Concentrations of Radionuclides (<Superscript>226</Superscript>Ra, <Superscript>232</Superscript>Th, <Superscript>40</Superscript>K,and <Superscript>137</Superscript>Cs) in Chernozems of Volgograd Oblast Sampled in Different Years

Data on the concentrations of natural (²²⁶Ra, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides and on the physicochemical properties of chernozems sampled in different years are presented. In 1952, upon the creation of the Penza-Kamensk state shelterbelt, three deep (up to 3 m) soil pits were examined within the former arable field under two-year-old plantations of ash and maple along the transect crossing the territory of the Beloprudskaya Experimental Station of the USSR Academy of Sciences in Volgograd oblast. The samples from these pits were included into the collection of dated soil samples of the Dokuchaev Central Soil Science Museum. Five pits were examined along the same transect in 2009: three pits under shelterbelts (analogues of the pits studied in 1952) and two pits on arable fields between the shelterbelts. In the past 57 years, certain changes took place in the soil structure, bulk density, and the content and composition of humus. The salt profile of soils changed significantly under the forests. The comparison of distribution patterns of natural soil radionuclides in 1952 and 2009 demonstrated their higher contents at the depth of 10–20 cm in 2009 (except for the western shelterbelt). Background concentrations of natural radionuclides in parent materials and relationships between their distributions and the salt profiles of soils have been determined; they are most clearly observed is the soils under shelterbelts. Insignificant contamination with ¹³⁷Cs (up to 34 Bq/kg) has been found in the samples of 2009 from the upper (0–20 cm) horizon. The activity of ¹³⁷Cs regularly decreases from the east to the west; the highest concentrations of this radionuclide are found in the topmost 10 cm. This allows us to suppose that ¹³⁷Cs was brought with aerial dust by eastern winds, and the shelterbelts served as barriers to the wind flow.     

Radioactive Contamination of Alluvial Soils in the Taiga Landscapes of Yakutia with <Superscript>137</Superscript>Cs, <Superscript>226</Superscript>Ra,and <Superscript>238</Superscript>U

The concentrations and distribution of ¹³⁷Cs in alluvial soils (Fluvisols) of the upper and middle reaches of the Markha River in the northwest of Yakutia and ²²⁶Ra and ²³⁸U in alluvial soils within the El’kon uranium ore deposit in the south of Yakutia have been studied. It is shown that the migration of radiocesium in the permafrost-affected soils of Yakutia owing to alluviation processes extends to more than 600 km from the source of the radioactive contamination. The migration of ¹³⁷Cs with water flows is accompanied by its deposition in the buried horizons of alluvial soils during extremely high floods caused by ice jams. In the technogenic landscapes of southern Yakutia, active water migration of ²³⁸U and ²²⁶Ra from radioactive dump rocks. The leaching of ²³⁸U with surface waters from the rocks is more intense than the leaching of ²²⁶Ra. The vertical distribution patterns of ²³⁸U and ²²⁶Ra in the profiles of alluvial soils are complex. Uranium tends to accumulate in the surface humus horizon and in the buried soil horizons, whereas radium does not display any definite regularities of its distribution in the soil profiles. At present, the migration of ²³⁸U and ²²⁶Ra with river water and their accumulation in the alluvial soils extend to about 30 km from the source.     

Tracing Rare Earth Element Sources in <Emphasis Type="Italic">Ucides cordatus</Emphasis> Crabs by Means of <Superscript>147</Superscript>Sm/<Superscript>144</Superscript>Nd and <Superscript>143</Superscript>Nd/<Superscript>144</Superscript>Nd Isotopic Systematics

This study tested for the first time ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd ratios as tracers of rare earth element (REE) sources in semi-terrestrial organisms from a subtropical estuary affected by fertilizer industry activities. The isotopic composition of claw muscles and shells of male crabs (Ucides cordatus) were obtained by thermal ionization mass spectrometry, and provided contrasting signatures incorporated from the physical components by the biota. Our findings showed that crab shells had isotopic compositions similar to seawater, while the claw muscles incorporated the isotopic signature of sediments contaminated by fertilizer. The isotopic ratios (¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd) proved that the anthropogenic source is transferring contaminants to the crabs, emerging as a reliable tool to diagnose REE pathway and source to the biota in impacted environments.     

