Salinization of groundwater in the Nefzawa oases region,Tunisia: results of a regional-scale hydrogeologic approach   总被引：1，自引：0，他引：1  

Mounira Zammouri  Tobias Siegfried  Tobias El-Fahem  Samiha Kriâa  Wolfgang Kinzelbach 《Hydrogeology Journal》2007,15(7):1357-1375

Groundwater pumped from the semi-confined Complexe Terminal (CT) aquifer is an important production factor in irrigated oases agriculture in southern Tunisia. A rise in the groundwater salinity has been observed as a consequence of increasing abstraction from the aquifer during the last few decades. All sources of contamination were investigated using hydrochemical data available from the 1980s. Water samples were taken from drains and observation wells tapping both the CT and the phreatic aquifers and analyzed with regard to chemistry, temperature, isotopes and other environmental tracers. Local salinization mechanisms are suggested, i.e. the upwelling of saline water from the underlying, confined Continental Intercalaire (CI) aquifer, as well as backflow of agricultural drainage water. At this stage, the main salt pan, the Chott el Djerid, is not a contamination source. A finite difference model was also developed to simulate groundwater flow and contaminant transport in the oases. Calibration for the period 1950–2000 was carried out in order to adjust geological and chemical system parameters. The simulation of planned extraction projects predicts a worsening of the present situation. Maintenance of the present abstraction regime will not reduce or stop the salinity increase.

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Résumé L’eau souterraine pompée dans l’aquifère semi-captif du Complexe Terminal (CT) est un facteur de production important pour l’agriculture des oasis irriguées du sud de la Tunisie. Une augmentation de la salinité de l’eau souterraine a été considérée comme la conséquence de l’augmentation des prélèvements dans l’aquifère au cours des dernières décades. Toutes les sources de contamination ont été étudiées à l’aide de données hydro-chimiques disponibles depuis les années 80. Des échantillons d’eau ont été prélevés dans des drains et des puits d’observation qui captent à la fois le CT et les aquifères phréatiques; la chimie, la température, les isotopes ainsi que d’autres traceurs environnementaux ont été analysés. Des processus locaux de salinisation sont proposés, comme par exemple la remontée d’eau salée en provenance de l’aquifère captif du Continental Intercalaire (CI) sous-jacent, ainsi que le reflux des eaux du drainage agricole. A ce stade, le principal marais salé, le Chott el Djerid, n’est pas une source de contamination. Un modèle aux différences finies a également été élaboré pour simuler les écoulements souterrains et le transport de contaminants dans les oasis. Une calibration pour la période 1950–2000 a été effectuée afin d’ajuster les paramètres des systèmes géologique et chimique. La simulation de projets planifiés d’extraction prédit une aggravation de la situation actuelle. La conservation du régime d’extraction actuel ne réduira ou ne stoppera pas l’augmentation de la salinité.

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Resumen El agua subterránea que se bombea del acuífero semi-confinado Terminal Complejo (CT) es un importante factor de producción en la agricultura de riego con oasis en el sur de Túnez. Se ha observado un incremento en la salinidad del agua subterránea como consecuencia de la abstracción creciente del acuífero durante las últimas décadas. Se investigaron todas las fuentes de contaminación usando datos hidroquímicos disponibles de la década de 1980s. Las muestras de agua se tomaron de drenajes y pozos de observación alojados tanto en el CT como los acuíferos freáticos y se analizaron en relación con química, temperatura, isótopos y otros trazadores ambientales. Se sugieren mecanismos de salinización local, i.e. el ascenso de agua salada a partir del acuífero confinado subyacente Intercalado Continental (CI), así como también retorno de flujo de agua de drenaje agrícola. En esta etapa, el pan salado principal, el Chott el Djerid, no es una fuente de contaminación. También se desarrolló un modelo de diferencia finita para simular el flujo de agua subterránea y el transporte de contaminantes en los oasis. Se calibró el modelo para el periodo 1950–2000 para de este modo ajustar parámetros del sistema químico y geológico. La simulación de los proyectos de extracción que se han planeado predice un empeoramiento de la situación actual. El mantenimiento del régimen de extracción actual no reducirá o detendrá el incremento de salinidad.

