Impacts Of Management Practices On Groundwater Conditions In The Eastern Province,Saudi Arabia

Insufficient attention has been given to management issues of groundwater in desertic aquifers, especially pumping policies and the proper design of well fields, i.e., the spatial distribution among wells and among well fields. In Saudi Arabia, many wells have been drilled in small areas, and in some parts of the Kingdom, groundwater pumping has increased drastically during the last two decades. Heavy pumping from large numbers of clustered wells in closely spaced well fields has resulted in unacceptable impacts on water levels and water quality in these areas. Numerical techniques were used to assess the impacts of this practice in parts of the Eastern Province. If the existing water-management policies and trend of increased pumping continue, a considerable additional drawdown will occur. Therefore, proper groundwater-management and conservation schemes need to be adopted. The approaches include optimization of well-field designs and well operations, and the implementation of effective irrigation-scheduling techniques. The implementation of a comprehensive irrigation water-management system in a large irrigation project has resulted in significant recovery of groundwater in the project area in the Eastern Province. RÉSUMÉ: Trop peu d'attention a été accordée aux questions de gestion des eaux dans les aquifères désertiques, particulièrement en ce qui concerne la règlementation des pompages et le groupement judicieux des puits, i.e., la répartition en surface des puits et des champs de puits. En Arabie Saoudite, de nombreux puits ont été forés sur des surfaces réduites, et, dans certaines parties du Royaume, le pompage des eaux s'est accru de façon spectaculaire dans les deux dernières déciennes. Un pompage important à partir d'un grand nombre de puits concentrés dans des ensembles rapprochés les uns des autres a eu des effets inacceptables sur le niveau et la qualité des eaux. Des techniques d'analyse numériques ont été employées pour évaluer les conséquences de ces modes de gestion dans certaines parties de la Province de L'Est. Si l'actuelle gestion des eaux se poursuit et le pompage continue de croître, il en résultera un abaissement considérable du niveau d'eau. Il est donc nécessaire d'adopter dans ces régions des méthodes de gestion et de conservation appropriées. Ces méthodes consistent, entre autres, à optimiser l'agencement des groupements de puits et de l'opération des puits, ainsi qu'à adopter des techniques efficaces pour programmer les horaires d'irrigation. L'adoption d'un sytème intégré de gestion des eaux dans un grand programme d'irrigation a provoqué une remontée substantielle des eaux souterraines dans la partie de la Province de L'Est correspondant à la zone du projet. RESUMEN: Los problemas de gestión de las aguas subterráneas en acuíferos desérticos no han recibido suficiente atención, especialmente en lo que respecta a las políticas de captaciones y al diseño adecuado de los campos de pozos, es decir, la distribución espacial de los pozos y de los campos de pozos. En Arabia Saudita, muchos pozos se han excavado en áreas pequeñas, y en algunas partes del Reino, el bombeo de agua se ha incrementado drásticamente durante las dos últimas décadas. El fuerte bombeo en un gran número de pozos de bombeo agrupados, situados en campos de extracción próximos, ha dado lugar impactos inaceptables en los niveles y en la calidad del agua en estas áreas. Se usaron técnicas numéricas para evaluar los impactos de esta política de extracción en partes de la Provincia Oriental. Si la política de gestión del agua actual y el incremento en el bombeo se mantienen, darán lugar a un descenso de niveles adicional considerable. Por tanto, en estas áreas es necesario adoptar esquemas apropiados de gestón y conservación de las aguas subterráneas. Esto incluiría la optimización de los diseños y de los criterios de operación de los campos de pozos y la adopción de técnicas de riego efectivas. La puesta en marcha de un sistema de gestión de aguas de riego, dentro de un gran proyecto de irrigación, ha dado como resultado una recuperación significativa de los niveles de agua en el área de proyecto, situada en la Provincia Oriental.     

An XPS study of the dissolution kinetics of chrysotile in 0.1 N oxalic acid at different temperatures

The dissolution of chrysotile is studied in regard to the surfaces analysis by photoelectron spectrometry. After leaching of chrysotile (Provenance: Thetford; about 200 mg of fibers of 1 cm length) in nonstirred 0.1 N oxalic conditions, the composition of the mineral surfaces is determined by XPS; kinetic curves of dissolution are given in the range 22–80°C. Two conditions for the rate-limiting step are involved for the explanation of the dissolution: diffusion of Mg²⁺ through the fibrous gel or dissociation of chrysotile. By the former, some values of the diffusion coefficient are proposed: D varies from 5·10^?19 cm²s^?1 to 5·10^?16 cm²s^?1, in the range 22–80°C. By the second model, the leaching rate is estimated from 3 Å (22°C) per h to 250 Å (80°C) per h. For the 2 models, the activation heat energy is in the range 15–20 Kcal.     

