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The State of Benthic Communities and Water Quality Evaluation in the Cheboksary Reservoir 总被引：1，自引：1，他引：1
Present-day quantitative and qualitative characteristics of the Cheboksary Reservoir have been investigated, and data on the biological diversity of benthic organisms have been compared to those of hydrobiological studies carried out in the region prior to the reservoir construction. The reservoir bottom communities include 75 species and forms of benthos. The reservoir water quality has been evaluated using different methods, including the determination of the degree of morphological structure abnormalities in chironomid larvae, regarded as sublethal indicators of bottom sediment pollution with toxic substances. 相似文献
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Frank Kienast Sebastian Wetterich Svetlana Kuzmina Lutz Schirrmeister Andrei A. Andreev Pavel Tarasov Larisa Nazarova Annette Kossler Larisa Frolova Viktor V. Kunitsky 《Quaternary Science Reviews》2011,30(17-18):2134-2159
Permafrost records, accessible at outcrops along the coast of Oyogos Yar at the Dmitry Laptev Strait, NE-Siberia, provide unique insights into the environmental history of Western Beringia during the Last Interglacial. The remains of terrestrial and freshwater organisms, including plants, coleopterans, chironomids, cladocerans, ostracods and molluscs, have been preserved in the frozen deposits of a shallow paleo-lake and indicate a boreal climate at the present-day arctic mainland coast during the Last Interglacial. Terrestrial beetle and plant remains suggest the former existence of open forest-tundra with larch (Larix dahurica), tree alder (Alnus incana), birch and alder shrubs (Duschekia fruticosa, Betula fruticosa, Betula divaricata, Betula nana), interspersed with patches of steppe and meadows. Consequently, the tree line was shifted to at least 270 km north of its current position. Aquatic organisms, such as chironomids, cladocerans, ostracods, molluscs and hydrophytes, indicate the formation of a shallow lake as the result of thermokarst processes. Steppe plants and beetles suggest low net precipitation. Littoral pioneer plants and chironomids indicate intense lake level fluctuations due to high evaporation. Many of the organisms are thermophilous, indicating a mean air temperature of the warmest month that was greater than 13 °C, which is above the minimum requirements for tree growth. These temperatures are in contrast to the modern values of less than 4 °C in the study area. The terrestrial and freshwater organism remains were found at a coastal exposure that was only 3.5 m above sea level and in a position where they should have been under sea during the Last Interglacial when the global sea level was 6–10 m higher than the current levels. The results suggest that during the last warm stage, the site was inland, and its modern coastal situation is the result of tectonic subsidence. 相似文献
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Nazarova L. B. Razjigaeva N. G. Diekmann B. Grebennikova T. A. Ganzey L. A. Belyanina N. I. Arslanov K. A. Kaistrenko V. M. Gorbunov A. O. Kharlamov A. A. Golovatyuk L. V. Syrykh L. S. Subetto D. A. Lisitsyn A. P. 《Doklady Earth Sciences》2019,486(1):494-497
Doklady Earth Sciences - Results of a paleolimnological investigation of a well-dated lake sediment section from Shikotan Island (Southern Kurils) showed that from ca 8.0 to 5.8 cal ka BP a warm... 相似文献
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Melt inclusions and hosting them highly magnesian olivine from rocks of Kamchatka and the Western Aleutian island arc were analyzed for copper content by LA-ICP-MS to determine the copper partition coefficient in primitive island-arc magmas. Based on measurements of 45 olivine–melt pairs, this coefficient was determined to be 0.028 ± 0.009 (2σ), which is the lowest value among previously published data. Mass-balance calculations of copper in a typical mantle peridotite using obtained partition coefficient indicate that its content in peridotite and primary mantle magmas is mainly determined by mantle sulfide. The Cu partition coefficient was also used to calculate the copper content in parental magmas of volcanoes of the Central Kamchatka Depression. Estimates obtained using copper content in phenocrysts of primitive olivine (Fo > 88 mol %) from these rocks are, on average, 139 ± 58 ppm (2σ), which exceed copper contents in primitive basalts (MgO > 8.5 wt %) of mid-ocean ridges (MORB 93 ± 31 ppm). This suggests the primary enrichment of Central Kamchatka magmas in copper and correlates with their more oxidizing conditions of formation as compared to MORB. 相似文献
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A.E. Self S.J. Brooks H.J.B. Birks L. Nazarova D. Porinchu A. Odland H. Yang V.J. Jones 《Quaternary Science Reviews》2011,30(9-10):1122-1141
