Articles

The article discusses the processes of transition to the aqueous phase and uptake from it by plants of stable (Cd) and radioactive (¹⁰⁹Cd) isotopes. Regularities of the distribution of Cd/¹⁰⁹Cd between different forms of their chemical compounds in the soil were revealed by means of sequental extraction procedure (SEP) according to the Tessier-Förstner method. It was shown that content of labile and conditionally labile forms of compounds (fraction F1-F3) of stable Cd was 1,2–1,8 times less than that of radioactive ¹⁰⁹Cd and, conversely, 2,4–5,3 times more fixed conservative forms of metal compounds (fraction F4-F6). The Cd concentration, ¹⁰⁹Cd activity concentration, distribution and concentration coefficients of natural Cd and ¹⁰⁹Cd radionuclide, accumulation and removal of metal by plants were evaluated. Values of enrichment coefficients of natural (stable) Cd contained in sequentially extracted chemical fractions by ¹⁰⁹Cd radioisotope were determined, the value of stock of labile cadmium compounds in studied soil was calculated. Based on the results of solid-state ¹³C NMR spectrometry, the qualitative composition of high-molecular organic compounds of the soil solution was determined and their ability to specifically sorb heavy metal cations was assessed.

An analysis of the isotopic composition of vegetation and organic matter of permafrost burozems in the south of the Vitim Plateau was carried out. The soil profile is characterized by a pronounced uneven distribution of carbon. The main part of carbon reserves is concentrated in the humus-accumulative horizon, down the profile — much lower.

Vegetation on burozems belongs to the C-3 type of photosynthesis. In legumes, forbs, and semi-shrubs, the aboveground parts are somewhat depleted in the ¹³C isotope compared to the underground ones. In trees, the content of 13C in branches, needles, and leaves differs slightly.

The isotope composition of carbon in the upper horizons of soils depends on the type of phytocenosis and has close values to δ¹³C in dominant plants. With depth, carbon isotope fractionation shows a clear vertical differentiation along the soil profile.

The carbon of humic acids in soils from the humus-accumulative horizon and from cryogenic fissures slightly differs in isotope composition. The composition of stable carbon isotopes of humic acids in the soil profile remains approximately at the same level. These data indicate the similarity of the processes of humic acids formation in the upper soil layers and in humus pockets.

Natural ¹³C abundance of different organic matter (OM) pools of Haplic Chernozem (Streleskaya steppe plot of the Central Chernozemic State Biospheric Reserve) isolated by granulo-densitometric fractionation was studied. Natural variations of the ¹³C/¹²C ratio (δ¹³C) allowed to confirm the sequence of OM decomposition in soils, which follows a continuum from fresh and partially decomposed organic materials in the discrete OM (Free and Occluded) to significantly/completely processed in the mineral-associated OM (Clay and Res). This is reflected in the increase of the δ¹³C value during passing from discrete to mineral–associated OM. All studied OM pools are subjected to microbial processing, but in different extent. Free OM, despite the fact that it consists of well-recognized plant material, is not always the most fresht and most undecomposed organic material. The «lighter» isotope signature of occluded OM as compared to free OM, despite its obvious higher degree of microbial processing, may be a consequence of its physical protection in microaggregates (unstable under the sonication) within the soil structural units. The most microbial processed mineral-associated organic material (Clay and Residue fractions) is characterized by the «heaviest» isotopic signature. The isotopic composition of carbon in the whole soil is mainly determined by the Residue fraction due to its quantitatively domination in the bulk soil.

The conceptual scheme allows to quantify the carbon (C) fluxes of in the OM pool / soil system. It was revealed that the main C fluxes in the OM pools go from the Free OM to the Residue fraction through unstable under the sonication microaggregates. The most probable C flows into the whole soil — unstable under the sonication microaggregates, as well as the Residue fraction, which are characterized by the lowest Δ¹³C values (difference between Δ¹³C of «sourse» and «product»).

