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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Temporal correlations of atmospheric mapping function errors in GPS estimation     

Borys Stoew  Tobias Nilsson  Gunnar Elgered  Per O. J. Jarlemark 《Journal of Geodesy》2007,81(5):311-323

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MHD Simulations of Relativistic Jets     

Tobias Leismann  Miguel-Angel Aloy  Ewald Müller 《Astrophysics and Space Science》2004,293(1-2):157-163

In a series of time dependent numerical simulations we have performed a parameter study of magnetised relativistic jets. We have found that the impact of the magnetic field on the morphology of a jet depends strongly on the configuration of the field.  相似文献   

Jovian satellite nomenclature     

Tobias Owen 《Icarus》1976,29(1):159-163

A brief review of the history of Jovian satellite nomenclature is given to indicate the background for the names proposed for the numbered satellites. The new names are consistent with established tradition and should cause minimal confusion with other named objects in the solar system.  相似文献   

The Comet Nucleus Tour (Contour); A NASA Discovery Mission     

Cochran  Anita  Veverka  Joseph  Bell  James  Belton  Michael  Benkhoff  Johannes  Benkhoff  Andrew  Clark  Benton  Feldman  Paul  Kissel  Jochen  Mahaffy  Paul  Malin  Michael  Murchie  Scott  Neimann  Hasso  Owen  Tobias  Robinson  Mark  Schwehm  Gerhard  Squyres  Steve  Thomas  Peter  Whipple  Fred  Yeomans  Donald 《Earth, Moon, and Planets》2000,89(1-4):289-300

In 1997, the COmet Nucleus TOUR (CONTOUR) was selected byNASA for a new start as part of the Discovery line. In this paper, we review the status of the mission, the mission timeline and the instruments to be flown. Detail is given of the science goals and how they are to be accomplished.  相似文献   

Analysis of the Slab Ocean El Nino atmospheric feedbacks in observed and simulated ENSO dynamics     

Dietmar Dommenget  Sabine Haase  Tobias Bayr  Claudia Frauen 《Climate Dynamics》2014,42(11-12):3187-3205

In a recent study it was illustrated that the El Nino Southern Oscillation (ENSO) mode can exist in the absence of any ocean dynamics. This oscillating mode exists just due to the interaction between atmospheric heat fluxes and ocean heat capacity. The primary purpose of this study is to further explore these atmospheric Slab Ocean ENSO dynamics and therefore the role of positive atmospheric feedbacks in model simulations and observations. The positive solar radiation feedback to sea surface temperature (SST), due to reduced cloud cover for anomalous warm SSTs, is the main positive feedback in the Slab Ocean El Nino dynamics. The strength of this positive cloud feedback is strongly related to the strength of the equatorial cold tongue. The combination of positive latent and sensible heat fluxes to the west and negative ones to the east of positive anomalies leads to the westward propagation of the SST anomalies, which allows for oscillating behavior with a preferred period of 6–7 years. Several indications are found that parts of these dynamics are indeed observed and simulated in other atmospheric or coupled general circulation models (AGCMs or CGCMs). The CMIP3 AGCM-slab ensemble of 13 different AGCM simulations shows unstable ocean–atmosphere interactions along the equatorial Pacific related to stronger cold tongues. In observations and in the CMIP3 and CMIP5 CGCM model ensemble the strength and sign of the cloud feedback is a function of the strength of the cold tongue. In summary, this indicates that the Slab Ocean El Nino dynamics are indeed a characteristic of the equatorial Pacific climate that is only dominant or significantly contributing to the ENSO dynamics if the SST cold tongue is sufficiently strong. In the observations this is only the case during strong La Nina conditions. The presence of the Slab Ocean ENSO atmospheric feedbacks in observations and CGCM model simulations implies that the family of physical ENSO modes does have another member, which is entirely driven by atmospheric processes and does not need to have the same spatial pattern nor the same time scales as the main ENSO dynamics.  相似文献   

Generation and evaluation of multitemporal digital terrain models of the Mt. Everest area from different optical sensors     

Tino Pieczonka  Tobias Bolch  Manfred Buchroithner 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):927-940

