PLUTONIUM IN THE GREAT LAKES 677 



0.1 0.2 0.3 0.4 



SiOj + CaC03, mg/mg 



0.5 



Fig. 1 1 Relation between total (in solution and on particles) plutonium and the content 

 of SiOo and CaC03 in particles from filtration (ANL-5. 7 m above bottom). 



1973 onward. The results of the concentration— time models presented above show that it 

 is unnecessary to assume that present levels reflect equilibrium between sediments and 

 water. The preceding arguments indicate that plutonium is released from dissolving 

 particles that may be localized in the benthic zone, depending on lake dynamics. 

 Redistribution of soluble plutonium in the water column can readily occur without 

 particle resuspension (oj^ = 0). 



The study of Chase and Tisue ( 1977) indicates that the material most available to be 

 resuspended (benthic floe residing above consolidated sediments) is probably hydro- 

 dynamically unsuited to appreciable upward movement in the water column. The benthic 

 floe consists primarily of organic-mineral aggregates, typically a few tens of microns in 

 diameter having bulk densities of about 1.05 g/cm^. The aggregates consist of diatom 

 frustules, calcite and other minerals, and other unidentified detritus. Particles with such 

 properties (7~ 20 jLtm) remain aggregates on resuspension and have Stokes' settling 

 velocities co^ of roughly 10~^ cm/sec, or about 500 m/yr (Lerman, Lai, and Dacey, 

 1974). Under normal conditions (excluding fall overturn) the vertical eddy diffusivity Ky 

 in the hypolimnion is on the order of 1 cm'^/sec, or ~3 X 10^ m'^/yr (Kullenberg, 

 Murthy, and Westerberg, 1973). Thus the scale length for the resuspended material flux in 

 the water column under steady-state conditions is Ky/ws "^ 5 m. The flux of resuspended 

 material is given by J = Jo e ^^ '^, where h is the height above the bottom and Jq 



