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 Estuary
Estuaries are semi-enclosed bodies of water which have a free connection with the open sea and within which the seawater is diluted by freshwater from the surrounding land. They extend from the upper limit of tidal influence to the open sea. In the Humber where the current flows are reduced, fine sediments are deposited forming extensive intertidal mudflats and sandflats. The Humber’s intertidal areas provide a complex and highly productive ecosystem that supports a wide range of habitats and species, such as invertebrates, which provide important sources of food for fish and birds. There is a colony of grey seals at Donna Nook and large numbers of river and sea lamprey, which are of international importance, pass through the Humber.
The erosion and accretion of sediments is a feature of Humber Estuary, which causes frequent movement of the shipping channels. Their morphology is also subject to regular spring-neap and winter-summer, erosion-deposition cycles, and in the upper reaches of the estuary, the steeply sloping bed produces a tidal bore that is particularly noticeable around Whitton Sands and in the tidal rivers.
Coastal Lagoons
Coastal lagoons are areas of shallow coastal saltwater of varying salinity, separated from the sea by sandbanks, shingle or, less frequently, rock. The Humber area is highly significant in a national context for coastal lagoons that have developed behind dune-capped barrier islands. The invertebrate fauna of the Humber’s lagoons includes three nationally scarce species.
Humberston Fitties, close to Cleethorpes is considered the third most important site of its type in Britain, and is one of the most northerly sites in Europe for the lagoon sand shrimp and a rare species of alga. Northcoates Lagoon complex includes lagoons of high and moderate salinity with a diverse species list that reflects the progression from marine to brackish habitat.
Atlantic Salt Meadows (more commonly known as saltmarsh)
Saltmarsh develops when salt-tolerant vegetation colonises intertidal sediments on the middle and upper reaches of intertidal areas where tidal inundation occurs less frequently. The Humber has an estimated 627ha of saltmarsh, having lost a significant area due to land claim in previous centuries. The composition of the Humber’s saltmarshes is unusual, over half is dominated by common reed and sea club-rush, especially in the inner estuary. Typical saltmarsh communities – pioneer marsh and low, mid and upper marsh communities are scarce, amounting to less than 1% of the total estuarine area.
The Humber Estuary supports saltmarsh on both its northern and southern banks, although in some places the upper marsh communities have been lost due to “coastal squeeze”. The saltmarshes of the Humber are predominantly ungrazed and provide a valuable habitat for wildlife. Coastal squeeze is the biggest threat to the remaining saltmarsh on the Humber, it is caused by sea defences that hinder the natural migration of the salt marsh inland, as sea level rises. Losses from costal squeeze can be mitigated against, by “managed realignment” that sets back the sea defences to provide land for the natural development of saltmarsh.
 Saltmarshes on the Humber provide essential feeding and roosting areas for waterfowl that feed on invertebrates, especially towards the mouth of an estuary, where the water gradually becomes more saline and the silt content of the sediment declines.
Salicornia (called locally samphire or glasswort)
Samphire is a pioneer saltmarsh plant that grows on the lower reaches of the saltmarshes where the vegetation is frequently flooded, it also grows on open creek sides and depressions or disturbed areas of upper saltmarsh. The samphire on the Humber germinates in May from a widespread dispersion of seeds over the whole marsh surface, and grows where the time between tides allows plants to become firmly anchored. Samphire provides an important feeding area and a food source for many species of waterfowl. Samphire is also collected locally for the table.
 Intertidal Mudflats and Sandflats
Intertidal mudflats and sandflats are submerged at high tide and exposed at low tide, when nearly 50% of the Humber’s bed is exposed. There are extensive areas of mudflats in the outer estuary, particularly inside Spurn Bight and Cherry Cobb. The effects of wave energy on the movement of sediment are largely restricted to the coastal reaches outside the estuary mouth, for example down the Lincolnshire coast and on the seaward side of Spurn; in these areas the intertidal flats are predominantly sandy.
Large scale reclamation took place in the Doncaster-Goole area in the 17th century and at Sunk island from the mid 18th to the beginning of the 20th century. There has been some land claim since but now compensation must be provided for any unavoidable losses resulting from flood defence or port works. The estuary has been slowly eroding in the outer and middle sections, whilst accretion occurs in the inner estuary. The accretion at Whitton Sands has reached the extent that vegetation is establishing, whilst Read’s Island is undergoing erosion.
The Humber Estuary also supports several sand dune systems covering an area of over 200ha. Coastal dunes develop behind a sandy beach with a surface that dries out between high tides. The dry sand is then blown landwards and if deposited above the high water mark and trapped by obstacles and vegetation, the dune system begins to grow. Although the dunes are above highest astronomical tide and therefore outwith the European Marine Site boundary, processes occurring within the site will affect them, particularly as the sandflats are their source of material.
 Subtidal Sandbanks
Subtidal sandbanks consist of sandy sediments that are permanently covered by shallow seawater, they may be composed of elongated, rounded or irregular ‘mound’ shapes that arise from horizontal, or sloping plains of sandy sediment. Communities associated with subtidal sandbanks include invertebrates and seaweeds that colonise the seabed or which live in the seabed sediments. Typically, these include worms, crustaceans, bivalve molluscs and echinoderms, mobile species may include shrimps, crabs and fish. Subtidal sandbanks are often important nursery areas for fish, with the Humber supporting 15% of the east coast population of juvenile plaice and large numbers of juvenile sole.
The subtidal area of the Humber Estuary is over 16,800 ha or 50% of the total area of the estuary, this provides an important breeding, sheltering and nursery area for marine fish species and a migratory corridor for Atlantic salmon, sea trout, eels and lamprey.
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