Response of the shortgrass steppe plant community to fire

Fire is an important driver of ecological pattern and process in grasslands worldwide, although its role in semi-arid systems is less well known. We used published studies and new experimental research to 1) provide a synthesis of existing knowledge of fire in the semi-arid grasslands of the North American Great Plains, and 2) assess the degree of similarity in semi-arid and mesic grassland responses to fire in this region. Based on published studies, burning has neutral to negative effects on aboveground productivity in semi-arid grasslands and variable effects on plant communities. To more rigorously assess fire effects, replicated experimental plots were established in ungrazed shortgrass steppe in northern Colorado and prescribed spring fire was applied in 2006 and 2007, 2006 only, or not at all. Aboveground net primary productivity decreased or remained unchanged with burning. Plant community changes included increases in perennial forbs, decreases in annual grasses and a positive response in annual forbs to the combination of fire and a wet spring in 2007. Combined, these results indicate that post-fire changes in productivity in semi-arid grasslands are neutral to negative, in contrast to positive responses in mesic grasslands, and not strongly negative as previously assumed.     

The effect of the irregularities of the shape of the Earth's core-mantle boundary on the observed acceleration of gravity

Summary The disturbing gravitational effect of the irregularities of the shape of the coremantle boundary are studied at a point on the Earth's surface. The effect is computed for models of local and zonal distribution of the disturbing masses under the assumption that the total mass of the Earth remains constant. Formulae giving the disturbing gravitational effect as a function of the distribution of the disturbing masses and of the position of the point of observation on the Earth's surface are derived for the individual models. Numerical values of the disturbances have been calculate in all cases.     

On reducing ambiguity in the interpretation of transient electromagnetic sounding data1

An attempt to resolve non-uniqueness in the interpretation of transient electromagnetic (TEM) sounding data using measured data alone is made. It is shown in the various examples studied that sufficiently early time measurements can be the determining factor in reducing the ambiguity caused by model equivalence. The early delay times thus play a dual role in transient soundings: they are responsible for resolving shallow structures and they may eliminate the ambiguity in the interpretation of geoelectric parameters of deeper targets. This is illustrated by the results of a follow-up TEM survey at the Dead Sea coast of Israel where the use of supplementary early time measurements allowed non-uniqueness in the determination of the depth to fresh/saline groundwater interface to be resolved.     

Conditions of magmatic crystallization of Na-bearing majoritic garnets in the earth mantle: Evidence from experimental and natural data

Results of experimental study at 7.0–8.5 GPa and 1300–1900°C of the systems pyrope Mg₃Al₂Si₃O₁₂ (Prp)-Na₂MgSi₅O₁₂ (NaGrt) modeling solid solutions of Na-bearing garnets, Prp-jadeite NaAlSi₂O₆ (Jd) in a simplified mode demonstrating melting relations of Na-rich eclogite, and Prp-Na₂CO₃ are presented. Prp-Na₂MgSi₅O₁₂ join is a pseudobinary that results from the decomposition of NaGrt on to coesite and Na-pyroxene. Synthesized garnets are characterized by Na admixture (>0.32 wt % Na₂O) and excess Si (3.05–3.15 f.u.). Maximal Na₂O concentrations (1.5 wt % Na₂O) are reached on the solidus of the system at 8.5 GPa. Clear correlation between Na and Si was established in synthesized garnets; this provides evidence for heterovalent isomorphism of the Mg + Al → Na + Si type with the appearance of Na₂MgSi₅O₁₂ component as a mechanism of such garnet formation. The Prp-Jd join is also pseudobinary that results from the formation of two series of solid solutions: (1) garnet (Prp-NaGrt-majorite) and (2) pyroxene (Jd-clinoenstatite-Eskola molecule), and the appearance of kyanite at the solidus of the system, where garnets with the highest Na₂O contents (>0.8 wt %) are formed. In spite of quite a wide field of garnet crystallization (20–100 mol % Prp), garnets with significant sodium concentration (>0.3 wt % Na₂O) are formed in a Jd-rich part of the system (20–50 mol % Prp). In the Prp-Na₂CO₃ system at 8.5 GPa garnet crystallizes in a wide range of starting compositions as a liquidus mineral containing up to 0.9 wt % Na₂O. Our experiments demonstrate that melt alkalinity, as well as PT-parameters control the crystallization of Na-bearing majoritic garnets. The results obtained provide evidence for the fact that the majority of natural diamonds with inclusions of Na-bearing majoritic garnets containing <0.4 wt % Na₂O were formed in alkaline silicate (carbonate-silicate) melts at a pressure of <7 GPa. Only a small portion of garnets with higher sodium concentrations (>1 wt % Na₂O) could be formed at a pressure of >8.5 GPa. 1 This article was translated by the authors.     

