Dune Slacks at Aberffraw

Anglesey contains some of the finest examples of coastal dune ecosystems in the UK. So what is a "dune slack" I hear you scream... well don't ask me I've never heard of them.
Taken from the Joint Nature Conservation Committee..

Dune slacks are low-lying areas within dune systems that are seasonally flooded and where nutrient levels are low. They occur primarily on the larger dune systems in the UK, especially in the west and north, where the wetter climate favours their development when compared with the generally warmer and/or drier dune systems of continental Europe. The range of communities found is considerable and depends on the structure of the dune system, the successional stage of the dune slack, the chemical composition of the dune sand, and the prevailing climatic conditions.

Dune systems at aberffraw Source: geograph.org.uk

We visited the dune slacks near Aberffraw with CEH so we could get an idea of what exactly they are. The Aberffraw Dunes are Sites of Scientific Interest (SSSI) and also Special Area of Conservation (SAC) as well as being an Area of Outstanding Beauty (AONB). We were taken around the site in two groups with Jenny - a PhD student and Hilary. We then examined the dunes in a number of ways; using Differential Levelling to determine the groundwater elevation from sea level, taking soil and water samples (to be analysed at a later date) and undertaking a botanical survey using quadrats.

These techniques were used by Jenny for her 3 year thesis on the effects nitrogen were having on the dunes as well as changes to the water table that are partly attributable to the growth of commercial forest in the surrounding catchment. Dune slacks can be classified into different systems dependent on the vegetative communities found. The NVC classification is as follows (source);

• SD13  Sagina nodosa – Bryum pseudotriquetrum dune-slack community,

• SD14  Salix repens – Campylium stellatum dune-slack community,

• SD15  Salix repens – Calliergon cuspidatum dune-slack community,

• SD16  Salix repens – Holcus lanatus dune-slack community,

• SD17  Potentilla anserina – Carex nigra dune-slack community.

With Hilary's help we were able to determine the composition of the dune slack system as SD14-15. We reached this decision by using 1m2 quadrats and identifying the species within each quadrat, as well as the percentage cover of each species, giving us an overall estimation of biodiversity.

Following the biodiversity measurments we went on to calculate the water table elevation from three dipwells on-site. Using a GPS system we located each dipwell, then measured the water level height using a "dipper" that emitted a beeping sound when in contact with water as well as taking a water sample from each dipwell using a pump. To measure the elevation of each dipwell a Theodolite was used;
"a Theodolite is a precision instrument for measuring angles in the horizontal and vertical planes"
This provided us with accurate measurements for determination of water table height.