ENVIRONMENTAL AND VEGETATIONAL RELATIONSHIPS OF LAKES, FENS AND TURLOUGHS IN THE BURREN

Abstract

The limestone country of the eastern Burren includes permanent lakes, extensive fens, and turloughs—depressions characterised by large fl uctuations in water levels that become dry in summer and have distinctive vegetation. Most of the larger lakes lie on an almost level surface, draining southwards via the River Fergus into the Shannon estuary; Lough Bunny drains through the limestone north towards Galway Bay. Field evidence indicates that the lakes and fens, whether they fl ood in winter or not, have a relatively constant summer water level, probably because the underlying limestone is sealed by glacial drift. Their vegetation follows a normal hydrosere succession from open-water deposits (mostly calcareous marl) to reed swamp and Schoenus fen, culminating locally in raised bog. Present-day exposed expanses of marl are products of erosion of a former peat cover. Turloughs are characterised by unconstrained fl uctuations of the water level through most or all of its vertical range. They occur where there is no barrier at the surface to drainage into the limestone, but there is suffi cient hydraulic resistance to underground fl ow to allow water levels to rise during winter and after heavy rain. The vegetation of typical turloughs has more in common with dune slack or fl ood meadow communities than with true fens. Michael C.F. Proctor (e-mail: M.C.F. Proctor@exeter. ac.uk), School of Biosciences, University of Exeter, The Geoffrey Pope Building, Stocker Road, Exeter EX4 4QD, UK. Cite as follows: Proctor, Michael C.F.