Андрей Сергеевич Торопов

Meromictic lakes are natural models for studying early diagenesis in the water column. Based on high‑resolution vertical profiles of trace elements (including redox‑sensitive metals and conservative tracers), five dissolved organic matter (DOM) components obtained by PARAFAC, and optical absorption descriptors, we show that the monimolimnion of Lake Mogilnoye (Barents Sea) is internally differentiated into three sublayers. Conservative tracers (Br, Sr, and Rb) exhibit a stepwise increase at 12–13 m, reaching 97% of seawater values for Br, indicating a deep intrusion of seawater through the base of the filtering dam. This intrusion is independently confirmed by a unique DOM fluorescence signature at 13 m: the microbial humic‑like component (K2) vanishes while protein‑like metabolites (K4) peak. Optical indices (SUVA₂₅₄, E₂/E₃, S_275–295) point to low‑aromatic, low‑molecular‑weight autochthonous DOM throughout the water column with a slight humification increase in the sulfidic zone. Correlation and PCA analyses reveal a tight coupling of the microbial humic‑like K2 component with Mn and Fe reduction (r ≈ 0.8), whereas the biogenic humic‑like K5 correlates with dissolved organic carbon and nutrients (r > 0.9), reflecting diagenetic release from sediments. Principal component analysis independently confirms the subdivision of the monimolimnion into heterogeneous layers and the presence of a deep seawater inflow. A two‑tier model of seawater supply to the meromictic basin is proposed. The upper flow consists of a mixture of seawater and lake water seeping through the dam body, distributed at depths of 3–5 m, but its low discharge prevents the formation of a distinct layer. At the base of the dam, a permanent deep inflow intrudes into the monimolimnion at the density‑equilibrium horizon (12–13 m). As a result, the classical four‑layer structure of the lake is redefined as a seven‑layer one, in which the monimolimnion represents a dynamic system of advective and diagenetic sublayers. This refined stratification of the anoxic zone has direct implications for paleoreconstructions based on metal and organic markers and for correct calculations of element accumulation and redistribution in heterogeneous layers.

Submarine groundwater discharge (SGD) is an important pathway of dissolved matter transport to coastal ecosystems, yet its identification in methane seep environments remains challenging because chemical signals are modified by sedimentary biogeochemical processes. This study evaluated hydrochemical tracers of SGD in methane seep sites, bacterial mat areas, and background sediments along the southern coast of Crimea (Black Sea). The studied settings exhibited distinct water chemical characteristics. Chloride concentrations decreased from 10.6 to 11.2 g L⁻¹ in background waters, to 8.7–9.3 g L⁻¹ in bacterial mat pore waters and to 7.7 g L⁻¹ in sediment–water interface waters, indicating the presence of a low-salinity water component. Dissolved silica increased by approximately one order of magnitude relative to background values at methane-associated sites. Methane concentrations ranged from 0.025 to 1058 μM, with the highest values occurring in bacterial mat areas. These zones were further characterized by sulfate depletion (down to 0.9 g L⁻¹), elevated normalized alkalinity, ammonium concentrations reaching 8000 μg L⁻¹, high sulfide contents, and low dissolved Fe concentrations consistent with iron sulfide precipitation. The results demonstrate that no single hydrochemical parameter is sufficient to identify SGD in methane-affected coastal sediments. Instead, the combined use of conservative tracers (Cl⁻ and DSi) and reactive constituents (SO₄²⁻, alkalinity, NH₄⁺, HS⁻, TDFe, and Mn²⁺) provides a robust hydrochemical framework for recognizing groundwater influence and evaluating associated biogeochemical transformations.

