排序方式： 共有57条查询结果，搜索用时 267 毫秒
1.
The influence of physical and biological processes on the ichthyoplankton communities in the Gulf of Sirte (Southern Mediterranean Sea) 
下载免费PDF全文
下载免费PDF全文 Angela Cuttitta Sergio Bonomo Salem Zgozi Angelo Bonanno Bernardo Patti Enza Maria Quinci Marco Torri Mohamed Hamza Abdul Fatah Daw Haddoud Akram El Turki Abdul Bari Ramadan Simona Genovese Salvatore Mazzola 《Marine Ecology》2016,37(4):831-844
This paper reports on the first study on the ichthyoplankton community structure in the Gulf of Sirte and its spatial distribution in relation to environmental conditions and zooplankton abundance. The results make an important contribution to the future management of fisheries in this unexplored, but much exploited, area. Biological samples were collected in July 2008 using a Bongo40 net. In total, 1914 larvae were found and 1652 of these were identified. In particular, bathypelagic taxa were the most abundant, followed by demersal, mesopelagic, pelagic and epipelagic taxa. The ichthyoplankton community had a patchwork distribution influenced by oligotrophic conditions, the bottom depth and oceanographical features. The results suggest that environmental forcings were able to transport the ichthyoplankton to productive areas. Indeed, maximum fish egg densities were found in coastal stations in correspondence with the Atlantic Tunisian Current inflow, whereas larvae were mainly concentrated in the east side of the Gulf, probably as a result of advection by the anticyclonic circulation. Additionally, the distribution patterns of the total larvae density and the different assemblages were well matched with the abundance of the zooplankton, probably determining final larval survival, growth and recruitment. 相似文献
2.
Reza Ghasemizadeh Xue Yu Christoph Butscher Ingrid Y. Padilla Akram Alshawabkeh 《Hydrogeology Journal》2016,24(6):1463-1478
In northern Puerto Rico (USA), subsurface conduit networks with unknown characteristics, and surface features such as springs, rivers, lagoons and wetlands, drain the coastal karst aquifers. In this study, drain lines connecting sinkholes and springs are used to improve the developed regional model by simulating the drainage effects of conduit networks. Implemented in an equivalent porous media (EPM) approach, the model with drains is able to roughly reproduce the spring discharge hydrographs in response to rainfall. Hydraulic conductivities are found to be scale dependent and significantly increase with higher test radius, indicating scale dependency of the EPM approach. Similar to other karst regions in the world, hydraulic gradients are steeper where the transmissivity is lower approaching the coastline. This study enhances current understanding of the complex flow patterns in karst aquifers and suggests that using a drainage feature improves modeling results where available data on conduit characteristics are minimal. 相似文献
3.
4.
Near-surface layer variations can degrade the desired response of seismic arrays which are typically used to attenuate horizontally traveling coherent noise and enhance vertically traveling signal. We investigate the effect of variations in the near-surface layer thickness on the performance of arrays by studying their impulse and wavelet responses. The models considered include the topographic variations and a channel in the base of weathering layer. The topographic variations include a dipping surface layer as well as a surface layer that follows a sine wave. The geological channel is assumed to be present under the entire receiver array as well as partially under a few receivers. We use Ricker wavelet and model plane wavefronts with incidence angles (90, 70, 45, 20, and 5 °) on a 12-element equally weighted array for the weathering layer models. We found that the array responses are more degraded for near-vertically traveling waves in all cases. The array responses are also found to be more degraded when channel variations are present underneath a few receivers as compared to the entire array length. We recommend designing a spatial filter or using single-sensor records after correcting for intra-array statics to preserve the reflection amplitudes in the presence of weathering layer variations. 相似文献
5.
Mapping groundwater conditions in different geological environments in the northern area of UAE using 2D earth resistivity imaging survey 总被引：1，自引：1，他引：0
A. M. Ebraheem M. M. Al Mulla M. M. Sherif O. Awad S. F. Akram N. B. Al Suweidi A. Shetty 《Environmental Earth Sciences》2014,72(5):1599-1614
A water resources database was developed and used to characterize the geological and hydrogeological settings of groundwater aquifers in the northern part of the United Arab Emirates. An intensive 2D Earth Resistivity Imaging (ERI) survey was conducted in selected areas to assess the available groundwater resources and delineate the salt-water intrusion. Drilling information of the existing monitoring wells as well as their records of water table elevations and groundwater salinity were used to measure the horizontal and vertical variations in lithology, degree of saturation, and groundwater salinity and thus to improve the interpretation of ERI data. The results of the chemical analyses of water samples collected from the wells along with the 2D ERI survey profiles were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D ERI data to identify and map three zones of water-bearing formation (fresh, brackish, and salt-water zones) in the coastal areas. The results indicated that the depth to the fresh-brackish interface exceeded 50 m at the upstream of the wadies and was in the order of 10 m or less in the vicinity of shoreline. Because of the high resistivity contrast between dry and water saturated fractured rocks; this method was very successful in detecting water-filled fractures and cavities in the carbonate aquifer. The application of this method was unsuccessful in clayey aquifers as it was not possible to isolate lenses of gravel and/or saturated with saline or brackish water from the surrounding clayey materials. 相似文献
6.
