INTRODUCTION TO SALTMARSH

Definitions and descriptions

Saltmarsh develops in temperate waters between Mean High Water of Spring tides (MHWS) and Mean Low Water of Neap tides (MLWN) where net accumulation of sediment occurs. Some degree of shelter from wave action is necessary so saltmarshes are found in inlets, estuaries and behind barrier islands or shingle spits. Under favourable conditions where there are extensive tidal flats and in the absence of enclosure, large areas of saltmarsh may develop.

Early saltmarsh vegetation is composed of a few salt-tolerant (halophytic) plants and is most often found on intertidal surfaces where disturbance of the roots of germinating pioneer plants are left undisturbed by tidal action for several days. Succession takes place as the vegetation develops and the surface of the saltmarsh is raised in response to stabilisation and sediment deposition. As vegetation becomes progressively covered by fewer and fewer tides, an increasingly diverse community of plants and animals develops. The nature of the plant communities is also influenced by sediment type and geographical location.

Traditional management

In temperate regions there are three key management concerns. The first two typically involve effects on the vegetation as a result of grazing (by both domestic stock and native herbivores) and the invasion of Spartina. The third is associated with marsh stability; a major issue when considering saltmarsh restoration, re-creation or creation.

Reasons to restore

Saltmarshes have long been the subject of a range of human activities causing habitat loss. Enclosure for agricultural use, ports and harbours and other infrastructure have reduced many saltmarshes to a narrow fringe along estuary shores. Recreational use, pollution and wave action (including wash from boats) can further damage the marsh. Saltmarsh erosion is a second key reason for restoration. In the UK this is exemplified by the 'saltmarsh squeeze'. In some areas (especially the USA) drowning, as a result of sea level rise, is implicated in sometimes large-scale losses.

States and values

Saltmarshes are important for a range of interests which are common to most of the larger examples. In particular they support a range of specialist plant communities and associated animals (especially breeding and wintering birds) and often have a high nature conservation interest. They also have economic significance providing grazing for domestic stock, shelter for early stages in the development of a number of commercial fish (e.g. bass) and often contribute to sea defences. They rarely exist in isolation and form an integral part of many estuaries, other tidal inlets and bays and deltas.

Two key issues have been identified which help to define the states and values of saltmarshes when considering restoration, namely:

1. Grazing management which has a significant effect on the vegetation and the nature of biodiversity of the saltmarsh. Four states are identified for saltmarsh vegetation which are determined by stock densities
   1. State 1 Heavily grazed;
   2. State 2 Moderately grazed;
   3. State 3 Ungrazed / Lightly grazed;
   4. State 4 Abandoned.
2. Erosion and/or accretion which changes the surface (vertical) and the (horizontal) stability of the saltmarsh. Three states are identified describing the physical state of the saltmarsh.
   1. Eroding;
   2. Dynamic equilibrium;
   3. Accreting.

Guidance (routes to restoration)

There are two general approaches to restoring saltmarsh which depend on whether the aim is to restore existing saltmarsh vegetation (mainly for nature conservation purposes) or the create or re-create saltmarsh habitat. The route to restoring degraded saltmarsh vegetation normally involves control of grazing regimes or the reintroduction of grazing on abandoned sites, where coarse vegetation has eliminated nature conservation interests. Creating new saltmarsh is a complex process which can involve re-establishing surface stability and with it vegetation on tidal flats and/or managed realignment. Changes in those processes, which help promote saltmarsh accretion (such as sea level change, tides and tidal range, sediment availability, freshwater flows and channel movements) also cause erosion. The two exist in a dynamic interaction which may result in a landward or seaward progression of the saltmarsh front. Depending on the balance between the two, management to promote the former and control the latter are key elements in any restoration strategy.

Key Publications:

• Background documents: (Long & Mason 1983; Adam 1990; Allen & Pye 1992; Packham & Willis 1997; Toft & Maddrell 1995) for a nature conservation perspective see Doody 1992a; Doody 2001 Chapter 5;
• Restoration guides: ( Environment Agency Saltmarsh management guide; Niedowski 2000; USA Saltmarsh Guide);
• Web sites: (The University of East Anglia http://www.uea.ac.uk hosts a saltmarsh restoration site).

Key References

Niedowski, N.L. 2000. New York State Salt Marsh Restoration and Monitoring Guidelines. New York State, Division of Coastal Resources & Division of Fish, Wildlife and Marine Resources.

Toft, A.R. & Maddrell, R.J. 1995. A Guide to the Understanding and Management of Salt Marshes . National Rivers Authority R&D Note, 324

References

Adam, P. 1990. Saltmarsh Ecology. Cambridge University Press, Cambridge, 461 pp. Cambridge Studies in Ecology

Allen, J.R.L. & Pye, K. 1992. Saltmarshes: Morphodynamics, Conservation & Engineering Significance. Cambridge University Press, Cambridge, 184 pp. Abstract...

Doody, J.P. 1992a. The conservation of British salt marshes. In: Saltmarshes: Morphodynamics, Conservation & Engineering Significance, ed.Allen, J.R.L. & Pye, K.Cambridge University Press, Cambridge, 80-114.

Doody, J.P. 2001. Coastal Conservation and Management: an Ecological Perspective. Kluwer, Academic Publishers, Boston, USA, 306 pp. Conservation Biology Series, 13

Long, S.P. & Mason, C.F. 1983. Saltmarsh Ecology. Blakie, London.

Packham, J.R. & Willis, A.J. 1997. Ecology of Dunes, Salt Marsh and Shingle. Chapman & Hall, London, 335 pp.