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Constraints on incipient charnockite formation from zircon geochronology and rare earth element characteristics     

A. Rimša  L. Johansson  M. J. Whitehouse 《Contributions to Mineralogy and Petrology》2007,154(3):357-369

We present high spatial resolution ion-microprobe U–Th–Pb geochronology and rare earth element (REE) data combined with cathodoluminescence (CL) and back-scattered electron (BSE) imaging for complex zircons in incipient charnockites from Söndrum, SW Sweden. Examination of closely paired samples across the dehydration zone demonstrates that incipient charnockite formation at Söndrum is a zircon-forming process. We determined the age of the dehydration event (i.e. charnockitisation) to 1,397 ± 4 Ma (2σ, MSWD = 1.7). This is the first successful attempt to date incipient charnockite formation using U–Pb systematics of zircon. Internal structure, chemical and isotopic characteristics of zircon indicate that the granitic pegmatite in the core of the incipient charnockite is a melting zone. Commonly observed bulk rock HREE depletion in incipient charnockites is not caused by zircon dissolution but by involvement of garnet as a reactant in the dehydration reactions. Moreover, REE patterns of the newly formed zircon are HREE-enriched, indicating non-concurrent growth and suggesting that the degree of charnockite depletion in HREE might be controlled by the volume of newly formed zircon.  相似文献   

The December 26th 2004 Tsunami Recorded along the Southeastern Coast of Brazil     

Carlos A. S. França  Afranio R. De Mesquita 《Natural Hazards》2007,40(1):209-222

Sea level measurements along the southeastern Brazilian coast, between 20° S and 30° S, show the effect of the Sumatra Tsunami of December 26, 2004. Two records from stations, one located inside an estuary and other inside a bay, shows oscillations of about 0.20 m range; one additional record from a station facing the open sea shows up to 1.2 m range oscillations. These oscillations have around 45 min period, starting 20–22 h after the Sumatra earthquake in the Indian Ocean (00:59 UTC) and lasting for 2 days. A computer modelling of the event reproduces the time of arrival of long shallow-water tsunami waves at the southeastern Brazilian coast but with slight longer period and amplitudes smaller than observed at the coast, probably due to its coarse resolution (1/4 of a degree). The high amplitudes observed at the coast suggest a mechanism of amplification of these waves over the southeastern Brazilian shelf.  相似文献   

Textural evolution of polyhedral olivine experiencing rapid cooling rates     

François Faure  Pierre Schiano  Gilles Trolliard  Christian Nicollet  Bernard Soulestin 《Contributions to Mineralogy and Petrology》2007,153(4):405-416

Dynamic crystallization experiments in the CaO–MgO–Al₂O₃–SiO₂ (CMAS) system have been used to investigate the change in crystal shape when pre-existing polyhedral olivine crystals are cooled rapidly (1,639–2,182°C/h). Polyhedral olivines are crystallized initially in a first step using a slow cooling rate (2°C/h), then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event. During this second episode small dendritic olivines also nucleate within the liquid phase. Observation of the experimental sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic morphology in the following sequence: polyhedral ⇒ hopper polyhedral ⇒ dendritic polyhedral. This evolutional sequence is discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine dynamic crystallization experiments and the integrated model of crystal growth by Sunagawa (Bull Minér 104:81–87, 1981, Morphology of crystals, Terra Scientific Publishing Company, 1987) is proposed.  相似文献   

Gravel washing wastes from Jarama river deposits (Spain): an undervalued natural raw material     