The large landmass of northern Russia has the potential to influence global climate through amplification of climate change. Reconstructing climate in this region over millennial timescales is crucial for understanding the processes that affect the global climate system. Chironomids, preserved in lake sediments, have the potential to produce high resolution, low error, quantitative summer air temperature reconstructions. Canonical correspondence analysis of modern surface sediments from high-latitude lakes, located in northern European Russia and central Siberia, suggests that mean July air temperature is the most significant variable explaining chironomid distribution and abundance. This strong relationship enabled the development of a chironomid-based mean July air temperature-inference model based on 81 lakes and 89 taxa which has a rjack2 = 0.92 and RMSEP = 0.89 °C. Comparison of taxon responses to July temperature between this Russian and existing Norwegian data-sets shows that the temperature optima of individual taxa were between 1 and 3 °C higher in the Russian data regardless of modelling technique. Reconstructions based on fossil assemblages from a Russian tundra lake core (VORK5) using a Norwegian chironomid-based inference model provide mean July air temperature estimates that are 1.0–2.7 °C colder than from the 81-lake Russian model and are also lower than the instrumental record from a nearby meteorological station. The Norwegian model also did not reconstruct decadal-scale fluctuations in temperature seen in the instrumental record. These observations suggest that chironomid-based inference models should only be applied to sediment cores which have similar climate regimes to the geographic area of the training set. In addition a 149 lake, 120 taxa chironomid-based continentality inference model was also developed from the modern Norwegian and Russian training sets. A 2-component WA-PLS model was the minimal adequate model with rjack2 = 0.73 and RMSEP = 9.9 using the Gorczynski continentality index. Comparison of reconstructed continentality indices from the tundra lake, VORK5, show close agreement with local instrumental records over the past 70 years and suggest that the model is reliable. Recent warming in the Arctic has been spatially and seasonally heterogeneous; in many areas warming is more pronounced in the spring and autumn leading to a lengthening of the summer, while summer temperatures have remained relatively stable. A continentality inference model has the potential to detect these seasonal changes in climate. 相似文献
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Nazarova Katherine A. Wasilewski Peter J. Dick Henry J.B. 《Marine Geophysical Researches》2000,21(5):475-488
Magnetic properties and bulk densities of 27 serpentinized harzburgite samples from the Islas Orcadas Fracture Zone, located in the vicinity of the Bouvet Triple Junction, have been measured and analyzed. Polished sections were examined using reflected light and scanning electron microscopy to characterize the size and geometric arrangement of opaque minerals. The relationship between the saturation magnetization (IS) and remanent coercive force (HR) is considered in terms of the amount of ferrimagnetic material and maghemitization. A suite of continental serpentinites from Canada is offered as contrast, to consider the role of weathering and maghemitization. Magnetite in the Islas Orcadas serpentinites is variably maghemitized, whereas continental serpentinites do not appear to contain maghemitized oxides. We verify this with optical microscopy, thermomagnetic analyses and cryogenic temperature cycling of saturation remanence. Maghemitization serves to reduce initial magnetic susceptibility, and introduce error in the use of IS to evaluate the magnetic mode of magnetite. The presence of maghemite and the existence of a three dimensional vein network for magnetite geometry would suggest that magnetic hysteresis parameters can not reliably indicate grain size. Magnetic hysteresis ratios fall in a restricted range regardless of coercivity. The apparent grain size configured in a three dimensional vein network plus maghemitization might be responsible for this observation. Maghemitization does not affect thermal magnetic stability and enhances the geophysical importance of remanence in serpentinites. Paleomagnetic data suggest that important information about the geologic circumstances for oceanic rock serpentinization is embodied in the paleomagnetic records. This observation may be very important for generation of long wavelength aeromagnetic and possibly even satellite magnetic anomalies. 相似文献
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B. A. Goldin Yu. I. Ryabkov N. A. Sekushin L. Yu. Nazarova A. M. Askhabov 《Doklady Earth Sciences》2011,436(1):25-27
This paper details the results of a comparative study of two materials having the same structure, but drastically different
radiophysical characteristics. Corundum ceramic samples were synthesized from pure substances by firing a charge in air at
1450°C for 1 h. The second material was prepared from natural ilmenite without heat treatment using an epoxy polymer binder.
Measurements of the transmission and reflection factors within the frequency range of 8–26 GHz indicate that corundum ceramic
samples scatter electromagnetic radiation (EMR) exhibiting a pronounced dispersion of the reflection and transmission factors.
On the contrary, ilmenite samples absorb EMR showing no dispersion at all. The differences in the radiophysical characteristics
are due to the presence of magnetic impurities in the crystal lattices of corundum and ilmenite and the specific features
of the spin-phonon interaction in dielectric and ferrite materials. 相似文献
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