排序方式： 共有44条查询结果，搜索用时 296 毫秒
21.
Distribution and characteristics of PAHs in sediments from the Mediterranean coastal environment of Egypt 总被引：3，自引：0，他引：3
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
22.
Assessment of persistent organochlorine pollutants in sediments from Lake Manzala, Egypt 总被引：2，自引：0，他引：2
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
23.
Model uncertainty is introduced into direct-current resistivity data by adding random changes to layer thicknesses in a ten-layer model. The resulting information is then aliased by generating a sounding curve which contains less information than the ten resistivities and nine thicknesses. These sounding curves are then inverted via the Backus-Gilbert algorithm using singular value decomposition to obtain solutions in terms of simpler two-or three-layer models. Quantitative results confirm what has been known qualitatively for many years as the principle of equivalence. An interesting result is that the geometric average of a given suite of noisy models is virtually identical to the best-fit model for the average of the noisy curves. The results show that the inversion of resistivity data by nonlinear least-squares parameter fitting is stable in the sense that noise in the data inverts to the same magnitude of noise in the model. 相似文献
24.
Distributions of alkylated chromans and C20 isoprenoid thiophenes were investigated in four organic-matter- and sulfur-rich black shales of Miocene age deposited in the ancient crater lake of the Nördlinger Ries (southern Germany), a meteorite impact crater. Paleosalinity parameters based on these compound classes generally confirm sedimentological evidence of increased salinity over certain periods of the lake's history, but the data from both groups of compounds are not consistent. Diagenetically related molecular constituents were therefore studied to estimate the sensitivity of these parameters. The influence of thiolanes on the isoprenoid thiophene parameter was found to be low, whereas too little is known at present about the origin and diagenetic fate of alkylated chromans to conclude definitely that an alkylated chroman paleosalinity parameter can reliably be applied to a wide range of depositional settings. 相似文献
25.
26.
H. Bouzekraoui A. Barakat A. Mouaddine M. El Youssi F. Touhami A. Hafid 《Environmental Earth Sciences》2018,77(11):413
Mapping can act as a preliminary tool for the protection of natural areas and for land-use management, as it uses an easily transmissible international language which cannot be misunderstood. Geoheritage mapping can provide great opportunities for the transfer of geosciences information to the large public and policy makers. Recently, the geotourism map appears as a basic tool for the protection and promotion of this geoheritage and as a means to activate and mediate the geotourism image of the region. Aït Bou Oulli Valley is located in Moroccan Central High-Atlas, precisely within the M’Goun geopark. It is characterized by a rich geodiversity with respect to other areas of Central High-Atlas Mountains. It harbors a wide-range of geological and geomorphological heritage, and an exceptional landscape of high Mountains. The valley attracts a number of tourists whose number is skyrocketing on a yearly basis, but their number remains limited due to the absence of promotion and mediation tools of its geoheritage and to the absence of the cartographic documentation. This study aims, hence to elaborate a new geotourism map of Aït Bou Oulli Valley using digital mapping tools and fieldwork. The map shows geosites and high mountain landscapes and offers an overview of the valley’s geoheritage. This map is supported by tourism-related infrastructure, which will provide useful information for tourists. It also highlights the valley geodiversity with a view to promoting its geotourism through the establishment of three new geo-hiking trails. 相似文献
27.
A. R. Awad S. A. Taqieddin A. S. Al-Homoud E. A. Barakat 《Environmental Geology》1997,30(3-4):198-208
This paper was mainly initiated to estimate some parameters of the quality and hydraulics of water in the vicinity of a proposed
dam site in Jordan. The assessment of the chemical character was carried out to examine the suitability of the groundwater
for domestic, municipal, industrial or irrigation use. Also, the anticipated problems associated with the quality of the reservoir
water were delineated. Pumping tests were conducted at some wells that were drilled within the dam site zone and drawdown-time
curves were constructed, by means of which the transmissivity and storage coefficients were assessed using two different methods.
Total dissolved solids and electrical conductance were also measured and the relationship between them established. In addition,
sodium ion concentrations at different piezometric tip elevations were measured in a number of wells that were previously
drilled inside the dam site zone. This data indicates that the water quality as expressed in terms of total dissolved solids,
electrical conductance, and sodium ion concentration limits do not comply with internationally recommended standards. The
usage of this water for usual domestic purposes is therefore not viable, while the utilization of this water for irrigation
purposes is very restricted.
Received: 1 September 1995 · Accepted: 2 April 1995 相似文献
28.
29.
Maher Omar Abdallah Shanableh Adnan Basma Samer Barakat 《Geotechnical and Geological Engineering》2003,21(3):283-295
Most of the topsoils encountered in United Arab Emirates and in the Arabian Peninsula are granular soils with small percentages
of silt and clay. Determination of the compaction characteristics of such soils is an essential task in preparing for construction
work. The accumulating experience over many years of soil testing in our laboratories suggested that there exists an underlying
trend that governs the compaction characteristics of such soils. As such, a study was undertaken to assess the compaction
characteristics of such soils and to develop the governing predictive equations. For the purposes of this study, 311 soil
samples were collected from various locations in the United Arab Emirates, and tested for various including grain-size distribution,
liquid limit, plasticity index, specific gravity of soil solids, maximum dry density of compaction, and optimum moisture content
following ASTM D 1557-91 standard procedure C. Following the development of the predictive equations, a new set of 43 soil
samples were collected and their compaction results were used to test the validity of predictive model. The range of variables
for these soils were as follows: percent retained on US sieve #4 (R#4): 0–68; Percent passing US sieve #200 (P#200): 1–26;
Liquid limit: 0–56; Plasticity index: 0–28; Specific gravity of soil solids: 2.55–2.8.
Based on the compaction tests results, multiple regression analyses were conducted to develop mathematical models and nomographic
solutions to predict the compaction properties of soils. The results indicated that the nomographs could predict well the
maximum dry density within ±5% confidence interval and the optimum moisture content within ±3%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
30.
Larbi Boudad Lahcen Kabiri Samer Farkh Christophe Falguères Louis Rousseau Jacques Beauchamp Élisabeth Nicot Guillaume Cairanne 《Comptes Rendus Geoscience》2003,335(5):469-478
A large travertine outcrop south of Errachidia, southern Morocco, was studied and U/Th dated. The carbonate fraction was provided by groundwaters then, as now, from the eastern High Atlas percolating through the regional Infra-Cenomanian aquifer. There were two main periods of accumulation at ca 262 kyr BP and 20–11.5 kyr BP separated by a long discontinuity with some limited weathering and erosion and correlated in part with a period of erosion at 30–20 kyr BP further to the west. The two travertine-deposition periods suggest increased rainfall and/or cooler thermal conditions in the eastern High Atlas source regions. Massive travertine accumulation ceased at the end of the Upper Pleistocene. To cite this article: L. Boudad et al., C. R. Geoscience 335 (2003).To cite this article: L. Boudad et al., C. R. Geoscience 335 (2003). 相似文献