Interpreting the 137Cs profiles observed in several small lakes and reservoirs in southern England

The depth distribution of bomb-derived 137Cs has been studied in cores collected from five small lakes and reservoirs with high sediment accumulation rates in southern England. An empirical approach was employed to demonstrate the influence of the catchment-derived 137Cs input and the post-depositional redistribution of 137Cs on the 131Cs profiles of the sediment cores. By incorporating the remobilisation of 137Cs and deposited sediment, a catchment-related 137Cs lake deposition model has been used to interpret the 137Cs inventories and concentrations in the lake and reservoir sediments in terms of sediment sources. A clear linkage between the 137Cs concentration in the lake sediment and that in catchment source soils has been established for the five water bodies. Estimates of the proportion of the total 137Cs inventory of individual sediment cores derived from the catchments ranged between 57% and 97%. These values emphasise the importance of the catchment-derived contribution to the overall 137Cs inventory of sediments in small lakes and reservoirs receiving significant sediment inputs from their catchments. The estimates of sedimentation rates for the water bodies provided by the cores were also used to estimate the sediment yields from their respective catchments.