Effect of the addition of granitic powder to an acidic soil from Galicia (NW Spain) in comparison with lime   总被引：1，自引：1，他引：0  

Benita?Silva  Remigio?ParadeloEmail author  Nuria?Vázquez  Eduardo?García-Rodeja  María?Teresa?Barral 《Environmental Earth Sciences》2013,69(2):429-441

The impact of diffuse pollution, agricultural land use and climate change on the long-term response of subsurface–surface water quality is not well understood, but is a prerequisite for evaluation of water management options. The goal of this study is to model geochemical evolution of water chemistry from the infiltration through soil into the unsaturated zone, transport through bedrocks and granular aquifers to a river in order to identify zones of steep concentration gradients and high dynamics under transient flow conditions. A numerical model was constructed comprising a 2-D 1,500 m × 150 m vertical cross-section of typical sedimentary rock formations, a glacio-fluvial quaternary gravel aquifer in the valley and soil layers. The model coupled saturated/un-saturated flow and reactive transport under steady state and transient conditions. Geochemical interactions, include intra-aqueous kinetic reactions of oxygen with dissolved organic matter, as well as kinetics of carbonate dissolution/precipitation. This model section was chosen to provide insight in to the principal processes and time scales affecting water chemistry along different flow paths. The numerical simulator MIN3P was used, a finite volume program for variably saturated subsurface flow and multi-component reactive transport. The results show that subsurface water residence times range from approximately 2 to 2,000 years. Different zones are to be expected with respect to the development of mineral equilibria; namely, purely atmospherically influenced, as well as open and closed system carbonate dissolution. Short-term responses to daily averaged changes in precipitation, however, are only visible to some extent in the shallower and near-river parts of flow system and solute loads. This can most likely be explained by directional changes in flow paths, indicating that equilibrium geochemical condition predominate at the hillslope scale, i.e. water quality depends on transport pathways rather than on kinetic effects. The extent of reducing conditions is controlled by the presence of organic-rich layers (i.e. peat deposits), the dissolution kinetics of aquifer organic matter and the subsequent mixing with oxygenated water by hydrodynamic dispersion.  相似文献   

Organochlorine compounds in sharks from the Brazilian coast     

Claudio Eduardo de Azevedo e Silva  Adriana de Cássia Lima Dias  José Lailson-Brito  Jean Remy Daveé Guimarães 《Marine pollution bulletin》2009,58(2):294-298

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Macroinvertebrate patterns along environmental gradients and hydrological connectivity within a regulated river-floodplain     

Belinda Gallardo  Mercedes García  Álvaro Cabezas  Eduardo González  María González  Cecilia Ciancarelli  Francisco A. Comín 《Aquatic Sciences - Research Across Boundaries》2008,70(3):248-258

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Seismic response of an urban bridge-support system in soft clay     

Juan M. Mayoral  Yolanda AlbertoManuel J. Mendoza  Miguel P. Romo 《Soil Dynamics and Earthquake Engineering》2009

The numerical simulation of an instrumented urban bridge support and its foundation system was conducted. The bridge works as a deck in a surface subway station and was built 12 yr ago in the so-called Lake Zone in Mexico City, where very soft clays, exhibiting low shear strength and high compressibility prevail. Since the beginning of its construction, pile loads, soil–raft contact pressures and the overall response of the foundation system have been monitored. Within this period, several earthquakes have occurred. Thus, an extensive database of accelerations, pore pressures and load histories have been recorded. In particular, this paper focuses on the bridge response observed during two moderated intensity events, the 2004, 6.3 M_w, Guerrero Coast and the 1999, 7.0 M_w, Tehuacan earthquakes. Finite element models were developed to reproduce the measured responses and to assess the soil–foundation-support performance for long-term conditions, including the effects of potential changes in the dynamic soil properties due to regional subsidence. The computed dynamic responses obtained with the simulation for the free field and structure compares fairly well with the recordings.  相似文献   

A non-parametric automatic blending methodology to estimate rainfall fields from rain gauge and radar data   总被引：1，自引：0，他引：1  

