Geochemical aspects of accumulation of macroelements in the subcolloidal fraction of bottom sediments at the Razdol’naya River-Amur Bay cross-section (the Sea of Japan)

The concentration of Si, Al, Mg, K, Ca, Na, Sr, and Ba in the subcolloidal fraction of sediments at the Razdol’naya River-Amur Bay cross-section is determined using the atomic emission spectroscopy method. Computed is the mean content of studied elements in the soil and river bottom sediments (to the mixing zone). Revealed are river bottom sediments with the high concentration of macroelements corresponding to the zone of mixing of fresh river water and salt sea water. It is demonstrated that the additional accumulation of macroelements (Ca, Na, and Sr) in these sediments is associated with the formation of hydroxides of Fe and Mn and processes of sorption (Mg, Ca, Na, K, Sr, and Ba) on clay minerals (hydromica and smectites).     

Arsenic content in water and bottom sediments in the areas of chemical weapon dumps in the Bornholm basin of the Baltic Sea

Data are considered on samples taken during the 2006–2008 expeditions from the water and bottom sediments in the areas where chemical weapon was dumped in the Bornholm basin. Arsenic concentration is detected with the X-ray fluorescence analysis and inversion voltammetry. Results are under consideration of the enhanced arsenic content and their relation to arsenic-bearing toxic agents. It is pointed out that arsenic contamination is local in character and at present is of no serious hazard to the natural environment.     

Bottom sediments and their role in surface water pollution with mercury (with a special reference to the Northern Dvina River Mouth and the Dvina Bay of the White Sea)

Mercury content in bottom estuarine sediments of the Northern Dvina River and the Dvina Bay of the White Sea is studied. Major regularities of the behavior of the metal and its compounds in bottom sediments of the water area are defined. The role of lithological composition, pH and Eh of the environment, the presence of hydrogen sulfide for determining the content and forms of the mercury presence in the bottom sediments of the region are studied. The sediments related to technogenic formations are specified. The paths and forms of mercury coming from bottom sediments to the near-bottom water level are detected, and the methylmercury content in the sediments is calculated.     

Dynamics of accumulation of heavy metals by subcolloidal fraction of bottom sediments is a result of biochemical processes in the marginal filter of the Razdol’naya River (the Amur Bay, the Sea of Japan)

Determined is the content of Fe, Mn, V, Cr, Cu, Zn, Pb, As, and Sc in the subcolloidal fraction of sediments of the Razdol’naya River marginal filter using the method of atomic emission spectroscopy. Proposed is one of the variants of separating biochemical zones with the increased content of Fe and Mn and other metals in the bottom sediments of the marginal filter: the river zone, the zone of flocculation and formation of Fe and Mn hydroxides, and the zone of biochemical metal accumulation (marine). In the sediments of the river zone and the zone of flocculation and formation of Fe and Mn hydroxides, two bottom areas are identified with the high content of the elements under study that is associated with long-term and seasonal variations of the river runoff.     

Assessment of possible mechanisms of decreasing <Superscript>137</Superscript>Cs concentrations in river waters affected by the Chernobyl NPP accident

The analysis of possible mechanisms of ¹³⁷Cs concentration changes in surface waters was performed in the process of preparation of reliable long-range forecasts of radioactive river contamination after the Chernobyl accident. The following mechanisms were considered: (1) radioactive decay; (2) advective transport with river waters; (3) irreversible sorption; (4) vertical migration deep into bottom sediments due to diffusion; (5) burial in clean bottom sediments. The data published on ¹³⁷Cs monitoring at Dobrush, on the Iput’ River in Belarus were used in the analysis. It is shown that the best agreement with the experimental results is achieved when the second, third, and fifth mechanisms are used in calculations. However, a dominating mechanism still cannot be chosen at the present stage of our study. Most probably, all of these mechanisms act simultaneously.     

