Aberffraw is located on the South-west coast of Anglesey, North Wales. It is named after the village and consists of a dune slack system!
Dune slack development
A dune slack is a valley between
sand dunes that has a seasonally high water table in winter, however they don’t
always flood in winter and depend upon a balance between evapotranspiration and
precipitation. It is interesting to note that most dune slack species do not
possess the adaptations that wetland plants have and have a shallow root system
as the high winter and low summer water table restricts the rooting depth.
A dune slack at Aberffraw have been formed by blowout form
the wind, meaning the sand has eroded down to the water table. This happens in
the foreshore first and these slacks are tidally influenced by brackish
incursions from the sea water and calcicole species. The older dune slacks occur
further inland are displaced by the younger slacks. The older slacks lose their
calcium influence from the brackish groundwater, become freshwater dominated and
eventually get completely cut off from the saline influence and become
more acidic due to accretion of organic matter which lowers the pH levels.
The vital season for dune slack species is March to May
after winter flooding and before summer drought. A species of toad often found
in Dune slacks, the Natterjack toad, needs to have a wet dune slack from May to
July to coincide with their breeding season.
Classification of a dune system is given according to the
water tables height and splits the dune system into four features, dry slacks,
wet slacks, semi aquatic wet slacks and dunes.
Sand dunes are under threat from a variety of different
pressures which include nutrient enrichment, climate change and inappropriate
management. Aberffraw is under threat
from nutrient input and it is suggested that groundwater seepage form an
agricultural field to the south east is loading the dune slacks with nitrogen
rich groundwater. As distance between the dune and field decreases, the
vegetation is taller, has which suggests
an external nutrient input coming from the field. The taller vegetation has a
higher litterfall, which increase nitrogen further and further increases
nitrophillous vegetation such as Mehtha aquatic.
The taller vegetation within the dune slack indicates nutrient enrichment
The water nutrient levels are being monitored monthly by using dipwells dug into dunes slack at increasing distance
from the field. A one by one meter vegetation plot was measured within 3 meters
of the dipwell to test the effect of groundwater nutrients on vegetation
communities. The survey measured relative frequency or % cover and abundance of
each species within a quadrat. We located the existing dipwells on site with a
handheld GPS after we were provided with 10 figure GPS co-ordinates.
The ground water flow direction was predicted using a
technique called differential levelling. This is done by taking the relative
height of the groundwater at each dipwell taking the assumption that ground water flows from higher to lower elevation. It is though the groundwater nitrogen
levels are within regulatory levels however there is still a negative impact
on the vegetation. The research could go towards reducing regulatory nitrogen
level allowed for dune slacks in the UK.
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