Lake bed environments, modern sedimentation and the glacial and post-glacial history of Windermere, UK

Miller, Helen (2014) Lake bed environments, modern sedimentation and the glacial and post-glacial history of Windermere, UK. University of Southampton, Ocean and Earth Science, Doctoral Thesis, 177pp.

Record type: Thesis (Doctoral)

Abstract

Windermere, the largest natural lake in England, is a glacial ribbon lake located in the southeast of the Lake District. High resolution geophysical datasets, combined with sediment analysis, geomorphological mapping and historical research have been used to investigate the lake bed environments, recent sediment record of pollution and glacial and post-glacial history of the lake and surrounding catchment.

The data are used to generate a present-day landscape map of Windermere, revealing a complex landform record characterised by nine sub-basins, separated by steps, ridges and isolated topographic highs related to the retreat of the British and Irish Ice Sheet (BIIS). Debris flows and anthropogenic features are superimposed on the general bathymetric framework formed since the Last Glacial Maximum.

Analysis of sediment cores and correlation with existing seismic data have revealed key stratigraphic facies extend across the lake basin, and consist of a drape of Holocene gyttja overlying glaciolacustrine and lacustrine sediment fill relating to retreat of the BIIS. Analysis of geophysical core properties have identified a peak in magnetic susceptibility and iron which possibly represents a change in relative input from different ice masses. Onshore mapping of Troutbeck Valley identifies a series of depositional environments, including recessional moraines formed by still-stands or small readvances of an outlet glacier. Following deglaciation through disintegration into a number of independent ice caps, major sediment redistribution led to formation of a large fan delta via paraglacial and post-glacial sedimentation.

The sedimentology of Windermere is characterised by five distinct lake bed facies showing a dominance of gyttja, representing recent Holocene sedimentation derived from the catchment over the last 10,000 years. Coarser sediments (gravel and fine sand) are found in lake-marginal shallow water. High resolution geochemical data, radiochronology and isotopic analysis have revealed significant increases in lead, zinc and copper in recent lake sediments. The principal sources of anthropogenic lead contamination are gasoline lead, Carboniferous coal (most likely source is coal fired steam ships) and lead derived from Carboniferous Pb-Zn mineralisation (mining activities). A number of up-system sediment traps have limited the amount of mining related heavy metals entering Windermere. As a result, many peaks in heavy metals do not correlate with periods of metal workings, but recent increases are possibly due to
flood-induced metal inwash. Elevated concentrations of zinc and filamentous growths on the lake bed are attributed to sewage inputs. Geophysical, physical and visual surveys of twelve demonstrated or putative spawning grounds of Arctic charr (Salvelinus alpinus) suggest suitable spawning habitat in Windermere is limited and siltation by fine sediments has occurred over the past 50 years.

The integrated approach used in this study has shown that a catchment analysis, using several datasets and techniques, can be used to inform wider regional and ice sheet wide glacial reconstructions. This approach, which can be applied to other lacustrine environments, is capable of determining modern lake bed habitats and the sediment record of pollution, and further demonstrates the value of lake sediments as a high resolution record of local and regional environmental change.

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