17 FIG. 7. Calculated 137Cs activity concentrations in bed sediments at points indicated in Figure 2. The time origin corresponds to October 1986. Key: USEV, POSEIDON, THREETOX, NRPA. FIG. 8. Calculated and measured mean 137Cs activity concentrations in water in several basins. Error bars are 1? standard deviations of the measured mean values. In cases where only one sample was measured error bars are not shown.