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11.
Sediment samples were collected from 30 different locations in Abu Qir Bay (Mediterranean Sea), East Alexandria, Egypt and analyzed for trace elements. The highest concentrations of most of the elements were observed in the nearshore stations in the vicinity of the major anthropogenic activities as industrial settlements, wastewater discharges, and agricultural drainage. In addition, mussel samples of Mactra corallina and Tapes decussata were collected corresponding to the sediment samples. Concentrations of As, Cd, Cr, Mn, and Zn in the mussel tissues were higher than concentrations in sediments, thus indicating their relatively high bioavailability. Sequential extraction procedure was performed on selected sediment samples. Significant correlations were observed between the concentrations of Cu, Mn, Pb, and Zn in the exchangeable fraction of the sediments and the corresponding tissues of M. corallina. The output of the risk assessment applied on the sediments revealed that adverse ecological effects to benthic species could occur and that a higher level of risk is expected from the exposure to Cd, Cr, Hg, and Zn. No adverse carcinogenic or non‐carcinogenic human health effects are expected from the consumption of the two mussel species from Abu Qir Bay.  相似文献   
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The Jeddah coast lies in the central eastern Red Sea, which is characterized by the predominant northwest winds and the associated wind waves throughout the year. A detailed investigation on the spectral wave characteristics in the nearshore regions of the Jeddah coast has not been carried out yet, primarily due to the lack of data. In the present study, we have analyzed the available wave spectra measured at two nearshore locations along the Jeddah coast using wave gauges. The wave spectra were separated into wind sea and swell components using a frequency-based algorithm, and the integral wave parameters corresponding to each component were derived. Although the measurements were limited to the summer season, notable features such as the diurnal variability and the superimposition of wind seas and swells have been identified from the spectra. The superimposition is mainly due to the interaction of the young swells propagated from the northern Red Sea and the local breezes prevailing along the coast at certain periods in a diurnal cycle. Based on the wave speed calculations and the estimated time shifts between the wind and waves, the potential swell regions have been backtracked.  相似文献   
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Natural Resources Research - This study assessed the groundwater productivity of the Dibdibba aquifer on the Karbala–Najaf Plateau, central Iraq, using three GIS-based tree machine learning...  相似文献   
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The Tinitine sub-watershed of Rheraya is renowned for its semiarid climate, irregular supply of water flow, and its historical floods; for these reasons, it is classified as vulnerable areas during a rainfall event. We conducted this study to propose flood prediction models adapted to this risky zone. For this, a hydrological method of flood forecasting rainfall-runoff used to determine a model conforms to the semiarid basin. This model is based on the articulation of the series production and transfer function. The goal of the production function is to determine the portion of the rainfall runoff, which is performed by two approaches that differ in their structures: (1) the first approach is based on the mathematical model of Horton; (2) the second approach is based on the determination of the part of the rain contributes to runoff and obtained by a spatial map of runoff coefficient (GIS). The transfer function is based on the two models of Clark and Nash, rainy efficient routes to the catchment outlet from a unit hydrograph. The characteristic parameters of these models are obtained through the application of mathematical optimization methods such as genetic algorithms. Thereby, the coupling function producing Horton (identified by the parameters: initial infiltration?=?15.03, final infiltration?=?0.3, and phi?=?0.45) and Clark transfer function (identified by the parameters CA?=?0.21 and CB?=?0.79) was given very satisfying results, mainly the low difference between observed and simulated hydrograph and Nash coefficient which is about 85%. This shows the interest of this coupling model in flood forecasting.  相似文献   
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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   
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Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were determined in surface and core sediment samples collected from Manzala Lake, the largest of the Egyptian coastal lakes. Total concentrations of OCPs and ∑7 PCBs (ICES) in sediments ranged from 0.63 to 31.31 ng/g and 0.26 to 31.27 ng/g, respectively. Geographical distribution indicates that levels of contaminants were significantly higher in areas which are mainly influenced by municipal discharge, indicating significant sources of these compounds in urbanised areas. The composition of DDT and its metabolites suggest old input of DDT. The levels of contaminants in Manzala Lake were similar or lower than those observed in comparable areas worldwide. The profiles of ∑OCPs and ∑PCBs in a core from a site heavily impacted by sewage discharge have highest concentrations in the surface core section indicating recent inputs. Assessment of ecotoxicological risk indicated that sediments in two sites were likely to pose potential biological adverse impact.  相似文献   
19.