Liquid radioactive waste injected into deep geologic horizons poses a long-term hazard for the environment. Uranium-238, a major component of the nuclear fuel cycle and radioactive waste, has long half-life, high mobility, high toxicity, and complex chemical behavior. Sorption is a crucial process for the radionuclides retention in geosphere and isolation of the waste. In the present work, sorption of U(VI) on the sediments from Severny deep disposal site (Krasnoyarsk, Russia) and reference minerals (quartz and clay) was studied in laboratory-simulated low-level alkaline liquid radioactive waste solutions. U sorption behavior is strongly pH-dependent. It was determined that in the wide pH range U uptake is mostly controlled by quartz in the specific conditions. As uranyl-carbonate complexes play important role in the alkaline medium, carbonate concentration affects the U retention. Contribution of the aquifer constituent minerals was estimated using autoradiography method. Surface complexation reactions for U(VI) sorption on the aquifer sediments were modelled.

The chemical composition of rivers is determined by catchment basin features, climatic conditions and anthropogenic influence. This study is devoted to the identification of the main natural and anthropogenic factors and patterns that determine the formation of the chemical composition of the Mzymta River and its tributaries in its middle and lower reaches. Data on hydrochemical parameters, content of biogenic compounds and trace elements, including heavy metals of the Mzymta River and its tributaries from the confluence of the Pslukh River with the Mzymta River to the confluence with the Black Sea, are presented. The result revealed that the lower reaches were characterised by higher concentrations of all nutrient compounds than the middle reaches. A group of trace elements (V, Al, Ti, Mn, Fe, Co, Cu, Pb and REE) whose concentrations have unidirectional changes as the waters move downstream has been identified. The waters of the Pslukh River and the Mzymta River in the area of its confluence with the Pslukh and Kepsha Rivers, as well as in the zone of influence of sewage and its estuary, are significantly enriched in trace elements relative to the median chemical constituents of river waters. In general, changes in the chemical composition of the Mzymta River are influenced by two factors, natural and anthropogenic, namely due to the different geological conditions of its main tributaries, the regime and gradient of the river in its middle and lower reaches and the impact of construction works in the river channels and wastewater discharge.

This work discusses the synthesis and structure of Mg _0.5 NpO ₂ CO ₃ · x H ₂ O solid phase, its transformation to KNpO ₂ CO ₃ and solubility of Np( v ) double carbonates with magnesium and potassium.

Radiostrontium ( ⁹⁰ Sr), a highly mobile radionuclide of environmental concern, can be strongly retained by soils via interactions with organic and mineral components.

Relevance. The need to identify new sources of industrial production of strategic metals that are critical for modern technologies. Aim. To study the geological and geochemical conditions that led to the formation of anomalous scandium concentrations in the coals of the western part of the West Siberian Basin. Methods. A range of modern analytical methods, including ICP-MS, INAA and scanning electron microscopy; statistical methods; geological and geochemical analysis of the migration and concentration of elements. Results and conclusions. In the western part of the West Siberian Basin, within the Shaim oil- and gas-bearing region, the authors have discovered the coals containing anomalous amounts of scandium, with no analogues in world practice. The maximum Sc content in coal is 83.6 ppm and in coal ash is 0.4%. In the future, this is a new industrial and genetic type of scandium deposits. Alongside Sc, coal ashes are also anomalously enriched in a group of siderophilic and lithophilic metals, including Zr, Ge, Nb, Y, and yttrium lanthanides. The forms of scandium occurrence in coal and the character of its distribution in coal seams point to a hydrogenic mechanism of anomaly formation. Studies shown that uniquely scandium-bearing coals are formed in areas with specific basement rock compositions, characterized by a significant proportion of basite-hyperbasite rocks. Weathering of these rocks leads to the formation of coal-bearing rocks enriched in scandium. During diagenesis and early catagenesis, soda water were formed in coal-bearing strata, favouring the transfer of scandium from terrigenous sediments and buried weathering crusts into solution, as well as its redistribution into coal seams, resulting in uniquely high scandium concentrations in coal. Based on the size of the studied area, the thickness of scandium-bearing strata, and the average metal content within them, the inferred resources of scandium can be estimated at 200 thousand tons.