Evidence for diffusive redistribution of 210Pb in lake sediments

Abstract

210Pb, 210Po, and ancillary geochemical parameters were measured in the sediments and pore waters of a lake with seasonally anoxic bottom waters. Substantial release of radionuclides to the water column has been documented at this site. Solid phase 210Pb profiles do not match the expected input history, suggesting that the radionuclide may be undergoing redistribution. High levels of the radionuclides were measured in pore waters, consistent with partition coefficients in the range from 10 3 to 10 4. The high pore water activities, apparent redistribution pattern, and the documented release of 210Pb from these sediments to the water column, all point to the possible importance of pore water diffusion as a 210Pb transport mechanism. The distribution of 210Pb in these sediments was successfully modeled using a combination of sediment burial and pore water diffusion without the need to invoke particle reworking. Theoretical analysis supports the idea that in some cases large dating errors can result if diffusive redistribution of 210Pb is neglected.