Patterns in the local assembly of Egyptian rodent faunas: Co-occurrence and nestedness     

M. Abu Baker  B.D. Patterson 《Journal of Arid Environments》2011,75(1):14-19

We studied co-occurrence patterns of 29 rodents across 308 sites in Egypt to evaluate spatial variation and non-randomness in community assembly (co-occurrence and nestedness). There was strong evidence for negative species association in the entire fauna. Negative associations can be traced to habitat segregation among species, the discreteness of habitats, low species richness at local assemblages due to aridity and low primary productivity, and allopatry of sibling species. Nevertheless, high degree of nestedness characterizes the entire collection, as tested by BINMATNEST and Aninhado. Species ranks in the packed matrix were significantly correlated with incidence, total abundance, number of coexisting species, total number of species combinations, and range size. Analyses of the assemblages by region and sampling intensity using Aninhado simulations confirmed the nestedness for the whole fauna and showed little or no nested structure in species incidences.Egyptian rodent faunas appear to be structured by a dynamic interplay of biotic and abiotic factors operating on distinct sets of species with shared habitat preferences and requirements. Local assembly patterns may result from interspecific interactions coupled with aridity and low productivity, habitat requirements, and historical factors. The harsh conditions of these arid regions led to the prevalence of species exclusion.  相似文献   

Dahab stream sediments, southeastern Sinai, Egypt: a potential source of gold, magnetite and zircon   总被引：1，自引：0，他引：1  

A. A. Surour  A. A. El-Kammar  E. H. Arafa  H. M. Korany 《Journal of Geochemical Exploration》2003,77(1):25-43

The stream sediments of Dahab area, southeastern Sinai, Egypt, were studied for their content of economic minerals. These sediments are immature as indicated by poor sorting and other mechanical parameters. They are derived from Precambrian basement rocks, which are mostly represented by granitic rocks in addition to lesser amounts of volcanics and gabbros. The mineralogical investigation revealed that these sediments contain considerable amounts of placer gold, Fe–Ti oxides and zircon.The concentrated Fe–Ti oxides comprise homogeneous magnetite and ilmenite in addition to ilmeno-magnetite, hemo-ilmenite and rutile–hematite intergrowths. Isodynamic separation of some raw samples of SIZE=1 mm revealed that up to 15.12% magnetic minerals can be recovered. Zircon shows remarkable variations in morphology, colour, chemistry and provenance. U-poor and U-rich varieties of zircon were discriminated containing UO₂ in the ranges of 0.04–1.19 and 3.05–3.68 wt.%, respectively. REE-bearing minerals comprise monazite, allanite and La-cerianite.On mineralogical basis, the present work suggests that Dahab stream sediments represent a promising target for further geochemical exploration for precious metals, especially gold. Fire assay data indicate that placer gold in the studied sediments sometimes reaches 15.34 g/t. Narrow gullies and valleys cutting the basement manifest the development and preservation of gold in this arid environment. Background concentration of gold and variation in lithology suggest multiple source of the metal in the investigated sediments.  相似文献   

Effect of The Atmosphere on UVB Radiation Reaching The Earth’s Surface:Dependence on Solar Zenith Angle          下载免费PDF全文

