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

Sampling was carried out at an upland peat site in Ireland to assess t he variability in Cs-137 deposition to soils and activity concentratio n 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 a nd activity in individual soil horizons were in all cases greater than 30%, and the relative variability between corresponding horizons tend ed to increase with depth. Samples of Calluna vulgaris and Juncus squa rrosus were taken at each soil sampling location and coefficients of v ariation for Cs-137 activity in these species were 12 and 20%, respect ively. The data was used to examine the relationship between the numbe r of samples analyzed in a survey, the variability within those sample s, and the way those two factors affect our ability to detect between- site differences in Cs-137 contamination levels. A methodology is deve loped for detection of between-site differences in Cs-137 contaminatio n under different experimental criteria. The data show that, of the sa mple types examined, between-site differences could be detected most e fficiently with C. vulgaris. Because of the variability associated wit h the Cs-137 content of each sample type, between-site differences cou ld be detected with fewer plant samples than soil samples. Plant-soil concentration ratios, transfer factors, and plant-plant ratios were ca lculated from the data, and the variability associated with each param eter was assessed. The variation among values for plant-plant ratios w as less than among concentration ratios, and the greatest spread of va lues was associated with plant-soil transfer factors.