137 Cs in Carpets of the Forest Moss Pleurozium schreberi, 1961-1973

Accumulation, retention and internal cycling of the fallout radionuclide 137Cs (physical half-life = 30.2 a) was studied in forest moss Pleurozium schreberi (Brid.) Mitt. collected in southern Sweden during the period 1961-1973. The highest 137Cs concentrations occurred in the green top parts of the living moss. A major part of the deposited 137Cs is available for transport from the dying to growing parts of the moss. Elimination of 137Cs from living moss, as well as from dead moss, throughout 1968-1973, can be characterized by the same mean residence time (4 ? 1 a). 137Cs and naturally occurring stable K show different behaviour in the moss, so that the 137Cs/K ratio is higher by a factor of approximately 2 in the dead parts of the moss than in the living parts. The vertical distribution of 137Cs in the moss-covered ground,has been described theoretically. Relative penetration of 137Cs is about 5 times higher in ground covered by mosscarpets than in ground covered by lichen-carpets. Throughout 1969-1973, the total amount of '37Cs retained in the moss-carpet was 64.2 ? 2.2 nCi m-2.