogged mud and sand
the high marsh is inundated less regularly and for short periods. Deposition rates are high as mud is left behind at slack water. The grasses of the elevated parts of the salt marsh need to tolerate even higher salt concentrations as sea water evaporates.
the transition zones at the landward edge of the salt marsh is only reached by extremely high springs tides or during storm surges.
Salt marshes form a buffer zone between mudflats and terrestrial habitats. These soft shores provide some of the richest habitats for shallow marine organisms and attract large numbers of wading birds. The marshes dampen wave activity and so protect the shore from erosion.
Saltmarsh occurs in areas that are periodically inundated by the sea, where the wave action is subdued and sediments are able to accumulate. It is therefore largely confined to estuaries and inlets. Near the mouths of estuaries and inlets, where the inundating water is highly saline, saltmarshes are dominated by succulent herbs and shrubs. The most common succulent herb in Tasmania is the beaded glasswort (Sarcocornia quinqueflora), and a common succulent shrub is shrub glasswort (Sclerostegia arbuscula). Where inflowing rivers and streams make the water less saline, tussock rushes, tussock sedges, tussock grasses and non-succulent herbs are more prominent. The saltmarsh rush (Juncus kraussii) is a common saltmarsh species.
From Tas. Govt.DPIWE Information sheet
Biodiversity Value of Saltmarsh
Saltmarsh is poorly reserved in Tasmania. It contains several rare and threatened plants including the blue wilsonia (Wilsonia humilis) and the saltmarsh statice (Limonium australe). Saltmarsh and its adjacent mudflats are used by many migratory birds, some of which are rare or threatened. Saltmarsh stabilises the coast and contributes significant amounts of organic material to estuaries. This is important for the food chain which contains the breeding stock of many commercial and non-commercial fish species. Saltmarshes in the north west and on King Island are important food sources for the endangered orange-bellied parrot (Neophema chrysogas ). From Tas. Govt.DPIWE Information sheet