Lake sediments, erosion and landscape change during the Holocene in Britain and Ireland

Lakes are excellent repositories of air-borne and especially stream-borne materials. It has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products. To these may be added a variety of palaeoecological indicators including pollen, fungi, Sphagnum leaves and faunal remains. Pollen analysis, in particular, enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance, grazing and crop cultivation Radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right. The use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 British and Irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late Holocene. Sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern Scotland and have either no clear signs of human impact, or only so towards the latter part of the Holocene. This pattern probably reflects a combination of factors including low population densities, thin soils and the 'sealing' effect of blanket peat, In contrast, all sites with accelerated erosion have indications of anthropogenic impact. This is often prior to levels of increased sedimentation showing a delay in system response. While the spread of dates for the start of the rise in sediment accumulation spans 6200-940 BP, three clusters are evident at 5295-4970, 4530-4235 and 2980-2810 BP. Radiocarbon inversions (mostly reversals) are evident for 18 sites. No obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils, including peats, around a particular site were pushed beyond an erosional threshold sufficient to 'age' the sediments deposited within the lakes. It is hoped that improvements in data quality will allow the refinement of such exercises in the Future and that lakes will he valued as repositories of long-term landscape sensitivity. (C) 2001 Elsevier Science B.V. All rights reserved.