As the tidal currents are slowed they begin to deposit material. This is fine-grained at first. It may be encouraged by the growth of eelgrass in submerged areas. Eel grass helps slow the currents further., Gradually uneven mud flats develop that are exposed at low tide. These mud flats can then become colonised by pioneer plant species., These plants are tolerant of salt and the periodic soaking of the sea caused by the tides. They are known as halophytes. They include species such as glasswort and sea blite. They are small and are annuals, new ones developing from seed each year., They gradually develop close vegetation over the mud. This allows colonisation by further types of plants such as sea aster, marsh grass and sea lavender. These form a dense mat of vegetation up to 15 centimetres high., This vegetation creates friction to slow the tidal currents even further. This causes yet more sediment to be deposited. Additionally, the vegetation itself traps particles. These accumulate eventually on the mud., The plants also produce leaves and stalks that die and help build up the sediment level. This vegetation waste or detritus can be up to 15 tonnes of dry matter per year., These processes combine to increase the level of the mud flats by between 1mm and 30mm per year. They also provide a food supply for other species, such as small invertebrates, to exploit., As the mud levels rise, complex creek systems evolve that channel the flowing and ebbing tides. These become deeper as the land rises. Eventually the land rises above sea level as new species such as rushes and reeds become established. These species are perennials, as are the trees such as alder and ash that appear., By this time the salt marsh succession is complete. This halosere or succession also shows species zonation. Zonation can be defined as a distinct spatial distribution., By this stage the upper levels of marsh are rarely covered by the sea. Only high spring tides and storms allow them to become inundated..

Salt Marsh development

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