The role of iron and sulfur in the visual appearance of lake sediment varves     

Veronika Gälman  Johan Rydberg  Andrei Shchukarev  Staffan Sjöberg  Antonio Martínez-Cortizas  Richard Bindler  Ingemar Renberg 《Journal of Paleolimnology》2009,42(1):141-153

Easily discernible sediment varves (annual laminations) may be formed in temperate zone lakes, and reflect seasonal changes in the composition of the accumulating material derived from the lake and its catchment (minerogenic and organic material). The appearance of varves may also be influenced by chemical processes. We assessed the role of iron (Fe) and sulfur (S) in the appearance of varves in sediments from Lake Nylandssjön in northern Sweden. We surveyed Fe in the lake water and established whether there is internal transport of Fe within the sediment. We used a unique collection of seven stored freeze cores of varved sediment from the lake, collected from 1979 to 2004. This suite of cores made it possible to follow long-term changes in Fe and S in the sediment caused by processes that occur in the lake bottom when the sediment is ageing. We compared Fe and S concentrations using X-ray fluorescence spectroscopy (XRF) in specific years in the different cores. No diagenetic front was found in the sediment and the data do not suggest that there is substantial vertical transport of Fe and S in the sediment. We also modeled Fe and S based on thermodynamic, limnological, and sediment data from the lake. The model was limited to the five components H⁺, e^?, Fe³⁺, SO₄ ^2?, H₂CO₃ and included the formation of solid phases such as Fe(OH)₃ (amorphous), FeOOH (aged, microcrystalline), FeS and FeCO₃. Modeling showed that there are pe (redox) ranges within which either FeS or Fe(OH)₃/FeOOH is the only solid phase present and there are pe ranges within which the two solid phases co-exist, which supports the hypothesis that blackish and grey-brownish layers that occur in the varves were formed at the time of deposition. This creates new possibilities for deciphering high-temporal-resolution environmental information from varves.  相似文献   

西伯利亚水库和叶尼塞河中物质及生态系统条件的预测：生物物理方法     

Andrei Degermendzhy  Vladimir Gubanov 《湖泊科学》1998,10(S1):203-228

An avenue to integrate theoretical, experimental and field research methods to forecast water quality in water bodies for different scenarios of water management is proposed. Exploration of the laws of organization, stability and controllability of laboratory "ideal" water microbial communities (model ecosystems) is the basis to build the following biophysical research chain:to formalize with primary field information a conceptual block-diagram of a water ecosystem →to real chemical and other density-dependent and population-growth-controlling factors → to find our limiting factors for natural ecosystems → to conduct experiments with isolated chemical factors and hydrobionts to derive kinetic dependencies and quantitative parameters→ to transfer regularities of operation and kinetic dependencies to the natural ecosystem→ retrospective verification of the model on the base of available field and derived theoretical-experimental data →prognostic calculations for the scenario. Efficiency of the approach is demonstrated in microalgal "blooming" models for Krasnoyarsk and Kantat reservoirs and in prognostication of radioecological state of great Yenisei river:1) radionuclide distribution in the Yenisei''s bottom sediment is nonuniform-"spotty"; 2) it is theoretically shown, that due to biological interactions and tro-phical radioniclide migration there is "spotive" type of space radionuclide distribution. The research is to make use of the novel methods of ecological biophysics:Monitoring:spectral analysis of surface waters (algal pigments), fluorescent techniques to evaluate productivity and condition of algae; rapid bioassays for water toxicity (bioluminescence, chemotaxis techniques). Kinetic experiments:microcosms on evaluating self-purification rates; special cultivators to evaluate the rates of growth of hydrobionts and radioactive engulfing, nutrition spectra; methods of finding growth limiting factors. Models:application of Bellman Principle to optimizing the river water use; theory and peculiarities of microbiological decomposition of pollutants in the river ecosystem. The composition of Prognostication Simulation Model is the next:1) hydrodynamical unit to calculate 2-dimensional space-time rate of stream on any depth; 2) hydrophysical unit to calculate:water temperature and level of solar radiation inside the water body; 3) ecosystem unit to calculate dynamic of concentration of phytoplankton, zooplankton, bacteria, major chemical matters and pollutants in water, content pollutants inside of hydrobionfs cells and dynamic of bentos; 4) radioe-cological unit to forecast the dynamic of radionuclides in the water body and bottom, their hydro-bont''s concentration; 5) database. Reservoirs and river models are provided by monitoring and kinetic experiments data.  相似文献   

Radiocarbon Ages and Environments of Deposition of the Wono and Trego Hot Springs Tephra Layers in the Pyramid Lake Subbasin, Nevada     

Larry V. Benson  Joseph P. Smoot  Michaele Kashgarian  Andrei Sarna-Wojcicki  James W. Burdett 《Quaternary Research》1997,47(3):251-260

Uncalibrated radiocarbon data from core PLC92B taken from Wizards Cove in the Pyramid Lake subbasin indicate that the Trego Hot Springs and Wono tephra layers were deposited 23,200 ± 300 and 27,300 ± 300¹⁴C yr B.P. (uncorrected for reservoir effect). Sedimentological data from sites in the Pyramid Lake and Smoke Creek–Black Rock Desert subbasins indicate that the Trego Hot Springs tephra layer was deposited during a relatively dry period when Pyramid Lake was at or below its spill point (1177 m) to the Winnemucca Lake subbasin. The Wono tephra layer was deposited when lake depth was controlled by spill across Emerson Pass sill (1207 m) to the Smoke Creek–Black Rock Desert subbasin.¹⁸O data from core PLC92B also support the concept that the Trego Hot Springs tephra fell into a relatively shallow Pyramid Lake and that the Wono tephra fell into a deeper spilling lake.  相似文献   

Vegetation and climate during the penultimate interglacial of the northeastern Russian Arctic: the Lake El'gygytgyn pollen record     

Wenwei Zhao  Andrei A. Andreev  Pavel E. Tarasov  Volker Wennrich  Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):507-515

We present a high‐resolution reconstruction of the vegetation and climate dynamics during the penultimate interglacial, corresponding with Marine Isotope Stage (MIS) 7, based on detailed palynological analyses of lacustrine sediments from Lake El'gygytgyn, northeastern Siberia. The analysed sediments were deposited between 246 and 181 ka ago (late MIS 8 to early MIS 6.6). The interglacial vegetation was characterized by herb and shrub (mainly alder and birch) dominated plant communities. Pollen‐based biome reconstruction shows a dominance of the tundra (TUND) biome, thus indicating rather open vegetation. Warmer intervals (MIS 7.5, 7.3 and 7.1) were marked by an increase in the cold deciduous forest (CLDE) biome scores and a synchronous decrease in the cold steppe (STEP) biome scores. The thermal maximum occurred during MIS 7.1, as indicated by the highest CLDE biome scores occurring in this period, and lasted ~10 ka, possibly favoured by the high precession‐related summer insolation and the legacy of the preceding mild and dry stadial (MIS 7.2). In contrast, MIS 7.3 and 7.5 were characterized by shorter durations (~4 ka) and lower summer temperatures. The preceding cold glacial and stadial (MIS 8 and 7.4, respectively) might have led to an extensive distribution of permafrost that hindered vegetation development during the subsequent warm intervals. MIS 7.4 and 6.6 were cold and wet, probably triggered by low obliquity values and coevally low precession‐related summer insolation. As a result, these periods were marked by significantly reduced summer temperatures and an enhanced snow‐ice albedo feedback. The obtained reconstructions provide potential scenarios for future climate changes and allow a better understanding of the relationship between vegetation, climate and external/internal forcings in the high latitudes.  相似文献   

Sensitivity analysis for parameter identification in quasi‐static poroelasticity     

Brice Lecampion  Andrei Constantinescu 《国际地质力学数值与分析法杂志》2005,29(2):163-185

This paper is devoted to the formulation of the direct differentiation method and adjoint state method in quasi‐static linear poroelasticity. We derive the strong and weak formulation of both methods and discuss their solutions using the finite element method. The techniques are illustrated and tested on two numerical examples for the case of isotropic and homogeneous material. The presented formulations can be extended to more complex behaviour in poromechanics. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The Kaidun meteorite: Composition and origin of inclusions in the metal of an enstatite chondrite clast     

Andrei V. IVANOV  Glenn J. MACPHERSON  Michael E. ZOLENSKY  Nataliya N. KONONKOVA  Lyudmila F. MIGDISOVA 《Meteoritics & planetary science》1996,31(5):621-626

Abstract— Metal nodules are one of the major textural components of Kaidun sample #01.3.06 EH3-4. In terms of structure, the nodules are of three types: (1) globular, (2) zoned with a massive core and globular mantle, and (3) nodules with no internal structure. The size and composition of the globules in the nodules and grains of metal of the matrix are almost identical: no greater than 20 μm and Ni, 5.95; Si, 3.33 wt%. The nodules contain small (usually <5 μm) inclusions of SiO₂; albitic glass; enstatite; roedderite; and a mixture of SiO₂ and Na₂S₂. This is the first reported occurrence of a simple sulfide of an alkaline metal in nature. The formation of the inclusions appears to be related to condensation of material onto the surfaces of metal grains. The nodules appear to have formed by aggregation of separate grains (globules) of metal, with conservation of condensates on the grain surfaces as inclusions. The inclusions probably condensed over a significant temperature range from 1400 to 600 K. The aggregation of metal grains and formation of the nodules probably occurred simultaneously with condensation.  相似文献   

