Forty years ago, Gower peninsular, Swansea County, became the U.K.’s first designated Area of Outstanding Natural Beauty. The Tourist guide for the Gower states:
Conflict in Oxwich Bay has therefore been happening all the time, with locals and tourists alike, utilising the beach and encroaching upon the dunes; ramblers and interest groups encouraged to walk in the reserve, all potentially contributing to the disruption of the ecosystem of the dunes. Sand dredging in the Bristol Channel is also causing concern, resulting in falls in natural re-supply of beach material.
Introduction to Oxwich Bay Area
Why the Oxwich Bay area is important
Background to the area
Oxwich Bay itself was formed about 100 million years ago when the sea eroded the soft shales lying between the harder limestone rocks, which can still be seen exposed at Oxwich Point and Great Tor. The sand, forming the dunes, originated in the Bristol Channel, where it was deposited during the Ice Age. During the last glaciation, as many as 6 to 8000 years ago, sea level as a whole was much lower than it is today; with this the Bristol Channel was abridged to a large river in the centre of a large plain. In the long run as the sea level rose the sand was re-worked and pushed shoreward.
“Oxwich Burrows” or the sand dunes at Oxwich stretch the whole length of the Bay. All of it under protection All of it a nature reserve. As can be seen from the aerial photograph (Fig 1:3) the dunes are mature and covered with extensive vegetation. The dunes area holds 300 different species of flowering plants because the dunes provide a great variety of environmental conditions.
Its marshes are a nature reserve of Special Scientific Interest. These Marshes were formed by the river, which runs through Oxwich, becoming blocked off by the expanding dunes and flooding the area behind the dunes with water.
Why Does Oxwich Bay Need Managing
As mentioned earlier, Oxwich Bay is an ecosystem. An ecosystem is a group of living things, plus the non-living things that need to work in synchronization with a delicate balance of INPUTS, PROCESSES and OUTPUTS. Thus parts of an ecosystem are linked together. For example: in a woodland ecosystem, rain is an input, which makes the trees grow, evaporation is the output.
There are many different ecosystems in the world. Some are small-scale, such as a pond, whilst others are large-scale and cover vast areas, such as a rainforest.
A medium scale ecosystem is the sand dune ecosystem, like that found at Oxwich Bay. Oxwich is a particularly fragile ecosystem because its component parts are extremely delicate. This means it is very susceptible to damage such as erosion, flooding or pollution. Not just at Oxwich Bay, erosion of surface soils due to the action of wind has become a major problem in arid and semi arid areas across the world.
The principal reasons making the management of the dunes so significant are as follows:
* The dune ecosystem is very brittle yet is an important example of ecosystem succession. If one part is damaged the system will break down.
* The dunes are very good for maintaining many different types of wildlife as it provides a unique habitat for flora and fauna such as marram grass, lizards, rabbits and certain types of birds.
* Because of the species diversity and impressive and pleasant environment of the bay coupled with its accessibility, the bay is an important source of income for the tourism industry and the Gower region, meaning the environment must be maintained if this is to continue.
* The dunes offer very good coastal protection .The dunes protect the inland environment from wave and storm attacks and are very useful in retaining the whole ecosystem.
Who manages The Oxwich Bay Nature Reserve
The Nature Conservancy Council (NCC) is the main manager of Oxwich Bay nature reserve and they employ voluntary workers/wardens to “look after” the area.
Numerous numbers of voluntary and public organisations help manage. Many simply come from local schools in the area, whereas the others are big organisations like the county wildlife trusts. For example the Glamorgan Wild Life Trust, The Royal Society for the Protection of Birds (RSPB) in conjunction with Local Authorities and the Government.
How Sand Dunes are Formed
Sand dunes are formed by winds blowing sand landward from the dry part of the beach.
* Well-developed dunes typically have a sinusoidal profile with the primary dune at the seaward edge of the beach and possible secondary dunes located farther inland.
* Vegetation on the dunes traps windblown sand on their downwind side and promotes dune growth and stability.
