First year of movement, distribution and availability of Cs 137 in the forest floor under tagged tulip poplars

Abstract

Influx, distribution, and leachability of Cs 137 in the forest floor were measured for environmental description. Rain, leachates, litter, soil and roots were collected under the crowns of tulip poplars ( Liriodendron tulipifera L.) tagged in May. The Cs 137 content of the samples was measured by scintillation counting. Before leaf fall 85 per cent of the Cs 137 in the forest floor was found in roots which consequently set the distribution pattern. Concentrations of Cs 137 in soil varied by 2 orders of magnitude within a few cm distance. Distribution of Cs 137 was less influenced by rainout and runoff. Ten soil cores of 7 cm 3, 2·1 cm dia. and 2 cm deep, were found sufficiently large to estimate local mean distribution of Cs 137 in litter and in soil, in the various seasons. Variabilities ( s as percentage of X) ranged from 31–62% of the mean. Leaf fall doubled the total amount of Cs 137 in the forest floor and increased the amount of Cs 137 in litter 15 fold. Leachability of Cs 137 in the fresh litter was nine times greater than in old litter and increased the content of mobile Cs 137 in the entire litter layer by two orders of magnitude. During winter more than half of the Cs 137 in litter and roots leached into the soil. In spring there was renewed rainout from the canopy. The large differences in amount, concentration, and leachability of Cs 137 over short periods of time and distances could only be measured by combining the results of detailed and frequent sampling using a variety of methods.