On the south coast of the UK, there is historical evidence of the loss of intertidal areas due to a combination of factors.  These include land reclamation and changes in area from sediment deficits, plant ‘die-back’ and glacial Isostasy is the Equilibrium in the earth's crust such that the forces tending to elevate landmasses balance the forces tending to depress landmasses.isostatic adjustment.  Significant losses are likely to continue without climate change but loss rates are likely to be exacerbated by accelerated sea level rise (Nicholls et al., 1999).

Inter-tidal habitats are dynamic and can respond to sea level rise by accreting vertically with the accumulation of sediments and migrating inland. Migration may, however, be impeded by the presence of fixed defence structures. In England, flood defences have removed most opportunities for landward migration (Nicholls and Wilson, 2001) and it is estimated that at least 40 – 100 ha a^-1 of saltmarsh is being lost (Environment Agency, 1999). Many marshes exhibit accretionary deficits; where accretionThe gradual extension of land by natural forces, as in the addition of sand to a beach by ocean currents, or the extension of a floodplain through the deposition of sediments by repeated flooding. is less than relative sea level rise reversion of vegetated surfaces to unvegetated mudflats may occur.

These factors put pressure on the ability of local agencies to achieve the requirements of statutory regulations such as the EC Habitats Directives. More long-term and flexible approach is needed, including the consideration of less geographically determined boundaries and additional planning approaches such as land-banking or habitat compensation.

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What is already happening – medium.

Saltmarsh loss recorded anecdotally but detailed, repeat surveys of marsh area to a common methodology lacking.

What could happen in the future – low to medium

(many unknowns e.g. regional variations in sea level rise; changes in wave climate; plant responses to global environmental change; changes in sediment supply; coastal management strategies)

• Impacts of beneficial use of dredged material and sediment recharge to intertidal areas.
• Creation of fluvial grazing marsh as a replacement for coastal grazing marsh; are they comparable from a nature conservation point of view?
• Uncertainties involving coastal geomorphologyThe study of the characteristics, origin, and development of landforms. (wave climates, sediment and accretionThe gradual extension of land by natural forces, as in the addition of sand to a beach by ocean currents, or the extension of a floodplain through the deposition of sediments by repeated flooding. rates) with future climate change.
• Ongoing long-term monitoring and data collection – physical and biological.

Intertidal areas are highly productive and provide a number of important functions including flood protection and wave dissipation, waste assimilation, nursery areas for fisheries and nature conservation. It has been observed that 200m of saltmarsh surface can reduce significant wave heightsThe distance between the trough and peak of a wave. by as much as 63% (Moller et al., 2001), reducing the need for costly sea defences, however with the loss of saltmarshes and intertidal areas sea walls may have to be upgraded to prevent areas flooding. Tidal saltmarshes have been identified as areas of high productivity providing a source of organic matter and nutrients for fish and a variety of invertebrates (Mitch & Gosselink, 1986; Lefeuvre & Dame 1994), as well as being important nursery grounds for commercial fish stocks such as sea bass, (Laffaille et al. 2001).

Sarah Gardiner, Susan Hanson, Robert Nicholls
University of Southampton, School of Civil Engineering and the Environment Highfield, Southampton, SO17 1BJ

Tom Spencer, Dan Friess
Cambridge Coastal Research Unit, University of Cambridge, Downing Place, Cambridge CB2 3EN