The aquatic vegetation of Llangorse lake, Wales

Abstract

A survey was undertaken to assess the present status of submerged, emergent and marginal vegetation in and around Llangorse lake in the Brecon Beacons National Park in Wales. The results of this survey were compared with those of previous surveys of the lake. The most profound change observed was the decline of a relatively diverse submerged macrophytic flora dominated by Potamogeton pectinatus L. and Zannichellia palustris L., from at least eigth species in 1973 to monospecific stands of Z. palustris by 1977. Although cultural eutrophication processes partly accounted for the macrophytic decline they did not adequately explain the survival of Z. palustris alone; it was considered that a combination of cultural eutrophication and mechanical disturbance was the prime causal factor for the occurrence of this unusual situation. A hydrographic survey of the lake was also undertaken and a map showing the submerged contours was produced.