Evaluation of mechanical and petrophysical properties of the karst limestone became essential to avoid future risks in the construction of new urban cities built on limestones. Therefore, this study aims to evaluate the impact of karsts phenomena on engineering properties of limestone foundation bed at Ar Riyadh in Saudi Arabia. Three hundred core plugs were obtained by rotary drilling at depths ranging from the ground surface to 20 m collected from 24 boreholes in two sites: (1) karst limestone (KL) at Al Aziziyah district and (2) massive hard limestone (HL) at Hittin district in Ar Riyadh city, Saudi Arabia. Petrographic, SEM, EDX, and XRD analyses are used to identify the mineralogical composition and microstructures of limestone samples. The petrophysical properties included the ovendry density, P-wave, and porosity where the mechanical properties covered the uniaxial compressive strength (UCS), point load strength index (PLI), and rock quality designation (RQD) for the karst and hard limestone samples. KL is characterized by 17.11% total porosity, 14.71% water absorption, 32.1 MPa UCS, 1.70 g/cm3 ovendry density (γ dry), 51% weathered RQD, 5.49 MPa medium shear strength, and low modulus of deformation of the plate loading test. HL showed 11.63% total porosity, 9.45% water absorption 43.1 MPa UCS, 2.50 g/cm3 ovendry density (γ dry), 78% hard to fresh rock affinity RQD, and 9.93 MPa high strength and high modulus of deformation of the plate loading test. For the water absorption (%), KL at Al Aziziyah district showed a range of 12.85–17.80% averaged 14.71%. HL at Hittin district varied between 7.04 and 11.29% with an average of 9.45%. KL proved to be dense with ovendry density (γ dry) averaged at 1.70 g/cm3 while HL showed very dense affinity of 2.50 g/cm3. KL clarified a UCS range from 22.5 to 40.1 MPa and an average of 32.1 MPa while HL showed a range from 35.4 t o 48.1 MPa with an average of 43.1 MPa. KL is moderately weathered with RQD average of 51% while HL showed a hard to fresh rock affinity of 78%. Point load test clarified a medium shear strength with 5.49 MPa for KL and high strength of 9.93 MPa for HL. Plate loading tests indicated low and high modulus of deformation for KL and HL, respectively. Results of petrographical analyses and XED of limestone samples showed that the strength parameters of samples mostly composed of micrite (mudstone/wackestone) and dolomite in hard limestone of Hittin district. In Al Aziziyah district (KL), the samples mostly consist of foraminifera and high amount of calcite as in karst limestone (wackestone/packstone). Rock mechanical tests with combination of fabric analyses have shown that strength parameters depend not only on the amount of karst but also on the amount of allochem. Major geomechanical differences between the two types of limestone provide the proper base for prioritizing areas to alleviate future risks and sustainable urban planning for decision makers. The karstic limestone, therefore, is considered as an acceptable foundation bed for light engineering structures. However, for heavy structures and buildings, improving the foundation bed strength by grouting, cement injection, and mat foundations is necessary to avoid future failure risks.  相似文献   
20.
Alaa Ali   《Journal of Hydrology》2009,374(3-4):338-350
Wetland restoration is often measured by how close the spatial and temporal water level (stage) patterns are to the pre-drainage conditions. Driven by rainfall, such multivariate conditions are governed by nonstationary, nonlinear, and nonGaussian processes and are often simulated by physically based distributed models which are difficult to run in real time due to extensive data requirements. The objective of this study is to provide the wetland restorationists with a real time rainfall–stage modeling tool of simpler input structure and capability to recognize the wetland system complexity. A dynamic multivariate Nonlinear AutoRegressive network with eXogenous inputs (NARX) combined with Principal Component Analysis (PCA) was developed. An implementation procedure was proposed and an application to Florida Everglade’s wetland systems was presented. Inputs to the model are time lagged rainfall, evapotranspiration and previously simulated stages. Data locations, preliminary time lag selection, spatial and temporal nonstationarity are identified through exploratory data analysis. PCA was used to eliminate input variable interdependence and to reduce the problem dimensions by more than 90% while retaining more than 80% of the process variance. A structured approach to select optimal time lags and network parameters was provided. NARX model results were compared to those of the linear Multivariate AutoRegressive model with eXogenous inputs. While one step ahead prediction shows comparable results, recursive prediction by NARX is far more superior to that of the linear model. Also, NARX testing under drastically different climatic conditions from those used in the development demonstrates a very good and robust performance. Driven by net rainfall, NARX exhibited robust stage prediction with an overall Efficiency Coefficient of 88%, Mean Square Error less than 0.004 m2, a standard error less than 0.06 m, a bias close to zero and normal probability plots show that the errors are close to normal distributions.  相似文献   
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