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41.
This study uses radiometric analysis (210Pb and 137Cs) of short sediment cores with high-resolution sampling (1-cm interval) to trace sedimentation rates in the Nile Delta lagoons,
particularly since completion of the Aswan High Dam in 1964. A declining trend in 210Pbex as calculated by the CIC model is clearly identified in about 10 cm of the upper-core sediments from the lagoons of Manzala
and Edku, accompanied by two spikes of 137Cs in cores from the lagoons of Burullus and Edku. These findings illustrate average post-dam sedimentation rates ranging
from 0.22 to 0.27 cm a−1 in the lagoons, in contrast with those found previously based on low-resolution sampling. The lower sedimentation rates in
the lagoons are a consequence of a dramatic reduction in riverine sediment load to the coastal area as a result of the damming.
Although widespread erosion occurs along the open estuarine coast, the lagoon setting remains calmer than before due to coastal
diking and freshwater regulation in the delta plain in the past decades. This provides the possibility of continuously preserved
radiometric records in the less-bioturbated lagoon sediments. Dating individual layers using the CRS model has revealed increasing
sedimentation rates in Manzala and Burullus since the 1980s, which can largely be explained as a consequence of the reduction
in lagoon area due to intensifying reclamation. The post-dam sedimentation in the shrinking lagoons may have some adverse
ecological consequences due to finer sediment’s affinity with pollutants. These findings would shed light on the environmental
conservation and socioeconomic development in the Nile Delta region. 相似文献
42.
Abdelhafid Fekkoul Yassine Zarhloule Mimoun Boughriba Alae-eddine Barkaoui Abdelhakim Jilali Salem Bouri 《Arabian Journal of Geosciences》2013,6(12):4917-4924
Located at the northeastern part of Morocco, the plain of Triffa is characterized by a semi-arid climate where water resources are rather fragile and influenced by a highly irregular rainfall distribution, both in time (annual and inter-annual distribution) and in space. The mean annual rainfall does not exceed 240 mm. In the Triffa plain, the impact of anthropogenic activities on the groundwater resources is reflected both by (a) the decrease in the piezometric level due to the over exploitation and droughts and (b) the deterioration of the chemical quality of water. Currently, this situation is felt mainly by the farmers. The unconfined aquifer is under stress due to the increase of the pollution rate, especially by nitrates that are above the WHO standards, and salinity. Organochlorine pesticides are ubiquitous and persistent organic pollutants used widely in agriculture. Due to their extensive use in agriculture, organic environment contaminants such as hexachlorocyclohexane, DDT, and DDD along organochlorine pesticides are distributed globally by transport through water. Pesticides such as aldrin, lindane, and heptachlor have also been detected and were considered as indicators showing the need to inform and to train farmers on the pesticides and fertilizers use in order to reduce the threat of groundwater contamination. 相似文献
43.
Khaled Gamal Ali 《Arabian Journal of Geosciences》2013,6(6):1753-1767
The El Sela area is a part of the basement complex of the Eastern Desert of Egypt and the Pan-African Shield. The area comprises outcrops of dismembered ophiolites thrust over arc volcano-sedimentary sequence and intruded by different syn- to post-tectonic granitoids. Structural analysis of the area enabled the separation and definition of four structural episodes: (E1) folding–thrusting episode associated with the cratonization of the arc/inter-arc rock association and the intrusion of the syntectonic (Older) granites. (E2) Upright folding episode associated with the compression and shortening to the ENE–WSW direction which is different from the NNW–SSE shortening direction during E1; at the end of E2, late tectonic granites were intruded. (E3) Post-tectonic granitic intrusion episode: two mica granite and granitic dikes were intruded during this episode. (E4) Fracturing, faulting, and post-granitic dike extrusion episodes caused different faults that took place after cratonization until the present. There are three generations of folds during ductile deformation (E1 and E2). The F2 folds are nearly coaxial (along ENE–WSW trend) with the F1 folds. The F3 folding is displayed by folds generally trending NNW–SSE. Therefore, the ENE–WSW and NNW–SSE trends can considered as preexisting discontinuities and mechanical anisotropy of the crust in the following structure episodes. Brittle deformation (E3 and E4) reveals the importance of those trends which control the multi-injections and many alteration features in the study area. During reactivation, a simple shear parallel to the inherited ductile fabrics was responsible for the development of mineralized structures along the ENE–WSW and NNW–SSE trends. So they can be considered as paleochannel trends for deep-seated structures and can act as a good trap for uranium and/or other mineral resources. Most of the uranium anomalies are delineated along ENE–WSW and NNW–SSE shear zones where quartz-bearing veins bounded the lamprophyre dike and microgranites and dissected them in relation to the successive fracturation and brecciation corresponding to the repeated rejuvenation of the structures. Therefore, the structural controls of the uranium mineralizations in the El Sela area appear to be related to the interaction between inherited ductile fabrics and overprinting brittle structures. 相似文献
44.