M.El-Nouby ADAM 《大气和海洋科学快报》2011,(3):139-145

The atmosphere protects humans,plants,animals,and microorganisms from damaging doses of ultraviolet-B(UVB) solar radiation(280-320 nm) because it modifies the UVB reaching the Earth’s surface.This modification is a function of the solar radiation’s path length through the atmosphere and the amount of each attenuator along the path length.The path length is determined by solar zenith angle(SZA).The present work explains the dependence of hemispherical transmittance of UVB on SZA.The database used consists of five years of hourly UVB and global solar radiation measurements.From 2001 to 2005,the South Valley University(SVU) meteorological research station(26.20°N,32.75°E) carried out these measurements on a horizontal surface.In addition,the corresponding extraterrestrial UVB(UVBext) and broadband solar radiation(Gext) were estimated.Consequently,the hemispherical transmittance of UVB(KtUVB) and the hemispherical transmittance of global solar radiation(Kt) were estimated.Furthermore,the UVB redaction due to the atmosphere was evaluated.An analysis of the dependence between KtUVB and SZA at different ranges of Kt was performed.A functional dependence between KtUVB and SZA(KtUVB=-a(SZA)+b) for very narrow Kt-ranges(width of ranges was 0.01) was developed.The results are discussed,and the sensitivity of △KtUVB to △SZA for very narrow Kt-ranges was studied.It was found that the sensitivity of △KtUVB to △SZA slightly increases with increased Kt,which means KtUVB is sensitive to SZA as Kt increases.The maximum correlation(R) between KtUVB and SZA was equal to-0.83 for Kt= 0.76.  相似文献   

Distribution and characteristics of PAHs in sediments from the Mediterranean coastal environment of Egypt   总被引：3，自引：0，他引：3  

Assem O. Barakat  Alaa Mostafa  Stephen T. Sweet 《Marine pollution bulletin》2011,62(9):1969-1978

To assess the contamination of polycyclic aromatic hydrocarbons (PAHs) in the Mediterranean coastal environment of Egypt, 26 sediment samples from the coastline, harbours, estuaries and coastal lakes were collected and analyzed. The sediment PAH concentrations of thirty-nine 2-6 ring PAHs ranged from 13.5 to 22,600 ng/g. PAH profiles varied according to the nature of the site and its proximity to sources. Industrialized and urbanized region showed high level of PAHs contamination. In general, the contamination levels of PAHs were similar to those observed in contaminated and slightly contaminated sediments of the Mediterranean Sea. Molecular indices based on ratios of selected PAH concentrations were used to differentiate PAHs from pyrogenic and petrogenic and mixed origins. Good correlations were observed between the petrogenic index, MP/P, A-PAHs/P-PAHs and HMW/LMW. Finally, PAH levels in sediments were compared with Sediments Quality Guidelines (ERM-ERL) for evaluation of probable toxic effects on organism.  相似文献   

Tectonostratigraphy and depositional history of the Neoproterozoic volcano-sedimentary sequences in Kid area,southeastern Sinai,Egypt: Implications for intra-arc to foreland basin in the northern Arabian–Nubian Shield     

《Journal of Asian Earth Sciences》2013

This paper presents a stratigraphic and sedimentary study of Neoproterozoic successions of the South Sinai, at the northernmost segment of the Arabian–Nubian Shield (ANS), including the Kid complex. This complex is composed predominantly of thick volcano-sedimentary successions representing different depositional and tectonic environments, followed by four deformational phases including folding and brittle faults (D₁–D₄). The whole Kid area is divisible from north to south into the lower, middle, and upper rock sequences. The higher metamorphic grade and extensive deformational styles of the lower sequence distinguishes them from the middle and upper sequences. Principal lithofacies in the lower sequence include thrust-imbricated tectonic slice of metasediments and metavolcanics, whereas the middle and upper sequences are made up of clastic sediments, intermediate-felsic lavas, volcaniclastics, and dike swarms. Two distinct Paleo- depositional environments are observed: deep-marine and alluvial fan regime. The former occurred mainly during the lower sequence, whereas the latter developed during the other two sequences. These alternations of depositional conditions in the volcano-sedimentary deposits suggest that the Kid area may have formed under a transitional climate regime fluctuating gradually from warm and dry to warm and humid conditions.Geochemical and petrographical data, in conjunction with field relationships, suggest that the investigated volcano-sedimentary rocks were built from detritus derived from a wide range of sources, ranging from Paleoproterozoic to Neoproterozoic continental crust. Deposition within the ancient Kid basin reflects a complete basin cycle from rifting and passive margin development, to intra-arc and foreland basin development and, finally, basin closure. The early phase of basin evolution is similar to various basins in the Taupo volcanics, whereas the later phases are similar to the Cordilleran-type foreland basin. The progressive change in lithofacies from marine intra-arc basin to continental molasses foreland basin and from compression to extension setting respectively, imply that the source area became peneplained, where the Kid basin became stabilized as sedimentation progressed following uplift. The scenario proposed of the study area supports the role of volcanic and tectonic events in architecting the facies and stratigraphic development.  相似文献   

