The Water Content of Soil

The Water Content of Soil

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The Water Content of Soil

The water content of soil is a major factor that will determine what
sort of plants are able to grow, and when considering a system of sand
dunes will have considerable effects on the zonation and succession of
that environment. In order to investigate this, trial experiments were
initially carried out in order to determine the most effective method
of assessing a section of the dunes and obtaining results. Once these
results had been obtained, adjustments to the original method were
made, and the process of gaining results took place.

After tabulating the results, and drawing appropriate graphs, I
concluded that within a system of sand dunes, zonation and succession
of plant species is present, and as the distance from the strand line
increases, so too does the water content of the soil. I also concluded
that the water content of the soil is affected by the aspect of its
position as well, which relates directly to its exposure.



An experiment to investigate how the water content of soil within a
system of sand dunes affect zonation and succession.


This investigation will take place on the southern coast of the Gower
Peninsula, at Oxwich Bay where an extensive system of sand dunes is
present. In order to complete a successful experiment with accurate
results, the investigation must be carefully planned out.

The complex structure and ecosystem of sand dunes must firstly be
researched and studied, drawing conclusions and predictions from any
information gained. Selecting the appropriate variables must also be
considered, while taking into consideration the relevant information
gained from the background information, and results from trial

Biological Knowledge

The following biological knowledge is all directly related to this
investigation and is essential for predicting trends, and being able
to give some sort of explanations for what is seen.

Community Ecology And Succession

A community is a group of interacting populations living in any given
area representing the living part of an ecosystem.

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The formation of
any community takes time, and building up a complex structure of
organisms occurs through a process of ecological succession.

An example that shows the development of a community is the
colonisation of bare rock. Algae and lichens initially colonize such
areas, forming what is known as the pioneer community. The gradual
build up of dead and decomposing material leads to the accumulation of
enough soil to support larger plant species such as ferns and mosses,
which are ultimately replaced by larger seed bearing plants. Some of
these will include grasses, shrubs, and trees.

This type of replacement of species by others over long periods of
time is a process known as ecological succession and this will
ultimately lead to the climax community. This is the state of an
environment which is the most productive to sustain and throughout
most of the low-lying areas of Britain, deciduous forest is the climax

There are also different types of succession that can occur; the first
of which is described above, whereby there is a colonisation of an
area lacking organic soil, where vegetation has never grown
previously. This type of succession is known as primary succession.

Secondary succession occurs where vegetation has grown, but has since
been destroyed by fire, farming or flood for example. Seeds and spores
of vegetative reproduction may already be present in the soil, and
thus influence the succession.


Within any habitat, there are very distinctive changes in the types
and numbers of organisms that are present. These changes are caused by
an environmental gradient, temperature for example, and this
distribution of different species, according to any number of
environmental factors, is known as zonation.

The boundaries between different zones are called transition zones and
these often contain populations of animals and plants specially
adapted for life in the transition zone. There will also be present
species that are characteristic of the two major communities, existing
at the limits of their tolerance range.

Zonation and Succession Within A Typical System Of Sand Dunes

A typical dune system has a basic structure and will show zonation and
succession of vegetation. The vegetation of a dune system is not
particularly tolerable to saline conditions (not halophytic), accept
near to the seaward margin, but instead shows adaptations typical to
plants found in areas of water shortage.

Dune systems can be divided up into different areas or zones, each of
which will show different types of vegetation present. The types of
vegetation found in each zone will be typical of that area, as each
section of the dune system will have its own, slightly different
environment. Therefore the vegetation found in these zones will be
adapted to cope with the various conditions that are characteristic of
each area.

The diagram below shows the basic structure and profile of a dune
habitat, and shows clearly the different zones that are found.


As can be seen from the diagram, the dune habitat can be broken down
into five main zones or regions.

