1.  There is no fixed vegetation on the mudflats; mats of marine algae (Enteromorphasp) occur and provide grazing for wintering brent geese and wigeon in the absence of eel grass (Zostera) which is no longer present.  This algae responds vigorously to eutrophic conditions.  Extensive algal mats may smother the flats and reduce the value of feeding grounds to waders.  Autumnal breakdown of these mats however, produces rich feeding grounds for benthic detrivores which provide food for waders.

2.  Colonisation by cord grass Spartina has been problematic on some mudflat sites in the UK.  At Gibraltar Point, this has not been witnessed.  In an accretion situation, pioneer saltmarsh plants will colonise the upper reaches of the flats eg Salicornia.  Saltmarsh development may then be quite rapid.  The New Saltmarsh (compt. 1/11/A) now exhibits a well developed mid- marsh community on what was a sandy beach in the 1960’s.  However, this trend may be reversed in response to ‘coastal squeeze’.

3.  Sediment characteristics vary over the intertidal zone.  Sediment character defined by particle size analysis is key to the structure of the feature and reflects all of the physical processes acting on it.  To the north, and away from the estuarine influence, the substrate of the intertidal flats is coarser, with a high sand and shell component.  A sandy beach predominates seaward of the shingle ridges north to Skegness. Large numbers of non- breeding gulls, terns and cormorants congregate on this stretch of coast.  Occasional expanses of mud can be extensive, where associated with mobile runnels or saltmarsh creek outflows, ie Greenshanks Creek.  From time to time, scouring of the sandflats may occur through wave action and result in the large-scale loss of material from the beach. During such periods, the underlying clay bed will become vulnerable to erosion.  Organic content, degree of oxidation and levels of penetrability are crucial elements of the sediment and contribute to its stability and colonisation by invertebrates.

4.  The intertidal mudflats support an incredibly rich fauna.  Some benthic invertebrates may occur at densities of up to 3000 animals per square metre.  Principle groups involved include crustacea, mollusca, arthropoda, oligochates and nematodes.  Of the Wash communities highlighted in the ‘Wash Natural Area Profile’, the soft mud community is significant at Gibraltar Point.  This community is characterised by lugworms Arenicola marina, with a large range of polychaetes and bivalves, such as Cerastoderma edule and Macoma baltica.

5.  These rich feeding grounds are replenished twice daily by the high tides and are fundamental for sustaining vast numbers of internationally important waders on passage and wintering grounds.  Grey plover, knot, dunlin, oystercatcher, bar-tailed godwit and curlew rely upon the mudflats whilst sanderling and ringed plover will exploit the sandflats.

6.  During the breeding season, public access is restricted.  The Wainfleet Haven and the flats at the southern end of the NNR are incorporated in the shorebird sanctuary. Outside of this period, there are no restrictions and present visitor pressure is not seen as a threat to the integrity of the flats.  Bait-digging however, occurs regularly on a small scale on the foreshore at the Seacroft end of the NNR.  On the whole, visitors avoid the mudflats in preference for the sandy beach areas.  The majority are involved in casual recreation and damage to these habitats is negligible.  Bait-digging in contrast does cause damage to the habitat through physical disturbance of the substrate and removal of lugworms.  This practise, whilst undesirable, occurs regularly on what is perceived to be a non- commercial scale.  Levels of activity will continue to be recorded.  The legal implications of this activity are complex.  Small numbers of sea anglers also occur periodically at the north end of the NNR.

7.  Other factors which influence the flats are anthropogenic directly or indirectly.  Concern is generated through the risk of pollution from industrial shipping which service the port of Kings Lynn.  Periodically, small patches of oil occur, probably resulting from illegal tank washings. The last major incident to affect mudflats on the Lincolnshire Coast was at Cleethorpes in 1998.  Collection and disposal of pollutant on sand or mudflat may be achievable pending vehicular access.  Thus policy differs from saltmarsh.  The Trusts emergency planning team has been set up to oversee any such future incidents. Eutrophication of estuarine mudflats has recently been highlighted as a concern.  Where high levels of nutrients enter the system, algal blooms may occur, smothering the mudflats and the prey items sought after by wading birds.  The River Steeping drains a large area of intensive arable land; nutrient load (particularly phosphates etc) may be high.  Extensive algal growth has occasionally been noted on the flats and indeed saltmarsh.

 

8.    Marine borne debris may occur on the flats as a result of marine fly-tipping or debris from the bombing range eg plastics, containers and tyres.