Study of the Santa Catarina aquifer system (Mexico Basin) using magnetotelluric soundings     

Michel Chouteau  Stefka Krivochieva  Ramiro Rodriguez Castillo  Tomas Gonzalez Moran  Virginie Jouanne 《Journal of Applied Geophysics》1994,31(1-4)

A tensor magnetotelluric test survey was carried out in the region of Santa Catarina, located in the Chalco sub-basin of the Mexico Basin. The objective was to define the stratification at depth with an emphasis on the geometry of the main aquifer of that region which is partially known from DC resistivity soundings and drilling. High-quality magnetotelluric soundings could be recorded in the immediate vicinity of large urban zones because the sub-surface is very conductive. Interpretation shows that the solid bedrock is located at a depth of at least 800 m to the south and 1300 m to the north; it could, however, be much deeper. Using complementary DC resistivity sounding and well-logging data, three main layers have been defined overlying the bedrock. These layers are, from surface to bottom, an unsaturated zone of sand, volcanic ash and clay about 10 m thick, followed by a very conductive (1.5 ohm·m) 200 m thick layer of sand and ash with intercalated clay, saturated with highly mineralized water, and finally a zone with resistivity increasing gradually to 60 ohm·m. The investigated deep aquifer constitutes most of this third layer. It consists of a sequence of sand, gravel, pyroclastites and mainly fractured basalts. MT resistivity soundings and magnetic transfer functions also indicate that a shallow resistive structure is dipping, from the northwest, into the lacustrine deposits of the basin. This geologic feature is likely to be highly permeable fractured basaltic flows, which provide a channel by which water contaminated by the Santa Catarina landfill may leak into the basin.  相似文献   

Sedimentary geochemical record of recent environmental changes around Lake Middle Marviken,Sweden     

Joyanto Routh  Philip A. Meyers  Tomas Hjorth  Mark Baskaran  Rolf Hallberg 《Journal of Paleolimnology》2007,37(4):529-545

Geochemical properties of sediments deposited in Lake Middle Marviken over the last 185 years record the impacts of a succession of environmental changes that have occurred in the watershed. Clear-cutting of forests for wood and charcoal and extensive water harnessing to support the local iron mills from 1897 to 1957 is recorded by low C/N ratios, high black carbon, and low TOC and N_total accumulation rates. Larger δ¹³C and δ¹⁵N values in sediments deposited during this period imply higher productivity. Fluctuations in N_total and P_total accumulation rates show that the lake chemistry has varied between P or N-depleted systems that affected the δ¹⁵N values. Organic matter in the sediments is predominantly immature terrestrial material. Furthermore, hydrocarbon CPI, TAR, and P_aq values conform with the observed geochemical trends, variations in organic matter sources, and changes in the watershed. Accumulation rates of Cd, Pb, Zn, and S remained mostly unchanged throughout the period of mining, but an increase from 1957 to 1980 is most likely associated with air-borne industrial and fossil fuel emissions from regional urbanization. In situ microbial processes, such as iron and manganese reduction, also appear to be important in carbon cycling and in affecting the sediment and water chemistry of this lake.  相似文献   

In situ target strength of the Baltic Sea herring and sprat     

Didrikas  Tomas; Hansson  Sture 《ICES Journal of Marine Science》2004,61(3):378-382

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Diel patterns in pelagic fish behaviour and distribution observed from a stationary, bottom-mounted, and upward-facing transducer   总被引：1，自引：1，他引：1  

Axenrot  Thomas; Didrikas  Tomas; Danielsson  Charlotte; Hansson  Sture 《ICES Journal of Marine Science》2004,61(7):1100-1104

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Lithostratigraphy and U-Pb zircon dating in the overturned limb of the Siviez-Mischabel nappe: a new key for Middle Penninic nappe geometry.     

