G. A. Leonova

Geochemical Characteristics of the Modern State of Salt Lakes in Altai Krai

A complex of analytical methods (atomic absorption spectroscopy AAS, synchrotron radiation X-ray fluorescence SR-XRF, and instrumental neutron activation analysis INAA) were used for analyses of 40 trace elements. In compliance with the conventional biogeochemical methods, enrichment factors EF were calculated for plankton relative to the average concentrations of elements in continental clay (shale) preliminarily normalized to Sc. In order to understand the concentration specifics of trace elements in living organisms inhabiting aquatic ecosystems of variable salt composition and geochemical characteristics, chemical speciation of elements was calculated for the brines of salt lakes by the WATEQ4F and Selektor-S computer programs. The enrichment of plankton in Hg in Lake Bol’shoe Yarovoe is caused not only by the chemistry of the mineralized brine (bittern), as follows from the Hg speciation in it, but also by anthropogenic contamination (Hg-bearing wastes from the Altaikhimprom chemical plants in the town of Yarovoe).

Biogenic Contribution of Minor Elements to Organic Matter of Recent Lacustrine Sapropels (Lake Kirek as Example)

An approximate biogenic contribution of minor elements to sapropel of Lake Kirek in West Siberia is estimated using the “model of direct inheritance” of their composition in plankton by OM of bottom sediments (Yudovich and Ketris, 1990). It is shown that the lifetime accumulation of P, Br, and Zn in copepod zooplankton of Lake Kirek notably affects the concentration of these elements in sapropelic mud (biogenic contribution is approximately 95–53%). The biogenic share of other elements in these sediments is substantially lower: approximately 30% for Sr and Ba; 26–16% for Ca, Pb, Cd, Cu, K, Mg, and Cr; and no more than 5% for As, Co, Fe, Ni, Ti, Y, and Mo.

Anomalous concentrations of zinc and copper in highmoor peat bog, southeast coast of Lake Baikal

When examining the peat deposit discovered in Vydrinaya bog, South Baikal region, the authors encountered anomalous Zn and Cu concentrations for highmoors being up to 600–500 ppm on a dry matter basis in the Early Holocene beds (360–440 cm) formed 11 000–8500 years ago. It has been demonstrated that Zn and Cu are present inside the plant cells of peat moss in the form of authigenic sulfide minerals of micron size. Apart from Zn and Cu, native Ag particles (5–7 um) have been encountered in the peat of the Vydrinaya bog at a depth of 390–410 cm; these particles formed inside the organic matter of the plasma membrane of peat moss containing Ca, Al, S, and Cu. This study suggests probable patterns of the formation of zinc sulfides, copper sulfides, and native silver in peat moss. The results obtained indicate that biogenic mineral formation plays a significant role in this system, which is a very important argument in the discussion on the ore genesis, in which physicochemical processes are normally favored, while the role of living matter is quite frequently disregarded.

Concentration of chemical elements by zooplankton of the White Sea

A technique of net sampling of zooplankton at night in the Kandalaksha and Dvinskii Bays and during the full tide in the Onezhskii Bay of the White Sea allowed us to obtain “clean” samples without considerable admixtures of terrigenous suspension. The absence of elements-indicators of the terrigenous suspension (Al, Ti, and Zr) in the EDX spectra allows concluding that the ash composition of the tested samples is defined by the constitutional elements comprising the organic matter and integument (chitin, shells) of planktonic organisms. A quantitative assessment of the accumulation of a large group of chemical elements (approximately 40) by zooplankton based on a complex of modern physical methods of analysis is presented. The values of the coefficient of the biological accumulation of the elements (Kb) calculated for the organic matter and the enrichment factors (EF) relative to the Clarke concentrations in the shale are in general determined by the mobility of the chemical elements in the aqueous solution, which is confirmed by the calculated chemical speciation of the elements in the inorganic subsystem of the surface waters of Onezhskii Bay.

