9,720 research outputs found

    Changes in hydrodynamic, structural and geochemical properties in carbonate rock samples due to reactive transport

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    Reactive transport plays an important role in the development of a wide range of both anthropic and natural processes affecting geological media. To predict the consequences of reactive transport processes on structural and hydrodynamic properties of a porous media at large time and spatial scales, numerical modeling is a powerful tool. Nevertheless, such models, to be realistic, need geochemical, structural and hydrodynamic data inputs representative of the studied reservoir or material. Here, we present an experimental study coupling traditional laboratory measurements and percolation experiments in order to obtain the parameters that define rock heterogeneity, which can be altered during the percolation of a reactive fluid. In order to validate the experimental methodology and identify the role of the initial heterogeneities on the localization of the reactive transport processes, we used three different limestones with different petrophysical characteristics. We tracked the changes of geochemical, structural and hydrodynamic parameters in these samples induced by the percolation of an acid fluid by measuring, before and after the percolation experiment, petrophysical and hydrodynamic properties of the rocks.Peer ReviewedPostprint (published version

    Obliquity histories of Earth and Mars: Influence of inertial and dissipative core-mantle coupling

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    For both the Earth and Mars, secular variations in the angular separation of the spin axis from the orbit normal are suspected of driving major climatic changes. There is considerable interest in determining the amplitude and timing of these obliquity variations. If the orientation of the orbital plane were inertially fixed, and the planet were to act as a rigid body in it response to precessional torques, the spin axis would simply precess around the orbit at a fixed obliquity and at a uniform angular rate. The precession rate parameter depends on the principal moments of inertia and rotation rate of the perturbed body, and on the gravitational masses and semiminor axes of the perturbing bodies. For Mars, the precession rate is not well known, but probably lies in the interval 8 to 10 arcsec/year. Gravitational interactions between the planets lead to secular motions of the orbit planes. In the rigid body case, the spin axis still attempts to precess about the instantaneous orbit normal, but now the obliquity varies. The hydrostatic figure of a planet represents a compromise between gravitation, which attempts to attain spherical symmetry, and rotation, which prefers cylindrical symmetry. Due to their higher mean densities the cores of the Earth and Mars will be more nearly spherical than the outer layers of these planets. On short time scales it is appropriate to consider the core to be an inviscid fluid constrained to move with the ellipsoidal region bounded by the rigid mantle. The inertial coupling provided by this mechanism is effective whenever the ellipticicy of the container exceeds the ratio of precessional to rotational rates. If the mantle were actually rigid, this would be an extremely effective type of coupling. However, on sufficiently long time scales, the mantle will deform viscously and can accommodate the motions of the core fluid. A fundamentally different type of coupling is provided by electromagnetic or viscous torques. This type of coupling is likely to be most important on longer time scales. In each case, the mantle exerts an equal and opposite torque on the core

    Characteristics of soil cover in Poland with special attention paid to the Łódź region

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    Published in: Natural environment of Poland and its protection in Łódź University Geographical Research, edited by E. Kobojek and T.MarszałThe vast majority (as much as 92%) of soil resources in Poland occur in lowlands and uplands, and only 8% of the area of Poland has the characteristics of mountain soils. Nearly a half (46%) of soils in Poland is created of sandy formations of various origins – usually with a slightly acidic pH. Soils of the Łódź region were mainly formed from sands, and to a lesser degree from clays, silts and organogenic formations. Brown, lessive, podzolic and rusty soils dominate here. Chernozems, fensoils, organogenic soils (peat, muck and silt soils) and rendzinas are also present. Owing to their sandy grain-size composition, they are most often light and very light for cultivation. Most soils are acidified. Socioeconomic and natural conditions have determined the utilisation structure of soils in the Łódź region, where arable lands constitute 60% of the area and grasslands – less than 10%

    Hydrological conceptual model characterisation of an abandoned mine site in semiarid climate : the Sierra de Cartagena-La Unión (SE Spain)

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    A comprehensive study at Sierra de Cartagena-La Unión (SE Spain) abandoned mine site was carried out to characterise the regime and water quality of the groundwater system after the mine closure. The system consists of five geologic fractured blocks belonging to the Alpujarride and Nevado-Filabride complexes. The aquifer units are composed of limestone and dolostone materials. Recharge is mainly controlled by the N-130 fault system, man-made induced fractures, open-pits and underground workings. Discharge is indicated from open pit lakes by the proximal dome-shaped groundwater level contours. Aquifer natural recharge, assessed by fracture density maps and chloride mass balance, provided consistent results. The water hydrochemical facies show a marked sulphate concentration and acidic pH (average pH of 2.53-6.30). A maximum concentration of 4,100 mg/L of Zn and 40,000 mg/L of sulphate was observed in open-pit lakes. Springs present the lowest residence time and are low mineralised with an average pH of 7.6. Geochemical modelling based on the PHREEQCI code indicates water undersaturation with respect to almost all related mineral species and anoxic conditions prevail in the system. Although an adequate understanding of the regional system is provided, a further detailed hydrochemical study is necessary to assess the undergoing geochemical changes

