New data on the character of 137Cs lateral and vertical migration in soil-litter-moss cover within undisturbed elementary landscape geochemical systems on the test site in the Chernobyl abandoned zone, Russia
Authors: Dolgushin Denis , Korobova Elena 
Published: March 2021

&lt;p&gt;A study of &lt;sup&gt;137&lt;/sup&gt;Cs distribution in two new landscape cross-sections characterizing the ELGS system (top-slope-closing depression) in the &amp;#8220;Vyshkov-2&amp;#8221; test site located in the Chernobyl abandoned zone, the Bryansk region, Russia, has been performed in 2020. The test site (70&amp;#215;100 m) is located on the Iput&amp;#8217; river terrace in a pine forest characterized by undisturbed soil-plant cover. The soil cover is presented by sod-podzolic sandy illuvial-ferruginous soils. The initial level of &lt;sup&gt;137&lt;/sup&gt;Cs contamination of the area varied from 1480 kBq/m&lt;sup&gt;2&lt;/sup&gt; to 1850 kBq/m&lt;sup&gt;2&lt;/sup&gt;. Cs-137 activity was measured in the soil, moss and litter cover along two parallel (the distance was 5 m) cross-sections with 1 m step. Moisture content was also determined in the studied objects to roughly assess the influence of water regime on radiocaesium migration. Surface &lt;sup&gt;137&lt;/sup&gt;Cs activity was measured in field conditions by adapted gamma-spectrometer Violinist-III. Cs-137 content in the soil and plant samples was determined in laboratory conditions by Canberra gamma-spectrometer with HPGe detector.&lt;/p&gt;&lt;p&gt;Analysis of the obtained data showed that a major part of &lt;sup&gt;137&lt;/sup&gt;Cs is now fixed in the soil layer 2-10 cm deep while the highest specific activity of radiocaesium is found at a depth of 2-8 cm that can be explained mainly by the burial of the initially contaminated layer under the annual leaf fall.&lt;/p&gt;&lt;p&gt;Along the first cross-section we observed positive correlation between &lt;sup&gt;137&lt;/sup&gt;Cs surface activity and the content radiocaesium in the top soil layer 0-2 cm (r&lt;sub&gt;0.05&lt;/sub&gt;=0.643, n=15). Cs-137 activity in the moss samples correlated with the radionuclide activity in soil samples 4-6 cm deep (r&lt;sub&gt;0.05&lt;/sub&gt;=0.627; n=15). In the moss samples the highest correlation was observed between the green and rhizoid moss parts (r&lt;sub&gt;0.01&lt;/sub&gt;=0.704, n=60). Correlation between radiocaesium activity of the green part of mosses and the underlain litter samples was lower, but also significant (r&lt;sub&gt;0.01&lt;/sub&gt;=0.612, n=60). Values of &lt;sup&gt;137&lt;/sup&gt;Cs activity in the rhizoid part of moss and in litter were also positively linked, but to a lower degree (r&lt;sub&gt;0.01&lt;/sub&gt;=0.402, n=60).&lt;/p&gt;&lt;p&gt;Along the second cross-section correlation between &lt;sup&gt;137&lt;/sup&gt;Cs surface activity and the content radiocaesium in the top soil layer 0-2 cm equaled to r&lt;sub&gt;0.05&lt;/sub&gt;=0.507 (n=7). Radiocaesium content in moss samples (green, rhizoid parts) and litter was higher correlated with &lt;sup&gt;137&lt;/sup&gt;Cs content in soil layer 2-4 cm (r&lt;sub&gt;0.05&lt;/sub&gt;=0.640; 0.410; 0.460, n=7). Similar to the first cross-section the highest correlation was observed between the green and rhizoid parts of moss (r&lt;sub&gt;0.01&lt;/sub&gt;=0.780, n=39). Relation between &lt;sup&gt;137&lt;/sup&gt;Cs activity in green part of moss and litter samples appeared smaller than along the first cross-section but still significant (r&lt;sub&gt;0.01&lt;/sub&gt;=0.419, n=39) while that between the rhizoid part of moss and litter was higher (r&lt;sub&gt;0.01&lt;/sub&gt;=0.509, n=39).&lt;/p&gt;&lt;p&gt;Performed study showed that&lt;strong&gt; &lt;/strong&gt;in the studied objects &lt;sup&gt;137&lt;/sup&gt;Cs secondary migration has a specifically stable character which may be related to spatial peculiarities of radionuclide migration in soil-plant cover controlled by water regime in the ELGS system. In our opinion this may form a characteristic cyclic variation of &lt;sup&gt;137&lt;/sup&gt;Cs activity observed along cross-sections of ELGS.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The reported study was funded by RFBR according to the research project &amp;#8470; 19-05-00816.&lt;/p&gt;