Investigation into the elemental composition of sapropel from Lake Kirek (West Siberia) by SR XFA technique

The synchrotron radiation X-ray fluorescence analysis (SRXFA) technique was applied for scanning two sapropel cores: 6.2 m (coordinates of boring 56°11′93″ N, 84°23′22″ E) and 3.6 m (56°10′93″ N, 84°22′94″ E), obtained at a depth of 5 and 7 m, respectively, in Lake Kirek (southern part of Tomsk oblast, West Siberia). Based on variations in the content of eight chemical elements in stratified core horizons, the geochemical types of the sapropels and their prevalence were established. In the sediment of the 6.2-m core within the overall boundaries of the Holocene, low-ferric calcareous sapropel dominates, the geochemical characteristic of which is presented by the average values of 13 chemical elements in the strata grouped by the main climatic periods of the Holocene. Organic-ferrous sapropel 90 cm in depth was uncovered in the 3.6-m core in the range 215–305 cm (age of 7-4 ka). For the other core horizons, the deposit is represented by calcareous sapropel, but with higher contents of iron in comparison with the first type. The geochemical differentiation of these two types of sapropels (in 3.6-m core) is characterized by average contents of 31 chemical elements. The consistency of the compositions and concentrations of chemical elements in sapropels in the Holocene section of the deposits is evidence of the identical formation conditions for these types of sapropel.

Transformation of organic matter in the Holocene sediments of Lake Ochki (south Baikal region): Evidence from pyrolysis data

Transformation of organic matter (OM) in Holocene sediments of Lake Ochki (southern coast of Lake Baikal) at the early stages of diagenesis has been studied using pyrolytic methods of Rock Eval (RE-pyrolysis) and pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS). OM has been analyzed in lacustrine sediments and their main producers, phytoplankton and zooplankton. Data on the distribution of hydrocarbon–biomarkers in sediments indicate an uninterrupted influx of terrigenous OM and transformation of OM precipitated by microorganisms. The analysis of molecular composition of pyrolysates makes it possible to assume a sharp change of sedimentation conditions in the upper part of sedimentary sequence (0–60 cm). It is shown that the macromolecular aliphatic kerogen structure begins to form in incoherent sediment at the very early stages of diagenesis.

X-ray fluorescence and electron microscopy study of plankton samples from the Novosibirsk reservoir

Five samples of plankton from the Novosibirsk reservoir are collected and analyzed by X-ray fluorescence. In combination with high sensitive atomic absorption spectroscopy (AAS), inductively coupled plasma mass spectrometry (ICP-MS), and instrumental neutron activation analysis (INAA), quantitative data on the concentrations of 52 chemical elements in plankton are obtained. Scanning electron microscopy is used to analyze the elemental composition of plankton samples from the Novosibirsk reservoir. This enables us to reveal the nature of the possible presence of minerals (of biogenic or terrigenous origin) that increase the ash content in the samples under study. The results of the studies provide an answer to the methodical question of whether the ash content of plankton samples is mostly determined by the presence of terrigenous elements in it or is in general formed by constitutional (biogenic) elements of skeletal and dermal tissues of planktonic organisms.

Geochemistry of Diagenesis of Organogenic Sediments: An Example of Small Lakes in Southern West Siberia and Western Baikal Area

Organogenic sediments (sapropels) in lakes are characterized by a reduced type of diagenesis, during which organic compounds are decomposed, the chemical composition of the pore waters is modified, and authigenic minerals (first of all, pyrite) are formed. Pyrolysis data indicate that organic matter undergoes radical transformatons already in the uppermost sapropel layers, and the composition of this organic matter is principally different from the composition of the organic matter of the its producers. The sapropels contain kerogen, whose macromolecular structure starts to develop during the very early stages of diagenesis, in the horizon of unconsolidated sediment (0–5 cm). The main role in the diagenetic transformations of organic matter in sediments is played by various physiological groups of microorganisms, first of all, heterotrophic, which amonifying, and sulfate-reducing bacteria. SO42− and Fe2+ concentrations in the pore waters of the sediments are determined to decrease (because of bacterial sulfate reduction), while concentrations of reduced Fe and S species (pyrite) in the solid phase of the sediment, conversely, increase. Comparative analysis shows that, unlike sapropels in lakes in the Baikal area, sapropels in southern West Siberia are affected by more active sulfate reduction, which can depend on both the composition of the organic matter and the SO42− concentration in the pore waters.