    Selection for novel, acid-tolerant Desulfovibrio spp. from a closed Transbaikal mine site in a temporal pH- gradient bioreactor

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    Almost all the known isolates of acidophilic or acid-tolerant sulphate-reducing bacteria (SRB) belong to the spore-forming genus Desulfosporosinus in the Firmicutes. The objective of this study was to isolate acidophilic/acid-tolerant members of the genus Desulfovibrio belonging to deltaproteobacterial SRB. The sample material originated from microbial mat biomass submerged in mine water and was enriched for sulphate reducers by cultivation in anaerobic medium with lactate as an electron donor. A stirred tank bioreactor with the same medium composition was inoculated with the sulphidogenic enrichment. The bioreactor was operated with a temporal pH gradient, changing daily, from an initial pH of 7.3 to a final pH of 3.7. Among the bacteria in the bioreactor culture, Desulfovibrio was the only SRB group retrieved from the bioreactor consortium as observed by 16S rRNA-targeted denaturing gradient gel electrophoresis. Moderately acidophilic/acid-tolerant isolates belonged to Desulfovibrio aerotolerans - Desulfovibrio carbinophilus - Desulfovibrio magneticus and Desulfovibrio idahonensis - Desulfovibrio mexicanus clades within the genus Desulfovibrio. A moderately acidophilic strain, Desulfovibrio sp. VK (pH optimum 5.7) and acid-tolerant Desulfovibrio sp. ED (pH optimum 6.6) dominated in the bioreactor consortium at different time points and were isolated in pure cultur

    Old carbon contributes to aquatic emissions of carbon dioxide in the Amazon

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    Knowing the rate at which carbon is cycled is crucial to understanding the dynamics of carbon transfer pathways. Recent technical developments now support measurement of the <sup>14</sup>C age of evaded CO<sub>2</sub> from fluvial systems, which provides an important "fingerprint" of the source of C. Here we report the first direct measurements of the <sup>14</sup>C age of effluxed CO<sub>2</sub> from two small streams and two rivers within the western Amazonian Basin. The rate of degassing and hydrochemical controls on degassing are also considered. We observe that CO<sub>2</sub> efflux from all systems except for the seasonal small stream was <sup>14</sup>C -depleted relative to the contemporary atmosphere, indicating a contribution from "old" carbon fixed before ~ 1955 AD. Further, "old" CO<sub>2</sub> was effluxed from the perennial stream in the rainforest; this was unexpected as here connectivity with the contemporary C cycle is likely greatest. The effluxed gas represents all sources of CO<sub>2</sub> in the aquatic system and thus we used end-member analysis to identify the relative inputs of fossil, modern and intermediately aged C. The most likely solutions indicated a contribution from fossil carbon sources of between 3 and 9% which we interpret as being derived from carbonate weathering. This is significant as the currently observed intensification of weather has the potential to increase the future release of old carbon, which can be subsequently degassed to the atmosphere, and so renders older, slower C cycles faster. Thus <sup>14</sup>C fingerprinting of evaded CO<sub>2</sub> provides understanding which is essential to more accurately model the carbon cycle in the Amazon Basin

    Effect of regional geology and mining activity on water quality : studies in the eMalahleni (Witbank) and South Rand coalfields

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    Abstract : Acidic drainage generated in mining environments has been a major concern for many years, especially since the acidic drainage leads to the deterioration of quality in water resources. South Africa is a waterscarce country, and solutions to try and counteract the spread of acidic drainage in mining environments are of major importance. Prediction of the potential for constituents to generate or neutralise acidity produced has become an integral part of the treatment and mitigation process employed in numerous industries. The use of modern methods in the determination of acid generation and neutralisation potential in earth moving environments is critical in the improvement of mitigation and treatment methods. Methods are frequently generated in order to improve on existing methods, assist existing methods, or change the way existing methods operate. In the process of creating new methods, complications are often encountered, leading to an extended time period in the creation process. The current method focuses on the analyses of acid-generating and acid-neutralising elements with the use of Inductively-Coupled Plasma Optical Emissions Spectrometry (ICP-OES). The method aims to assist in the prediction of acid generation/neutralisation potential of samples and improve the efficiency by reducing the period it takes for successful prediction to be carried out and analysing an array of minerals considered to be involved in acid generation and neutralisation reactions. Samples were subjected to nitric and hydrochloric acid as a means of leaching out sulphate and sulphide sulphur species, respectively. Subjecting the samples to acid also releases readily-dissolving elements (likely to be involved in acid-neutralising reactions) and compounds into the leachate. The content of elements that are constituents of acid-producing minerals (Fe, S) are compared to elements that constitute acid-neutralising minerals (Ca, Mg, Na, K). A balance between the respective minerals allows for the determination of the acid-generating and acid-neutralising potential as part of Acid Base Accounting (ABA) procedures...M.Sc. (Geology

    The distribution and origins of acid groundwaters in the South West Agricultural Area

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    Misconceptions About Caves and Karst: Common Problems and Educational Solutions

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    Provides pedagogical insight concerning learners' pre-conceptions and misconceptions about groundwater, caves, karst The resource being annotated is: http://www.dlese.org/dds/catalog_DLESE-000-000-010-102.htm
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