<P> A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides . It is dominated by dense stands of 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 delivery of nutrients to coastal waters . They also support terrestrial animals and provide coastal protection . </P> <P> Salt marshes occur on low - energy shorelines in temperate and high - latitudes which can be stable or emerging, or submerging if the sedimentation rate 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 . 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 from a salt marsh in that instead of herbaceous plants, they are dominated by salt - tolerant trees . </P> <P> Most salt marshes have a low topography with low elevations but a vast wide area, making them hugely popular for human populations . 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 - valley marshes . Deltaic marshes are associated with large rivers where many occur in Southern Europe such as the Camargue, France in the Rhone delta or the Ebro delta in Spain . They are also extensive within the rivers of the Mississippi Delta in the United States . In New Zealand, most salt marshes occur at the head of estuaries 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 . 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 . </P> <P> Salt marshes are sometimes included in lagoons, and the difference is not very marked; the Venetian Lagoon in Italy, for example, is made up of these sorts of animals and or living organisms belonging to this ecosystem . They have a big impact on the biodiversity of the area . Salt marsh ecology involves complex food webs which include primary producers (vascular plants, macroalgae, diatoms, epiphytes, and phytoplankton), primary consumers (zooplankton, macrozoa, molluscs, insects), and secondary consumers . </P>

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