An integrated lake-catchment approach for determining sediment source changes at Aqualate Mere,Central England |
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Authors: | Nathan J Pittam Ian D L Foster Tim M Mighall |
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Institution: | (1) Department of Geography, Environment and Disaster Management, Coventry University, Priory St., Coventry, CV1 5FB, UK;(2) Department of Molecular and Applied Biosciences, School of Biosciences, University of Westminster, Cavendish Campus, 115 New Cavendish Street, London, W1W 6UW, UK;(3) Department of Geography, Rhodes University, P.O. Box 94, Grahamstown, 6140 Eastern Cape, South Africa;(4) Department of Geography and Environment, School of Geosciences, University of Aberdeen, Elphinstone Road, Aberdeen, AB24 3UF, UK; |
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Abstract: | This paper raises fundamental questions about the sole use of paleolimnological techniques to identify sediment sources and
develop catchment management plans. The concept of an integrated lake: catchment framework was established 30 years ago, yet
paleolimnologists occasionally fail to appreciate the dynamics of the contributing catchment. This is especially critical
when the predominant source of sediment accumulating in a lake is allochthonous. In this paper we argue that a detailed appraisal
of catchment sources and investigation of historical documentary evidence is needed to identify and evaluate the relative
significance of sediment sources. We used such an approach at Aqualate Mere, Shropshire, UK. Mineral magnetic and radionculide
signatures of potential catchment sources and accumulating lake sediments were compared in an attempt to match the sources
to sediments deposited in the Mere. Dated lake sediments indicate there has been an increase in sedimentation rate and the
relative amount of minerogenic material delivered to the Mere over the last 200 years. In contrast to a previous study at
the same site, there is no evidence to attribute this increase to an overspill from a nearby canal. Other catchment disturbances
include landscaping in parkland surrounding the Mere in the early nineteenth century and drainage systems installed to improve
catchment agriculture over the last ca. 150 years. Both activities may explain the change in sedimentation rates and types,
independent of the hypothesized canal origin. Although our results exclude the canal as a major sediment source, identifying
the contribution of other potential catchment sources remains problematic. 137Cs inventories for the lake are similar to those recorded at a local reference site, suggesting little influx of 137Cs-bearing topsoil, yet 137Cs activities remain high in the upper 20–30 cm of the lake sediment profile, indicating a topsoil origin. Combined radionuclide
and mineral magnetic signatures proved to be relatively poor discriminators of potential sources, and the high atmospheric
pollution load from the West Midland conurbation has probably altered recent lake sediment signatures. Although further research
is required to identify the origins of recent (last ca. 200 years) minerogenic sediment inputs to the Mere, we suggest that
the combined lake: catchment approach offers a more rigorous method for understanding the impact of catchment disturbance
than analysis of the paleolimnological record alone. |
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Keywords: | Palaeoenvironmental reconstruction Environmental magnetism Landscape disturbance Catchment source tracing Mere |
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