THE VARIABILITY IN FALLOUT CONTENT OF SOILS AND PLANTS AND THE DESIGN OF OPTIMUM FIELD SAMPLING STRATEGIES

Sampling was carried out at an upland peat site in Ireland to assess the variability in Cs-137 deposition to soils and activity concentration in individual vegetation species. A 3,600 m(2) quadrat was laid out, and a soil core was extracted within each of sixteen 20 x 20 cm soil monoliths. The coefficient of variation values for Cs-137 deposition and activity in individual soil horizons were in all cases greater than 30%, and the relative variability between corresponding horizons tended to increase with depth. Samples of Calluna vulgaris and Juncus squarrosus were taken at each soil sampling location and coefficients of variation for Cs-137 activity in these species were 12 and 20%, respectively. The data was used to examine the relationship between the number of samples analyzed in a survey, the variability within those samples, and the way those two factors affect our ability to detect between-site differences in Cs-137 contamination levels. A methodology is developed for detection of between-site differences in Cs-137 contamination under different experimental criteria. The data show that, of the sample types examined, between-site differences could be detected most efficiently with C. vulgaris. Because of the variability associated with the Cs-137 content of each sample type, between-site differences could be detected with fewer plant samples than soil samples. Plant-soil concentration ratios, transfer factors, and plant-plant ratios were calculated from the data, and the variability associated with each parameter was assessed. The variation among values for plant-plant ratios was less than among concentration ratios, and the greatest spread of values was associated with plant-soil transfer factors.