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Shoreline Management Coastal Features - Salt Marshes A fascinating feature of the Sefton Coast is the salt marsh. Found largely to the north of the Sefton Coast around Marshside and Crossens, with small areas around Birkdale and the mouth of the River Alt at Hightown. Definition Salt marshes are almost flat areas of the intertidal area that are comprised of usually fine sediment that supports plants and animals that are very tolerant to the extreme conditions that are present there. Salt marshes are important areas for sea defence and for specialised habitat for both plants and animals. Features Salt marshes form in the landward area of the intertidal zone that is only covered by the sea for relatively short periods of time at high tide, and is uncovered for the majority of the tidal cycle. Short plants characterise the vegetation of the marshes, with the plants usually falling into 'zones' of 'lower marsh' which contains the pioneering salt-tolerant plants of Spartina (cord grass) and Salicornia (glasswort). These plants exist in conditions of waterlogging and unstable sediment, and survive being frequently covered by the tide and damaged by waves. Further inland, the vegetation changes through a zone of 'mid marsh' to 'high' or 'upper marsh', where tidal inundations occur less often, the sediment underneath is more stable, and there is likely to be less physical damage to the plants by waves. Plants such as Aster tripolium (sea aster), Limonium vulgare (sea lavender), Puccinellia maritima (salt marsh grass or sea meadow grass) and Halimione portulacoides (sea purslane) exist in these zones. The presence of the plants on the marsh also further adds to its development, by adding organic matter to the marsh, both above and below the surface. Creeks are an important feature of salt marshes, being channels that allow the sea to both flood into the marsh, and drain out again. Although having the appearance of river channels, creeks differ in that the water flows in both directions through them depending on the state of the tide, and that whereas rivers are at their most energetic when full of water, creeks are at their most sluggish when full. Salt pans are a feature of salt marshes and can take two forms, called 'primary pans' and 'channel pans'. Primary pans are areas of marsh that are shallow, roughly circular, un-vegetated depressions on the surface of the marsh. There is still discussion about how they are formed, with the main theories being either uneven deposition of sediment when the marsh is first forming, or due to tidal litter 'scouring' the surface and preventing plants from growing in the area. Channel pans are more elongated depressions, formed by a section of marsh creek becoming cut-off from the rest of the creek system. Monitoring Salt marshes provide a valuable asset to the coast in terms of sea defence. The vegetation on the marsh dissipates the energy of incoming waves, preventing higher energy more destructive waves reaching the land. As marshes are so dependent for their survival on the relationship between sediment supply, wind and wave conditions, and vegetation they are particularly susceptible to changes due to sea level. Because of their dependence on these variable factors, they are not static features, with monitoring required to assess the changes that take place. The two images show the same area of saltmarsh, the top image is a normal colour aerial photography whilst the bottom image is false colour aerial photography, the vegetation can clearly be seen as pinks and reds in the bottom image, showing the benefits of false colour aerial photography.. Due to their location salt marshes can sometimes be difficult to survey due to health and safety issues. Within Sefton the marshes are surveyed using a number of methods, for the accessible areas the marshes are surveyd with GPS equipment to record their elevation and extent. For the areas which aren't accessible we use remote sensing, such as aerial photography, False colour aerial photography and Lidar surveys. Home Page - Top www.seftoncoast.org.uk

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