Cs-137 availability for soil to understory transfer in different types of forest ecosystems

A quantitative analysis of Cs-137 bioavailability in forest soils in the lo ng term after the Chernobyl NPP accident based on a 3-year (1996-1998) inve stigation is presented. Five forest sites with different trees, composition and properties of soil were studied to identify factors determining radioc aesium transfer to different understory species. The following parameters w ere investigated:Cs-137 activity concentrations and its speciation in vario us horizons of forest soil, accumulation of this radionuclide by different species of understory vegetation and distribution of root biomass in the so il profile. It has been shown that one decade after the deposition maximum Cs-137 activity in soil of the experimental sites considered is located in different soil layers dependent on moisture regime, characteristics of litt er and soil properties. A linear dependence between aggregated transfer fac tors for different species and groups of species of understory vegetation a nd exchangeable and available fractions of radiocaesium in soil was found. The vertical distribution of Cs-137 activity, percentage of exchangeable ra diocaesium in each horizon of litter and soil, as well as distribution of r oot systems (mycelia) over the soil profile are key factors governing varia tions in the availability of Cs-137 for transfer to all forest understory c omponents. (C) 2001 Elsevier Science B.V. All rights reserved.