Retrospective of radioactive fallout from data on sampled bottom sediments in closed water bodies

A method for identifying past radiation events from dated layers of bottom sediments in stagnant water bodies is described. Results of an experimental study (2005–2006) of the samples of bottom sediments in the pond of the Timiryazev dendropark in Moscow are considered. The sediment layers are dated with ²¹⁰Pb. The same radionuclide is used as a tracer for calculating the rate of sedimentation in the pond, which is estimated at 0.3–0.4 cm/year. The maximum ¹³⁷Cs values are detected in the 0–24 cm column at depths of 7 and 13 cm. The ¹³⁷Cs peak at a depth of 13 cm is dated as 1963, which reflects the maximum global fallout from the atmospheric nuclear weapon tests. A small peak of this radionuclide at 7 cm is dated as 1986. It appears to be attributed to the long-range fallout after the Chernobyl NPP accident. The origin of the ¹³⁷Cs maximum at a depth of 13–14 cm is confirmed by characteristic ratios of radionuclide pairs available in the global fallout in the Moscow region. The ratios of ⁹⁰Sr/¹³⁷Cs = 0.6 and ^239,240Pu/¹³⁷Cs = 0.03 in the 13–14 cm layer are characteristic of the global radioactive fallout from nuclear explosions. In the layers above this maximum, such ratios vary sharply toward the enhanced ¹³⁷Cs content in the fallout.     

Studying the influence of cyclonic activity on suspension distribution in the sea water of the northwestern Black Sea

Processes of roiling, transport-diffusion, and deposition of fine disperse bottom sediments are studied in the northwestern shelf of the Black Sea in different synoptic situations connected with the passage of cyclones. Movement of atmospheric disturbances with velocities of 5 and 15 m/s along three trajectories typical of this region is considered. A nonlinear sigma-coordinate numerical model is used to calculate hydrodynamic and suspension concentration fields. The bottom areas, most sensitive to erosion, and the areas of maximum accumulation of depositions due to their sedimentation are determined. The change in suspension distribution in the surface layer with time is studied.     

Monitoring of polycyclic aromatic hydrocarbons in the Lake Baikal basin in the areas of intensive anthropogenic impact

Presented are the results of studying the content of polycyclic aromatic hydrocarbons and benz(a)pyrene in the lake water, in sewage waters of the enterprise, and in the upper 2-cm layer of bottom sediments in the area of the sewage discharge of Baikal Pulp and Paper Mill (BPPM), in bottom sediments in the north of Lake Baikal in the area of the Baikal-Amur Railroad, and in the channel and delta front of the Selenga River. The results were obtained at Hydrochemical Institute in 1981?C1989. The different content of benz[a]pyrene was determined for the first time in bottom sediments (sands and silts) for the bottom area of polygons in the mentioned regions. An intensive pollution exceeding significantly the normalized parameters for the benz[a]pyrene in bottom sediments is registered in the BPPM area only and its content in other areas does not exceed the background values on the whole.     

Analysis of accumulation factor of cesium 137 in bottom sediments of surface water bodies

The accumulation factor of radionuclides in river and water body bottom sediments K is an integral magnitude and depends on many parameters. With a two-compartment migration model (water-bottom sediments) an analytical relation is established for the conditions of a steady-state process of radioactive transfer for calculating K depending on the known parameters of radionuclide migration in the aquatic environment. With a reference to cesium 137 the calculated factor value is found for silty sediments in rivers and water bodies under characteristic summertime parameters of migration. The numerical analysis showed that the coefficient of radionuclide distribution in the water-suspension system and turbidity influence mostly the K value for cesium 137. For the practical use of this coefficient, a scheme of its correction is suggested depending on turbidity. An example of its practical use for calculating cesium 137 in water is considered. The calculated and measured volumetric activity values are intercompared.     