The total content of lead, the content of its acid-soluble and mobile forms of compounds in sod-carbonate soils of the impact zone of the Cherepovets Steel Mill (Vologda region) were studied. The isotopic composition of lead of its specified forms of compounds has been determined. It is shown that lead, being a part of the gas and dust emissions of the enterprise, is detected in increased quantities up to 6–10 km in the north direction studied by us from the source of pollution. The penetration of technogenic lead compounds down the soil profile up to horizon B is observed. The isotopic ratios of lead ²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁷Pb studied by us reveal clear dependencies on the lead content in soils. For all isotopic ratios in the series «total lead < acid-soluble lead < mobile lead», the contribution of technogenic lead compounds to its isotopic composition increases, since in the same series there is an increase in the proportion of technogenic lead compounds from its total amount. Extrapolation of the dependence of the ratio ²⁰⁶Pb/²⁰⁷Pb on the lead content in the low content area gives the value of this ratio in the range of 1,19–1,25, which corresponds to the isotopic composition of the total lead of the background soils of the European part of Russia. In high polluted soils near Steel Mill, this ratio decreases to 1.10, which corresponds to numerous literature data. The choice of isotope ratio is crucial for obtaining more detailed information about the nature and sources of technogenic lead contamination of soils. Thus, in soils with a low lead content, according to the values of the isotope ratio ²⁰⁸Pb/²⁰⁷Pb, lead is released associated with another source of pollution, presumably from a city thermal power plant operating on coal.

From 1978 to 2021, the migration parameters and dynamics of the distribution of ¹³⁷Cs in arable and virgin soils of the Tula region were studied. Identical patterns of distribution of ¹³⁷Cs from global and Chernobyl fallout in the soil profile of leached chernozems were revealed. On arable land, agrotechnical measures contribute to the uniform distribution of ¹³⁷Cs in the arable soil layer. In virgin soil horizons of chernozem soils of meadow phytocenoses, the processes of redistribution of radionuclides in the surface layers were most active in the first 10-year period after the fallout, which this contributed to the equalization of ¹³⁷Cs content in layers 0–2 and 2–5 cm and its increase in the 5–10 cm layer to more than 30% by the beginning of 2000. Nowadays, more than 75% of the ¹³⁷Cs content in virgin chernozem soils of the Tula region is concentrated in the upper 15 cm layer, and the penetration depth of radionuclides reaches 40–45 cm.

From 1978 to 2021, the migration parameters and dynamics of the distribution of ¹³⁷Cs in arable and virgin soils of the Tula region were studied. Identical patterns of distribution of ¹³⁷Cs from global and Chernobyl fallout in the soil profile of leached chernozems were revealed. On arable land, agrotechnical measures contribute to the uniform distribution of ¹³⁷Cs in the arable soil layer. In virgin soil horizons of chernozem soils of meadow phytocenoses, the processes of redistribution of radionuclides in the surface layers were most active in the first 10-year period after the fallout, which this contributed to the equalization of ¹³⁷Cs content in layers 0–2 and 2–5 cm and its increase in the 5–10 cm layer to more than 30% by the beginning of 2000. Nowadays, more than 75% of the ¹³⁷Cs content in virgin chernozem soils of the Tula region is concentrated in the upper 15 cm layer, and the penetration depth of radionuclides reaches 40–45 cm.

The study of ¹³⁷Cs and K behavior in «soil-plant» system of chernozem zone in remote period after Chernobyl accident was carried out. Experimental plots in agrosystems such as wheat, soybean, buckwheat, rapeseed, sunflower, grass mixture, and natural biosystem of a dry meadow were selected in the central part of Plavsk radioactive hotspot in Tula region. The level of ¹³⁷Cs soil contamination was 171 ± 26 kBq/m² (498 ± 100 Bq/kg). Average gross K content in soils was 2,0 ± 0,1%, including exchangeable K — 235 ± 54 mg/kg and non–exchangeable K — 816 ± 116 mg/kg. Vertical distribution of ¹³⁷Cs within contaminated 30-cm soil layer of agrosystems, as well as gross K, was uniformly accumulative, while K_ex and K_non-ex distribution was regressive and accumulative. At the same time, ¹³⁷Cs microdistribution in root zone was invariant, and gradient enrichment of soil near the root surface was shown for mobile forms of potassium. Intensity of ¹³⁷Cs transfer from soils to plants for all studied crops was 1–2 orders lower than intensity of K root uptake. Element distribution between plant organs differed. ¹³⁷Cs distribution was acropetal for Cereals and basipetal for crops from other families, and K was distributed basipetally in all tested plants.