Multitemporal digital terrain models (DTM) are an important source for many purposes such as the detection of areas, which are susceptible to natural hazards such as landslides and glacial lake outburst floods, or for the examination of changes in glacier thickness. To exploit the potential of stereo satellite and aerial imagery for time series analysis, the employed methodology and software can be critical. A statistical analysis based on quartiles is presented to eliminate the influence of registration and elevation errors in DTMs. For our analysis, we used multi-temporal airborne and spaceborne stereoscopic images. The oldest images were recorded in the 1960s by the US American reconnaissance satellite Corona, while the most recent imagery are 2007 Cartosat-1 stereo scenes, along with one ASTER stereo pair. Complex panoramic distortion and limited spatial resolution resulted in the Corona and ASTER DTMs having the highest RMSEz. Due to differing acquisition techniques, applied software packages and temporal differences DTMs will never be identical. Therefore, we propose a relative vertical accuracy assessment with a master DTM. We chose the Cartosat-1 DTM as it showed the highest absolute accuracy. Inaccuracies between the master and the slave DTMs were adjusted by means of trend surfaces and outliers were successfully eliminated applying the interquartile range.  相似文献   

Geochemistry of volcanic fluids     

Salvatore Inguaggiato  Hiroshi Shinohara  Tobias Fischer 《Bulletin of Volcanology》2011,73(4):369-371

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Comparing satellite derived precipitation datasets using the Hillslope River Routing (HRR) model in the Congo River Basin   总被引：1，自引：0，他引：1  

R. E. Beighley  R. L. Ray  Y. He  H. Lee  L. Schaller  K. M. Andreadis  M. Durand  D. E. Alsdorf  C. K. Shum 《水文研究》2011,25(20):3216-3229

In this paper, three satellite derived precipitation datasets (TRMM, CMORPH, PERSIANN) are used to drive the Hillslope River Routing (HRR) model in the Congo Basin. The precipitation data are compared spatially and temporally in two forms: (1) precipitation magnitudes, and (2) resulting streamflow and water storages. Simulated streamflow is assessed using historical monthly discharge data from in situ stream gauges and recent stage data based on water surface elevations derived from ENVISAT radar altimetry data. Simulated total water storage is assessed using monthly storage change values derived from GRACE data. The results show that the three precipitation datasets vary significantly in terms of magnitudes but generally produce a reasonable hydrograph throughout much of the basin, with the exception of the equatorial regions of the watershed. The satellite datasets provide unreasonably high values for specific periods (e.g. all three in Oct–Nov; only CMORPH and PERSIANN in Mar–Apr) in the equatorial regions. Overall, TRMM (3B42) provides the best spatial and temporal distributions and magnitudes or rainfall based on the assessment measures used here. Both CMORPH and PERSIANN tend to overestimate magnitudes, especially in the equatorial regions of the Basin. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Distribution of n-alkanes in lacustrine sediments from subtropical lake in Brazil     

Daniele Botelho de Souza  Karina Scurupa Machado  Sandro Froehner  Cristóvão Fernandes Scapulatempo  Tobias Bleninger 《Chemie der Erde / Geochemistry》2011,71(2):171-176

The geochemical composition of lake bed sediments of a tropical reservoir in Brazil have been investigated. The C, N, P composition showed almost no variation between the different sampling points. All samples contained inorganic phosphorus (IP) ranging from 52 to 70%. The Redfield ratios show that the lake is without significant anthropogenic inputs. Most of the organic matter is composed by higher plants decomposition revealed in the total organic carbon (TOC):nitrogen (N) ratio ranging from 15.4 to 57.2. Also, TOC:organic phosphorus (OP) ranged from 265.3 to 933.6, suggesting that most of the organic matter has terrestrial origin from wood plants. The ratios suggest that most organic matter is influenced by the terrestrial characteristics of the watershed. Furthermore, the relative abundance of n-alkane homologues in the sediments was investigated. All samples have been analyzed for the n-alkanes C₈ to C₄₀. The sediments were dominated by n-alkanes C₂₅–C₃₈. It is concluded that n-alkane in sediments mainly come from terrestrial plants, however there is a contribution of submerged aquatic plants, especially in those sites in deeper areas of the lake. On the basis of P_aq index the n-alkanes in sediments comes from terrestrial plants, however there is a contribution from emerged/floating plants.The investigated lake seems to be considered as meso to eutrophic. Because of the relatively high primary productivity in the lakes, there is a substantial organic-matter flux to the sediments, which rapidly becomes anoxic. According to the pristine/phytane ratio the sediments represent an anoxic environment with values found between 0.38 and 1.72.  相似文献