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Coastal ProcessesSaltmarsh Salt marshes are essentially vegetated mudflats, these mudflats are made up of very fine sediments and they form in sheltered areas e.g. Ribble or Mersey estuaries. The sediments that form the mudflat are clays and silts; these particles are between 0.001 and 0.02mm in size. The silts and clay particles are held in suspension in water. In a sheltered area where the water is calm the sediment drops out of suspension and starts building up to form mudflats, which can then become salt marshes. As the height of the mudflat increases there are periods of time when the sea does not cover it it is at this point that plants can start to inhabit it. Salt marshes can be described as low, middle or high, this refers to their height and their vegetation. Low salt marsh is the early stage; here the height above the tide is low. The height of a salt marsh depends on a number of features, strength of tides, amount of light, amount of sediment carried and salinity. When the tide goes over the salt marsh, fine sediments are deposited, these build up over time. The first plants to grow on a salt marsh are marsh samphire, (Salicornia) this is a coloniser species. It is a specialised plant as it can cope with high salinity and tidal inundation. As plants emerge they help to trap fine sediments on their leaves and stems as well as producing leaf litter, which goes towards increasing the height of the salt marsh.
There are two other features of a salt marsh, which need to be mentioned. The first is saltpans and the second is salt marsh creeks. Saltpans are small pools, which develop when vegetation is starting to colonise the salt marsh. They develop when the vegetation is starting to spread and patches of the marsh are unvegetated. In these areas salt water collects in pools. The water in the pools then evaporates leaving saline conditions where no vegetation can grow. The rest of the marsh grows around the pools.
Salt marsh creeks are drainage channels, when the marsh flood, water drains away into the creeks. The creeks also carry tidal flows, which do not flood the actual marsh.
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As the salt marsh increases in height it is subjected to different conditions as it floods less and is exposed more, so other species e.g.sea aster (Aster maritime) and sea purslane (Halimione portulacoides) can grow. This is middle salt marsh and these plants out compete the coloniser species for resources such as nutrients, light and space. Again due to sediments being deposited and the amount of leaf litter, the salt marsh increases in height, this leads to high salt marshes and a change of vegetation e.g. sea lavender (Limonium vulgare) and sea pink (Armeria maritime). Once a salt marsh is a certain height it is mature and becomes stable.
