Illtyd Pools, Brecon: description and conservation

The Mires Research Group of the British Ecological Society examined Traeth Mawr and Traeth Bach, two closely-adjoining mires near Brecon, Wales, in September 1984. Both occupy former lake basins with late-glacial deposits overlain with fen peat. At Traeth Bach, this continues to the surface but, at Traeth Mawr, it is overlain by ombrotrophic peat with Sphagnum. The absence of this deposit from Traeth Bach may reflect differences in successional infilling or its removal by peat excavation (for which there is some evidence in both basins). It almost certainly does not reflect major differences in chemical conditions in the two basins as both contain base-rich water (at least at depth). Such water (derived from springs and seepages) irrigates part of the margin of Traeth Mawr forming a base-rich partial lagg and permits an unusual juxtaposition of plant species and vegetation types. Parts of the ombrotrophic surface are badly gullied and, perhaps in response to this, in places the surface is rather dry and degraded (with some trees). Moreover, marginal base-rich water can now penetrate into the ombrotrophic area along the eroded gullies, leading to further changes in its floristic character. A plan for management is proposed.