Scenario-based earthquake loss estimation for the city of Cairo,Egypt     

《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(2):92-112

This paper describes a multi-tiered loss assessment methodology to estimate seismic monetary implications resulting from structural damage to the building population in Greater Cairo. After outlining a ground-shaking model, data on geological structures and surface soil conditions are collated using a considerable number of boreholes to produce a classification of different soil deposits. An inventory database for the existing building stock is also prepared. The seismic vulnerability of representative reinforced concrete building models, designed according to prevalent codes and construction practices, is evaluated. Capacity spectrum methods are utilised for assessing the structural performance through a multi-level damage scale. A simplified methodology for deriving fragility curves for non-ductile reinforced concrete building classes that typically constitute the building population of the city is adopted. In addition, suitable fragility functions for unreinforced masonry constructions are selected and used for completing the loss model for the study area. The results are finally used to build an event-based loss model caused by possible earthquakes in the region.  相似文献   

Neoproterozoic podiform chromitites in serpentinites of the Abu Meriewa–Hagar Dungash district, Eastern Desert, Egypt: Geotectonic implications and metamorphism     

Fawzy F.  Abu El Ela  Esam S.  Farahat 《Island Arc》2010,19(1):151-164

Podiform chromitites hosted in serpentinites (after harzburgite and dunite) and talc‐carbonate rocks from the Abu Meriewa–Hagar Dungash district (MHD), Eastern Desert of Egypt, together with metagabbros, pillow metavolcanics, and metasediments, form an ophiolitic mélange formed during the Neoproterozoic Pan‐African Orogeny. The chromitites show massive, disseminated, and nodular textures. Chromite cores in chromitites have high and restricted ranges of Cr# (0.65–0.75) and Mg# (0.64–0.83), implying primary compositions not affected by metamorphism. Therefore, they are used as reliable indicators of parent magma composition and tectonic affinities of these highly metamorphosed rocks. On the contrary, the altered rims are high‐Cr, low‐Fe³⁺ spinel (rather than ferritchromit) enriched in Cr, Fe, and Mn, and depleted in Al and Mg (Cr# = 0.75–0.97, Mg# = 0.29–0.79), due to equilibration with interstitial silicates during regional metamorphism up to transitional greenschist–amphibolite facies at about 500–550°C. The primary chromite compositions suggest derivation from a high‐Mg tholeiitic, to possibly boninitic, parental magma in a supra‐subduction zone (arc–marginal basin) environment, similar to the spatially associated metavolcanic rocks. The MHD chromitites are most probably formed by melt–rock interaction mechanisms. The high Cr# of the investigated chromites suggests high degrees of partial melting of a depleted harzburgite source by interaction with primitive basaltic melt of deeper origin followed by mixing. Such Cr‐rich chromites are common in chromitites from the Eastern Desert of Egypt, implying broad thermal anomalies, possibly linked to an important geodynamic feature of the Arabian–Nubian Shield (ANS) evolution. This could revive interest in models that involve asthenospheric uprise, related to plume interaction or most probably due to oblique convergence of arc terranes during early evolution of the ANS.  相似文献   

Facies and sequence stratigraphy of fluvio-lacustrine deposits: Cretaceous Nubian succession of the Saharan platform (SW Egypt)     

《Proceedings of the Geologists' Association. Geologists' Association》2017,128(2):271-286

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Groundwater flow modeling of Quaternary aquifer Ras Sudr,Egypt     

