Distributions and seasonal variability of dissolved organic nitrogen in two estuaries in SW England   总被引：4，自引：0，他引：4  

El-Sayed A. Badr  Alan D. Tappin  Eric P. Achterberg   《Marine Chemistry》2008,110(3-4):153-164

Nitrogen loadings to coastal waters have increased over the last century, resulting in deterioration in water quality. In this study we investigated the distributions and seasonality of dissolved organic nitrogen (DON), and its relationship to total dissolved nitrogen (TDN), for two anthropogenically influenced estuarine systems in southwest England. Concentrations of DON in both estuaries were generally < 80 μM. DON showed non-conservative distributions, resulting from external and internal inputs and in situ reactivity. DON contributed 38 ± 22% (range 4–79%, Yealm) and 36 ± 17% (range 4–84%, Plym) to the TDN pool, with lower values generally observed in the fresher samples relative to the more saline samples. DON was a larger fraction of the TDN pool during the summer and autumn relative to winter and spring, indicating the influence of bacterioplankton release on nitrogen cycling in the estuaries. Ammonification and nitrification were observed in the estuaries, processes which were reproduced in incubation experiments using bioreactors. The bioreactor experiments showed that 12% h^− 1 of the DON flux from the River Plym may be available to bacteria, indicating significant removal of DON during the residence time of the water in the estuary (a few days). The bioavailable nature of the DON means that this N fraction significantly adds to the eutrophication burden of the receiving coastal waters, and therefore cannot be ignored in environmental assessments.  相似文献   

Editorial     

El-Sayed El-Bushra 《GeoJournal》1986,13(2):101-101

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Comparative studies on analytical methods for the assessment of petroleum contamination in the marine environment II. Gas chromatographic analyses     

Hassan Awad 《Marine Chemistry》1981,10(5):417-430

Although determinations of hydrocarbons in the marine environment are usually based on the same analytical steps, i.e. organic solvent extraction, column chromatographic purification, and hydrocarbon detection and identification; variations in equipment and solvent systems used in the extraction step, and also in the columns for purification and analysis, seriously impaired the development of a consistent data base concerning oil pollution on a global scale.Many authors and conferences emphasized the need, in this field, for a comparative study on the efficiency of various published analytical techniques.Fifteen techniques with 24 applications were chosen and applied to a fixed weight of uniform samples of sediments, mussels, fish, shrimps and green algae. The final hydrocarbon extracts were analyzed individually on a 2 m stainless-steel packed column (SE 30).The results obtained from this work showed considerable variations in the efficiency of different techniques from identical samples. The hydrocarbon yields varied from 94 to 1.4 ppm in sediments, from 40 to 9 ppm in mussels; from 216 to 1.3 ppm in fish; from 8.3 to 3.1 ppm in shrimps; and from 343 to 273 ppm in algae, all relative to wet weight of the samples. The gas chromatograms of the hydrocarbons obtained were found to be quite different with regard to peak intensities and distributions. This means that hydrocarbons obtained by the application of different techniques varied in their compositions and relative concentrations of their constituents. These results confirm what was already obtained and discussed previously using spectrofluorometric analyses.It can be concluded that it is necessary to establish a standard technique for the preparation of marine samples, for extraction and purification of the hydrocarbon extracts which should be applied by all laboratories specializing in this field.  相似文献   

Site response assessment of an urban extension site using microtremor measurements,Ahud Rufeidah,Abha District,Southwest Saudi Arabia     

Almadani  Sattam  Abdelrahman  Kamal  Ibrahim  Elkhedr  Al-Bassam  Abdulaziz  Al-Shmrani  Awad 《Arabian Journal of Geosciences》2015,8(4):2347-2357

Arabian Journal of Geosciences - Microtremor horizontal-to-vertical spectral ratio (HVSR) method has been conducted at 33 sites in Ahud Rufeidah urban expansion zone in order to assess the...  相似文献   

Integrated geophysical interpretation for the area located at the eastern part of Ismailia Canal, Greater Cairo, Egypt     