I. Blanco-García  M. Rodas  C. J. Sánchez  J. Alonso-Azcárate 《Environmental Geology》2007,52(6):1097-1115

This work presents the main characteristics of 97 quarry wastes, collected in 23 gravel pits, from the Jarama river area, Madrid province, Spain. In this area, more than 2.5 × 10⁶ ton of silty-clay waste are generated every year, and no applications have as yet been defined for them. This work is the first systematic study of the fine fractions generated from the Jarama river quaternary deposits, playing part in the comprehension of this complex terrace systems. Quartz, potassium feldspar, plagioclase, calcite, and complex mixtures of phyllosilicates, such as smectite, illite, kaolinite, chlorite and illite/smectite mixed layer, have been detected. Two sets of waste which are recognized according to the calcite content, have been directly related with the terrace level beneficed in the Jarama river, and the position along the valley. Calcite concentrates in the wastes produced in the lower course, where Henares and Tajuña tributaries promote an extensive change in the geochemistry of underground water, and locally, in the petrology of quarried conglomerates. This clear distinction by location between calcite-bearing and calcite-free wastes is essential for potential applications, such as soil conditioning, raw materials for brick or tiles, etc. The wastes studied can be considered as a potential source of industrial raw materials because of their uniformity and large volume. This suggestion is now being carried out, with an attempt at assessing the possibilities of using these mining wastes as ceramic raw materials.  相似文献   

A comparison between fluorite mineralizations in the central Anatolian Massif: Trace-element contents     

Ș. Koç  N. Özșahin  A. Rençber  Ö. Özmen 《Geochemistry International》2007,45(5):509-517

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Modeling surface roughness degradation of rock joint wall during monotonic and cyclic shearing   总被引：2，自引：0，他引：2  

Tikou Belem  Mountaka Souley  Françoise Homand 《Acta Geotechnica》2007,2(4):227-248

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Application of the FAO quantitative and SINDI methods to assess the quality of different soils in Castilla-La Mancha (Spain)     

V. González-Quiñones  A. de la Torre  M. P. García  A. Polo  R. Jiménez-Ballesta 《Environmental Geology》2007,53(3):527-531

In the region of Castilla-La Mancha (Spain), over half of the soils are under cropping. This vast agricultural activity, combined with other anthropological uses, has led to a deterioration of the soil quality and virtual degradation. Therefore, it was deemed to assess the quality of these soils, which was achieved by applying two different methods. Three soils, representative of typical conditions in this community, were sampled and diverse properties were analysed in order to apply two different approaches. The first soil evaluation was carried out by a traditional method developed by FAO using a productivity index, whereas the second method consisted of the application of a new method called SINDI, developed in New Zealand. Both approaches make an evaluation based on a number of indicators that differs in each case. These differences explain why each method ranked the soils studied in different order reaching diverse conclusions on their quality.  相似文献   

Testing the predictive power of seagrass depth limit models     

Carlos M. Duarte  Núria Marbà  Dorte Krause-Jensen  María Sánchez-Camacho 《Estuaries and Coasts》2007,30(4):652-656

The power of equations predicting seagrass depth limit (Z_c) from light extinction (K _z) was tested on data on seagrass depth limits collected from the literature. The test data set comprised 424 reports of seagrass colonization depth and water transparency, including data for 10 seagrass species. This data set confirmed the strong negative relationship betweenZ _c andK _z. The regression equation in Duarte (1991) overestimated the realized seagrass colonization depths at colonization depths < 5 m, while there was no prediction bias above this threshold. These results indicated that seagrass colonizing turbid waters (K _z 0.27 m^-1) have higher apparent light requirements than those growing in clearer waters. The relationship between seagrass colonization depth and light attenuation shifts at a threshold of light attenuation of 0.27 m^-1, requiring separate equations to predictZ _c for seagrass growing in more turbid waters and clearer waters, and to set targets for seagrass restoration and conservation efforts.  相似文献   

Recent changes in flood risk in the Gran La Plata,Buenos Aires province,Argentina: causes and management strategy     

María Isabel Andrade  Olga Eugenia Scarpati 《GeoJournal》2007,70(4):245-250

The paper analyses the causes of flood occurrence in the Gran La Plata, Buenos Aires Province, Argentina, and the changes that have occurred since the 1970s. The area is characterized by serious deficiencies in the use and management of water resources. The main factors are: (1) flood risk information is not updated; (2) urban building organization does not consider the flood risk; (3) the topography and other physical features are not taken into account in urban development. This research considers some specific problems, especially in data availability, and suggests ways to solve them, including improved analytical methodology. One of the main objectives is to analyse flood risk in social terms, producing a map of flood risk from the “human social vulnerability” point of view. The results suggest that flood risk has increased since the 1980s and that this is associated with changes in precipitation patterns that have also been aggravated by lack of controls on urban development. The poorer areas with the lowest level of infrastructure and public services, many of them developed over the last quarter-century, are especially vulnerable.  相似文献