Oleg Stepanets

Biogeochemistry of the Russian Arctic. Kara Sea: Research results under the SIRRO project, 1995–2003

The Kara Sea is an area uniquely suitable for studying processes in the river-sea system. This is a shallow sea into which two great Siberian rivers, Yenisei and Ob, flow. From 1995 to 2003, the sea was studied by six international expeditions aboard the R/V Akademik Boris Petrov. This publication summarizes the results obtained, within the framework of this project, at the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Various hydrogeochemical parameters, concentrations and isotopic composition of organic and carbonate carbon of the sediments, plankton, particulate organic matter, hydrocarbons, and dissolved CO2 were examined throughout the whole sea area at more than 200 sites. The δ13C varies from −22 and −24‰ where Atlantic waters enter the Kara Sea and in the North-eastern part of the water area to −27‰ in the Yenisei and Ob estuaries. The value of δ13C of the plankton is only weakly correlated with the δ13C of the organic matter from the sediments and is lower by as much as 3–4‰. The paper presents the results obtained from a number of meridional river-sea profiles. It was determined from the relations between the isotopic compositions of plankton and particulate matter that the riverwaters carry material consisting of 70% detrital-humus matter and 30% planktonogenic material in the river part, and the material contained in the off-shore waters consists of 30% terrigenous components, with the contribution of bioproducers amounting to 70%. The carbon isotopic composition of the plankton ranges from −29 to −35‰ in the riverine part, from −28 to −27‰ in the estuaries, and from −27.0 to −25% in the marine part. The relative lightness of the carbon isotopic composition of plankton in Arctic waters is explained by the temperature effect, elevated CO2 concentrations, and long-distance CO2 supply to the sea with riverwaters. The data obtained on the isotopic composition of CO2 in the surface waters of the Kara Sea were used to map the distribution of δ13CCO2. The complex of hydrocarbon gases extracted from the waters included methane, C2–C5, and unsaturated C2=–C4= hydrocarbons, for which variations in the concentrations in the waters were studied along river-estuary-sea profiles. The geochemistry of hydrocarbon gases in surface fresh waters is characterized by comparable concentrations of methane (0.3–5 μl/l) and heavier hydrocarbons, including unsaturated ones. Microbiological methane with δ13C from −105 to −90‰ first occurs in the sediments at depths of 40–200 cm. The sediments practically everywhere display traces of methane oxidation in the form of a shift of the δ13C of methane toward higher values and the occurrence of autogenic carbonate material, including ikaite, enriched in the light isotope. Ikaite (δ13C from −25 to −60‰) was found and examined in several profiles. The redox conditions in the sediments varied from normal in the southern part of the sea to highly oxidized along the Novaya Zemlya Trough. Vertical sections through the sediments of the latter exemplify the complete suppression of the biochemical activity of microorganisms. Our data provide insight into the biogeochemistry of the Kara Sea and make it possible to specify the background values needed for ecological control during the future exploration operations and extraction of hydrocarbons in the Kara Sea.

Geoecological investigations of the Ob-Irtysh River Basin in the Khanty-Mansi Autonomous region: Yugra in 2006–2007

This paper reports the results of the investigations of 2006–2007 on the distribution and migration forms of artificial radionuclides and chemical elements in the Ob-Irtysh water system. Three regions were studied. One of them is a local segment of the Ob River upstream from the confluence with the Irtysh River; its investigation allowed us to estimate the general radioecological state of the aquatic environment affected by the activity of the Tomsk 7 plant. The second region is a local segment of the Irtysh River upstream from its confluence with the Ob River, where the influence of emissions from the NPO Mayak could be estimated. The third region is the water area of the Ob River after its confluence with the Irtysh River. It characterizes the real level of radioactive and chemical contamination of the middle reaches of the Ob River.In order to explain horizontal variations in the distribution of radionuclides in the upper layer of bottom sediments collected at various sites, the results of sorption-kinetic experiments with radioactive tracers in the precipitate-solution system were used. The investigation of the migration forms of trace elements and radionuclides occurring in river water was based on the method of tangential-flow membrane filtration.Chemical element contents were determined in 400-ml water samples. A set of Millipore polysulfone membranes with pore sizes of 8, 1.2, 0.45, 0.1, and 0.025 μm was employed. Taking into account the ultralow specific concentrations of radionuclides in the water, they were analyzed in 300–500 litre samples using Millipore polysulfone membranes with pore sizes of 0.45 μm and 15 kDa. This allowed us to estimate the percentages of cesium-137 and plutonium-239, 240 in the suspended particulate fraction, colloids, and dissolved species.