Sultan Awad Sultan  Fernando A. M. Santos  Ahmad Sobhy Helaly 《Arabian Journal of Geosciences》2011,4(5-6):735-753

The integrated geophysical interpretation for the different geophysical tools such as resistivity and gravity is usually used to define the structural elements, stratigraphic units, groundwater potentiality, and depth to the basement rocks. In the present work, gravity and resistivity data were utilized for detecting the groundwater aquifer and structural elements, as well as the upper and lower surfaces of the subsurface basaltic sheet in an area located at the eastern side of Ismailia Canal, northeastern Greater Cairo, Egypt. Two hundred and ten gravity stations were measured using an Autograv instrument through a grid pattern of 50?×?50 m. The different required corrections were carried out, such as drift, elevation, tide, and latitude corrections. The final corrected data represented by the Bouguer anomaly map were filtered using high- and low-pass filters into regional and residual gravity anomaly maps. The resulting residual gravity anomaly map was used for gravity modeling to calculate the depths to the upper and lower surfaces of the basaltic sheet. The resulting gravity models indicated that the depths to the upper surface of the basaltic sheet are ranged between 26 and 314 m, where the shallower depths were found around the southern and eastern parts. The depths to the lower surface of the basaltic sheet are varied from 86 to 338 m, and the thickness of the basaltic sheet is ranged from 24 to 127 m, where the biggest thicknesses were found around the southern and northern parts of the study area. Forty-two vertical electrical soundings (VES) were carried out using Schlumberger configuration with AB/2 spacings ranged from 1.5 to 500 m. 1D quantitative interpretation was carried out through manual and analytical interpretations. The VES data were also inverted assuming a 3D resistivity distribution. The results from the 3D resistivity inversion indicated that the subsurface section consists of sand, sandstone, and sandy–clays of Miocene deposits overlying the basalts. Such basaltic features (of Oligocene age) are underlain by Gabal Ahmar Formation of Oligocene deposits, which are composed of sand and sandstone. Therefore, two aquifers were deduced in the area. The first is the Miocene aquifer (shallower) and the other is the Oligocene aquifer (deeper).  相似文献   

The use of connectivity clusters in stochastic modelling of highly heterogeneous porous media     

Mohamed A. Awad  Ahmed E. Hassan  Hesham M. Bekhit 《Arabian Journal of Geosciences》2018,11(5):98

Stochastic geostatistical techniques are essential tools for groundwater flow and transport modelling in highly heterogeneous media. Typically, these techniques require massive numbers of realizations to accurately simulate the high variability and account for the uncertainty. These massive numbers of realizations imposed several constraints on the stochastic techniques (e.g. increasing the computational effort, limiting the domain size, grid resolution, time step and convergence issues). Understanding the connectivity of the subsurface layers gives an opportunity to overcome these constraints. This research presents a sampling framework to reduce the number of the required Monte Carlo realizations utilizing the connectivity properties of the hydraulic conductivity distributions in a three-dimensional domain. Different geostatistical distributions were tested in this study including exponential distribution with the Turning Bands (TBM) algorithm and spherical distribution using Sequential Gaussian Simulation (SGSIM). It is found that the total connected fraction of the largest clusters and its tortuosity are highly correlated with the percentage of mass arrival and the first arrival quantiles at different control planes. Applying different sampling techniques together with several indicators suggested that a compact sample representing only 10% of the total number of realizations can be used to produce results that are close to the results of the full set of realizations. Also, the proposed sampling techniques specially utilizing the low conductivity clustering show very promising results in terms of matching the full range of realizations. Finally, the size of selected clusters relative to domain size significantly affects transport characteristics and the connectivity indicators.  相似文献   

Synoptic features associated with dust transition processes from North Africa to Asia   总被引：1，自引：0，他引：1  

Adel M. Awad  Abdul-Wahab S. Mashat 《Arabian Journal of Geosciences》2014,7(6):2451-2467

