Interpretation of caesium-137 profiles in lacustrine and other sediments: the role of catchment-derived inputs

Abstract

The caesium-137 profiles obtained in many investigations which have attempted to use caesium-137 measurements as a means of assessing the rate of accumulation of recent lake sediments, have not conformed to the classic shape expected from the record of fallout input. Such deviations have been accounted for in terms of post-depositional mobility of the caesium-137 input (e.g. bioturbation) and delayed inputs from the drainage basin. There have, however, been few attempts to determine the likely character of the drainage basin input and to analyse the role of such inputs in influencing the precise form of the caesium-137 profile. This paper presents the results of an attempt to employ existing knowledge concerning the behaviour of caesium-137 in soils and the processes of sediment mobilization to predict the likely form of the record of caesium-137 input to a lake or river floodplain from its drainage basin. The influence of this input on the profile shape will depend on the relative importance of the atmospheric fallout to the lake or floodplain surface and the drainage basin input to the total caesium-137 inventory in the sediment core, and on the land use and sediment sources in the drainage basin. By incorporating the drainage basin input into a simple model of caesium-137 accumulation in lake and floodplain sediments, it was possible to account for the profile shapes measured in four cores investigated by the authors and therefore to verify their utility for assessing rates of sediment accumulation.