Carlos A. Velasco-Forero  Daniel Sempere-Torres  Eduardo F. Cassiraga  J. Jaime Gómez-Hernández 《Advances in water resources》2009

Quantitative estimation of rainfall fields has been a crucial objective from early studies of the hydrological applications of weather radar. Previous studies have suggested that flow estimations are improved when radar and rain gauge data are combined to estimate input rainfall fields. This paper reports new research carried out in this field. Classical approaches for the selection and fitting of a theoretical correlogram (or semivariogram) model (needed to apply geostatistical estimators) are avoided in this study. Instead, a non-parametric technique based on FFT is used to obtain two-dimensional positive-definite correlograms directly from radar observations, dealing with both the natural anisotropy and the temporal variation of the spatial structure of the rainfall in the estimated fields. Because these correlation maps can be automatically obtained at each time step of a given rainfall event, this technique might easily be used in operational (real-time) applications. This paper describes the development of the non-parametric estimator exploiting the advantages of FFT for the automatic computation of correlograms and provides examples of its application on a case study using six rainfall events. This methodology is applied to three different alternatives to incorporate the radar information (as a secondary variable), and a comparison of performances is provided. In particular, their ability to reproduce in estimated rainfall fields (i) the rain gauge observations (in a cross-validation analysis) and (ii) the spatial patterns of radar fields are analyzed. Results seem to indicate that the methodology of kriging with external drift [KED], in combination with the technique of automatically computing 2-D spatial correlograms, provides merged rainfall fields with good agreement with rain gauges and with the most accurate approach to the spatial tendencies observed in the radar rainfall fields, when compared with other alternatives analyzed.  相似文献   

The local environment of H ii galaxies     

Eduardo Telles  Steve Maddox 《Monthly notices of the Royal Astronomical Society》2000,311(2):307-312

We have carried out an investigation of the environments of low redshift H  ii galaxies by cross-correlating their positions on the sky with those of faint field galaxies in the Automatic Plate Measuring Machine (APM) catalogues. We address the question of whether violent star formation in H  ii galaxies is induced by low-mass companions by statistically estimating the mean space density of galaxies around them. We argue that even if low-mass companions were mainly intergalactic H  i clouds, their optical counterparts should be detectable at faint limits of the APM scans.
A significantly positive signal is detected for the H  ii galaxy–APM galaxy angular cross-correlation function, but the amplitude is poorly determined. The projected cross-correlation function has a higher signal-to-noise ratio, and suggests that the amplitude is slightly lower than for normal field galaxies. This implies that these bursting dwarf galaxies inhabit slightly lower density environments than those of normal field galaxies, consistent with other studies of emission-line galaxies. This suggests that in these dwarf starburst galaxies, star formation is not always triggered by tidal interactions, and a significant fraction must have a different origin.  相似文献   

Dating Gondwanan continental crust at the Rio Grande Rise,South Atlantic     

Roberto Ventura Santos  Carlos Eduardo Ganade  Christian M. Lacasse  Iago S. L. Costa  Ivo Pessanha  Eugenio P. Frazo  Elton L. Dantas  Jos A. Cavalcante 《地学学报》2019,31(5):424-429

Crystalline continental rocks and associated crust‐contaminated basaltic rocks were unexpectedly dredged on the crest and at seamounts of the Rio Grande Rise, South Atlantic. Zircon U–Pb ages of one gabbro (ca. 2,200 Ma) and four granitoids (between ca. 1,430–480 Ma) indicate that the breakup of SW Gondwana left behind continental fragments of dominantly African age. These rocks may have been incorporated into the oceanic lithosphere by complex processes including rifting and interaction of the Tristan‐Gough mantle plume with hyperextended continental margins. Until ca. 80–70 Ma, the Rio Grande Rise and an old portion of the Walvis Ridge formed a conjugate pair of aseismic ridges, and the Tristan‐Gough plume was positioned at the Mid‐Atlantic Ridge. The finding of continental rock fragments in one of these conjugate pairs opens new perspectives on the mechanisms of continental break‐up, the nature of this conjugate pair, and the geodynamic evolution of rifted Gondwana margins in the South Atlantic.  相似文献   

