Beryllium-7: The Cinderella of fallout radionuclide sediment tracers?

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Current concern for the sustainable management of soil resources and the many adverse effects of increased sediment loads on streams and river systems has generated a need for more information on rates and patterns of soil loss and an improved understanding of catchment sediment budgets. Traditional measurement techniques are frequently unable to meet the requirements and fallout radionuclides have been shown to offer considerable potential for tracing the mobilization, transfer, redistribution and storage of soil and sediment within catchments and river systems. Caesium-137 and lead-210 have been the most widely used fallout radionuclide sediment tracers, but their half-lives mean that the information that they provide is in most instances limited to the medium term (e.g. 25–120 years). The need for information on shorter timescales has directed attention to the potential for using beryllium-7, which has a considerable shorter half-life, for tracing soil and sediment redistribution over short timescales (e.g. days–weeks). To date, however, there have been relatively few attempts to exploit this potential. This situation is likely to be in part a reflection of the emphasis of early work on 137Cs and 210Pb and the more recent nature of work using 7Be. However, it may also reflect the limitations and constraints imposed by the nature of 7Be fallout and the short half-life of this radionuclide. This contribution explores recent work in using 7Be as a sediment tracer and the constraints imposed by its origin and behaviour. Attention is directed to fallout inputs, the application of 7Be to tracing soil and sediment redistribution on slopes and on river floodplains, its use as a source fingerprint and other related applications. The likely future potential of 7Be as a sediment tracer is assessed.

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