Sand Dunes,Mud Flats,Salt Marsh
The North East Lincolnshire coastline is also the gateway of the
Humber Estuary. It is regarded by ornithologists as one the top 10
estuaries in Europe, providing a vital staging post for migratory
birds, and some 140,000 feed here during the winter months.
Habitats include saltmarshes, mud flats, sand dunes and sand banks
all adding to the wildlife of the area.
The importance of the estuary was recognised in 1988 when it was
designated some areas a Site of Special Scientific Interest (SSSI).
This has been endorsed by European Directives making it a Special
Protected Area (SPA), a Special Area for Conservation (SAC) and a
European Marine site. The area is also recognised by the Ramsar
Convention on Wetlands as a wetland of international
importance.
Sand Dune Formation
A sand dune needs the following three things to form:
1. A large amount of loose sand in an area with little
vegetation -- usually on the coast or in a dried-up river, lake or
sea bed
2. A wind or breeze to move the grains of sand
3. An obstacle that causes the sand to lose momentum and settle.
This obstacle could be as small as a rock or as big as a tree.
Where these three variables merge, a sand dune forms. As the
wind picks up the sand, the sand travels, but generally only about
an inch or two above the ground. Wind moves sand in one of three
ways:
1. Saltation: The sand grains bounce along in the wind. About 95
percent of sand grains move in this manner.
2. Creep: When sand grains collide with other grains -- like
clay or gravel -- causing them to move. Creep accounts for about 4
percent of sand movement.
3. Suspension: Sand grains blow high in the air and then settle.
About 1 percent of sand moves this way.
Mud Flats
Mud flats are typically found in areas where the tidal waters
flow slowly, such as sheltered bays, estuaries, rias and along
gently shelving coasts.
A mixture of very fine silts from tidal waters and alluvium from
rivers dropping their load as they reach the sea, is deposited,
causing a build up of mud layers, called mud flats. Mud flats are
covered at high tide and exposed as the tide drops. In rias, mud
flats are often found in the remains of the valleys that were
tributaries to the main submerged river. In such areas, remains of
the original watercourses can sometimes be seen as channels carved
out of the mud, down which a little fresh waters may be seen
flowing at low tide. All mud flats are usually crisscrossed by
winding channels that are kept open by tidal action. Unless these
channels are fed by active water sources, such as streams and
rivers, they will usually dry out at low tide and contain no
water.
Where the muds are sufficiently stable to support vegetation,
salt marshes may form, or in tropical areas, mangrove swamps.
Salt Marsh
A salt marsh forms when incoming tides carry and deposit
sediment across low-lying land, resulting in wet mudflats.
Saltwater grasses then slowly take hold and spread, stabilizing the
land through the growth of root systems. As the plants decay and
sediment builds up, peat deposits accumulate, forming a rich
habitat that supports the growth of hundreds of diverse
organisms.
A salt marsh is thus a place where the land meets the sea,
created through tidal action over a span of hundreds of years. This
unique habitat is confined to a narrow coastal fringe along
shallow, protected bays. A healthy marsh maintains a delicate
balance between salt water and fresh water, especially further
inland where a salt marsh may merge with a brackish area or a
freshwater swamp. Closer to the shoreline, the ebb and flood of
daily tides creates zones:
* The Lower Marsh is often submerged under saltwater, and
supports the growth of organisms adapted to high salinity and lots
of moisture.
* The Upper Marsh is a drier area, where plants tolerate lower
salt concentrations.
* The salt pans are small depressions that trap and hold water
on a high tide.
* The highest edges of the marsh are only reached by extremely
high tides, such as during a storm.
As you walk along the edge of the marsh, observe whether the
tide is low or high, and try to identify the various zones created
through the action of the tides.
To log the cache upload a picture of yourself or GPSr with the
mud fats behind you and E-mail me the answer's to the following
questions
1) Estimate the height of the sand dunes .
2) Estimate the width of the dune to your right as you look out
to sea.
Any logs without a photo will be deleted