Intertidal mudflats and sandflats are submerged at high tide and exposed at low tide. They form a major component of estuaries and embayments in the UK but also occur along the open coast. The physical structure of intertidal flats can range from the mobile, coarse-sand beaches of wave-exposed coasts to the stable, fine-sediment mudflats of estuaries and embayments. This habitat type can be divided into three broad categories: clean sands, muddy sands and muds, although in practice there is a continuous gradient between them. Within this range, the plant and animal communities present vary according to the type of sediment, its stability and the salinity of the water.

Mudflat areas are exposed at low tide and may extend for many square kilometres. Those mudflats which are adjacent to saltmarsh areas provide important feeding grounds for many shore and sea birds. They also offer important breeding sites for over-wintering birds. The richness of the fauna contained within the feature is a major determinant in the diversity and number of birds which feed from mud and sand flats. However, just as the macrofauna community is important for the species of birds which populate mud and sand flats, so birds contribute with other factors to the control of these communities through predation.

One of the main factors influencing the environment of intertidal areas is the degree of wave action. This is particularly the case for mud and sand flat areas as the intensity of the wave action will determine the sorting of the surface sands, gravels and silts. This is highlighted by Elliot (1998) who state that "increased littoral and tidal currents carry away finer material and leave coarser, well sorted sands and gravels whilst in more sheltered areas settlement of finer material is possible, as found on intertidal mudflats."

As with many other coastal features, mud and sandflats can be changed considerably by natural events. Periodic increases in wave action can severely alter the appearance of the intertidal region and storms can remove considerable amounts of material from sandbanks. In addition, increased rainfall can cause natural impacts on the feature including scouring of intertidal areas.

In addition to the physical characteristics of intertidal mud and sand flats, the biological communities within these features are also important to feature stability. Micro and macro biological species such as bacteria and polychaete worms contribute to the long term stability of the feature. Disturbance to the layering of the mud or sand flat can have consequences for these species. In particular, although some water breathing species have adapted to air exposure, such as Scolelpis squamata, many need to burrow into the sediment to avoid drying out and dying from air exposure.

There are a number of human pressures influencing mud and sand flats including:

• land claim for development
• squeeze through sea level rise
• provision of recreation facilities
• recreational activities
• dredging
• pollution/nutrient stimulation

Other factors that can affect mud and sand flat species include:

• salinity
• temperature
• dissolved oxygen content

It is unlikely that recreation could affect any of these factors to such a degree that it would have a significant effect on the feature or the species it supports.

The tables below summarise the potential threats to mud and sand flats from land and waterborne processes.

Water based processes

Land based processes

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