Seasonal variations in radionuclide transfer in a Mediterranean grazing-land ecosystem

We made quarterly determinations of the transfer coefficients and effective transfer coefficients for the radionuclides Cs-137, Sr-90, K-40, Ra-226, R a-228 and Th-228 over a full annual cycle, in a Mediterranean grazing-land ecosystem. The input and output fluxes of the radionuclides between the dif ferent compartments of this ecosystem were quantified for the following pro cesses: root uptake; variation in root and aerial biomass; pasture producti on; translocation; leaf fall; efflux due to grazing action; resuspension an d subsequent aerial deposition of radionuclides. We observed there to be a marked seasonal variation for this type of ecosystem in both the transfer c oefficients and the radionuclide fluxes, which impedes the soil-plant trans fer being characterized on the basis of values that are constant with time. (C) 2001 Elsevier Science Ltd. All rights reserved.