Saltmarsh - State 2, dynamic equilibrium

A saltmarsh is said to be in dynamic equilibrium when sequences of erosion and accretion result in no overall change in marsh area. This may involve periods when the saltmarsh front is moving landward or sea ward depending on the influence of erosional forces. In the Severn Estuary (see Figure opposite) sequences of erosion create cliffs at the marsh edge, which may be followed by regrowth as estuary channels change their course. A series of steps can develop as new saltmarsh extends to seaward of the eroding cliff face. Similar situations occur in other estuaries such as the Solway Firth (Cumbria and Dumfries and Galloway, Scotland) and Morecambe Bay, Lancashire, England.

Caption: Different saltmarsh levels on the Welsh shore of the Severn Estuary. Three levels caused by cycles of erosion can be seen in the middle distance of the picture.

This state is also recognised when the marsh mosaic includes a sequence of vegetation types with saltpans, dissected by channels and saltmarsh creeks (see Figure opposite). Whilst change is less obvious, at least over relatively short periods of time, the dynamic is created by the development of the saltmarsh structure through succession and subsequent change in the pattern of the saltmarsh surface.

Caption: Mature marsh with tidal creeks and mid to upper saltmarsh communities, Abbots Hall, Essex

Comment: This state provides the greatest potential value for nature conservation interest to develop.