SEDIMENTATION-RATES, RESIDENCE TIMES AND RADIONUCLIDE INVENTORIES IN LAKE BAIKAL FROM CS-137 AND PB-210 IN SEDIMENT CORES

RADIONUCLIDES in lake sediments may act as indicators of the sedimentation rate of particles on which they are adsorbed; these rates in turn provide a direct indication of the residence times of particles in the water column. The radionuclide Cs-137 is anthropogenic (an atomic-bomb product), so that its concentration in sediments also reveals the input history of this species and thus a record of atmospheric contamination by this nuclide in the lake's watershed. Here we report measurements of Cs-137 and the natural radionuclide Pb-210 in cores from several stations throughout the three basins of Lake Baikal. The results confirm earlier indirect estimates 1 of the mean sedimentation rate, and show that the effective settling rate of these radionuclides is the same as that in the Great Lakes; the longer residence times for Lake Baikal are therefore simply a consequence of its greater depth. As well as allowing estimates of fluxes at the sediment-water interface 2-4, our results provide information on the timing of palaeolimnological events 5, on the existence of different depositional zones throughout the lake, on the long-term (decadal) diffusion of nuclides in sediments 6 and for the development of mass-balance models for sediments and contaminants 7-9.