Human impact on Subatlantic slopewash processes and landform development at Lake Jasień (northern Poland)

Abstract

A survey of the Lake Jasień area (northern Poland) demonstrates the relationship between human economic activity and the course of slopewash processes during the Subatlantic. In the catchment area of the erosional-denudational valley affected by prolonged human economic activity in the early Iron Age (the Hallstatt period) and the pre-Roman period, deforestation may have led to activation of hillslope processes. A manifestation of this activation is a fossil cut in the bottom of the valley and sediments of hillslope origin filling it, lying on top of sediments dated to 450 BC–100 cal. AD. The intensity of the hillslope processes may have been modelled by climate changes involving cooling and humidification.The most recent documented increase in the intensity of denudation occurred around the middle of the 17th century. Deposited on top of sediments dated to 1456 AD–1638 cal. AD and 1453 AD–1797 cal. AD is a sequence of hillslope sediments developed in the form of diluvium and tillage diamicton filling the bottom of the valley and the closed depression.Faster denudation in the landform catchments and accumulation on their bottoms were caused by deforestation of those areas and using them as farmland, as indicated by old cartographic materials. The cooling and humidification of the climate during the Little Ice Age may also have contributed to the acceleration of the agrotechnical denudation. In areas unaffected by deforestation, no noticeable traces have been found of active denudation processes during the Subatlantic. This may suggest that hillslope processes did not play a major role in lowland forested areas of the Temperate Zone.