Vertical Distribution Of 137Cs Research Articles

The effect of sorption properties of soil minerals on the vertical migration rate of cesium in soil

The vertical distribution of137Cs is shown for two types of soil: silly loamy “supposed” soil and silly lessive one, slightly eroded, occuring in the vicinity of Lublin (Eastern Poland). Based on the distribution data the vertical migration rates of137Cs are calculated for both soils. These rates are found to be 0.045 and 0.3 cm/year respectively. The percent contribution of137Cs originating from the damaged reactor in Chernobyl is also calculated. The kinetics of cesium adsorption and its adsorption isotherms on minerals separated from the tested soils are also studied. The sorption of Cs on soil minerals markedly affects the migration rate of137Cs in soil. The experimental results indicate that, among the extracted mineral fractions, the largest adsorption takes place on marls from the silly loamy soil. This work is supplemented by results of a physicochemical analysis of the studied soils.

Caesium-137 and strontium-90 distribution in a soil profile

This paper reports the 90Sr and 137Cs distribution measured in 1987, 1989 and 1990 along a soil profile in a grassland, located in the North of Italy. The vertical distribution of 137Cs in soil due to the Chernobyl accident was used to validate the RABES (RAdionuclides BEhaviour in Soil) model (Velasco et al., 1991).

Dual radiotracer measurement of zoobenthos‐mediated solute and particle transport in freshwater sediments

Gamma spectroscopy methods have been applied to determine the effects of Stylodrilus heringianus and Pontoporeia hoyi, two freshwater benthic macroinvertebrates, on the reworking of sediments and the transfer of solutes across the sediment‐water interface. Natural lake sediments (sieved to remove organisms) and overlying water were contained in temperature‐regulated rectangular plastic cells. A submillimeter layer of sediment solids labeled with 137Cs was deposited on the sediment interface while overlying water was spiked with 22Na. After addition of Stylodrilus (oligochaete worms) and Pontoporeia (crustacean amphipods) to these microcosms, the vertical distributions of 137Cs (a tracer of particle transport) and 22Na (a tracer of solute transport) were determined at daily to weekly intervals for 3 months by scanning the length of the cells with a well‐collimated NaI detector. In cells with Stylodrilus, the 137Cs layer moved downward at a rate that decreased exponentially with time. The displacement of the layer is the result of the conveyor‐belt feeding mode of this organism. The rate of marked layer burial is consistent with that of other freshwater annelids (0.18×10−5 cm d−1 individual−1 m−2; 11.6°C). The exponential decrease in burial rate is ascribed to uniformly distributed feeding of Stylodrilus within the feeding zone of 4.4 cm. In cells with Pontoporeia, 137Cs activity was smeared downward in time owing to eddy diffusive mixing of sediments over a small range (1–2 cm). In cells without worms, the veneer of Cs active material remained at the interface while the penetration of 22Na into sediments was consistent with diffusion in free solution with small corrections for sediment porosity and sorption (KD = 0.17). The effective diffusion coefficient De for 22Na in this cell (8.2×10−6 cm2 s−1) was essentially the same as that for a cell that had been inhabited by worms for 3 weeks and then poisoned with formalin just before addition of 22Na. Thus the presence of biogenically reworked sediments (with pelletized materials and remnant burrow structures) did not affect solute transport. In cells with live Stylodrilus, penetration of 22Na within the feeding zone was considerably more rapid, implying an apparent De twice as high as in cells without worms. Inferences based on the particle reworking results were used to develop an illustrative transport model that includes advective as well as diffusive terms. Advective transport arises from the incorporation of 22Na into pore fluids moved downward as a result of conveyor‐belt feeding. The model indicates that within the feeding zone, solute transport is dominated by advection and that the apparent enhancement of De in pure diffusion models is really the result of solute flow induced by particle reworking. In cells with Pontoporeia, De is approximately twice that in control cells. In these cells, 22Na profiles may be treated theoretically without advection.

137Cs diffusion in the highly organic sediment of Hidden Lake, Fraser Island, Queensland

The vertical distribution of 137Cs (originating from nuclear fallout since 1954) in the highly organic sediment of Hidden Lake is found to be inconsistent with 14C and 210Pb data. Mathematical models of bioturbation indicate that this mechanism cannot explain the discrepancy. Diffusive migration of 137Cs is modelled using the experimentally determined value of ≈140 for the distribution coefficient, KD, of 137Cs in Hidden Lake sediment. It is concluded that 137Cs is diffusing in the sediment at an effective rate of c. cm2 s-1 due to the low value of KD The diffusive mechanism is further modified by adsorption or absorption at or near the sediment-water interface.

Vertical distribution of 137Cs and its accumulation rate in lake sediments.

Vertical distributions of 137Cs in the sediments of Lake Biwa, Lake Suigetsu and Lake Mikata were measured by the non-destructive gamma counting technique using a germanium-lithium detector. Possible sedimentation rates were estimated based upon the depth of 137Cs penetrating into the sediments.

137 Cs in the reindeer lichen Cladonia alpestris: deposition, retention and internal distribution, 1961-1970.

Abstract The accumulation of the fallout radionuclide 137Cs has been studied in a large number of samples of the important reindeer lichen Cladonia alpestris, collected in the Lake Rogen area (62.3°N, 12.4°E) in central Sweden during the period 1961–1970. The maximum area-content of 137Cs in the lichen carpet occurred in 1965 and 1966, and amounted to 46–66 nCi/m2, which corresponds to a dry mass content of 34–52 nCi/kg, due to the special characteristics of the lichen carpet and of the locality itself. In September 1970 the 137Cs levels for the whole lichen carpet were 50–80 per cent of the values obtained in 1965. The vertical distribution of 137Cs has been studied during 1966–1970 and the results indicate the existence of a short-time internal cycling of the radionuclide in the lichen carpet, so that in dry periods certain amounts of 137Cs are forced up to the top regions of the carpet and in periods of high precipitation washed down to its lower layers. The concentration of 137Cs at various depths recorded in carefully field-fractionated samples of lichen, gelatinous matter, humus and soil collected in the “normal” years 1969 and 1970 follows the empirically found relation c = constant *exp(−1.6 z0.75), where c denotes the 137Cs concentration in dry matter (nCi/kg) at the dry mass depth z (kg/m2). For comparison with the 137Cs results, the vertical distribution of two other alkali metals, potassium and sodium have also been studied. According to increasing penetration of the lichen carpet, the elements can be arranged in the following sequence: 137Cs = K ≪ Na. The principal ways for elimination of 137Cs from undisturbed carpets of Cladonia alpestris are physical decay of the radionuclide and the continuous growth of the lichen plants, the latter combined with a continuous decomposition of older material.

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.