Pool-and hummock patterning in a southern Pennine blanket mire. II. The formation and erosion of the pool system

1 Inferences about the processes leading to surface patterning, pool formation and gully erosion in a Southern Pennine blanket mire are drawn from the 15-m stratigraphic profile from Alport Moor described in Part I. 2 Four successive stages in the development of the present mire surface are recognized: a topographically differentiated dry bog vegetation c. 2800 years ago, which then developed into a wet rather featureless mire surface by c. 200 Cal BC; an extended phase between c. 200 Cal BC and 1250 Cal AD when hummock-hollow differentiation was taking place over the mire surface; and drier bog vegetation since c. 1250 Cal AD, probably following incision of the main drainage gullies. 3 Preserved remains of Sphagnum occurred in 52% of the peat samples analysed for macrofossils. In the peat profile the Sphagnum remains were concentrated into five essentially continuous and nearly horizontal bands, separated by intervening regions where Sphagnum was scarce or absent. 4 The temporally discontinuous distribution of Sphagnum in the stratigraphic profile is shown to be an overall response to climate change (Sphagna increasing in abundance during periods of wetter climate), modified by site-specific responses to ongoing topographic differentiation and the incidence of erosion. 5 It is suggested that high pollen values of Cyperaceae found in the pollen record from Alport Moor and some other Southern Pennine sites might record the local spread of Eriophorum angustifolium across bare wet peat, and might thus indicate times when the mire surface was under stress. 6 Site-specific differences in the patterns of Sphagnum abundance over the last 1200 years in the study area and on the nearby Featherbed Moss are used to follow the development of the erosion system on Alport Moor. 7 The currently eroded mire surface on much of Alport Moor has arisen from at least three processes acting on the pool-and-hummock system: (a) the drawing-off of water from the pools by endotelmic streams extending headwards from the main streams of the catchment area, probably at least 1000 years ago; (b) extensive drying-out of pools and hummocks during the drier climatic conditions between c. AD 1150 and 1300; (c) subsequent human modification of the mire vegetation by burning, grazing and, latterly, air pollution. 8 Sphagnum was lost from the mire surface generally on Alport Moor by 400-500 years ago. Only the disappearance of the moss Racomitrium lanuginosum from the hummocks might be attributed to the deleterious effects of air pollution.