MICROBIAL IMMOBILIZATION AND RECYCLING OF CS-137 IN THE ORGANIC LAYERS OF FOREST ECOSYSTEMS - RELATIONSHIP TO ENVIRONMENTAL-CONDITIONS, HUMIFICATION AND INVERTEBRATE ACTIVITY

The Cs-137 content of the microbial biomass in the organic layers of 1 0 German forest sites was quantified with a modified fumigation/extrac tion method. A K(Cs) factor was calculated for biomass Cs-137 from the difference between unfumigated and fumigated samples by means of labo ratory cultures. The size of the estimated K(Cs) factors varied betwee n 1.54 and 2.90 (mean, 2.17; S.D., 0.48). The microflora at the differ ent forest sites contained between 1 and 56% of the total amount of Cs -137 found in the organic layers (mean, 13%). Litterbag experiments sh owed that Cs-137 was actively transported into the L layer by the micr oflora and that this effect was enhanced by the mesofauna. It is concl uded that the immobilization and recycling of Cs-137 by the microflora in the organic layer of forest soils is determined by three major fac tors: Cs-137 availability, growth conditions of the microflora and bio tic interactions.