Environmental Pollution 45 (1987) 275-289 Chemical and Ecological Effects of a Pennine Peat-Slide C. P. McCahon,* P. A. Carlingl" & D. Pascoe* * Department of Applied Biology, UWIST, PO Box 13, Cardiff, CF1 3XF, Wales, Great Britain + Freshwater Biological Association, The Ferry House, Far Sawrey, Ambleside, Cumbria LA22 0LP, Great Britain (Received 15 September 1986; accepted 12 November 1986) A BS TRA C T A peat landslide which occurred in Upper Teesdale in 1983 is described. The slide followed thunderstorm rainfall of a very rare intensity (104.8mm in 2"5 h) and a long predicted return period (2500 years). A large mass of peat (30000 tonnes wet weight) entered the headwaters of the River Tees, resulting in chemical changes such as increases in suspended solids, iron, aluminium and lead in the river, and a consequent fish kill. The probable cause of thefish kill was the high suspended solid content (particularly peat and iron hydroxide) of the flood water. Effects on the invertebrate fauna of the River Tees are also considered. INTRODUCTION Bog-bursts or peat-slides are rapid mass-movement features which consist, respectively, of a flow of semi-liquid peat or a translational slide of blocks of fibrous peat (Carling, 1986a). In the latter case, the peat blocks usually break up, so that, in both situations, finely comminuted peat detritus may enter streams and rivers adjacent to the hill-slope failures. Mass-movements of peat typically are associated with ombrogenous mires and are presently most common in the uplands of Ireland and northern England. In earlier times, bursts also occurred in raised bogs in lowland areas, such as the Cheshire-Lancashire Plain, but today these mires have, in the main, been effectively drained and reclaimed for agriculture. 275 Environ. Pollut. 0269-7491/87/$03'50 © Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain