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   

Potential impact of climate change on aquatic insects: A sensitivity analysis for European caddisflies (Trichoptera) based on distribution patterns and ecological preferences   总被引：1，自引：1，他引：0  

Daniel Hering  Astrid Schmidt-Kloiber  John Murphy  Sofie Lücke  Carmen Zamora-Muñoz  Manuel Jesús López-Rodríguez  Thomas Huber  Wolfram Graf 《Aquatic Sciences - Research Across Boundaries》2009,71(1):3-14

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The life history of Serratella ignita (Poda, 1761) (Insecta: Ephemeroptera) in a temporary and permanent Mediterranean stream     

Manuel J. López-Rodríguez  J. Manuel Tierno de Figueroa  Javier Alba-Tercedor 《Aquatic Sciences - Research Across Boundaries》2009,71(2):179-188

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A length-biased version of the Birnbaum-Saunders distribution with application in water quality     

Víctor Leiva  Antonio Sanhueza  José M. Angulo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(3):299-307

In this article, we develop a new model based on the Birnbaum-Saunders distribution that results to be both useful and practical for environmental sciences. The density, distribution and hazard functions, moments and properties of this new model are presented. A graphical analysis of the density is also provided. Furthermore, we estimate parameters, propose asymptotic inference and discuss influence diagnostics by using likelihood methods for the new distribution. An illustrative example with real data related to water quality indicates the adequacy on the new distribution.  相似文献   

Shear effects on hollow section piers under seismic actions: experimental and numerical analysis   总被引：1，自引：0，他引：1  

Raimundo Delgado  Pedro Delgado  Nelson Vila Pouca  António Arêde  Patrício Rocha  Aníbal Costa 《Bulletin of Earthquake Engineering》2009,7(2):377-389

Shear effects are often a very important issue on the seismic behaviour of piers, particularly for hollow section bridge piers. In fact, for this type of piers the cyclic response is similar to that of a structural wall in which both the transverse reinforcement ratio and the detailing can play an important role on its performance, even likely to be determinant in terms of the failure mechanism. On the other hand, codes and design guidelines are usually very conservative concerning shear capacity in order to avoid any shear failure mechanism likely to trigger well known catastrophic consequences. Therefore, research studies on this topic are still needed for a better understanding of pier cyclic shear response and also for improvement of the performance under seismic actions. Pursuing this general objective, this paper partially reports on an experimental/numerical campaign carried out on 1:4 reduced scale bridge piers in order to highlight and investigate shear-type problems. Within the scope of this paper, two specimens types were selected having equal rectangular hollow section (900 × 450 mm², 75 mm thick) but different transverse reinforcement detailing, namely one with a single stirrup per wall (representative of typical bridge construction without seismic design requirements) and another with multiple stirrups, according to Eurocode 8 provisions. Numerical simulations of the experimental results were also conducted aiming at contributing for complete and consistent interpretations of experimental results. Detailed modelling was performed allowing for realistic simulations of the non linear behaviour, particularly suitable when a significant shear component is involved. Therefore, the numerical strategy was based on a detailed 3D FEM discretization using a two-scalar variable damage model for the concrete constitutive law and a suitable cyclic behaviour law for steel bars represented by truss elements. Results have shown that shear deformation and failure modes are well simulated, while providing detailed insight concerning concrete damage pattern and distribution of yielding on the transverse and longitudinal reinforcement.  相似文献   

Study of Metal Distribution in Raw and Screened Swine Manure   总被引：1，自引：0，他引：1  

Ricardo Luís Radis Steinmetz  Airton Kunz  Valderi Luiz Dressler  Érico Marlon de Moraes Flores  Ayrton Figueiredo Martins 《洁净——土壤、空气、水》2009,37(3):239-244

