The potential for paleolimnology to determine historic sediment delivery to rivers |
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Authors: | I D L Foster A L Collins P S Naden D A Sear J I Jones Y Zhang |
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Institution: | (1) School of Science and Technology, The University of Northampton, Newton Building, St George’s Avenue, Northampton, NN2 6JD, UK;(2) Soils, Crops and Water, ADAS, Woodthorne, Wergs Road, Wolverhampton, WV6 8TQ, West Midlands, UK;(3) Centre for Ecology and Hydrology, Crowmarsh Gifford, Wallingford, Oxon, UK;(4) Department of Geography, University of Southampton, Highfield, Southampton, S017 1BJ, UK;(5) School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK;(6) Geography Department, Rhodes University, Grahamstown, 6140, Eastern Cape, South Africa |
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Abstract: | Establishment of water quality criteria to guide catchment sediment management is required by the European Union (EU) Water
Framework Directive. The topic, however, is hotly contested among scientists and policy makers. Existing legislation with
regard to fine sediment was set by the EU Freshwater Fish Directive. Its guideline, i.e. mean annual suspended sediment concentration,
is 25 mg l−1. Such a static target fails to capture the episodic nature of sediment transport. Furthermore, application of such global
standards is inappropriate for a pollutant that is strongly controlled by spatial variation in key catchment drivers. Paleolimnology
offers an approach for assessing background sediment pressures on watercourses, enabling determination of values for times
pre-dating agricultural intensification. We propose that Modern Background Sediment Delivery to Rivers (MBSDR) across England
and Wales can be determined using paleolimnology to quantify maximum feasible sediment reduction. No management programme
should aim to reduce sediment loss to values below those resulting from background, natural physiographic and/or hydrological
controls. Lacking generic tools to quantify process linkages between sediment pressures and biological impact, we propose
that MBSDR could be taken to represent ecological demand for sediment inputs into watercourses required to support healthy
aquatic habitats. In situations where generic tools exist for coupling sediment pressures and ecological impacts, assessment
of MBSDR could be used to correct the gap between current or future projected sediment loss and biological condition. Existing
paleolimnological data on sediment yields across England and Wales are presented to illustrate the approach and provide preliminary
national estimates of MBSDR. We briefly consider the basis for reconstructing sediment yields using a paleolimnological approach
and analyse temporal trends in published sediment yield, inferred for a range of landscape types. We also attempt to correlate
sediment accumulation rates (SARs) with sediment yields to extend the MBSDR data base. Preliminary maps were generated to
identify regions where further sediment yield data are needed to produce a more robust estimate of the spatial distribution
of MBSDR across England and Wales. |
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