Mass Movement and Erosion of a Southern Pennine Blanket Peat

Abstract

Pollen and macrofossil analyses were carried out at 19 sites within a 1-km2 area of Featherbed Moss, Derbyshire. The sites covered a range of uneroded and eroded blanket peat types. Pollen diagrams were compared using 5 dated horizons between 1580 A.D. and 3600 B.C. (calibrated dates). These pollen horizons formed a template for comparing the macrofossil stratigraphy at the 19 sites, and for calculating the rates of peat accumulation at 6 sites. Peat accumulation rates varied considerably, both within and between sites, 6-96 g m-2 yr-1 (measured as dry mass). The most striking differences occurred in the time interval 400-1000 A.D., when some sites showed an increased rate of peat accumulation and others a decreased rate. Pollen and macrofossil types indicative of better drained peat (Empetrum and Vaccinium pollen, leaves of Phacomitrium lanuginosum) occurred at several sites towards the end of this interval. These changes are interpreted as resulting from the onset of erosion 1000-1200 yr ago. Two features of the growth of the peat blanket on Featherbed Moss are suggested to have been of major importance in ultimately bringing about its degradation and erosion: a very early spread of peat over flatter ground to the limits imposed by topography (so that no further lateral extension was possible); and a rapid build-up of largely unhumified Sphagnum peat over more consolidated peat after 400 A.D. In conjunction, these features resulted in an unstable peat mass developing on parts of Featherbed Moss by 700-800 A.D. The onset of peat erosion on Featherbed Moss 100-1200 yr ago is interpreted as a natural phenomenon, instituted by a series of bog slides and bursts around the margin of the peat blanket. These led to the formation of drainage gullies extending back into the peat, slumping of the marginal peat downslope, and drawing-off of water from the pools of the hummock-hollow complex on the watershed. Over much of the Moss wet Sphagnum-dominated bog surface developed after .apprx. 1100 A.D., and partial recolonization of some of the earlier erosion features may have occurred. The death of Sphagnum from air pollution some 200-300 yr ago led to renewed peat erosion, which is still in progress.