Beach And Shingle Ridge

The shingle ridge is the first zone that can be seen on the diagram,
and is very important when considering the origins of the dune system.
It is here where the first fragments of humus develop; it is the
presence of this organic material in the soil that is essential for
the healthy growth of vegetation. There are a number of sources that
result in the build up of humus, some of which include, bird
droppings, pieces of dead sea life (e.g. seaweed, crabs), the
occasional dead chic or small mammal etc. All of this material adds up
to the total amount of organic material that forms in the soil.

The moisture that is required for the growth of plants is required by
the underlying shingle, a reliable source of fresh water. When these
rocks are cooled, often during night, condensation forms on the
surfaces of these rocks, and this provides just enough moisture for
well adapted plant species to gain a hold.

Embryo Dunes

The next zone shown in the diagram is known as the embryo dunes and it
is here where the first signs of vegetation can be seen, and this is
in form of pioneer plants. Being so close to the sea salt, the pioneer
plants of the embryo dunes must be able to retain their fresh water
supplies very effectively. Sea Couch and Sea Sandwort can be found in
this zone, and as they become established, reproduce and decay, they
make way for the less demanding species of pioneer grasses.

Yellow Dunes

These less demanding species make up what is known as the yellow dunes
and include species such as Lyme Grass and Sand Couch. However,
perhaps the best adapted of these grasses is the Marram plant (Ammophila),
and although Marram Grass cannot tolerate being covered by the sea, it
has an amazing unlimited vertical and horizontal growth by means of
rhizomes. The Marram plant grows taller and more extensive as the dune
itself builds up, and because the outer-most part of the plant becomes
further and further away from the water below the surface, the Marram
Grass has become well adapted to survive in arid conditions.

A feature typical to Lyme Grass, Sea Couch and Marram Grass is the
rolling of their leaves, forming long tubes with a hollow center.
Consequently, the stomata of the leaves end up on the inside of the
tube, and not only does this greatly reduce water loss through
transpiration, but it also acts as a cavity that is capable of
trapping and holding moist air.

The constant movement of sand is essential to the pioneer plants such
as Marram Grass as this stimulates new growth producing fresh shoots.

Grey dunes

As you move still further back along the dune system, you begin to see
the next zone of succession known as the Grey Dunes. These were formed
over hundreds of years, and unlike the Yellow dunes, the sand/soil is
well packed and firm, containing much higher levels of humus. Here
mosses and lichens can be seen growing, along with clover.,
dandelions, erect grasses and a host of ordinary inland species.

Dune Slack

The final zone that can be identified, known as the dune slack, is
situated in between the ridges of the dune hills where there are a
number of relatively sheltered hollows. In these hollows that are more
or less insulated from the wind and sea, a constant deposition of
animal and vegetation humus occurs. This allows the soil to hold much
more water, and the levels soon build up allowing the development of
general aquatic and marsh plants. Some of the species present include
Meadow Buttercups, Purple Orchids, mosses and Liverworts.

Species That Are Commonly Found In Sand Dunes Environments

The following tables below show give lists of species that are typical
to the various zones within a sand dune system.

Strand Line

Binomial Name

Common Name


Cakile Maritima

Sea Rocket

4-petalled pale to deep lilac flowers; greyish, fleshy leaves that are
deeply lobed

Honkenya Peploides

Sea Sandwort

5-petalled greenish flowers; grows just above the strand line

Salsola Kali

Prickly Saltwort

Prickly spines on tops of leaves which are sharp narrow and fleshy

Yellow Dunes

Binomial Name

Common Name


Ammophila Arenaria

Marram Grass

Rolled, sharp tipped cylindrical leaves; clumps together

Leymus Arenarius

Lyme Grass

Broad, hairy leaves, often found growing in close proximity to Marram

Elymus Farctus

Sand Couch

A bluish plant, rarely over 50cm in height, with hairy leaves.

Carex Arenaria

Sand sedge

Creeping rhizomes several cm under the surface of the sand are
present, sending up a few stiff and channeled leaves.