The history and dynamics of a welded pyroclastic dam and its failure

Igneous intrusions in coal seams are found in 80 % of coal mines in the Huaibei coalfield, China, and coal and gas outburst accidents have occurred 11 times under a 120-m-thick sill in the Haizi mining field. The magma’s heat had a significant controlling effect on coal seam gas occurrence. Based on theoretical analysis, experimental tests and site validation, we analyzed the temperature distribution following magma intrusion into coal measure strata and the variations in multiple physical parameters and adsorption/desorption characteristics between the underlying coal seams beneath the sill in the Haizi mining field and coal seams uninfluenced by magma intrusion in the adjacent Linhuan mining field. The research results show that the main factors controlling the temperature distribution of the magma and surrounding rocks in the cooling process include the cooling time and the thickness and initial temperature of the magmatic rock. As the distance from sill increases, the critical effective temperature and the duration of sustained high temperatures decrease. The sill in the Haizi mining field significantly promoted coal seam secondary hydrocarbon generation in the thermally affected area, which generated approximately 340 m³/t of hydrocarbon. In the magma-affected area, the metamorphic grade, micropore volume, amount of gas adsorption, initial speed of gas desorption, and amount of desorption all increase. Fluid entrapment by sills usually causes the gas pressure and gas content of the underlying coal seams to increase. As a result, the outburst risks from coal seams increases as well.     

Long term variations in the mesospheric mean flow observed at Grahamstown (South Africa) and Adelaide (Australia)

The seasonal and interannual behaviour of monthly mean winds at a height of 90 km recorded at Grahamstown (33.3°S, 26.5°E) and Adelaide (34.5°S, 138.5°E) between 1987 and 1994 are compared. The zonal wind is found to be consistently stronger at Grahamstown and is always eastward, whereas at Adelaide it sometimes reverses. Maxima tend to occur near the solstices, the primary maximum during summer at Grahamstown, in agreement with satellite results, and during winter at Adelaide. The meridional wind also tends to be stronger at Grahamstown, but at both stations is predominantly northward with a maximum in summer and generally not as strong as the zonal component. This seasonal behaviour is reasonably well understood in terms of the interaction of the mean flow with gravity waves propagating up from below, with coriolis forces also playing an important role in the case of the meridional wind. Satellite observations do not generally support the idea that longitudinal differences between the stations could be attributed to the presence of a tropospheric/stratospheric stationary wave. It is suggested that these differences are more probably associated with local effects. Interannual zonal wind patterns at the two sites are similar over the summer months but are less well correlated during the rest of the year. The underlying causes of this variability are not well understood but are most probably global in nature, at least during the summer.     

Petrologic, isotopic, and radiometric age constraints on the origin and tectonic history of the Malino Metamorphic Complex, NW Sulawesi, Indonesia

The Malino Metamorphic Complex (MMC) is located at the western end of the north arm of Sulawesi. It consists of mica schists and gneisses (derived from proximal turbidite and granitoid protoliths), with intercalations of greenschist, amphibolite, marble, and quartzite, forming an E-W elongated dome-like structure bounded on all sides by faults. The age of the MMC is constrained between Devonian and Early Carboniferous. This Paleozoic age, the presence of Archean and Proterozoic inherited zircons, and the isotopic signature of the mica schists and gneisses indicate that the terrane was derived from the New Guinea-Australian margin of Gondwana. Similarities with basement rocks in the Bird’s Head suggests a common origin. Greenschists forming a discontinuous selvage (metamorphic carapace) around the complex were derived from adjacent autochthonous Paleogene formations. The rocks of the MMC show a Barrovian-type progression from greenschist through epidote-amphibolite to amphibolite facies. P–T estimations suggest a depth of burial of up to 27–30 km. K/Ar and 40Ar/39Ar cooling ages of 23–11 Ma, and a 7 Ma age for unconformably overlying volcanic rocks, indicate that the complex was exhumed during the Miocene. Two tectonic scenarios are considered: 1. the continental fragment docked with Sulawesi during the Mesozoic and was exhumed as a metamorphic core complex during the Miocene; 2. it was subducted beneath the north arm during the late Oligocene and then rapidly returned back to the surface.