The recent sedimentation history of the esk estuary, Cumbria, U.K.: The application of radiochronology

Abstract

The sediments of the Esk estuary, Cumbria, contain a variety of radionuclides which are derived from the British Nuclear Fuels Ltd (BNFL) reprocessing plant at Sellafield, Cumbria. In principle the total ecosystem of the Esk estuary is labelled with a variety of radionuclides which we have studied in order to investigate fundamental process which take place in estuaries; also to improve our knowledge of relationships which exist between the rate of release of radionuclides in the BNFL source term and their distribution in the Esk. On the basis of defined sampling procedures we have dated the rate of sedimentation for the major sediment types of the system using six different radionuclides, and four independent methods, including a procedure of statistical modelling. The model is based upon procedures for matching the shape of the BNFL radionuclide release profile over a period of ∼ 10 y, with that for the distribution of radionuclides in profiles of sediment cores. Good agreement is obtained for the match. In the Esk a large proportion of the radionuclides which are retained in sediments are associated with particulate matter and surfaces of sediment debris; in accreting sediments these deposits have not been disturbed during the past ∼ 30 y. In modelling the releases of radionuclides from point sources, attention needs to be paid to the chemical and physical composition of the source term, as this can influence the subsequent distribution of radionuclides in nearshore and estuarine marine ecosystems.