Welcome to Flats and Marshes of the Wash

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This wiki is an experiment in the online presentation of local biodiversity as a concept map. The area chosen was described in the UK 1977 Nature Conservation Review as the Wash Flats and Marshes. The Review was the first attempt of the UK Government to make a selection of biological sites of national importance to nature conservation in Britain. The Wash Flats and Marshes were described in the Site Accounts section as follows:

C.20. THE WASH FLATS AND MARSHES,
NORFOLK-LINCOLNSHIRE

This great area of sand–silt flats and their fringing salt marshes is sealed off from the low-lying Fenlands behind by a long series of sea walls bounding the whole inlet, but receives the drainage of the three main Fenland rivers, the Welland, Nene and Ouse, and exerts a tidal influence on these for some distance inland.

It has been divided into five sections, mainly between these river mouths, but the long western shore has been arbitrarily separated into two, midway between the dune and shingle peninsula of Gibraltar Point and the Welland mouth.

(a) Gibraltar Point–Wrangle TF 570608-440470. 6000 ha
(b) Wrangle–Welland TF 440470-350340. 4000 ha
(c) Welland–Nene TF 350340-490260. 5700 ha
(d) Nene–Ouse TF 490260-600230. 5300 ha
(e) Ouse–Hunstanton TF 600230-690440. 5300 ha

Flats (23 700 ha)
The Wash is one of the two largest areas of estuarine flats in Britain, the only other system of comparable size being that of Morecambe Bay, where the sediment is coarser in general and less lime-rich. Although the occurrence of Zostera (Z. noltii) appears to be limited to the lime-rich flats of the Welland estuary, the Wash Flats have large populations of Enteromorpha, other algae, and invertebrates which provide a rich food source for wildfowl and waders. The Wrangle flats of section (a) are one of the main haunts of the dark-bellied brent goose in Britain (3000 birds –distinct from those of the Essex coast), which here feeds mainly on Enteromorpha. The area also carries a flock of 2000 pink-footed geese and probably a similar number of wigeon. This is the most important part of the Wash for geese, though smaller numbers of these birds occur in other parts, notably the Welland estuary, which also has the largest population of duck (wigeon – 7500; shelduck 1500; mallard – 750; and teal – 300). The sea off the northeast shore has valuable populations of seaducks (common scoter – 2000; velvet scoter – 100; scaup and eider –several hundred). The former Wash population of up to 15 000 pink-footed geese has declined, but shelduck have increased and this is now an important wintering haunt of the species.

The Wash Flats also carry the second largest wintering population of waders in Britain, with a total population of over 180 000 birds. There are especially large flocks of knot (85 000), dunlin (45 000), curlew (12 000) and oystercatcher (10 000), and considerable numbers of redshank, sanderling, bar-tailed godwit, grey plover (half of the British population) and ringed plover. This is also an important area for waders on migration, and some species complete an interrupted moult on the Wash.

The sandbanks of the Wash support populations of both species of seals native to Britain. The number of grey seals is small: groups of 10 to 20 are to be seen on Dogs Head Sand in the northern part of the Wash. By contrast, the Wash is by far the most important breeding area for the common seal, which is to be found in large numbers (c. 3000-5000). Most of the sandbanks on which these seals haul out are located around the mouths of the rivers Nene, Welland and Ouse.

Marsh (2600 ha)
The marshes bordering the Wash are probably, in aggregate, the most extensive in Britain, but they have not been properly surveyed. Virtually all of them have developed outside sea walls, and vary in width from a few metres to about 1.5 km. In floristics they appear to be characteristic of the south-east England marshes on fine sediment, with Salicornia spp., Puccinellia maritima and Spartina anglica as usual pioneers, and an abundance of Halimione portulacoides, Aster tripolium var. discoideus, Limonium spp., Suaeda maritima and Triglochin maritima. The vegetation appears to be rather uniform, and diversity is limited by the sea walls, since most of the older marsh behind has been converted to grazing marsh and, more recently, this has been turned mainly into arable land. Ditches here have brackish conditions with a typical flora, similar to those of the north Kent fleets, but there tends to be a steady loss of interest as this reclaimed land becomes more intensively used.

The marshes are valuable as the feeding and roosting places of waders, though some of these birds (especially dunlin) rest on arable land when they are displaced by high tides in the estuary. Exceptional tides may force all the waders to resting places behind the sea wall. The main roosts are on the marshes at Snettisham/Wolferton, Terrington, Holbeach/Dawsmere and at Gibraltar Point. It thus seems likely that, while the botanical interest of the Wash salt marshes is probably well represented by those of the North Norfolk Coast, these saltings represent an integral part of the ornithological habitat which gives the Wash its international importance. Frampton/Kirkton marsh, lying immediately north of the Welland estuary, is the only remaining area of unreclaimed high saltings in the southwest Wash, and has a vast colony of black-headed gulls and some common terns.