Estuaries

The extensive saltmarsh and mudflats of the Dee and Mersey estuaries and the adjacent North Wirral foreshore are significant sites for wildlife. These biologically productive habitats, with their characteristic saltmarsh and mud-dwelling communities, are the wintering haunt of wildfowl and waders in tens of thousands. Specifically, the estuaries are internationally important for pintail, shelduck, wigeon, dunlin, oystercatcher, redshank, grey plover, know, turnstone and teal.

These habitats continue to evolve through the processes of erosion and deposition. The pattern of colonisation in the Dee had been radically influenced by the creation of the Dee Cut, dug to offset the natural sedimentation of the estuary, which prevented Chester from remaining a port. The Dee catchment and its estuary have retained a good water quality to the present day, supporting significant fisheries as well as outstanding wildlife.

The tidal scour in the Mersey estuary results in continually shifting channels which influence the rate of erosion and deposition on the extensive mudbanks. The Mersey catchment and its estuary suffer serious environmental degradation, receiving effluent from the major industrial sites and conurbations in the North West. The Mersey Basin Campaign has been established to counter this environmental decline.

Mudflats
Mudflats are created by the deposition of sediments in estuaries, these sediments generally consist of silts and clays with a high organic content. They frequently occur as part of the natural sequence of habitats between the sub-littoral zone and vegetated saltmarshes. Mudflats absorb wind and wave energy from the sea, thus reducing erosion damage to saltmarshes and coastal defences, and so reducing the risk of tidal flooding in low-lying coastal areas.

Although mudflats often appear barren they support a huge biomass and are highly productive. The surface can be thickly coated with algae, while under the surface are a wealth of invertebrates including cockles, ragworms, and shrimps. This abundance of life makes mudflats very important feeding areas for wildfowl and waders, able to support huge flocks. When submerged by high tides mud flats are also important for fish, and nursery areas for flatfish. They are also important as resting areas, a function that is enhanced by their relative inaccessibility and freedom from disturbance.

Both the Mersey and Dee estuaries and the North Wirral foreshore feature significant areas of intertidal sand and mud flats. These are of very high nature conservation importance as feeding and resting areas for internationally important populations migrant and over-wintering wildfowl and waders.

Saltmarsh
Coastal saltmarshes comprise the upper, vegetated portions of intertidal mudflats. Saltmarshes are usually restricted to comparatively sheltered locations in estuaries, saline lagoons, behind barrier islands, at the heads of sea lochs and on beach plains. The development of saltmarsh is dependent on the presence of mudflats. Saltmarsh vegetation consists of a limited number of salt tolerant plants adapted to regular immersion by the tides. At the lowest level pioneer plants can withstand up to 600 immersions per year where the upper saltmarsh can only tolerate a few tides per year. Saltmarsh communities are affected by many factors such as climatic differences from west to east, sediment types, decreasing salinities and land management. For example, on traditionally grazed sites, saltmarsh vegetation is shorter and dominated by grasses. Saltmarshes are a very important habitat for plant species and a resource for wading birds and wildfowl. Acting as high tide refuges for waterfowl, breeding sites for terns, gulls, waders and passerines (skylark and meadow pippit) in autumn and winter. In winter, large flocks of swans, geese and ducks rely on saltmarshes. They provide an exhilarating and evocative landscape and seascape.

In Wirral, the majority of coastal saltmarsh is found in the Dee Estuary between Parkgate and Heswall. Small areas occur at West Kirby and at New Ferry on the Mersey. The saltmarsh between Parkgate and Heswall is still accreting the oldest parts being over 50 years old. None of the Wirral saltmarshes are grazed. Some loss of pioneer saltmarsh occurs at West Kirby and Hoylake due to beach cleaning by WBC.