THE SOURCES OF REGIONAL ELDERLY POPULATION GROWTH: MIGRATION AND AGING-IN-PLACE *     

Andrei Rogers  Jennifer Woodward 《The Professional geographer》1988,40(4):450-459

A region's elderly population has two sources of growth: net migration and the net aging-in-place of its resident population. This paper outlines a method for identifying the projected relative contribution of these two sources of elderly population growth over time, and illustrates it with data for the states of Arizona, California, Florida, Illinois, and New York. The sources of elderly population growth differ between regions and over time.  相似文献   

Comparison of methods for quantifying consumer spending on retail using publicly available data     

Derek T. Robinson  Andrei M. Balulescu 《International journal of geographical information science》2018,32(6):1061-1086

Data and estimates on the spatial distribution of consumer spending form the foundation of retail location analysis and location-allocation spatial interaction models. The presented research presents and compares four methods to estimate consumer spending that combine different levels of detail in household spending data across multiple levels of household aggregation (i.e. census units). Results demonstrate that these methods, which use publicly available census data, can capture a substantial amount of reported sales. Furthermore, comparison of the best method with the de facto industry standard for business data in Canada shows a strong correlation (R2 > 0.85) across space and is within 10% of aggregate industry-derived spending estimate. Analysis of the spending data across space finds that the majority of spending occurs in census metropolitan areas with high spending clusters that offer unique opportunities for retail location. We interrogate the socio-demographic characteristics of the population in these high spending clusters and find that only a few variables are required to explain a large proportion of the variance in consumer spending. The overarching outcome of the presented research is that small-to-medium businesses, planners, and municipalities do not need expensive proprietary data to estimate and predict consumer spending and market demand.  相似文献   

Microbial dechlorination of dioxins in estuarine enrichment cultures: effects of respiratory conditions and priming compound on community structure and dechlorination patterns     

Shiang Fu Q  Barkovskii AL  Adriaens P 《Marine environmental research》2005,59(3):177-195

The effect of respiratory conditions and priming compound on dechlorination patterns of heptachlorodibenzo-p-dioxins (HpCDD) was investigated using estuarine sediment-eluted cultures in the presence and absence of 20 mM sulfate, and 0.2 microM 2-bromodibenzo-p-dioxin (2-BrDD) as a priming compound. Electron balance calculations based on fatty acid turnover, hydrogen production, and electron acceptor depletion/methane formation indicated that whereas fermentative processes dominated in sulfate-free incubations, sulfate-reduction was predominant in the sulfate-amended incubations. The dechlorination of 1,2,3,4,6,7,8-HpCDD exhibited the following trends: (i) the relative yields of product formation did not exceed 30% and the presence of 2-BrDD increased the yield by up to 10%; (ii) sulfidogenic conditions resulted in a lower 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) formation, and the presence of 2-BrDD decreased the formation of 2,3,7,8-TCDD by additional 4-5-fold; (iii) the presence of 2-BrDD effected a predominance in lateral (2,3,7,8 positions) over peri (1,4,6,9 positions)-dechlorination. Denaturing gradient gel electrophoresis (DGGE) banding patterns indicated significant shifts of microbial community structure in response to terminal electron accepting processes as well as to the presence of the priming compound. The latter resulted in a similar community structure independent of dioxin spike, indicating that subsets of populations in the sediment are capable of exploiting the new niche provided by the priming compound.  相似文献   

Analysis of seawater and different highly saline natural waters by capillary zone electrophoresis     

Andrei R. Timerbaev  Keiichi Fukushi 《Marine Chemistry》2003,82(3-4):221-238

Innovative applications of capillary zone electrophoresis (CZE) to the determination of inorganic ions in environmental aquatic samples of high salinity and, particularly, in seawater are reviewed. Emphasis is placed on advanced approaches utilized for securing separation performance from being degraded by the presence of matrix salts and for simultaneous separation of ions different in natural abundance. Also covered are methodologies of present or possible use to evolve the method's practical utility to trace-level ions. Surveyed procedures are tabulated for the purpose of facilitating the method selection or further development. In addition, brief background information on basic methodological principles of CZE in inorganic ion analysis is given for a better orientation of those intending or just beginning to put CZE to work. Finally, possible future research trends and developments of CZE in the area are briefly discussed.  相似文献