* Blowouts are wind-scoured breaks in the dune or depressions in the dune ridge and commonly occur if vegetation is destroyed.
* Dunes are best developed if sand is abundant, onshore winds are moderately strong and persistent, the tidal range is large and the beach is wide and gently sloping.
* Sand saltates (bounces) up the windward side of the dune, collects in the wind-shadow at the top and periodically slides down the leeward face of the dune when the accumulation of sand becomes over-steepened, resulting in dune migration.
* Wave erosion of sand dunes transports sand offshore and creates a steep scarp at the base of the dune.
* Dunes act as a natural barrier and prevent inland flooding by the sea.
* Human activity that damages vegetation leads to dune destruction by blowouts and wash over by storm waves.
Cross section diagram and ecological succession of the dunes
An idealised section through a dune area is shown on Figure 1:4.
The sand dunes are divided into zones, and these are summarised below.
Different species of vegetation grow in each of the zones in relation to how long the sand deposits have been there. The degree of stability of the zone is very important in determining which plants become established.
The list below describes the environment in each of the zones, across the succession, from the sea towards the land:
* Embryo Dunes – first build up of sand, large areas of exposure, sand held together by the roots of Marram Grass.
* Fore Dune – Intermediate between Embryo and Yellow dune, quickly attain features of Yellow dune.
* Yellow Dunes – soil fertilised by decaying plants, supporting a greater number of vegetation species, like lyme grass.
* Grey Dunes or Fixed Dunes – have decaying plants, fertilised soil, deeper soil, more nutrients; more species, different types of species and also visiting insects, animals. More risk from “blow out” due to wind erosion.
* Dune Slacks – Flat marshy areas at sea level so salt marsh generally; final change of vegetation (e.g. trees), “Climax Community”.
Methodology for Undertaking Dune Transects
The survey was undertaken on one weekday during early June 2003. The class were broken up into groups of five and two transects chosen by each of the groups.
During the whole day the group experienced torrential rain that hampered efforts to record the data being obtained. Photographs were to be taken of important and interesting aspects of our study work and of the dune features and management techniques. Unfortunately the rain ruined my camera and I have no photographs to illustrate this coursework.
On our trip to Oxwich Bay we recorded various data, the data we were looking for was sorted into primary (being the most important) and secondary (not so important).
Angle of slope
The distance from front of dune
Estimated soil depth
%age of ground covered with vegetation
Number of vegetation species
To achieve the Primary Data
1) To measure slope angle and distance the group had ranging poles, a tape measure and a trigger operated clinometer.
2) Ranging poles were placed to form the ends of five metre baselines, stretching up to fifty metres from the seaward edge of the dunes.
3) To achieve the accuracy of measurement setting up the base lines, the group used tape measures stretched across the ground to measure off five metres at the end of each baseline.
4) Whilst the ranging poles were in position one of the group members aimed a clinometer held at the first colour change down the first ranging pole to the same point on the second pole, to find the angle of slope. The distance and angle in degrees were recorded.
5) The final detail to record was the soil depth at the midpoint of the same five-meter baselines (two point five metres). To get this detail the group would gently push a metre rule graduated in centimetres into the soil. When the rule could not be pushed further the group would record the depth in centimetres as the depth of soil.
To achieve the Secondary Data
When this primary task was completed the group spent time to record the secondary data which generally relates to vegetation. To do this a “Quadrat” was placed on the ground at the midpoint of the baseline. The “Quadrat” was one meter square and in that selected size of square the following were recorded:
* The percentage of the ground covered with vegetation by visual estimate of the amount of bare sand.
* The number of vegetation species based on a booklet of typical species.
* The dominant species of those seen, again from the booklet.
Sand Dune Transect 1 Data Table1:1
Sand Dune Transect Data Table 1:2
Analysis, Transects 1 and 2
The results, on the whole were not very accurate, this is down to the extremely poor weather conditions in the area on that day. The weather affected our ability to lay out the baselines, restricted the time allowed to record data and just generally restricted the time on the dunes.
But with some results in hand we were able to conclude the recording of the data into Tables 1:1 and 1:2 above.
