Time dependent vertical distribution of 137Cs in an acid forest soil

Wien

1996

S. 77-84

2 Abb., 9 Lit. Ang.

Artikel aus einer ZeitschriftUnselbständiges Werk

200131574

Vertical migration of 137Cs from the Chernobyl fallout was investigated in an undisturbed forest soil (Dystric Cambisol) under spruce. Comparing 137Cs data of different layers (litter, 0-5 cm, 5-10 cm, 10-20 cm) from 1993 with those measured in 1995 reveals a decreasing trend which exceeds the effect of radioactive decay. But 9 years after the deposition event 48% of radiocaesium soil inventory derived from the Chernobyl accident remained in the litter layer of the forest soil. The vertical distribution of 137Cs contamination (corrected for decay to 86-05-01) was determined as 27.8 kBq m-2 in the litter layer, 22.8 kBq m-2 and 4.4 kBq m-2 in the subsequent 5 cm soil increments and 2.4 kBq m-2 in 10-20 cm depth of mineral soil. Residence half-times were evaluated by application of a compartment model. The values increased significantly in each of the investigated layers between 1993 and 1995, in litter (5-0 cm) from 5.3 a to 7.3 a, in the Ah1 layer (0-5 cm) from 9.6 to 12.6 a, in the Ah2 layer (5-10 cm) from 1.6 to 2.5 a and in the A/B layer (10-20 cm) from 0.7 to 1.0 a. The results support the theory, that the binding of radiocaesium to different soil components is a rather slow process which retards the vertical migration of radiocaesium in forest soils with growing efficiency. The high mobility of caesium in the deeper soil layers partly could be interpreted as a result of cycling processes, where root uptake leads to an upward migration of cations into the living biomass of vegetation.