PO-210 AND PB-210 REMOBILIZATION FROM LAKE-SEDIMENTS IN RELATION TO IRON AND MANGANESE CYCLING

The behavior of 210Po and 210Pb was studied in the water column of an oligotrophic, dimictic lake. Direct uptake of the radionuclides by sediments was negligible compared to removal on particles, and 210Pb scavenging was 4 times that of 210Po. Both nuclides were found to be significantly remobilized from sediments into the stratified, anoxic water column. Releases seem to be linked to the cycling of the transition metals, iron and possibly manganese. The distribution of both iron and 210Pb in stratified, anoxic waters can be modeled as constant release and rapid horizontal mixing/dilution; vertical turbulent transport had a negligible effect on element distributions. Upon contact with oxygen, iron rapidly reprecipitates, forming a particulate maximum and rescavenging 210Pb. Unlike 21Pb, much 210Po is released from sediments before overlying water becomes completely anoxic, leading to unsupported 210Po. 210Po cycling in the stratified water column is more complex than that of 210Pb, and additional removal mechanism(s) may be active, including perhaps oxidation of soluble Po(II) to insoluble Po(IV). © 1990, American Chemical Society. All rights reserved.