Biodiffusion of 7Be and 210Pb in intertidal estuarine sediment

The profiles of 7Be and 210Pb in three kinds of sediments from the intertidal zones of the Tatara-Umi estuary, Fukuoka, Japan were measured. In a silty area, they were fitted on a simple biodiffusion model with the diffusion coefficients of (1–8) × 10−7cm2s−1. Radioactive tracers of 22Na, 85Sr, 134Cs, 59Fe, 54Mn, 57Co and 65Zn were added to the untreated or heated cores of the undisturbed sediments to examine bioactivity on the transfer of the radionuclides In the heated cores, paniculate tracers were hardly transferred. In the untreated cores, they were diffused heterogenously and showed peaks at intermediate depths, which suggested biodiffusion with conveyor-belt deposit feeders. Paniculate radionuclides in estuarine sediment in the silty area are supposed to be biodiffused mainly with macroorganisms such as crabs and bivalves.