In situ mineral <Superscript>15</Superscript>N dynamics and fate of added <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript> in hoop pine plantation and adjacent native forest in subtropical Australia

Background, aim, and scope  Hoop pine (Araucaria cunninghamii) is a nitrogen (N) demanding indigenous Australia softwood species with plantations in Southeast Queensland, Australia. Soil fertility has declined with increasing rotations and comparison study of N cycling between hoop pine plantations, and adjacent native forest (NF) is required to develop effective forest management for enhancing sustainable forest production and promoting environmental benefits. Field in situ mineral ¹⁵N transformations in these two forest ecosystems have not been studied. Hence, the present study was to compare the differences in soil nutrients, N transformations, ¹⁵N fluxes, and fate between the hoop pine plantation and the adjacent native forest. Materials and methods  The study sites were in Yarraman State Forest (26°52′ S, 151°51′ E), Southeastern Queensland, Australia. The in situ core incubation method was used in the field experiments. Mineral N was determined using a LACHAT Quickchem Automated Ion Analyzer. ¹⁵N were performed using an isotope ratio mass spectrometer with a Eurovector elemental analyzer. All statistical tests were carried out by the SPSS 11.0 for Windows statistical software package. Results  Soil total C and N were significantly higher in the NF than in the 53-year-old hoop pine plantation. Concentrations of NO₃ ^– were significantly higher in the NF soil than in the plantation soil. The plantation soil had significantly higher ¹⁵N and ¹³C natural abundances than the NF soil. The NF soil had significantly lower C/N ratios than the plantation soil. NO₃ ^––N was dominated in mineral N pools in both NF and plantation soils, accounting for 91.6% and 70.3% of the total mineral N pools, respectively. Rates of net nitrification and net N mineralization were, respectively, four and three times higher in the NF soil than in the plantation soil. The ¹⁵NO₃ ^––N and mineral ¹⁵N were significantly higher in the NF soil than in the plantation soil. Significant difference in ¹⁵NH₄ ⁺–N was found in the NF soil before and after the incubation. Discussion  The NF soil had significantly higher NO₃ ^––N, mineral N, total N and C but lower δ¹⁵N, δ¹³C, and C/N ratios than the plantation soil. Moreover, the rates of soil net N mineralization and nitrification were significantly higher, but ammonification rate was lower in the NF than in the plantation. The NF soil had many more dynamic N transformations than the plantation soil due to the combination of multiple species and layers and, thus, stimulation of microbial activity and alteration of C and N pool sizes in favor of the N transformations by soil microbes. The net rate of N and ¹⁵N transformation demonstrated differences in N dynamic related to the variation in tree species between the two ecosystems. Conclusions  The change of land use and trees species had significant impacts on soil nutrients and N cycling processes. The plantation had larger losses of N than the NF. The NO₃ ^––N and ¹⁵NO₃ ^––N dominated in the mineral N and ¹⁵N pools in both forest ecosystems. Recommendations and perspectives  Native forest soil had strong N dynamic compared with the plantation soil. Composition of multiple tree species with different ecological niches in the plantation could promote the soil ecosystem sustainability. The ¹⁵N isotope dilution technique in the field can be quite useful for studying in situ mineral ¹⁵N transformations and fate to further understand actual N dynamics in natural forest soils.     

Pb<Superscript>2+</Superscript> adsorption on birnessite affected by Zn<Superscript>2+</Superscript> and Mn<Superscript>2+</Superscript> pretreatments

Purpose  

Lead contamination is ubiquitous, and much attention has been paid due to its toxicity. The phyllomanganate birnessite is the most common Mn oxide in soils. The MnO₆ octahedral layers may have significant Mn vacancies in the hexagonal birnessites. Among heavy metal ions, birnessites possess the greatest adsorption affinity and capacity for Pb²⁺. The aim of this study was to understand the relationship between vacant Mn octahedral sites and Pb²⁺ adsorption.     

Agroecological optimums concerning saturation with calcium of soils contaminated by <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr

A close negative correlation between the biological availability of ⁹⁰Sr and ¹³⁷Cs for agricultural crops and the content of exchangeable calcium in soils has been revealed in a field experiment performed for soddy-podzolic loamy sandy soil. The efficiency of soil saturation with exchangeable calcium regarding ⁹⁰Sr discrimination is much higher in soils with a low supply of plants with this nutrient. For the bulk of the studied crops, the minimal biological availability of ⁹⁰Sr is registered at 1200–1400 mg/kg (6.0–7.0 mg-equiv./100 g) of the exchangeable calcium content in the soil and that of ¹³⁷Cs is registered at 1000–1100 mg/kg (5.0–5.5 mg-equiv./100 g). The crop productivity varies significantly depending on the exchangeable calcium content in the soil.     