Using these data we were able to plot fairly accurate scaled transects depicting the general shape of the dunes along the line of survey and individual slope angles over the five meter base lengths. These plots are given as Figures 1:6 and 1:7 (see wallet).
Included on these transect plots are the secondary data shown in the Tables to give a visual impression of the variation of these aspects with slope angle and distance along the survey line.
With this data in the correct format we are able to see that over the total 50 meter length the measured the height of the dune rises roughly to 13 or 14 meters over both transects. The shape of the dune is broadly similar between transects with steeper slopes over the first 20meters then flattening off.
There are differences in shape between the two transects. Transect 2 has a smoother convex shape over the flatter slopes between 20meters and 50meters distance. Transect 1 on the other hand is more irregular over individual base lines, has an almost flat middle section from 20 to 35meters, rising only half a meter, with a steeper rise from 40 to 50meters. The combined Transect profiles are also shown on Figure 1.8 for comparison.
Using these same plots, Figures 1:6 and 1:7, it is clear that only the first 10 to 15 meters of the dunes are not fully covered in vegetation i.e. it is only the steeper slopes of the fore dune that have no vegetation. It is of interest to note that slopes of a similar angle at the end of Transect 1 (40-50meters distance) are however 100% covered. So the slope is not the controlling factor, it is perhaps the location that is most influential.
Soil depth in the area has no distinct pattern, but the only similarity is that the greatest depth measured is 26 centimetres on Transect 1, and this is located between 30-35metres distance, similar to Transect 2’s greatest measurement of 33centimeters of soil depth that is located at 35-40 meters distance. Both of these maximum depths occur towards the back end of the transects, where most measurements of soil depth exceed 20centimeters.
Plotting various graphs to see if these relationships can be confirmed or if there are other relationships between individual elements has tested these initial observations.
Slope Angle –
* Distance – (Fig 1:8) – Shows that Transect 1 is more variable in slope angle to Transect 2; that both transects are different but that there are flatter slopes beyond 20m and this ties in with the observations of the transect plots.
* Vegetation Cover – (Fig 1:9)-There is not a great noticeable trend on the graph, the slope angle does not really affect the vegetation cover. A factor that could influence the amount of vegetation is that the higher the slopes angle the lower the vegetation cover might be because the wind could affect it.
Soil Depth –
* Distance – (Fig 1:10) -Shows a nice correlation over the distance, with only one exception with the soil deeper then 50cm. Most points range between a soil depth of 10cm and 20 cm up to 25m distance, then increase to 20 and 30cm over the remainder.
* Slope Angle – (Fig 1:11)- There is a slight trend shown by Transect 1 with increasing soil depth with flatter slopes. Transect 2 however is very variable and may have a reverse trend. This may reflect the method of measurement, which was not particularly accurate. Pushing in the meter rule may not fully indicate soil depth only loose ground. However one would expect more soil on flatter slopes due to easier accumulation as plants die off.
* Vegetation Cover – (Fig 1:12) -The graph suggests that there is no relationship between soil depth and vegetation cover, only that a lot of points at 100% cover occur over the estimated depths of soil cover, ranging from 10cm to 30cm. For depths of soil less than 10cm a relationship might appear, as it would be expected that a point would arise where soil depth did reflect the density of growth. However the production of soil might be less where grasses such as marram are present, because these grow predominantly in sand.
* Species – (Fig 1:13) There are more species with more soil depth but the trend is poor and there is a lot of scatter in the data.
* Distance – (Fig 1:14) -A good relationship that indicates the amount of vegetation cover on the ground increases quickly over the measured distance, it can be seen that from 15m along Transect 2 there is a noticeable trend with all points lining up on a smooth curve, with one exception. This point could suggest a small blow out or a footpath
* Distance- (Fig 1:15) – It can be quickly seen that the number of species increases with distance along the transects. Tables 1 and 2 confirm that the predominant species was marram in the early sections that also have the steepest slopes and less soil cover. Other grasses become predominant, further along the transects.