Environmental Engineering Reference
In-Depth Information
during the summer. The larger pool to the northwest seems to have become a sinkhole and now only con-
tains a small area of shallow water during the wettest periods. A further much larger sinkhole, where the
largest stream from Cefn Bryn Common disappears underground, lies some 400 metres to the northwest
of Broad Pool. On the Duke of Beaufort's commons map of 1826 this sinkhole is shown coloured blue,
suggesting it was filled with water, although it is labelled as a sink. The depression now never holds any
standing water except in exceptionally wet conditions, and is covered with grass and bracken. From this
evidence it appears that sinkholes can form from areas that begin life as pools, and it is possible that this
could happen to Broad Pool at some stage.
There are also a number of pools, including Red Pool, along the ridgeline to the south of Arthur's
Stone (Fig. 136). These features, including those that are ephemeral, are important not only for watering
stock but also for a wide range of insects and other invertebrates. They contain many of the common
aquatic invertebrates such as water bugs, water beetles, mayfly nymphs, stoneflies and caddis flies, to-
gether with a number of dragonflies. These pools are especially significant for the invertebrates that oc-
cur in the stock-trampled margins, as the damp peaty soils at the edges are generally a valuable habitat
for invertebrates. In the 1950s and 1960s Fonseca (1973) recorded numerous rare flies from the Gower
commons, including representatives from families such as the Tabanidae, Dolichopodidae and Muscidae,
which have larvae that live in damp soil. These records are difficult to relate to specific sites, however,
and it would be useful to have a modern study.
FIG
136.
Red Pool, an ephemeral pool on the ridge of Cefn Bryn Common. The stock-trampled margins are an im-
portant, and under-recorded, habitat for invertebrates. (Jonathan Mullard)
Ephemeralpoolsareaseverelythreatenedhabitat,associatedmainlywithheathland.Theyareusually
thought to be restricted to heathland in southern England, but this is obviously not the case. Nationally,
likepoolsofalltypes,theyhavebeenlostduetodestruction byagricultural activities, althoughthisisnot
anissueontheGowercommons. Ironically mostofthethreats toephemeral poolscomefrominappropri-
