8 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



12 16 20 



DEPTH IN CORE, cm 



24 



32 



Fig. 2 Histogram of the distribution o.f plutonium in a sediment core from Lake Erie. 

 The two peaks correspond to the material deposited during years of maximum fallout, 

 1963 and 1959, respectively. The dashed line represents the predicted distribution based 

 on a sedimentation rate of 1.15 cm/yr at the surface and a mixing depth due to 

 bioturbation of 4 cm. 



reflect the history of releases from Windscale (Hetherington, Jefferies, and Lovett, 1975; 

 Hetherington, 1978). Profiles measured in sediments from the Santa Barbara channel 

 show a continuing input of plutonium due to erosion of California soils and direct input 

 from faUout (Koide, Griffin, and Goldber , 1975). 



In other cores from Lake Michigan and Lake Erie, it is possible, by comparing 

 plutonium and cesium profiles with those for ^^'^Pb, to estimate the effects of 

 biotic activity on lake sediments (Robbins and Edgington, 1975) and to identify massiye 

 disturbances in sediments of the Crest Lakes due to large storms (Edgington and 

 Robbins, 1976). 



Some sediment cores from Lake <)ntario have plutonium concentration profiles 

 exhibiting subsurface maximums similar ro those found in Lake Michigan and Lake Erie 

 (Bowen, 1976; Edgington and Robbins 1976). However, in other cores from Lake 

 Ontario and Buzzards Bay, the profiles -low no subsurface maximums (Livingston and 

 Bowen, 1976; Bowen, Livingston, and Burke, 1976). In these cores it is clear that there 

 must be mixing downward by physical or biological processes. Repeated coring in 

 Buzzards Bay from 1964 to 1973 showed that there was a small net loss of plutonium in 



