Turnover of 137Cs in ‘soil–tree’ system: An experience of measuring the isotope flows in a Siberian conifer forest

Publication date: December 2016
Source:Journal of Environmental Radioactivity, Volume 165
Author(s): Vladimir L. Gavrikov, Ruslan A. Sharafutdinov, Aleksandr R. Mitev
Little attention has been paid to the uptake of ¹³⁷Cs in natural forests under low levels of the isotope fallout when no immediate ecological danger presents. Here we present the extended assessments of the soil-to-plant and canopy-to-litter flows of ¹³⁷Cs recently evaluated in a native Siberian forested area. The area undergoes a typical after-fire long term succession, with light-conifer upper story being followed by undergrowth of Siberian fir and other dark-conifer species. The one-year-old needles of Siberian fir were found to accumulate the largest concentration of the isotope, 4.10 Bq/kg oven-dry weight during the first growth season, as compared with older needles that accumulated 4.67 Bq/kg oven-dry weight in 2–3 years of growth. Based on these data an approach was developed that, hypothetically, can allow one to estimate the ¹³⁷Cs activity concentration in soil solutions. Direct activity measurements in the soil solutions were not possible. The isotope activity in soil solutions was estimated to be 0.0061–0.0105 Bq/L. Based on the original data from the litter fall the annual flow of the isotope from the upper canopy to on-ground litter was found to be 0.42–0.84 Bq/m². The amount of ¹³⁷Cs that returns yearly back from canopy with falling litter was estimated to be 0.012–0.015% of the total soil isotope content. A combination of the estimations obtained in our study with the values of global ¹³⁷Cs fallout allowed us to assess the ages (the time of formation) of horizons of the soils in the area.



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