Sand Dunes - formation, case study, damage, investigating

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  • Created on: 23-09-13 20:39
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Sand dunes are accumulations of sand stabilised by vegetation. The development of a coastal
dune system requires a source of sand, and an onshore prevailing wind of at least 4.5 metres per
second.
Sand dune ecosystems are usually found at the sediment sink. This is because longshore drift deposits all
the material from the sediment cell here. Once deposited, the sand is dried by the wind and then carried up
the beach. When the grains land they dislodge a couple more grains, which in turn take to the air and do the
same. This process is called saltation. The grains will stop moving when they reach an obstruction such as
driftwood.
Saltation is helped or hindered by:
Wind velocity.
Grain size and shape.
Dampness of sand.
An obstacle present around which deposition of sand occurs and vegetation grows.
Embryo dune The first part of the dune to develop. Stabilisation occurs via marram and sand twitch /
couch grass, which act as traps for sand. The plants must adapt to living with harsh winds and salty water.
The embryo dunes are made of very inorganic material and have a very alkaline pH of 89. The alkaline pH is
due to the presence of shell fragments in the sand. This is also a very dry environment and the rapid
drainage and exposed nature of the site make it difficult for plant growth. Vegetation cover is sparse with
perhaps 80% of the dune being exposed sand. Winter storms can sometimes wash away this dune but it
builds up again in the summer.
Fore dunes ­ After the embryo dunes are the older, higher dunes called fore dunes. Here there is almost as
much marram grass as sea twitch. In this area there is very harsh wind so the marram grass helps to keep
the sand in place.
1st to 3rd dune ridge (yellow dunes) The conditions for plant growth improves with increases distance
from the beach. The pH in these dunes is now reduced and is now only slightly alkaline (perhaps 7.5) and

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There is more shelter and less salt is carried by the wind. With these better
conditions the number and range of plants increases covering, in places, the entire sand surface. Less than
10% of the dunes are now visible sand. The material here is much more organic. Sometimes they are referred
to as yellow dunes because of the high proportion (c. 20%) of visible sand.
Grey dunes ­ These are the very last dunes.…read more

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The table above shows how much different vegetation (flora) grows in the different areas of the dunes.
There is a huge biodiversity here and by walking through the dunes you are passing through 6+ different
ecosystems.
Dune Grasses
Sand couch / twitch grass
Couch is able to survive in the hostile environment by being resistant to salt, and is able to withstand
drought, storing water in its succulent leaves. It also thrives on burial by the accumulating sand.…read more

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Trampling by people is an arresting factor that can halt succession. The effects of this are:
Physical damage the crushing and flattening of leaves and stems. Over time this leads to more
bare ground leading to the dunes being more vulnerable to wind.
Less biodiversity as some of the insects that life in the dunes will die.
Soil compaction heavy footpath use can lead to the formation of blowouts.…read more

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Studland Sand Dunes
Studland Bay is located in the Isle of Purbeck in Dorset and is popular with tourists. It can be
accessed by ferry from the desirable area of Sandbanks in Poole during the summer. It is only a few
minutes drive from the resort of Swanage and most visitors arrive by car. This area has a status of
National Nature Reserve (NNR) and Site of Special Scientific Interest (SSSI).…read more

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Investigating the dunes
Beach Transect
You would use a systematic approach along the beach and then a stratified method at the dunes. This is
because you can take a measurement in each slack and each ridge or more often.
The area that has the best quality dunes would be used as a control area.
In bad quality areas, the ridges may be much smaller or even nonexistent.…read more

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