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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 42 (2004), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 18 (1998), S. 0 
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Five inorganic geochemical data sets with ion balances less than or equal to 5% (for different hydrogeologic basins in Mexico) were used to construct specific conductance (SC) vs. total dissolved solids (TDS) curves for each aquifer. These curves allow one to proxy the specific conductance for inorganic water quality. The data from these five curves were integrated to form a “global” curve for Mexico. The equation that defines the line is SC = 1.40 TDS + 18. We propose that, in addition to allowing ground water monitoring, establishing a SC vs. TDS curve may be implemented to monitor drinking water supplies such as wells and reservoirs. If anomalously high values are observed, this would warrant detailed geochemical sampling.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 40 (2002), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 34 (1996), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Eight Schlumberger soundings and four Wenner anisotropy measurements were conducted in the northwestern section of the Yucatan Peninsula for hydrogeological investigations of a karst aquifer. This system is influenced by a circular high permeability zone (Ring of Cenotes) probably related to the Chicxulub Impact Crater. Schlumberger soundings and Wenner anisotropy measurements show that the karst aquifer can be modeled as an electrically anisotropic medium. Anisotropy is related to preferential permeability directions channeling ground-water flow within the aquifer. Directions of maximum permeability were determined using Wenner anisotropy measurements. Electrical soundings were conducted at different sites near the Ring of Cenotes. Resistivity values decrease toward the Ring of Cenotes supporting the hypothesis that selected segments of the Ring have high permeability. Several soundings were conducted in order to study lateral permeability variations along the Ring. A high permeability section can be identified by low resistivity models and is related to a zone of high cenote density. A low permeability section of the Ring was found showing high resistivity models. This zone overlaps with an area of low cenote density. Electrical soundings were used to determine the depth of the fresh-water lens; the interface was detected along two profiles perpendicular and parallel to the Ring of Cenotes resulting in a depth that ranged from 18 m near the coast up to 110 m in the southeastern part of the study area. The predicted depths of the interface using electrical methods showed a good correlation with Ghyben-Herzberg and measured interface depths at some sites. Discrepancies between calculated and interpreted interface depths at two sites may be explained by horizontal-to-vertical permeability anisotropy.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our study was carried out on zircons from the Beloc site (no. 1) in Haiti11, and on a 30-g carbonate-rich polymict breccia sample (with 20-25% of clasts, consisting of 0.2-2.0 mm silicate basement rocks) from the Y6 drill hole (sample N13, from a depth of 1,100-1,103 m), located within and 50 km ...
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Since the original proposition by Alvarez et al.s that the K/T boundary was marked by a giant impact which led to the extinction of over half the species on Earth, researchers have been searching for the source crater for a large K/T impact event9"14. Identification of impact-glass spherules (and ...
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our analysis is based on core samples of melt rocks and breccia units from two Petroleos Mexicanos exploratory wells within the Chicxulub structure: Chicxulub 1 (Cl), located near the centre of the structure, and Yucatan 6 (Y6), located 60 km south-southwest of the centre2'3. Silicate rocks ...
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-515X
    Keywords: bog ; DOC ; fen ; geochemistry ; hydrogeochemistry ; hydrology ; peatland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We studied the factors causing spatial and temporal patterning of interstitial water chemistry in Crystal Bog, a 7 ha northern Wisconsin kettle-hole peatland. Over the course of the snow-free season Crystal Bog exhibited spatial and temporal patterns in chemistry, especially hydrogen-ion, dissolved organic carbon, and specific conductance. The peatland contains a 0.5 ha pond that has water more dilute than the interstitial water of the surrounding peatland. The direction of groundwater flow between the lake and the peatland was seasonally dependent. In the spring and early summer, flow was from the lake into the peatland, especially on the eastern side of the lake. This flow resulted in a plume of relatively dilute surface interstitial water in the peatland. In mid and late summer direction of groundwater flow was from the peatland into the lake and the dilute plume was reduced in areal extent. By fall the direction of water flow was again from the lake to the peatland. The spatial and temporal heterogeneity in water chemistry produced by the seasonal variation in the direction of horizontal water flow was substantial. Minimum and maximum observed concentrations of dissolved organic carbon (DOC) in the interstitial water of the peatland, for example, differed by more than a factor of three, and pH ranged between 3.8 and 5.0. Correlations of DOC with anion deficit and hydrogen ion concentration and experiments of photo-oxidation of water samples showed that organic acids were the primary cause of acidity in the peatland. Specific conductance was highly correlated with DOC, probably because of DOC's correlation with the very conductive hydrogen ion. In Crystal Bog it was possible to use the relatively simple measure of specific conductance to estimate the temporal and spatial distribution of the more difficult to determine DOC.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1435-0157
    Keywords: Key words Mexico ; overexploitation ; salt-water/fresh-water relations ; contamination ; hydrochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé L'aquifère littoral de la vallée d'Hermosillo (Sonora, NW du Mexique) a été surexploitée au cours des derniers quarante ans pour assurer une activité agricole dans l'un des secteurs irrigués les plus importants du Mexique. La surexploitation est due au développement de plusieurs cônes de rabattement de la nappe à plus de 50 m au-dessous du niveau marin. Les activités humaines dans cette région sont responsables d'une contamination de l'aquifère par une intrusion salée à partir du golfe de Californie et par de fortes concentrations en nitrates. Une zonation hydrogéochimique de l'aquifère, basée sur la présence de différents types d'eaux, a conduit à identifier une bande côtière large d'environ 30 km, affectée par l'intrusion salée. La conductivité des eaux échantillonnées et l'interprétation du rapport Na/Cl×1000 ont été utilisées pour localiser les trois panaches principaux d'intrusion dans la bande côtière. Le bruit de fond en nitrates dans l'aquifère est de quelques ppm, mais des teneurs atteignant 17 ppm sont observées dans certains puits. L'irrigation à partir d'eaux usées brutes et la migration de contaminants dans des secteurs à fort gradient hydraulique vers les cônes de rabattement sont probablement responsables des pics localisés de concentration en nitrates.
