Holocene sediment dynamics in an upland temperate lake catchment: climatic and land-use impacts in the English Lake District

Abstract

Accelerated erosion and transport of fine sediment from upland temperate catchments can reflect increased erosivity and/or erodibility, due in turn to climatic and/or human forcing. Identification of sediment fluxes and sources over Holocene timescales can both enable understanding of the relative impacts of these forcings and provide perspective on recent sediment fluxes. Here we present a ~ 5500 yr record of sediment fluxes and sources from Lake Bassenthwaite in the English Lake District, utilizing magnetic measurements and fuzzy clustering, coupled with independent pollen and archaeological records, to identify the timing and impact of catchment disturbance. This record shows that recent sediment flux increases (ie, within the last 150 years) are unprecedented in scale throughout the mid—late Holocene and appear to be in response to specific human changes occurring within the catchment. Earlier episodes of human activity, from the mid Holocene onwards, show no link with increased lake sediment fluxes, indicating either limited catchment impact and/or `buffering' through within-catchment sediment storage. Increasingly intensive land use and reduction of sediment storage through revetment construction on a key inflow, Newlands Beck, have resulted in 3 × increases in lake sediment flux. These data may be significant for other upland temperate areas, as increasing land-use pressures and reduced sediment storage capacity may not only increase contemporary sediment flux, but increase sensitivity to predicted increases in rainfall and storminess as a result of global climate change.