Introduction • Land claim • Coastal squeeze

Land claim

The embanking and reclamation of many estuaries (e.g The Wash and the Ribble estuary, see figures below) throughout the UK since Roman times, for agricultural and industrial purposes has had significant effects on saltmarsh morphology and ecology.

Saltmarsh enclosure for agricultural use in The Wash (from Living with the Sea, 2003)

Saltmarsh enclosure for agricultural use in the Ribble Estuary (from Doody, 2001)

Decreases in intertidal areas occur as land is reclaimed and embanked, affecting the progression of the tidal wave and tidal prism. Two main responses to embankment and reclamation occur: (a) enhanced intertidal accretion due to reduction of the tidal prism, as velocities are reduced and sediment can accumulate more readily, and (b) enhanced erosion outside the sea wall due to the concentration of excess tidal energy. In the second case, remaining saltmarshes on the outside of a sea embankment are likely to experience erosion due to lowering of the intertidal flats, retreat of the marsh edge and internal dissection as marsh creeks undergo deepening, widening and headward extension (Pye, 2000). The main channel may try and reach a new equilibrium through re-deposition of sediment but, in areas of ebb-dominance, a high proportion of the sediment may be exported to the open sea (van der Wal and Pye, 2004).

From an ecological perspective, sea walls built to exclude the tide are normally positioned on the upper, most diverse zone of the marsh, because enclosure has usually only been undertaken when saltmarsh is successionally advanced. This has resulted in the loss of the more mature saltmarsh, together with its associated fauna, as well as the truncation of the sequence of transitions to more terrestrial or freshwater/brackish habitat, thereby affecting other species that use the upper marsh for part or all of their life cycle.

Parts of southeast England also demonstrate more complex patterns of reclamation where, during the 19th and 20th centuries, some areas of reclaimed marsh were abandoned to the sea as economic conditions deteriorated and the maintenance of sea walls was scaled down. Following abandonment, new saltmarshes became established on those parts of the re-flooded land that were high enough in the tidal frame to allow plant colonization. New creek systems became established, eventually re-establishing a more natural pattern in equilibrium with hydraulic conditions (Crooks and Pye, 2000).

At the present time, the saltmarshes and associated areas of agricultural land along the coasts of much of eastern and southern England, as well as within the Severn Estuary, form a patchwork of semi-natural and higher, un-natural marsh landscapes. These landscapes reflect a complex history and the (often) partial adjustment of the saltmarsh to the process conditions and environmental forcing factors that now operate.