Florian Genier  Jean-Luc Epard  François Bussy  Tomas Magna 《Swiss Journal of Geoscience》2008,101(2):431-452

Detailed field work and zircon analysis have improved the knowledge of the lithostratigraphy at the base of the Siviez-Mischabel nappe in the Mattertal (St-Niklaus-Törbel area). They confirm the existence of an overturned limb and clarify the structure of the St-Niklaus syncline. The following formations can be observed:

• Polymetamorphic gneisses; composed of paragneisses, amphibolites and micaschists (Bielen Unit, pre-Ordovician).
• Fine-grained, greyish quartzite and graywacke with kerogen-rich horizons (Törbel Formation, presumed Carboniferous).
• Green or white micaschists characterized by brown carbonate spots associated with white conglomeratic quartzites (Moosalp Formation, Early Permian).
• Massive, green or white, fine grained, microconglomeratic or conglomeratic quartzites with characteristic pink quartz pebbles (Bruneggjoch Formation, Late Permian-Early Triassic).

This coherent overturned sequence can be observed from the St-Niklaus area to the Moosalp pass to the north. Detailed mapping revealed that the St-Niklaus syncline is symmetrical and connects the overturned limb of the Siviez-Mischabel nappe to the normal series of the Upper Stalden zone. U-Pb zircon geochronology on magmatic and detrital zircons allowed constraining ages of these formations. Detrital zircons display ages ranging from 2900 ± 50 to 520 ± 4 Ma in the Törbel Formation, and from 514 ± 6 to 292 ± 9 Ma in the Moosalp Formation. In addition, the Permian Randa orthogneiss is intrusive into the polymetamorphic gneisses and into the Permo-Carboniferous metasediments of the overturned limb of the Siviez-Mischabel nappe. This revision clarified also the lithostratigraphy of the nearby and subjacent Lower Stalden zone composed of an overturned limb with Permo-Carboniferous formations. This has critical implications for the tectonic setting of the nappes in the region, speaking for few recumbent folds with well preserved normal and overturned limbs instead of a succession of imbricate thrust sheets in a normal stratigraphic position.  相似文献   

Internal structure of the aeolian sand dunes of El Fangar spit, Ebro Delta (Tarragona, Spain)     

Inmaculada Rodríguez Santalla  María Jos Snchez García  Isabel Montoya Montes  David Gmez Ortiz  Tomas Martín Crespo  Jordi Serra Raventos 《Geomorphology》2009,104(3-4):238-252

This paper presents an analysis of the dune field dynamics of El Fangar Spit in the Ebro Delta (Spain), associating it with the internal structure of dunes carried out with ground-penetrating radar and supported by data from topographic DGPS. These analyses are of great importance to ascertain the state of the internal structure of dunes as an important element in their stability and, therefore in their evolution. The internal structure shows accretion and progradation sequences of dunes over beach deposits, which depend on dune morphology (height, crest orientation) and location, as well as the processes acting on them.  相似文献   

Identifying the flow pattern and natural recharge at a strategic groundwater resource in the Dornogobi Province,Mongolia     

Adam Ricka  Tomas Kuchovsky  Batmunkh Damdindorj  Vilem Fürych  Antonin Kopriva  Khukhuu Puntsag 《水文科学杂志》2018,63(9):1408-1423

The strategic project of economic development in the Dornogobi Province in Mongolia is dependent on water supply. Thus a comprehensive hydrogeological characterization was focused on the Upper Cretaceous multi-aquifer system north of Sainshand city. A conceptual model was developed to discover the groundwater flow pattern essential to correct the setting of the numerical model of groundwater flow created using MODFLOW to assess the natural recharge of the aquifer. The conceptualization was based on geological and hydrogeological characterization. However, the evaluation of hydrochemistry proved to be the key factor revealing the principal feature of the groundwater flow pattern, which is the presence of preferential flow zones. These zones allow for intensive transfer of relatively fresh Na(Mg,Ca)?HCO₃-dominated groundwater into discharge areas, where it leaks into the Quaternary aquifer. The numerical model suggested an enormous natural recharge of 22 100 m³/d, originating in 64% of the preferential flow zones.  相似文献   

Modelling multiseasonal preferential transport of dissolved organic carbon in a shallow forest soil: Equilibrium versus kinetic sorption     