A transparent aqueous-saturated sand surrogate for use in physical modeling   总被引：3，自引：0，他引：3  

Ivan L. Guzman  Magued Iskander  Eduardo Suescun-Florez  Mehdi Omidvar 《Acta Geotechnica》2014,9(2):187-206

This paper presents the geotechnical properties of a new family of synthetic transparent soils made of fused quartz, saturated with a matched refractive index water-based sucrose solution, suitable for modeling the behavior of sand in small-scale model tests. The dry density ranged between 1,134 and 1,358 kg/m³. The peak angle of friction was found to range from 46° to 57°. The average hydraulic conductivity was 1.7 × 10^?5 cm/s. The compressibility index (C _c) ranged from 0.34 to 0.57. The main advantage of fused quartz over available sand surrogates made of silica gel is that its solid structure better models the behavior of natural sand. The matching pore fluids are inert and non-toxic, which facilitates their use in educational settings. The availability of a safe and easy-to-use transparent sand permits measurement of three-dimensional deformation patterns and flow characteristics in controlled research experiments. The introduction of an aqueous solution permits the use of two immiscible pore fluids, one made of mineral oil and the other made of a sucrose solution, for modeling multiphase flow problems, as well as coupled flow-deformation problems.  相似文献   

Tide-induced head fluctuations in coastal aquifers of variable thickness     

Julián Eduardo Cuello  Luis Guarracino 《水文研究》2020,34(21):4139-4146

In this work, a new analytical solution to describe tide-induced head fluctuations in aquifers of variable thickness is presented. The proposed model assumes a finite and confined aquifer with a thickness that increases or decreases quadratically with the distance to the coast. A closed-form analytical solution is obtained by solving a boundary-value problem with both a separation of variables method and a change of variables method. This solution is a generalization of the solution obtained by Cuello et al., Hydrogeological Journal, 2017, 25, 1509–1515. The analytical solution is expressed in terms of the wedging parameter, a parameter that depends on the length and thicknesses at the coast and at the inland edge of the aquifer. Positive values of the wedging parameter describe aquifers with increasing thickness towards land and negative values describe aquifers with a decreasing thickness in the inland direction. The comparison of the new solution and the solution for a finite aquifer with constant thickness indicates that the sign of the wedging parameter enhances or decreases the amplitude of the tide-induced signal. However, the differences in time-lag between both solutions are negligible near the coast. The slope factor, which quantifies the inconsistencies between aquifer diffusivities estimated from attenuation and time-lag data, is computed and analysed. Near the coast, slope factor values greater than one are obtained for negative wedging parameters while slope factor values less than one are obtained for positive wedging parameters. The analysis of the new solution also indicates that more reliable estimates of the hydraulic diffusivity can be obtained from time-lag data.  相似文献   

Petrology of pumices of April 1993 eruption of Lascar (Atacama, Chile)     

Bernard Déruelle  Oscar Figueroa A.  Eduardo Medina T.  Jose Viramonte G.  Mario Maragaño C. 《地学学报》1996,8(2):191-199

Lascar Volcano (Atacama, Chile) erupted on 18–20 April 1993. Several sub-Plinian explosions occurred, and some were mushroom-shaped. The highest column rose up to 23 km. Ash clouds crossed South America eastwards. Dacite pumice falls made of blocks and ashes were deposited on the flanks of the volcano as a result of collapsed columns. The pumice contains phenocrysts of plagioclase, enstatite, augite, biotite, magnetite and ilmenite and small crystals of apatite. The 1992 previous andesite dome inside the crater was destroyed. Banded blocks resulting from mingling of the dacitic pumice and andesite from the dome are found in the pumice flow. Both the lava dome and the pumice are representative of the Lascar high-K magma unit. Dacitic pumice is a product of crystal fractionation of the andesitic magma.  相似文献