Mikhail Ivanov

Sulfate Reduction Potential in Sediments in the Norilsk Mining Area, Northern Siberia

Abstract The purpose of this study was to characterize the distribution and activity of sulfate-reducing bacteria in tailings and sediments impacted by effluents from mining and smelting operations in the Norilsk area in northern Siberia. The Norilsk mining complex involves three smelter operations, a hydrometallurgical plant, and extensive tailings areas located in the permafrost zone. Sulfate reduction rates measured with a 35SO4 2− tracer technique under various in-situ conditions ranged from 0.05 to 30 nmol S cm−3 day−1. Acetate and glucose addition greatly stimulated sulfate reduction, whereas lactate had less effect. The most pronounced stimulation of sulfate reduction (6.5-fold) was observed with phosphate amendment. Most-probable-number (MPN) counts of sulfate-reducing bacteria in media with glucose, ethanol, lactate, and acetate as electron donors were generally highest at around 107 cells ml−1. The actual MPN counts varied with the sample, electron donor, and incubation conditions (pH 7.2 vs. pH 3.5; 28°C vs. 4°C). Enrichment cultures of sulfate-reducing bacteria were established from a sample that showed the highest rate of sulfate reduction. After multiple serial transfers, the dominant sulfate-reducers were identified by fluorescence in situ hybridization using genus and group-specific 16S rRNA-targeted oligonucleotide probes. Desulfobulbus spp. prevailed in ethanol and lactate enrichments and the Desulfosarcina-Desulfococcus group dominated in acetate and benzoate enrichments. Psychrophilic Desulfotalea-Desulfofustis and moderately psychrophilic Desulforhopalus spp. were identified in enrichments incubated at 4°C, but they were also found in mesophilic enrichments.

Microbiology of formation waters from the deep repository of liquid radioactive wastes Severnyi

The presence, diversity, and geochemical activity of microorganisms in the Severnyi repository of liquid radioactive wastes were studied. Cultivable anaerobic denitrifiers, fermenters, sulfate-reducers, and methanogens were found in water samples from a depth of 162-405 m below sea level. Subsurface microorganisms produced methane from [2-(14)C]acetate and [(14)C]CO(2), formed hydrogen sulfide from Na(2) (35)SO(4), and reduced nitrate to dinitrogen in medium with acetate. The cell numbers of all studied groups of microorganisms and rates of anaerobic processes were higher in the zone of dispersion of radioactive wastes. Microbial communities present in the repository were able to utilise a wide range of organic and inorganic compounds and components of waste (acetate, nitrate, and sulfate) both aerobically and anaerobically. Bacterial production of gases may result in a local increase of the pressure in the repository and consequent discharge of wastes onto the surface. Microorganisms can indirectly decrease the mobility of radionuclides due to consumption of oxygen and production of sulfide, which favours deposition of metals. These results show the necessity of long-term microbiological and radiochemical monitoring of the repository.

Complex rotation in two-dimensional mesh calculations for quantum systems in uniform electric fields

A computational method for calculations of quasi-steady states of quantum systems is developed on the basis of a complex coordinate transformation and multi-dimensional mesh solution of Schrodinger equations. The two-dimensional implementation of the method is applied to the hydrogen atom, a hydrogen-like system with a screened Coulomb interaction potential and the hydrogen molecular ion H2+ in external electric and parallel electric and magnetic fields. Detailed calculations are carried out for the ground state of the hydrogen atom in parallel electric and magnetic fields. All the systems are considered in cylindrical coordinates (ρ,z). The complex coordinate transformation is applied to the coordinate z, both in the form of a classical complex rotation (atom-like systems) and in the form of a smooth exterior complex scaling. The boundaries of applicability of these methods are studied. In comparison with the boundary-condition method, developed previously, the complex coordinate transformation approach allows one to obtain more precise and stable results for the strong electric field regimes with |ImE|≈|ReE|.

FRACTIONATION OF STABLE ISOTOPES OF CARBON AND SULFUR DURING BIOLOGICAL PROCESSES IN THE BLACK SEA

The paper presents literature and authors’ own data on the isotopic composition of sulfur and carbon compounds in the water column and bottom sediments of the Black Sea. The fractionation factors of stable isotopes have been compared with the rates of sulfate reduction, photoand chemosynthesis, methanogenesis, and anaerobic oxidation of methane. In the water column and bottom sediments, the inverse relationship between 32S and 34S fractionation and sulfate reduction rate (measured in situ with the use of NaSO4) was observed. The isotopic composition of hydrogen sulfide in the water column (δ34S = -40.0‰) differs greatly from δ34S of the reduced sulfur compounds of bottom sediments; this confirms the hypothesis that H2S forms in the water column itself. Seasonal dynamics of δ13C of phytoplankton-produced organic carbon was revealed; it was demonstrated that some changes in the isotopic composition of POC occur in the chemocline as a result of the photoand chemosynthetic activity of microorganisms. The data on the isotopic composition of the three main sources of the Black Sea methane are presented. δ13C of the biogenic methane produced in bottom sediments reaches -67.6‰; δ13C of methane from cold methane seeps reaches -65.8‰; δ13C of methane from mud volcanoes ranges from -30.0‰ to -75.0‰. The large-scale process of microbial oxidation of methane results in the production of methane-derived carbonates (δ13C values range from -27.2‰ to -45.6‰). Using the data on the rates of methanogenesis and anaerobic oxidation of methane as well as the data on the isotopic composition of methane, the balance between the methane flux into the water column and its oxidation has been calculated. It was found that the annual methane production and oxidation in the anoxic zone of the Black Sea are 62.9 and 77.7·1010 mol m−2, respectively. About 80% of methane production is concentrated in the water column and 20% of methane is produced in mud volcanoes and cold seep areas (10% each).

Systems with non-separable spatial variables in strong electric fields: mesh computational method

A mesh computational method for calculations of complex energy eigenvalues of quantum systems described by Schrodinger equations with non-separable spatial variables is developed. Complex eigenvalues of the energy are calculated for the ground state of the hydrogen atom and for a hydrogen-like system with a screened Coulomb interaction potential in strong electric fields by means of solving Schrodinger equations in cylindrical coordinates with the outgoing wave boundary condition. The method is also applied to the simplest diatomic molecule . Complex eigenvalues of the energy E are calculated for the ground and two excited states of a molecular ion in strong electric fields F directed along the molecular axis. The real parts of the energy and half-widths of a level are obtained as functions of the internuclear distance R. The equilibrium internuclear distance for the ground state of is obtained as a function of F from F = 0 up to when a minimum on potential curve E(R) disappears. These results are in good agreement with experimental data on in intense laser beam fields.