Jaromir Dusek  Michal Dohnal  Tomas Vogel  Anne Marx  Johannes A.C. Barth 《水文研究》2019,33(22):2898-2917

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Determination of potential mine water discharge zones in crystalline rocks at Rozna,Czech Republic   总被引：3，自引：2，他引：1  

Adam Ricka  Tomas Kuchovsky  Ondra Sracek  Josef Zeman 《Environmental Earth Sciences》2010,60(6):1201-1213

The Rozna Mine is one of the last active uranium mines in Europe. When the mine is closed and flooded, the natural groundwater flow pattern will be partly restored. Re-established groundwater flow system will be associated with an increase of groundwater discharge into draining rivers and streams. Since the groundwater inflows to streams can be contaminated by the mine water, the groundwater drainage characteristic of fractured aquifer should be carefully identified. Several methods of groundwater discharge zones identification were used including morphological analysis, thermometry, and electrical conductivity (EC) measurements. Stream temperatures and EC at more than 700 points in the area covering about 85 km² were measured. The measurements were performed during winter period, when stream discharges were low and there was a maximum temperature contrast. There was a frequent presence of preferential discharge zones with resulting anomalous temperatures and electric conductivity values of stream water. The results show evident correlation of discharge zones with surface morphology and geological settings. Just like the aquifer discharge characteristics, the aquifer is strongly heterogeneous. The thermometry supported by measurement of EC proved to be a useful tool for large-scale investigation of groundwater flow and drainage in fractured aquifers.  相似文献   

Impact of ocean model resolution on CCSM climate simulations   总被引：1，自引：1，他引：0  

Ben P. Kirtman  Cecilia Bitz  Frank Bryan  William Collins  John Dennis  Nathan Hearn  James L. Kinter III  Richard Loft  Clement Rousset  Leo Siqueira  Cristiana Stan  Robert Tomas  Mariana Vertenstein 《Climate Dynamics》2012,39(6):1303-1328

The current literature provides compelling evidence suggesting that an eddy-resolving (as opposed to eddy-permitting or eddy-parameterized) ocean component model will significantly impact the simulation of the large-scale climate, although this has not been fully tested to date in multi-decadal global coupled climate simulations. The purpose of this paper is to examine how resolved ocean fronts and eddies impact the simulation of large-scale climate. The model used for this study is the NCAR Community Climate System Model version 3.5 (CCSM3.5)—the forerunner to CCSM4. Two experiments are reported here. The control experiment is a 155-year present-day climate simulation using a 0.5° atmosphere component (zonal resolution 0.625 meridional resolution 0.5°; land surface component at the same resolution) coupled to ocean and sea-ice components with zonal resolution of 1.2° and meridional resolution varying from 0.27° at the equator to 0.54° in the mid-latitudes. The second simulation uses the same atmospheric and land-surface models coupled to eddy-resolving 0.1° ocean and sea-ice component models. The simulations are compared in terms of how the representation of smaller scale features in the time mean ocean circulation and ocean eddies impact the mean and variable climate. In terms of the global mean surface temperature, the enhanced ocean resolution leads to a ubiquitous surface warming with a global mean surface temperature increase of about 0.2?°C relative to the control. The warming is largest in the Arctic and regions of strong ocean fronts and ocean eddy activity (i.e., Southern Ocean, western boundary currents). The Arctic warming is associated with significant losses of sea-ice in the high-resolution simulation. The sea surface temperature gradients in the North Atlantic, in particular, are better resolved in the high-resolution model leading to significantly sharper temperature gradients and associated large-scale shifts in the rainfall. In the extra-tropics, the interannual temperature variability is increased with the resolved eddies, and a notable increases in the amplitude of the El Ni?o and the Southern Oscillation is also detected. Changes in global temperature anomaly teleconnections and local air-sea feedbacks are also documented and show large changes in ocean–atmosphere coupling. In particular, local air-sea feedbacks are significantly modified by the increased ocean resolution. In the high-resolution simulation in the extra-tropics there is compelling evidence of stronger forcing of the atmosphere by SST variability arising from ocean dynamics. This coupling is very weak or absent in the low-resolution model.  相似文献