Medhat A. El-Bihery 《Environmental Geology》2009,58(5):1095-1105

Recently, Ras Sudr (the delta of Wadi Sudr) area received a great amount of attention due to different development expansion activities directed towards this area. Although Quaternary aquifer is the most prospective aquifer in Ras Sudr area, it has not yet completely evaluated. The present work deals with the simulation of the Quaternary groundwater system using a three-dimensional groundwater flow model. MODFLOW code was applied for designing the model of the Ras Sudr area. This is to recognize the groundwater potential as well as exploitation plan of the most prospective aquifer in the area. The objectives were to determine the hydraulic parameters of the Quaternary aquifer, to estimate the recharge amount to the aquifer, and to determine the hydrochemistry of groundwater in the aquifer. During this work, available data has been collected and some field investigation has been carried out. Groundwater flow model has been simulated using pilot points’ method. SEAWAT has been also applied to simulate the variable-density flow and sea water intrusion from the west. It can be concluded that: (1) the direction of groundwater flow is from the east to the west, (2) the aquifer system attains a small range of log-transformed hydraulic conductivity. It ranges between 3.05 and 3.35 m/day, (3) groundwater would be exploited by about 6.4 × 10⁶ m³/year, (4) the estimated recharge accounts for 3 × 10⁶ m³/year, (5) an estimated subsurface flow from the east accounts for 2.7 × 10⁶ m³/year, (6) the increase of total dissolved solids (TDS) most likely due to dilution of salts along the movement way of groundwater from recharge area to discharge area in addition to a contribution of sea water intrusion from the west. Moreover, it is worth to note that a part of TDS increase might be through up coning from underlying more saline Miocene sediments. It is recommended that: (1) any plan for increasing groundwater abstraction is unaffordable, (2) reliable estimates of groundwater abstraction should be done and (3) automatic well control system should be made.  相似文献   

Hydro-environmental status and soil management of the River Nile Delta,Egypt     

H. H. Elewa  A. H. El Nahry 《Environmental Geology》2009,57(4):759-774

The sea level rise has its own-bearing on the coastal recession and hydro-environmental degradation of the River Nile Delta. Attempts are made here to use remote sensing to detect the coastal recession in some selected parts and delineating the chemistry of groundwater aquifers and surface water, which lie along south-mid-northern and coastal zone of the Nile Delta. Eight water samples from groundwater monitoring wells and 13 water samples from surface water were collected and analyzed for various hydrochemical parameters. The groundwater samples are classified into five hydrochemical facies on Hill-Piper trilinear diagram based on the dominance of different cations and anions: facies 1: Ca–Mg–Na–HCO₃–Cl–SO₄ type I; facies 2: Na–Cl–HCO₃ type II; facies 3: Na–Ca–Mg–Cl type III, facies 4: Ca–Na–Mg–Cl–HCO₃ type IV and facies 5: Na–Mg–Cl type V. The hydrochemical facies showed that the majority of samples were enriched in sodium, bicarbonate and chloride types and, which reflected that the sea water and tidal channel play a major role in controlling the groundwater chemical composition in the Quaternary shallow aquifers, with a severe degradation going north of Nile Delta. Also, the relationship between the dissolved chloride (Cl, mmol/l), as a variable, and other major ion combinations (in mmol/l) were considered as another criterion for chemical classification system. The low and medium chloride groundwater occurs in southern and mid Nile Delta (Classes A and B), whereas the high and very high chloride (classes D and C) almost covers the northern parts of the Nile Delta indicating the severe effect of sea water intrusion. Other facets of hydro-environmental degradation are reflected through monitoring the soil degradation process within the last two decades in the northern part of Nile Delta. Land degradation was assessed by adopting new approach through the integration of GLASOD/FAO approach and Remote Sensing/GIS techniques. The main types of human induced soil degradation observed in the studied area are salinity, alkalinity (sodicity), compaction and water logging. On the other hand, water erosion because of sea rise is assessed. Multi-dates satellite data from Landsat TM and ETM+ images dated 1983 and 2003 were used to detect the changes of shoreline during the last two decades. The obtained results showed that, the eroded areas were determined as 568.20 acre; meanwhile the accreted areas were detected as 494.61 acre during the 20-year period.  相似文献