Role of methane clathrates in past and future climates

Methane clathrates are stable at depths greater than about 200 m in permafrost regions and in ocean sediments at water depths greater than about 250 m, provided bottom waters are sufficiently cold. The thickness of the clathrate stability zone depends on surface temperature and geothermal gradient. Average stability zone thickness is about 400 m in cold regions where average surface temperatures are below freezing, 500 m in ocean sediments, and up to 1,500 m in regions of very cold surface temperature (<-15 °C) or in the deep ocean. The concentration of methane relative to water within the zone of stability determines whether or not clathrate will actually occur. The geologic setting of clathrate occurrences, the isotopic composition of the methane, and the methane to ethane plus propane ratio in both the clathrates and the associated pore fluids indicate that methane in clathrates is produced chiefly by anaerobic bacteria. Methane occurrences and the organic carbon content of sediments are the bases used to estimate the amount of carbon currently stored as clathrates. The estimate of about 11,000 Gt of carbon for ocean sediments, and about 400 Gt for sediments under permafrost regions is in rough accord with an independent estimate by Kvenvolden of 10,000 Gt.The shallowness of the clathrate zone of stability makes clathrates vulnerable to surface disturbances. Warming by ocean flooding of exposed continental shelf, and changes in pressure at depth, caused, for example, by sea-level drop, destabilize clathrates under the ocean, while ice-cap growth stabilizes clathrates under the ice cap. The time scale for thermal destabilization is set by the thermal properties of sediments and is on the order of thousands of years. The time required to fix methane in clathrates as a result of surface cooling is much longer, requiring several tens of thousands of years. The sensitivity of clathrates to surface change, the time scales involved, and the large quantities of carbon stored as clathrate indicate that clathrates may have played a significant role in modifying the composition of the atmosphere during the ice ages. The release of methane and its subsequent oxidation to carbon dioxide may be responsible for the observed swings in atmospheric methane and carbon dioxide concentrations during glacial times. Because methane and carbon dioxide are strong infrared absorbers, the release and trapping of methane by clathrates contribute strong feedback mechanisms to the radiative forcing of climate that results from earth's orbital variations.Gordon J. MacDonald is Vice President and Chief Scientist of The MITRE Corporation, 7525 Colshire Drive, McLean, VA 22102.     

Computing the methane cycle elements in the aquatic ecosystems of the Sea of Azov and the World Ocean based on empirical formulae

Empirical relationships between methane concentration and the rates of its oxidation and emission in the sediment-water-atmosphere system are computed using the experimental data and the data presented in the literature. For the Sea of Azov and the World Ocean the possibility is demonstrated of using the empirically derived formulae to compute the methane cycle elements in aquatic ecosystems. The comparability of methane volumes in the water column and bottom sediments as well as of those oxidized and released from water and sediments computed using these formulae, demonstrates the adequacy of the obtained formulae. It is shown that depending on morphological parameters of reservoirs of aquatic ecosystems and on their volume and area, the ratio of the amounts of methane that is oxidized and released to the atmosphere, changes as well as the rate of its turnover.     

Present-day characteristics and trends of long-term changes in ecological and toxicological conditions of the Tsimlyansk Reservoir

The analysis of ecological and toxicological conditions of the Tsimlyansk Reservoir and of trends of long-term variations of hydrochemical, hydrobiological, and biotesting parameters is carried out on the basis of long-term data of Roshydromet regular observations (1984?C1991) and authors?? studies (1990, 2006?C2007). It is revealed that, according to the complex of chemical parameters, the water pollution level decreased by the end of the period and is relatively low at present, although the pollution is of stable nature and the toxic and carcinogenic compounds are discovered in the water and in bottom sediments. The most dangerous display of the reservoir eutrophication is a ??bloom?? of algae characterized by the prevalence of blue-green algae (Cyanophyta) amounting to 100% of the total biomass in some samples; the species being able to discharge the toxins to the water (Aphanisomenon flos-aquae, Microcystis aeruginosa, Anabaena flos-aquae) often prevail. During biotesting, the samples of water and bottom sediments in a number of cases exerted a toxic effect on the water organisms and, most likely, the toxicity increases with time. Although different parts of the reservoir differ considerably in ecological and toxicological parameters, an ecologically unfavorable situation emerged in the reservoir ecosystem due to the pollution, eutrophication, and toxicophication.     

Influence of intrareservoir and meteorological factors on the rate of oxygen demand by valley reservoir sediments

Analyzed are the spatial and temporal variations of the sediment oxygen demand rate in the Mozhaisk Reservoir. It is demonstrated that this rate in summer depends both on the sediment characteristics and on the biological and meteorological factors. It is revealed that the content of labile organic substances in the silt is of great importance for the oxygen consumption rate (all other factors being equal). The inflow of these substances to the bottom is regulated by the water column stratification depending considerably on weather conditions. Estimated is the contribution of main organic matter consumers in the bottom sediments.     

Prognostic mapping of radioactive contamination fields formed in the past

New data are obtained on cesium 137 contamination after the Chernobyl NPP accident of settlements, agricultural lands, and forest areas in four Russian regions most affected by the accident: the Bryansk, Kaluga, Orel, and Tula regions. The new information was used to qualify the database on radioactive contamination of these areas. The renewed database was used as a basis for compiling maps on the terrain contamination by cesium 137 in 2006 and a series of prognostic maps with a ten-year interval from 2016 to 2056. The assessment of the dynamics of a change in the zonal areas with different levels of contamination by cesium 137 and the time when the patterns of respective contamination levels disappear in these areas is specified.     