Contamination of terrestrial ecosystem components with <Superscript>90</Superscript>Sr, <Superscript>137</Superscript>Cs,and <Superscript>226</Superscript>Ra caused by the deterioration of the multibarrier protection of radioactive waste storages

The spatial-temporal features of the radioactive contamination of terrestrial ecosystem components caused by the deterioration of the multibarrier protection of regional radioactive waste storages of the State Research Center of the Russian Federation-Leipunskii Institute of Physics and Power Engineering at the input of radionuclides into the soil and ground water were studied. The composition of the radioactive contamination was determined, and the hydrological and geochemical processes resulting in the formation of large radioactive sources were described. The natural features of the radioactive waste storage areas favoring the entry of ⁹⁰Sr, ¹³⁷Cs, and ²²⁶Ra into the soils and their inclusion in the biological turnover were characterized. The directions of the horizontal migration of ⁹⁰Sr, ¹³⁷Cs, and ²²⁶Ra and the sites of their accumulation within the superaquatic and aquatic landscapes of a near-terrace depression were studied; the factors of the ⁹⁰Sr accumulation in plants and cockles were calculated. The results of the studies expand the theoretical concepts of the mechanisms, processes, and factors controlling the behavior of radionuclides at the deterioration of the multibarrier protection of radioactive waste storages. The presented experimental data can be used for solving practical problems related to environmental protection in the areas of industrial nuclear complexes.     

The exchangeable fraction of selectively sorbed <Superscript>137</Superscript>Cs in soils and natural sorbents as a function of the K<Superscript>+</Superscript> and NH<Stack><Subscript>4</Subscript><Superscript>+</Superscript></Stack> concentrations

The exchangeable portion of the selectively sorbed ¹³⁷Cs extractable by a 1 M ammonium acetate solution (α _Ex ) for soils, illite, bentonite, and tripolite was found to increase with the increasing concentration of the competitive cation M⁺ (K⁺ or NH₄⁺) and can be approximated by a logarithmic relationship. For clinoptilolite, the values of α _Ex did not depend on the concentration of M⁺. The expression 1 − α _Ex (C _M=n )/α _Ex (C _M = 16) as a function of the M⁺ concentration (where α _Ex (C _M=n ) is the α _Ex value at the competitive cation concentration equal to 16 mmol/dm³) was proposed to compare the dependence of α _Ex on the concentration of K⁺ or NH₄⁺in different sorbents. For soils and illite, these dependences almost coincided, which indicated that the selective sorption of ¹³⁷Cs in soils is determined by the presence of illite-group minerals.     

Purification and isotopic signatures (<Emphasis Type="Italic">δ</Emphasis><Superscript>13</Superscript>C, <Emphasis Type="Italic">δ</Emphasis><Superscript>15</Superscript>N, Δ<Superscript>14</Superscript>C) of soil extracellular DNA

The aim of this work was to obtain pure extracellular DNA molecules so as to estimate their longevity in soil by an isotope-based approach. Extracellular DNA molecules were extracted from all horizons of a forest soil and purified by the procedure of Davis (Purification and precipitation of genomic DNA with phenol–chloroform and ethanol. In: Davis LG, Dibner MD, Battey JF (eds) Basic methods in molecular biology. Appleton & Lange, Norwalk, 16–22, 1986) without (DNA1) or with (DNA2) a successive treatment with binding resins followed by elution. The two differently purified DNA samples were compared for their A₂₆₀/A₂₈₀ ratio, polymerase chain reaction (PCR) amplification and natural abundance of stable (¹³C and ¹⁵N) and radioactive (¹⁴C) isotopes. The purity index and the PCR amplification did not differentiate the efficiency of the two purification procedures. The isotopic signature of DNA was more sensitive and was strongly affected by the purification procedures. The isotopic measurements showed that the major contaminant of extracellular DNA1 was the soil organic matter (SOM), even if it is not possible to exclude that the similar δ ¹³C, δ ¹⁵N and Δ¹⁴C values of DNA and SOM could be due to the use of SOM-deriving C and N atoms for the microbial synthesis of DNA. For extracellular DNA2, extremely low values of Δ¹⁴C were obtained, and this was ascribed to the presence of fossil fuel-derived substances used during the purification, although in amounts not revealed by gas chromatography-mass spectrometry analysis. The fact that it is not possible to obtain contaminant-free DNA molecules and the potential use of soil native organic compounds during the microbial synthesis of DNA make it not achievable to estimate the age of soil extracellular DNA by radiocarbon dating.     