Radiogeochemical studies of the features of radionuclide distribution at the sites of dumping of radioactive wastes of the Novaya Zemlya Archipelago

This paper presents the results of the studies performed from aboard the R/V Akademik Boris Petrov of the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, in 2002–2004 aimed at surveying the sites of dumping of potentially dangerous objects in Stepovoy, Abrosimov, and Tsivol’ka bays of the Kara Sea. These studies coupled the instrumental facilities of acoustic survey with the visual examination of the objects recovered and also included sampling of the bottom sediments and near-bottom water in the vicinity of the objects and away from them. Subsequently, the samples collected were analyzed using direct gamma spectrometry and radiochemical concentrating selected radionuclides. This allowed us to obtain a statistically reliable database on the specific concentrations of radionuclides (cesium, strontium, cobalt, and plutonium) in the water column and in the bottom sediments. In selected parts of Stepovoy and Abrosimov bays, at the sites where containers were located, local areas with contaminated bottom sediments were registered in the immediate vicinity of the objects, in which significant concentrations of Cs-137 were detected. We also carried out experiments with the samples of the collected bottom sediments on the determination of the kinetic parameters of sorption in the sediment-solution system using the method of radioactive indicators. Taking into account the hydrological conditions, the results obtained allow one to explain particular features of radioactivity distribution in selected aquatic areas. Based on a comparison between the results of the studies performed in 1992–1994 and 2002–2004, we estimated the dynamics of the changes in the mean level of specific concentrations of radionuclides in the regions of the location of sunken objects in shallow-water bays of the Novaya Zemlya Archipelago. The registration of elevated concentrations of corrosive elements in the surface layers of the bottom sediments in these zones suggests a necessity of a multidisciplinary study consisting of regular repeated measurements at reference points in different areas aimed at before-the-fact prevention of possible leakages of radioactive substances from the sunken objects, which might result in a significant contamination of the environment.

Ecological and geochemical investigations in the Ob estuary at sites of hydrocarbon exploration drilling

During recent years, the basins of the Kara Sea (Kamennomysskaya, Obskaya, and Chugor’yakhinskaya structures) in the Russian Federation have been considered as promising regions for oil and gas exploration and, simultaneously, as possible paths of relatively cheap pipeline and tanker transportation of hydrocarbons projected for recovery. On the other hand, exploration operations, recovery, and transportation of gas pose a considerable risk of accidents and environmental pollution, which causes a justified concern about the future state of the ecological system of the Gulf of Ob and the adjoining parts of the Kara Sea. Therefore, regular combined environmental investigations (monitoring) are the most important factor for estimating the current state and forecasting the dynamics of the development of estuary systems. The program of investigations (schedule, station network, and measured parameters) is standardized in accordance with the international practice of such work and accounts for the experience of monitoring studies of Russian and foreign researchers. Two measurement sessions were performed during ecological investigations in the region of exploration drilling: at the beginning at final stage of drilling operations and borehole testing; in addition, natural parameters were determined in various parts of the Ob estuary before the beginning of investigations. Hydrophysical and hydrochemical characteristics of the water medium were determined and bottom sediments and water were analyzed for various pollutants (petroleum products, heavy metals, and radionuclides). The forms of heavy-metal occurrence in river and sea waters were determined by the method of continuous multistep filtration, which is based on water component fractionation on membrane filters of various pore sizes. These investigations revealed environmental pollution by chemical substances during the initial stage of drilling operations, when remains of fuels, oils, and solutions could be spilled, and part of the chemical pollutants could enter the environment. Owing to horizontal and vertical turbulent diffusion, wave mixing, and the effect of the general direction of currents in the Ob estuary from south to north, areas are formed with elevated concentrations of the analyzed elements and compounds. However, the concentration levels of chemical pollutants are practically no higher than the maximum admissible concentrations, and their substantial dissipation to the average regional background contents can be expected in the near future. Our investigations allowed us to determine in detail the parameters of anthropogenic pollution in the regions affected by hydrocarbon exploration drilling in the Obskii and Kamennomysskii prospects in the Gulf of Ob and estimate their influence on the ecological state of the basin of the Ob River and the Kara Sea on the whole.