sup(239,240)Pu, 241Am and 232Th in lakes: the effects of seasonal anoxia

A pond which undergoes seasonal anoxia as a result of thermal stratification was studied to assess the possible release of actinide elements from anoxic sediments to the pond waters. Concentration profiles of sup(239,240)Pu, 241Am, 232Th, iron and manganese in the water column show significant increases in concentration for all elements in the anoxic deep waters. However, calculated total inventories of the elements in the pond water indicate no apparent input of actinide elements to the system during summer stratification. Similar inventory calculations for sup(239,240)Pu, in a previously studied system support the results of this study. The lack of a significant increase in pond inventories of actinide elements coupled with a lack of correspondence of concentration profiles of the actinide elements to the seasonal Fe and Mn concentration profiles argues that the increases in concentrations observed for these elements in anoxic bottom waters result from the downward transport of material already in the water column rather than release from the sediments. (author)