Role of plants in the spatial differentiation of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr statuses on the aggregate level

The increased concentration of an element in plant biomass compared to the soil mass is an essential condition for the differentiated spatial distribution and status of the element on the aggregate level. Two forms of this differentiation have been revealed for ¹³⁷Cs and ⁹⁰Sr. Transfer of ¹³⁷Cs from plant roots and concentration on the surface of soil aggregates have been established experimentally. Indirect data also point to the potential localization of ¹³⁷Cs on the surface of intraaggregate pores. The effect of radionuclide concentrating on the outer and inner surfaces of aggregates is due to the rapid and strong fixation of cesium microamounts by mineral soil components. ¹³⁷Cs from the surface of aggregates is more available for the repeated uptake by plant roots than from the intraped mass. The distortion of this spatial differentiation mainly occurs during the reaggregation of soil mass, which in turn decreases the availability of the radionuclide to plants. For ⁹⁰Sr, its elevated concentration in the form of organic residues has been revealed in the inter- and intraaggregate pore space. However, due to the high diffusion rate, ⁹⁰Sr is relatively rapidly (during several months under pot experimental conditions) redistributed throughout the entire volume of soil aggregates and its major part gradually passes into the phase of humic compounds, to which the radionuclide is bound by exchange sorption. The high level of the next root uptake (higher than for ¹³⁷Cs by one to two orders of magnitude) favors the permanent renewal of loci with increased ⁹⁰Sr concentrations in the inter- and intraaggregate pore space in the form of plant residues.     

A liquid chromatographic/mass spectrometric method to evaluate <Superscript>13</Superscript>C and <Superscript>15</Superscript>N incorporation into soil amino acids

Purpose  

Amino acids are highly associated with biogeochemical cycling and represent an important potential source and sink of carbon (C) and nitrogen (N) in terrestrial ecosystems. Tracing the isotope dynamics of amino acids can improve the understanding of the origin and transformation of amino acids in soil matrix at process-levels; hence, the liquid chromatographic/mass spectrometric (LC/MS) method to evaluate ¹³C or ¹⁵N enrichment in amino acids is necessary to be established.     

Use of a double radioactive label (<Superscript>54</Superscript>Mn and <Superscript>14</Superscript>C) in the study of organomineral manganese compounds

A fundamentally new approach to the study of natural organomineral materials was proposed. A procedure was developed for using a double carbon-metal label in the systemic study of organomineral complexes of soils and conjugated landscape objects. A significant effect of water-soluble organic ligands on the migration of manganese in soils was shown. It was found that mineral manganese compounds were transformed into organomineral ones differing in composition, solubility, and stability, and the complex of humus substances in podzolic soil was a peculiar matrix on which a complex system of organomineral compounds was developed. The input mechanism of organomineral complexes with different molecular weights (MWs) into plants was studied. Pot experiments using a root exudates sampling procedure and a double radioactive label (⁵⁴Mn and ¹⁴C) showed that the organomineral complexes of Mn with the fulvic acid fraction (MW > 10000) came intact to corn roots. The fulvic acid fraction (MW 380) and manganese ions independently passed from the soil solution into the young plants.     

Short-term uptake of <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript> into soil microbes and seedlings of pine,spruce and birch in potted soils

Short-term competition between soil microbes and seedlings of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth) for N was assessed in a pot study using (¹⁵NH₄)₂SO₄ as a tracer. Seedlings were grown in organic and mineral soil, collected from a podsol soil; 3.18 mg (¹⁵NH₄)₂SO₄ per pot were injected into the soil, corresponding to 4 µg ¹⁵N g^-1 d.m. (dry matter) mineral soil and 17 µg ¹⁵N g^-1 d.m. organic soil. The amounts of N and ¹⁵N in the seedlings and in microbial biomass derived from fumigation-extraction were measured 48 h after addition of ¹⁵N. In the mineral soil, 19–30% of the added ¹⁵N was found in the plants and 14–20% in the microbial biomass. There were no statistically significant differences between the tree species. In the organic soil, 74% of the added ¹⁵N was recovered in the microbial biomass in birch soil, compared to 26% and 17% in pine and spruce soils, respectively. Correspondingly, about 70% of the ¹⁵N was recovered in pine and spruce seedlings, and only 23% in birch seedlings. In conclusion, plants generally competed more successfully for added ¹⁵NH₄ ⁺ than soil microbes did. An exception was birch growing in organic soil, where the greater amount of available C from birch root exudates perhaps enabled micro-organisms to utilise more N.     