A combination of different scientific techniques has been utilized to estimate the initial firing temperature and kiln atmosphere of a collection of Islamic painted sherds excavated from an archaeological site in northern Jordan. Scanning electron microscope investigation of samples refired at different temperatures proves that the pottery was fired at around 750°C in an oxidizing atmosphere. Similar results were obtained by the thermal analysis study using thermogravometric, differential thermogravemetric and differential thermal analysis and by the temperature-minerological scale analysis. The obtained results shed light on the manufacturing techniques adopted by the Islamic potter of the period. © 1999 John Wiley & Sons, Inc. 相似文献
7.
El-Arabi Shendi Akram Aziz Khalid Mamoun Mohamed Gamal 《Environmental Earth Sciences》2017,76(22):783
Very low frequency electromagnetic (VLF-EM) measurements were carried out in Wadi Isbayia area, south Sinai Peninsula, to test the efficiency of the VLF-EM method in the exploration of sulphide mineralization in arid environments. The VLF-EM field measurements, including tilt angle, real and imaginary components of the received VLF field, were carried out along fifteen profiles covering a quartz monzonite bedrock. Interpretation of the VLF measurements, in the light of geological information, has showed that sulphide minerals in the Wadi Isbayia area extend from the ground surface to a depth of about 200 m. However, the structural lineaments, especially faults, have controlled the distribution of the sulphide mineralization. A few of polished sections for rock samples, collected from the sites of the VLF-EM anomalies in the study area, have been prepared and examined by ore microscopy which confirmed the presence of pyrite and chalcopyrite as well as iron oxides, disseminated in the quartz monzonite bedrock. These results showed that the VLF-EM method is an effective tool in the exploration of sulphide minerals in the arid environments. 相似文献
8.
The frequent appearance of some hydro-environmental hazard features, such as waterlogging and soil salinization along the susceptible zones at Northwest Sinai area (NWSA), has put serious challenges and obstacles for a correct and efficient land use planning of this region, for several decades. Although previous studies have shown that the whole region of Northern Sinai is greatly affected by the tectonic movements associated with the Syrian Arc folding system (SAS), NWSA is barren of any obvious surficial structures. The current work aims to investigate the effect of subsurface tectonic features on the hydrogeologic regime of NWSA.Hydrogeological and remote sensing data were integrated with ground geophysical gravity and magnetic measurements, using the geographic information system. Data integration asserts the role played by buried tectonic features not only in governing the landforms of the upper water-bearing quaternary formations but also in controlling their flow regime.Two major subsurface structures were identified through interpreting the geophysical measurements. A buried dome-like structure, dominating the central part of the mapped area, coincides with the radial flow pattern observed on the water table map. At the southwestern corner of the study area, an elevated groundwater level, caused by continuous groundwater accumulation at the discharge boundary, is superimposing a subsurface block-faulted depression. The waterlogging features (saturation of the soil by groundwater and inundation of local depressions due to rising of water table) dominating the discharge lowlands of NWSA support the conclusion that a buried block-faulted structure exerts a strong influence on the thickness and groundwater flow regime of the shallow quaternary aquifer. 相似文献
9.
Muhammad Rafique Saeed Ur Rahman Muhammad Akram Matiullah 《Environmental Earth Sciences》2012,66(4):1225-1232
This paper presents the results of indoor radon concentration measurements in 120 dwellings of district Sudhnuti of Azad Kashmir. Measurements were taken with CR-39 passive alpha track detector. CR-39 based box type radon detectors were installed in a bedroom and living rooms of each house. The detectors were retrieved after exposing to indoor radon for period of 6 months and then etched in 6 M NaOH at 80°C for 16 h, the observed track densities were converted in to the indoor radon concentration. Indoor radon concentration varied from 20 ± 12 to 170 ± 4 Bq m−3 for the houses of the district Sudhnuti. Arithmetic mean (AM), geometric mean (GM) and geometric standard deviations (GSD) were found to be 82 ± 6, 77 ± 6 and 1.51, respectively. The minimum value of weighted average radon concentration was recorded in one of the house of Mang town, whereas the maximum value was found in the Pattan Sher Khan region. Doses due to indoor radon exposure vary from 0.50 ± 0.31 to 4.28 ± 0.11 mSv year−1 AM, GM and GSD. of mean effective doses were found to be 2.06 ± 0.13, 1.95 ± 0.18 and 1.51, respectively. According to the recommendations made by the Health Protection Agency, UK (200 Bq m−3) all the houses surveyed are within the safe limits. 相似文献
10.
For the first time, the calcareous nannofossils of marly deposits near Kerman (Bardsir area) have been studied. This study presents the integrated (calcareous nannofossils) biostratigraphy of the Bardsir section in the Kerman basin, Central Iran. In most parts of Central Iran, the Upper Cretaceous sequence is complete and continuous and is divided into two groups: Cenomanian–Touronian flysch and Campanian–Maastrichtian flysch. Flyschs composed of sets of green marl sequences (Coniacian–Santonian) have been separated to reduce the basin depth and refer to the relative calm. Bardsir is located 57.6 km from Kerman (Central Iran). The lithology of this area includes light green marl with layers of calcareous siltstone, limestone, and flysch rocks. In this study, 24 samples were taken and prepared with smear slide. Most species were photographed with a light microscope. As a result of this study, 30 genera and 42 species of nannofossils have been identified. A high-resolution calcareous nannofossil biostratigraphic study has been carried out, allowing the division of the studied section into eight biozones of Late Santonian to Early Maastrichtian age (CC17–CC24). 相似文献