Methane concentration in the atmospheric boundary layer from the measurements at north pole-36 and north pole-39 drifting ice stations

Episodic emissions ofmethane with the concentration of4 ppm to the lower atmosphere near the continental slope of the Arctic Ocean are considered. It is revealed that such methane emissions can be associated with the erosion of sediments containing gas hydrates, for example, as a result of the effects of mudflows caused by the instability of slope currents as well as by the geologic activity in the zone of significant depth drops. The high background concentration of methane is registered in the central part of the Arctic Ocean that is probably provoked by biologic activity within sea ice and on its bottom.     

Problems in determining spatial inhomogeneity of <Superscript>137</Superscript>Cs fallout for estimating rates of erosion-accumulative processes

The issues of assessing variability of ¹³⁷Cs fallout of global and Chernobyl origin at reference sites are discussed with a purpose to use this isotope as a tracer for estimating the rates of erosion-accumulative processes. It is shown that local variability of soil contamination by ¹³⁷Cs at reference sites is within 7–20%, which makes it possible to use the isotope as a tracer. When studies are conducted within drainage basins, the available trend of the atmospheric ¹³⁷Cs fallout should be taken into account in assessing the soil and sedimentation redistribution.     

Energy balance of the intertidal zone of Western Hudson bay I: Ice‐free period

Abstract

This study reports on tower measurements from the intertidal zone taken during the ice‐free period between August 1 and September 20, 1985. Sea and air temperatures showed ranges of 8 and 14°C, respectively, and both were colder during onshore than during offshore winds. Onshore winds were associated with a nearly saturated atmosphere whereas offshore ones were quite dry. Surface albedo was twice as great for low tide as for high tide. The ratio net/solar radiation was 13% less at low tide owing to both the larger albedo and the stronger long‐wave radiation loss. Heat fluxes into the bottom sediments were small with net gains in August and net losses in September. During the day, heat storage in the water was large and positive. This occurred even with the tide out, when the ponded water continued to warm. At night the water gave up heat, both for low and high tide, and especially late in the season. The latent heat flux was always positive and was largest by day during low tide and by night during high tide. The sensible heat flux was positive for onshore winds and often negative for offshore winds. Under all wind directions heat storage constituted 60% of net radiation, the latent heat flux 35% and the remainder was proportioned equally between the sensible heat flux and the flux into the bottom sediments.     

A mathematical model of water and sediment flow in open river channels

A one-dimensional mathematical model of water and sediment flow in open channels is proposed based on the forces influencing a water stream and bottom and stream sediments. The equations of water and sediment flow are closed by the equations of continuity of stream, velocity of particle motion in a stream, and the equation of balance of kinetic energy and moving particles: joint calculation of stream hydraulic characteristics and sediment discharge is performed. Hydraulic resistances are retrieved not from the Chezi formula, but based on the balance of forces and kinetic energy. A sediment discharge is calculated from velocities and the number of moving solid particles instead of empirical relationships whose accuracy is usually low. The model is verified against the data of experiments in hydraulic flumes with glass and sand bottom. Comparison with independent data in the glass flume in a wide range of water discharges and bottom inclinations showed a high accuracy of calculation of hydraulic characteristics (relative error is less than 4%). The experimental data showed that the accuracy of sediment discharge calculated by the model exceeds the accuracy of the calculation using traditional empirical formulas.     

乌鲁木齐市环境污染现状分析及防御对策

对乌鲁木齐市环境污染现状作了分析，重点分析大气污染、水环境质量、污染物排放、噪声环境以及其它环境问题，较为综合地反应了乌鲁木齐市环境总体状况，并就污染问题提出防御对策。     

Levels of persistent organic pollutants in the components of the Lake Baikal unique ecosystem

Experimental results are presented of the estimation of pollution levels of Lake Baikal unique ecosystem (air, surface and deep water, soil, bottom sediments, and aquatic biota) with persistent organic pollutants (POPs) which were included to the list of Stockholm Convention (polychlorinated biphenyls, organochlorine pesticides, toxaphene, and polybrominated diphenyl ethers). The ranges of POPs concentration are determined and statistical characteristics (mean and median) over the period of observations are calculated. It is demonstrated that the wide variation range of POPs concentration depends on environmental factors and on the POPs source (local sources or global transport).