Eryngium Maritimum

Sea Holly

Spiny Greyish leaves, with pale blue flowers.

Senecio Jacobaea

Common Ragwort

Dark green leaves, and daisy-like leaves

Festuca Rubra

Red Fescue

Reddish leaf sheath, panicles-used for lawn grass.

Grey Dunes

Binomial Name

Common Name


Arenaria Serpyllifolia

Thyme-leaved Sandwort

Grey leaves, and flowers with small white petals.No more than 2-3
inches in height.

Ononis Repens


Trailing stems, rooting at intervals near the base.

Rosa Pimpernelifolia

Burnet Rose

An upright, spiny, bushy plant; creamy white flowers and hairless

Sedum Acre

Biting Stonecrop

Short stalks with some bearing flowers, and others with overlapping
leaves tipped with crimson.


After conducting research and gaining relevant background information
concerning sand dune ecology, I can hypothesis on certain matters.
Firstly, I expect to see zonation and succession occurring clearly as
I move further from the strand line. I expect to find species that are
well adapted to arid conditions in those areas closer to the strand
line, and those which require more shelter and soils capable of
holding greater volumes of water, further inland. I also expect to see
a direct relationship between the aspect of a dune, and the water
content of the soil at that point.


The first and most obvious prediction to make is that within the
system of sand dunes at Oxwich Burrows, I will see clear patterns of
zonation and succession. I also predict that as I move away from the
strand line, the water content of the soil will increase.

However, due to the varying height and shape of the dunes, within each
separate dune hill, the water content of the soil will vary depending
on whether it is the seaward or leeward side. This is because I would
expect the top of the seaward side of a dune, to be much more exposed
to the coastal environment than the bottom of the leeward side.
Therefore I would expect the former to have a much lower soil water
content than the former.


My initial aim was very 'open-ended' leaving many possibilities and
details that have to be considered in more detail. The nature of this
investigation means that there are many variables that have to be
looked at in order to conduct a successful investigation.

The following list shows the variables that will be considered during
the planning of this investigation. It must be decided which of the
possible vaiables are to be varied, which of them are to be kept
constant, and those which do not have any great relevance to this

- Distance from the strand line

- Aspect

- Percentage cover of vegetation

- Species Diversity

- Height above sea level

- Humus content of soil

- Water content of soil

- pH of soil

- Air temperature

- Humidity of air

- Light intensity

- Distance between transect poles

- Position in quadrat of soil sample taken

- Depth of soil sample taken

The list above shows all of the possible variables, and factors that
could be considered when undertaking this investigation. However, it
is clear that all of these cannot be included in this investigation
and therefore the most important should be discussed.

Key Variables

These are the variables which will play a major part in my
investigation and therefore have to be explained in further detail.
These variables will either be controlled, and varied in a regular
pattern (e.g. distance from the stand line), or they are those
variables which cannot be controlled, but the way in which they vary
will be the basis behind this investigation.

Distance From the Strand Line

The whole of this investigation will be based around this variable, as
areas of land will be investigated at different distances from the
strand line. As I intend to look at succession within the sand dunes,
this is clearly an essential factor to consider.

Therefore the distance from the strand line will be varied, but the
increase in distance from the strand line will be kept constant, i.e.
the distance between the transect poles will be kept constant.

Water Content of Soil

Within my initial aim it was made clear that the water content of the
soil would be investigated. The water content of the soil is an
essential factor that effects the vegetation; therefore I would expect
to see a clear pattern between this, and the types of plants growing
in the dunes. However, although this factor is a variable that must be
considered, it is clearly one that cannot be controlled and will
hopefully show patterns similar to what has been predicted.

Variation In Vegetation

Rather than looking at the number or percentage cover of vegetation, I
am interested in looking at the types of species found in the dunes.
By looking at how the different species vary throughout the dune
system, I will be able to consider the different zones, and also look
at succession.


