Radionuclide Behaviour and Transport in a Coniferous Woodland Ecosystem: The Distribution of Radionuclides in Soil and Leaf Litter

A coniferous woodland in the vicinity of theBritish Nuclear Fuels reprocessing plant atSellafield, Cumbria, was used to examine the spatial,temporal and depth distribution of ¹³⁴Cs,¹³⁷Cs, ²³⁸Pu, ^239+240Pu and ²⁴¹Amin soil and leaf litter. All the radionuclides, withthe exception of ¹³⁴Cs, showed a consistent fallin accumulated soil and litter deposits withincreasing distance from the woodland edge nearest toSellafield. ¹³⁷Cs levels in soil declined from 53to 28 kBq m^-2, ^239+240Pu from 5.5 to 3.6 kBqm^-2 and ²⁴¹Am from 2.9 to 1.1 kBq m^-2within 100 m of the forest edge. This decline isattributed to greater deposition occurring at theleading edge of the woodland. The uniform depositionpattern of ¹³⁴Cs in soil is consistent with thehypothesis that, at the time of sampling, thesedeposits derived largely from wet deposition duringpassage of the Chernobyl plume over Cumbria in May1986. Results for the leaf litter indicate a similarspatial distribution to that observed in soil.Radionuclide concentrations were also similar but thisis not attributable to adventitious soil contaminationbecause significant differences between isotopicratios of ¹³⁴Cs:¹³⁷Cs and ²³⁸Pu:^239+240Pu imply that the contamination on leaflitter is of more recent origin than that in soils.