Uptake, turnover and transport of radiocaesium in boreal forest ecosystems

The study was mainly addressed to aspects on the redistribution of the Chernobyl fallout within and output from a coniferous forest ecosystem. The only detected pathway for Cs to exit the ecosystem was via discharge from mires. About 40% of the deposition on mires discharged via stream water during the snow-melt 1986. The residual fraction discharged at an annual rate of 30% from water saturated fractions and about 2% from drier fractions of the studied mire. No loss of Cs from ridges and moraine slopes to ground water was detected. The main transfer from the canopy to the forest floor occurred during the first year. The estimated transfer from throughfall and litterfall during May 1986 to May 1996 was 50% of the estimated total deposition in the ecosystem. The contribution from herbivory was estimated to 1% of the deposition. In 1987 the fraction of Cs that was retained in the above ground parts of a Scots pine stand was only 4%. The Cs intercepted in mosses and lichens were slowly transferred to the litter and humus layers. Cs in vegetation with green parts above ground during the fallout decreased rapidly during the first vegetation season The ranking in Cs of the studied plants was fireweed < birch < pine < bilberry < heather which seems to be a general trend in the boreal region. Except for mires, the boreal forests of northern Sweden will recover from the deposition of Cs at a rate which is mainly determined by the radioactive lifetime of 137Cs. Moose meat, berries and mushrooms produced in the boreal region will give rise to a small but significant internally absorbed dose to man during several years. 57 refs, 9 figs, 5 tabs