The evolution of alkaline, saline ground- and surface waters in the southern Siberian steppes

Groundwaters, river and lake waters have been sampled from the semi-arid Siberian Republic of Khakassia. Despite the relatively sparse data set, from a diversity of hydrological environments, clear salinity-related trends emerge that indicate the main hydrochemical evolutionary processes active in the region. Furthermore, the major ion chemistry of the evolution of groundwater baseflow, via rivers, to terminal saline lake water, can be adequately and simply modelled (using PHREEQCI) by invoking: (i) degassing of CO2 from groundwater as it emerges as baseflow in rivers (rise in pH); (ii) progressive evapoconcentration of waters (parallel accumulation of Cl−, Na+, SO42−, and increase in pH due to common ion effect); and (iii) precipitation of calcite (depletion of Ca from waters, reduced rate of accumulation of alkalinity). Dolomite precipitation is ineffective at constraining Mg accumulation, due to kinetic factors. Silica saturation appears to control dissolved Si in low salinity waters and groundwaters, while sepiolite saturation and precipitation depletes Si from the more saline surface waters. Gypsum and sodium sulphate saturation are only approached in the most saline environments. Halite remains unsaturated in all waters. Sulphate reduction processes are important in the lower part of lakes

Bacteria of the sulfur cycle in the sediments of gold mine tailings, Kuznetsk Basin, Russia

The number and diversity of culturable microorganisms involved in sulfur oxidation and sulfate reduction were investigated in the oxidized sediments of gold mine tailings, Kuznetsk Basin, Russia. The sediments had a low pH (2.4–2.8), high SO42− content (up to 22 g/l), and high concentrations of dissolved metals. The arsenic content was as high as 1.9 g/l. Bacterial phylogeny in microcosms was investigated by amplification of 16S rRNA gene fragments with subsequent denaturing gradient gel electrophoresis (DGGE). Spore-forming bacteria Desulfosporosinus were the only bacteria revealed for which the capacity for dissimilatory sulfate reduction is known. Strain Desulfosporosinus sp. DB was obtained in pure culture, and it was phylogenetically remote from other cultured and uncultured members of the genus. No sulfate-reducing members of the Deltaproteobacteria were detected. The Firmicutes members were the most numerous phylotypes in the microcosms, including a separate cluster with the similarity to Pelotomaculum not exceeding 94%. Acidithiobacillus ferrooxidans and A. caldus were found in anaerobic and microaerophilic microcosms. The number of sulfate reducers did not exceed 9.5 × 102 cells/ml