    Abstract: Resumen El acuífero costero del Valle de Hermosillo, en el estado de Sonora, al noroeste de México, ha sufrido una sobre-explotación durante las últimas cuatro décadas con el objeto de mantener la actividad agrícola en una de las mayores áreas de regadío de la República Mexicana. Esta sobre-explotación ha provocado el desarrollo de varios conos de descenso y la reducción de los niveles freáticos hasta valores de 50 m por debajo del nivel del mar. Como consecuencia de las actividades antrópicas, el acuífero se ha contaminado por intrusión salina desde el Golfo de California y por el aumento en la concentración de nitratos. Se ha realizado una zonificación hidrogeoquímica del acuífero, basada en la presencia de distintas familias de agua, que ha conducido a la identificación de una banda costera de unos 30 km de anchura afectada por intrusión salina. La conductividad y la relación iónica Na/Cl del agua muestreada se usaron para la localización de los tres grandes penachos de intrusión existentes. El valor de fondo del contenido en nitratos es de alrededor de 4 ppm, pero se han medido valores de hasta 17 ppm. El riego con agua residual no tratada y el movimiento de los contaminantes en zonas de altos gradientes hidráulicos son los posibles responsables de estos picos en la concentración de nitratos.
    Notes: Abstract  The Valley of Hermosillo coastal aquifer, state of Sonora, northwestern Mexico, has been over-exploited for the last four decades, in order to maintain agricultural activity in one of the most important irrigation districts of the Mexican Republic. The over-exploitation has resulted in the development of several drawdown cones and in the lowering of the water table to as much as 50 m below mean sea level. Contamination of the aquifer in the form of salt-water intrusion from the Gulf of California and high nitrate concentrations is the consequence of human activities. A hydrogeochemical zonation of the aquifer, based on the presence of different water families, led to the identification of a coastal band approximately 30 km wide that is affected by salt-water intrusion. Conductivity of the sampled water and the interpretation of the ratio Na/Cl×1000 was used to identify the location of three major intrusion plumes in this coastal band. The background nitrate contamination of the aquifer is about 4 ppm, but contents as great as about 17 ppm occur in some wells. Irrigation with raw sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for localized peaks of the nitrate concentration.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1435-0157
    Keywords: Key words Contamination ; hydrochemistry ; karst ; Mexico ; water supply
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé Les eaux de cinq cénotés, qui sont normalement utilisées pour des activités de plein air, dans la région touristique de Cancun–Tulum (Mexique), ont été soumises à analyses chimiques pour savoir si les cénotés peuvent être considérés comme des sources d'eau potable. Plusieurs paramètres dépassent les normes mexicaines en matière d'eau potable; mais comme ceux-ci ne posent pas de problème réel de santé, quatre des cinq cénotés peuvent être captés pour l'eau potable. Les contaminants habituels dans les eaux de la presqu'île du Yucatan, coliformes fécaux et concentrations élevées en nitrate, sont la plupart du temps au-dessous des normes (respectivement 0 à 460 germes/100 ml et 0,31 à 1,18 mg/l). Bien que ces quatre cénotés satisfassent aux normes, il est nécessaire de mettre en place des règles précises de l'utilisation de l'eau souterraine, afin d'éviter la contamination par les germes fécaux et par les nitrates, ainsi que l'intrusion marine.
    Abstract: Resumen Se analizó hidroquímica y bacteriológicamente el agua de algunos cenotes localizados a lo largo del corredor turístico Cancun–Tulum, que actualmente se utilizan para diversas actividades recreativas, para determinar su potencial de uso como fuente de abastecimiento de agua potable. La mayor parte de los parámetros excedieron los criterios establecidos en la Norma Mexicana para Agua Potable (NMAP), sin embargo, como éstas no representan una riesgo para la salud, el agua de cuatro de los cinco cenotes puede ser emplada como fuente de abastecimiento de agua potable. Los contaminantes comúnes del agua subterránea de la península de Yucatán, coliformes fecales y nitratos, se encuentran en la mayoría de los casos por debajo de la NMAP (0–460 NMP/ 100 ml y 0.31–1.18 mg/l, respectivamente). A pesar de que estos cuatro cenotes cumplen con la NMAP, es necesario desarrollar una política de manejo adecuada del agua subterránea para evitar la contaminación de este recurso (fecal y por nitratos), así como la intrusión de agua salina.
    Notes: Abstract  Waters from five cenotes that are currently being used for aquatic recreational activities and that lie along the Cancun–Tulum touristic corridor, Mexico, were evaluated hydrochemically to determine whether the cenotes may be considered as potential drinking-water sources. Several parameters exceed the Mexican Drinking Water Standards (MDWS), but since they do not pose a significant health threat, four of the five cenotes may be used as drinking-water sources. The common contaminants in the Yucatan Peninsula, fecal coliforms and nitrate, are in most cases below the MDWS (0–460 MPN/100 ml and 0.31–1.18 mg/L, respectively). Although these four cenotes meet the MDWS, a careful groundwater management policy needs to be developed to avoid contamination (fecal and nitrates) and salt-water intrusion.
    Type of Medium: Electronic Resource
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