Some indices of biological cycle of <Superscript>137</Superscript>Cs and <Superscript>39</Superscript>K in forest ecosystems of Bryansk woodland in the remote period after chernobyl fallouts

The features of the biological cycle of ¹³⁷Cs and ³⁹K in the remote period after Chernobyl fallouts are considered on the example of forest ecosystems of Bryansk woodland. It is demonstrated that the maximum amount of ¹³⁷Cs in the total phytomass is concentrated in wood, the minimum amount of ¹³⁷Cs, in the external bark layers; for the annual production, in assimilating organs and the external bark layers, respectively. The distribution of ³⁹K in the total phytomass and the annual production is almost identical to that of ¹³⁷Cs. The arrival of ¹³⁷Cs to the soil with litter in pine and birch forests has recently been equal approximately to 50% of the capacity of the biological cycle. It mostly arrives with the assimilating organs (needles and leaves). In pine forests the return of ³⁹K into the soil with litter is closest to that observed for ¹³⁷Cs.     

Dynamics of Chernobyl <Superscript>137</Superscript>Cs contamination fields at long distances

Structural changes in the ¹³⁷Cs contamination fields in natural and agroecosystems of the northern forest steppe (the remote zone of the Chernobyl accident) were studied. It was shown that the lateral and vertical distribution of ¹³⁷Cs in soils of different biogeocenoses depends on the features of functioning biogeocenoses and the spatial variation of the initial fallout. The effect of biogeocenosis on the spatial variation of the contaminant distribution increases with time. At present, the variation of primary distribution in soils of agrocenoses is changing. The soils of forest biogeocenoses have retained the features of primary distribution, particularly in the upper 0-to 5-cm sublitter layer. The ¹³⁷Cs penetration depth is greatest in the soils of layland and functioning agrocenosis and least in the soils of forest biogeocenoses.     

Specific <Superscript>137</Superscript>Cs-sorption capacity parameters of soils and mineral sorbents

The selective sorption of cesium by some soils, minerals, and natural mineral sorbents was studied using new methodological and experimental approaches. It was found that the total capacity of two types of highly selective sorption sites significantly differing (by several orders of magnitude) in the selectivity coefficients of Cs-K ion exchange makes up 0.5–6% of the total capacity of the ion exchanger. The values of the radiocesium interception potential were determined for the studied soils and minerals.     

Net and gross mineral N production rates at three levels of forest canopy retention: evidence that NH<Subscript>4</Subscript><Superscript>+</Superscript> and NO<Subscript>3</Subscript><Superscript>−</Superscript> dynamics are uncoupled

Alternative silvicultural systems were introduced in Coastal Western Hemlock forests of British Columbia, Canada, to reduce disturbance incurred by conventional clear-cutting and to maintain the forest influence on soil nutrient cycling. As we hypothesized, in situ pools and net mineralization of NH₄ ⁺ were lower under no and low disturbance (old-growth forest and shelterwood) compared to clear-cuts (high disturbance); in situ pools and net production of NO₃ ⁻ were very low across all treatments. Gross transformation rates of NH₄ ⁺ increased while those of NO₃ ⁻ decreased with increasing disturbance, suggesting that these processes were uncoupled. We conclude that shelterwood harvesting reduces the impact on forest floor NH₄ ⁺ cycling compared to clear-cutting, and that neither low nor high disturbance intensity results in substantial NO₃ ⁻ accumulation, as what occasionally occurs in other ecosystems. We hypothesize that the uncoupling of NH₄ ⁺ and NO₃ ⁻ dynamics may be due to the predominance of heterotrophic nitrification by lignin-degrading fungi that oxidize organic N rather than NH₄ ⁺–N, and whose activities are suppressed at high NH₄ ⁺ concentrations.     

Structure of humic acids in zonal soils from <Superscript>13</Superscript>C NMR data

The structure of humic acids (HAs) in zonal soil types—soddy-podzolic soils (two samples), gray forest soil (one sample), and chernozems (two samples)—was quantitatively studied by ¹³C NMR spectros-copy. In the series considered, the content of unsubstituted carbon in the aromatic fragments of HAs increased, and the fraction of unsubstituted aliphatic structures decreased. HAs of soddy-podzolic soils were found to be enriched with carbohydrate fragments compared to HAs of chernozems and gray forest soil. The carbon skeleton of HAs from typical rich chernozem contained significantly more aliphatic and carbohydrate fragments compared to typical chernozem, which probably reflected the lower degree of HA transformation in rich chernozem.