The growth of industrial swine production over the last few years has led to a growth in concern over effluents generated by the activity. Several elements, mainly toxic metals, can be present in swine wastewater and can have a serious environmental impact. It is important, therefore, to know the metal concentration before the discharge of wastewater. In this work the temporal metal distribution in swine manure and its potential reduction using coarse (2 mm) and fine (<0.45 μm) liquid‐solid separation techniques were investigated. In order to do this, different swine manure sample preparation methods for Al, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr and Zn determination by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) were tested. The acid mixtures used to digest the manure sample significantly affected the metal recovery. Good analyte recoveries were observed with nitric acid/hydrogen peroxide mixtures or nitric acid/perchloric acid mixtures. Sulfuric acid/hydrogen peroxide mixtures produced inconsistent results and poor recoveries, mainly for Ba and Pb. It was observed that metal concentrations in swine manure varied greatly with time, up to one order of magnitude, due to changes in swine production such as feed and animal numbers. Metals concentrations observed in the raw wastewater exceeded Brazilian limits for discharge into water bodies and recommendations for agricultural use. Results obtained from the liquid‐solid separation study showed that metals in the raw swine manure were not removed with coarse screening. However, the major fraction of metals were removed by filtration (0.45 μm), with the exception of Na, K and Sr. Thus, the use of liquid‐solid separation techniques that capture the fine solid fractions (and associated metals) from raw manure can have a favorable impact on the environment and contribute to swine production wastewater treatment.  相似文献   

Assessment of the hydraulic slope flow approach using a mesoscale model     

Daniel Martínez  Joan Cuxart 《Acta Geophysica》2009,57(4):882-903

The simplified hydraulic two-layer model for a katabatic flow is analysed using the outputs from a high-resolution mesoscale simulation. A stably stratified night is simulated for the Duero basin, a complex terrain area located in the northern Spanish plateau, with large vertical and horizontal spatial resolution. Well-defined katabatic flows on the basin slopes are generated by the simulation, that are relatively stationary and quasi-bidimensional for some areas in the central part of the night. The bulk quantities used in the two-layer approach as well as the different terms in the equations are computed from the three-dimensional information provided by the mesoscale simulation. This method allows to inspect how well the simplified approach represents the katabatic flow generated by the mesoscale model. The study shows that the hydraulic model allows for a comprehensive analysis of the basic mechanisms of the slope flows but is not able to close the budget equations, since the residuals are large.  相似文献   

Modelling a torrential event in a river confluence     

M. Roca  J.P. Martín-Vide  P.J.M. Moreta 《Journal of Hydrology》2009,364(3-4):207-215

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Implications of long-term land-use change for the hydrology and solute budgets of small catchments in Amazonia     

Sonja Germer  Christopher Neill  Tobias Vetter  Joaquín Chaves  Alex V. Krusche  Helmut Elsenbeer 《Journal of Hydrology》2009,364(3-4):349-363

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Petrogenesis of the mafic igneous rocks of the Betic Cordilleras: A field, petrological and geochemical study     

Maria Teresa Gómez-Pugnaire  Peter Ulmer  Vicente López-Sánchez-Vizcaíno 《Contributions to Mineralogy and Petrology》2000,139(4):436-457

Mafic igneous rocks are widespread in the Nevado-Filábride Complex, the lowermost metamorphic unit of the internal zones of the Betic Cordilleras. They form intrusive, small, discontinuous bodies, predominantly dikes with subordinate small lava flows. The entire complex underwent alpine compressional metamorphism during the Paleogene continental collision, resulting in eclogites and blueschists in the mafic bodies and high-pressure assemblages in the intruded metasediments. Locally, weakly metamorphosed or completely unmetamorphosed igneous rocks with the same textural features occur as patches surrounded by eclogitized igneous rocks. The bulk rock chemistry of unmetamorphosed and completely metamorphosed mafic igneous rocks is consistent with an alkaline to transitional tholeiitic magmatism with typical within-plate geochemical characteristics. All but a few samples are nepheline normative and display REE and trace element characteristics typical of continental, rift-related magmatism. This conclusion is strongly supported by the mineral chemistry of the major constituents, in particular the calcic Ti-rich character of clinopyroxene, the lack of orthopyroxene, and the occurrence of kaersutitic amphibole. Incompatible trace element abundances and Sr and Nd isotopes support the provenance of these magmas from a variably metasomatized previously depleted sub-continental lithospheric mantle source. Received: 5 July 1999 / Accepted: 28 February 2000  相似文献