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Sixty-five sediment samples and 25 water samples were collected from Al-Mujib reservoir, central Jordan, in order to investigate
the heavy metal and ionic contamination assessment. Therefore, to achieve this aim, water and sediment samples were collected
during winter and summer seasons (2007) from Al-Mujib reservoir and the areas surrounding it. The study shows that there are
elevated levels of SO4
2−, Cl− and Na+ in reservoir water, which might originate from anthropogenic activities in the reservoir catchment area. In addition, the
reservoir water has higher total hardness (TH) values together with high Ca and Mg contents. This might be attributed to pH
of reservoir water and the nature of the rocks exposed in the catchment area. The average levels of heavy metals in reservoir
sediments are Fe = 14,888.1, Cu = 17.8, Zn = 88.6, Ni = 38.7, Cd = 4.4, Mn = 337.9 and Pb = 6.1 mg/kg, which are lower than
that observed in Wadi Al-Arab reservoir, northern Jordan. The values of enrichment factor are Cd = 35.5, Ni = 3.02, Zn = 2.54,
Cu = 1.26, Mn = 1.2 and Pb = 0.57; these values indicate that heavy metals in sediments of Al-Mujeb reservoir have a different
anthropogenic incrimination inputs. The study showed that the sediments are polluted with Cd, relatively contaminated with
Ni and Zn and uncontaminated with respect to Mn, Pb and Cu. 相似文献
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Crack coalescence in rock masses was studied by performing a series of biaxial compresion tests on specimens made of rock-like
material. Specimens of size 63.5 × 27.9 × 20.3 cm, made of 72% silica sand, 16% cement (Type I) and 12% water by weight were
tested. The joint inclination angle was maintained at 45°, while the offset angle i.e. angle between the plane of the joint
and the line that connects the two inner tips of the joints, was changed from 0° to 90° with an increment of 15°. Three levels
of lateral stress were used; 0.35 MPa, 0.7 MPa and 1.5 MPa on each sample. HP data acquisition system was used to record the
data for each sample. In each sample, four LVDTs were fixed to measure the axial and lateral displacement along the sample.
The failure mechanisms were monitored by eye inspection and a magnifier to detect crack initiation and propagation. For each
test, the failure surfaces were investigated to determine the characteristics of each surface. Wing cracks initiated at the
tip of the joint for the low confining stress applied, while at higher confining stresses wing cracks also initiated at the
middle of the joint. Secondary cracks initiated at the tip of the joint due to shear stress. Three modes of failure took place
due to coalescence of the secondary and wing cracks. The bridge inclination was the main variable that controlled the mode
of failure. For bridge inclination of 0°, the coalescence occured due to shear failure and for bridge inclination of 90° the
coalescence occurred due to tensile failure while for the other bridge inclinations coalescence occured due to mixed tensile
and shear failure. 相似文献
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Two expeditions (October 1989 and May 1992) were carried out to two points of the main Amazon River channel and four tributaries. The Solimões and Madeira rivers, taking their origin in the Andes, are whitewater rivers. The Negro River is a typical acid, blackwater river. The Trombetas River flows through bauxite‐rich areas, and is characterized by low concentrations of dissolved humic substances. The 238U, 234U, 232Th and 230Th activities were recorded from dissolved, suspended particulate phases and river bank sediments. The latter were analysed for their 226Ra, 228Ra and 210Pb contents, and also subjected to leaching with 0·2 M hydroxylamine–hydrochloride solution to determine the concentrations of radionuclides bound to amorphous Fe hydroxides and Mn oxides and hydroxides. The dissolved U average concentration in the Amazon system is ten times lower than the mean world river concentration. The uranium concentration observed at Óbidos in the lower Amazon (0·095 µg L?1), where the U content in the river bank sediments and suspended matter is lowest, suggests U release from the solid phase during river transport. About 485 t of U are transported annually to the Amazon delta area in dissolved form, and 1943 t bound to suspended particulate matter. Total U and Th concentrations in the river bank sediments ranged from 1·59 to 7·14 µg g?1 and from 6·74 to 32 µg g?1, respectively. The highest concentrations were observed in the Trombetas River. The proportion extracted by means of the hydroxylamine solution (HL) was relatively high for U in the Trombetas river bank sediment (31%) and for Th in the Solimões sediment (30%). According to the alpha recoil effects, the 234U/238U activity ratios of the Andean river waters and downstream Amazon water (Óbidos) were >1, but were <1 in the Negro River (at Manaus). The activity ratios of dissolved U correlate with pH and also with the U activity ratios in the river bank sediment hydroxylamine extracts. As expected, the 234U/238U activity ratios in river bank sediments were <1 in the Andean rivers and in the downstream Amazon, but they were >1 in the Trombetas and Negro rivers. Such ratios probably result from the binding of dissolved uranium to solid sediment. The 228Th/232Th ratios of river bank sediments were close to unity (except for the Negro River, where it is lower), suggesting no significant Th exchanges between the river water and the sediment. The 226Ra/232Th activity ratios were <1, and the 226Ra/228Ra activity ratios generally were significantly higher than the activity ratios of their respective parents. This perhaps is the result of easier leaching of the 226Ra parent, 230Th, from solid material (owing to the alpha recoil effect) than of the 228Ra parent. Uranium and thorium isotopes were used as tools to evaluate the chemical weathering rate of rocks in the Amazon system, which was estimated to be 2·7 cm 1000 year?1 s?1. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Natural Hazards - In recent years, changes in precipitation caused by climate change resulting from global warming lead to great floods in world. This climate change causes drought in some regions,... 相似文献
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The eastern coast of the Red Sea is characterized by the presence of numerous marine heads that differ in terms of shape, size, geological setting, structures, and composition. This difference directly affects geomorphological evolution. In the present study, Ras Al-Shabaan was chosen as a most important area in this coast. Field investigations supported with photo-interpretation techniques were performed for studying of geomorphological features of Ras Al-Shabaan. On the other hand, the remotely sensed imagery data has been used extensively in the identification of geological and geomorphological details of Ras Al-Shabaan. The geomorphological studies showed that depositional processes of wadis and channels are predominant at the Ras Al-Shabaan coast. The changes in geomorphological and geological data of Ras Al-Shabaan were identified by remote sensing image software. Two Landsat ETM+ images from 1990 and 2010 have been processed. The analysis of remote sensing data combined with field investigations and reference data were used to monitor, delineate, and describe the geomorphological changes of Ras Al-Shabaan coast during proceedings of supervised classification of ground units. Hence, the change detection statistics have been used in ground units. Geological and geomorphological maps were digitized by using ArcGIS software. Remote sensing techniques and geographic information system (GIS) were employed in order to monitor the results of changes occurred in the line of the coast. The satellite image processing and water index data were transferred to the ArcGIS program to draw the coast lines and to stand on the changes occurred. Thereby, it was possible to identify the most prominent landforms and geomorphic units of this area. Results showed that platforms, barriers, rocky heads, islands, coral reefs, submerged reefs, tidal channels, dissolution grooves, sabkhas, inlet system, waves work, and shoreline processes were included in coastal prominent landforms. The circumstances that formed this coast are not permanent, as it is changing rapidly and continuously due to erosion and uplift processes. 相似文献
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