El Bahariya Oasis is a part of the great groundwater reservoir of the Western Desert of Egypt. The different stratigraphic units, the water-bearing zones, aquifer potentiality conditions, and the favorable locations for drilling new wells were evaluated by carrying out 24 Schlumberger vertical electrical soundings (VESs), along with the data of some wells drilled in the near vicinity of the measuring sites. The results of the interpreted field data revealed the presence of ten distinctive subsurface geoelectric layers; a thin surface, dry loose sand and gravel, sandy clay and shale interclations, saturated coarse sand layer, shale and clay, and saturated fine sandstone and saturated coarse sandstone. The aquifer is a multilayer aquifer with different thicknesses represented by the fourth, sixth, eighth, and tenth geoelectric layers. Results also revealed that the thicknesses of the water-bearing horizons increase towards the east direction, consequently the aquifer potentiality increases. Therefore, the best production well locations are in that direction. Depth to water starts from 40 m at VES no. 14 and increases gradually toward the east to reach 66 m at VES no. 5. Hydrogeochemical analysis of two groundwater samples taken from Ein El Ezza and well no. 2 showed that groundwater in the study area is suitable for agricultural purposes but not for human consumption due to the high iron content. Recommendations concerning site selection for drilling new productive groundwater wells are given. 相似文献
45.
We report on the statistical properties of the microwave enhancement (brightness temperature, area, fine structure, life time
and magnetic field strength) in coronal holes observed over a period of several solar rotations. 相似文献
46.
El-Sayed Mohamed Salem 《Arabian Journal of Geosciences》2008,1(2):97-110
Strong-motion parameters, peak ground acceleration, peak ground velocity, and peak ground displacement depend on several factors,
such as the source of earthquake, distance between the source and site, and the characteristics of that site. Five seismographs
and two accelographs were installed by the Egyptian Geological Survey team along the western side of the Gulf of Aqaba from
Taba to Sharm El-Sheikh to record seismic events during the period from September 1995 to June 1996. During this period, two
events were recorded by the accelographs. The two accelographs were located on the surface of the basement rocks, the first
near the epicenter and the second at a farther distance. However, the farthest accelograph recorded higher values compared
to the nearer one. Fault mechanics are an important factor in determining the values of strong motion parameters, where the
direction of the rupture line plays an important role in detecting the values of strong motion parameters, the strong motion
parameters and damage effects seem to be attenuated very fast in the direction perpendicular to the rupture line. This can
be interpreted by the fact that the farthest accelograph lies at the extension of the fault rupture (azimuth = 30°), while
the nearer one was perpendicular to the strike of the fault rupture. 相似文献
47.
The procedures for the determination of phosphate are based on the reduction of molybdophosphoric heteropoly acids using ascorbic acid. Measurements of the complex products formed with rhodamine B and chlorophenol red dyes and the reduced molybdophosphoric acid are made at 490 and 510 nm with molar absorptivities of 28571 and 20949 l/mol. cm with each dye, respectively. Phosphate could be determined in the concentration ranges of 0.44 to 1.21 and 0.44 to 1.32 μg/l PO4-P with rhodamine B and chlorophenol red dyes, respectively. The results obtained are compared with those of molybdophosphoric acid with rhodamine B and chlorophenol red using stannous chloride as reducing agent. These procedures are used for the determination of phosphate in the Kingdom of Saudi Arabia. 相似文献
48.
Temperature profiles from 25 boreholes were used to understand the spatial and vertical groundwater flow systems in the Western Nile Delta region of Egypt, as a case study of a semi-arid region. The study area is located between the Nile River and Wadi El Natrun. The recharge areas, which are located in the northeastern and the northwestern parts of the study area, have low subsurface temperatures. The discharge areas, which are located in the western (Wadi El Natrun) and southern (Moghra aquifer) parts of the study area, have higher subsurface temperatures. In the deeper zones, the effects of faults and the recharge area in the northeastern direction disappear at 80 m below sea level. For that depth, one main recharge and one main discharge area are recognized. The recharge area is located to the north in the Quaternary aquifer, and the discharge area is located to the south in the Miocene aquifer. Two-dimensional groundwater-flow and heat-transport models reveal that the sealing faults are the major factor disturbing the regional subsurface thermal regime in the study area. Besides the main recharge and discharge areas, the low permeability of the faults creates local discharge areas in its up-throw side and local recharge areas in its down-throw side. The estimated average linear groundwater velocity in the recharge area is 0.9 mm/day to the eastern direction and 14 mm/day to the northwest. The average linear groundwater discharge velocities range from 0.4 to 0.9 mm/day in the southern part. 相似文献
49.
Thick forest cover and poor infrastructures are the major hindrances for detailed lithologic mapping in an inaccessible montane landscape. To overcome these limitations, we utilize a Landsat 5 TM image to map lithology using vegetation and drainage pattern as an indicator of underlying rock types in a heavily forested region of the Chittagong Hill Tracts area located in southeastern Bangladesh. We use supervised and unsupervised classifiers for a vegetation-based approach while on-screen digitization is used for drainage patterns-based mapping. Field observations were used for mapping lithology and evaluating accuracy. Overall, our results agree well with the current geologic map and improve it by providing a more spatially detailed distribution of the sandstone and shale. The performances of all approaches are good at the inner and outer flanks of anticlines located in the study area while the drainage pattern mapping performs best at the mid-flank area. 相似文献
50.