The aspect of different parts of the dune is something that will
obviously vary quite substantially. The aspect of a particular part of
the dune will have an effect on how exposed that area is, and thus
will effect the water content of the soil, and ultimately what will
grow there.

· The rest of the variables that were mentioned do not need to be
considered further because they will not play a part in this
investigation. Whether or not they can be controlled or not, isn't
important as they will not have an effect in the final outcome.

Initial Problems To Be Considered

After conducting research into sand dune ecology and considering the
variables that should be controlled or varied etc., I have identified
a number of problems that must be addressed before planning any trial
or main experiments.

1. Due to the fact that a dune system can stretch back from the strand
line a considerable distance, and there is only a certain amount of
time available to conduct practical work, I should not expect to see
the full process of succession that ultimately results in the climax
community. I would expect to see much of the dune slack zone, but hope
to see zonation as far as the grey dunes.

2. As indicated in the aim of this investigation, a major section of
the actual experiment is the process of identifying various different
species of plants and vegetation. However, due to the fact that my
knowledge of botany is limited, I should expect to come across species
that I am unable to identify. If this occurs then the plants should
still be recorded, even if it is not eventually compared to other
data. Any species that are found which I am not able to identify will
be allotted a letter instead and this will used instead of its
official name.

Trial Experiment

The aim of conducting a trial experiment is to be become well
equainted with the method being used, and identify any further
problems with the method itself or generally. I will also conduct a
trial experiment to insure that the transect line chosen takes a path
that shows a fair representation of the dunes, and does not pass
through any major obstructions.

Once I have conducted a trial experiment I can analyze the results and
make any modifications that are necessary; this will enable me to gain
accurate results when conducting the actual investigation.


· Clinometer

· Ranging Poles (x2)

· Tape measure

· Quadrat (0.5m )

· Trowel

· Identifying books

· Compass

· Sticky labels

· Plastic bags


A ranging pole was placed into the ground at a point along the strand
line. A quadrat was then placed down next to the pole in such a way
that two of its sides were parallel with the strand line, and the
bottom left hand corner was in contact with the pole.

The aspect of the quadrat was recorded using the compass, and a soil
sample was taken. The quadrat was then examined, recording any
vegetation that was present.

Once the quadrat had been examined, the next ranging pole was placed
down, 10m from the first, in a line perpendicular to the strand line.
The tape measure was used to measure the distance. At this stage, a
clinometer was used to measure the angle from the top of the first
pole, to the top of the second pole.


N.B. this method will obviously not show every change in the profile
of the dune, however it should give an accurate estimate for this

At the point where the second ranging pole was placed into the ground,
a quadrat was also placed down in exactly the same way as before.

This procedure was carried out for a total distance of 30m and if any
of the plants found within a quadrat could not be identified a small
sample was taken and labeled.


Quadrat Letter

Distance From Strand Line (M)

Aspect (°)

Species Record








Marram Grass

Sea Sandwort




Marram Grass


Dune Fescue




Marram Grass

Sand Sedge

Dune Fescue


Plant A

Plant B

Plant C

Analysis of Results

After conducting a trial experiment and testing my proposed method, I
can now identify the problems that arose, and modify my procedures

The actual procedure of taking the transect line proved to be
successful, and I found that the method being used was easy to
perfect. As I am happy with the results shown in the table above, I
have decided to use these in the actual experiment, and when I begin
to conduct the main investigation I will begin from where I finished
in the trial experiment; from the 30m mark.

However, recording the species that are present is only one part of
the investigation as the second part of the method involves taking a
soil sample and measuring its water content. A problem arose in that I
was not sure where and at what depth to take the soil sample from and
it soon became aware to me that this should be perhaps kept constant
for each quadrat, in order to give accurate and reliable results.
Therefore there were no soil water contents recorded, and this needs
to be repeated in the main investigation.
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