Aerosol index data from the total ozone mapping spectrometer satellite and reanalysis data from the National Center for Environmental Prediction and the National Center for Atmospheric Research are useful in the study of synoptic properties of the dust storms that carry dust from North Africa to Asia during the spring season for the period 1979 to 2006. In this study, we analyzed the synoptic properties of dust cases that pass through the transition zone between North Africa and Asia. We identified the dust cases to study by looking, inside transition zone, at events with an aerosol index greater than 2. We then divided the identified cases, depending on the spread and strength of the dust inside the transition zone, into seven categories ranging from weak events to moderate events to violent events. We found the common synoptic characteristics in all these categories as follows: The high pressure belt located over northern Africa allows the low pressure belt located over the South African Sahara to move northward; a pressure gradient between these two atmospheric systems directs from south to north; an increase in the pressure gradient leads to increased in both of the event’s dust and the amount of dust moves to North Africa from the Sahara; an additional pressure gradient between the western Azores high pressure system and the low pressure system located over the Arabian Peninsula directs from west to east; the stronger the pressure gradient, the greater the amount of dust in the event and moving a large amount of dust from Northeast Africa to Asia. To verify that these characteristics capture the essence of dust events from North Africa to Asia, we checked if they were also common to two additional extremes categories and two extremes events. The results confirmed the continued existence of these common characteristics.  相似文献   

Geomechanical evaluation of Pliocene natural aggregates as pavement materials     

El-Sayed Sedek Abu Seif 《Arabian Journal of Geosciences》2014,7(4):1567-1576

Asphaltic roads and constructions in Egypt annually consume a huge amount of aggregates. The physical and geomechanical properties of these aggregates have controlled their performance in which they are used. All road pavements require the efficient use of locally available materials if economically constructed roads are to be built. More than 650 million m³ of fine and coarse aggregates are herein selected to be the tonnage of the present study. The studied Pliocene aggregates have smoothed grading curves and neither a deficiency nor excess of any one particle size, generally produce good mixtures with fewer voids between particles. The litho-particles of coarse aggregates are composed mainly of granites, gneisses, granodiorite, gabbro, and quartz particles. The sand equivalent value of fine aggregates varies from 95 to 97 %. The specific gravity values of the studied aggregates vary from 2.72 to 2.74 gm/cm³ for coarse aggregate and range from 2.51 to 2.54 gm/cm³ for fine aggregate. The Los Angles abrasion value varies from 19 to 24 %. Both coarse and fine aggregates meet the international standards which are suitable for usage as subbase and surface course aggregates, respectively.  相似文献   

Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes     

Alina Marie Hasbi  Mohammed Awad Momani  Mohd Alauddin Mohd Ali  Norbahiah Misran  Kazuo Shiokawa  Yuichi Otsuka  Kiyohumi Yumoto 《Journal of Atmospheric and Solar》2009,71(17-18):1992-2005

This paper investigates the ionospheric and geomagnetic responses during the 28 March 2005 and 14 May 2005 Sumatran earthquakes using GPS and magnetometer stations located in the near zone of the epicenters. These events occurred during low solar and geomagnetic activity. TEC oscillations with periods of 5–10 min were observed about 10–24 min after the earthquakes and have horizontal propagation velocities of 922–1259 m/s. Ionospheric disturbances were observed at GPS stations located to the northeast of the epicenters, while no significant disturbances were seen relatively east and south of the epicenters. The magnetic field measurements show rapid fluctuations of 4–5 s shortly after the earthquake, followed by a Pc5 pulsation of 4.8 min about 11 min after the event. The correlation between the ionospheric and geomagnetic responses shows a good agreement in the period and time lag of the peak disturbance arrival, i.e. about 11–13 min after the earthquake.  相似文献   

Decrease in the clear air transmission at Helwan Observatory site     

J. S. Mikhail  B. B. Baghos  M. Y. Tawadrous  Y. E. Helali  H. Awad  KH. I. Khalil  M. El-Saftawe  M. Ibrahim 《Earth, Moon, and Planets》1995,70(1-3):143-149

Clear air atmospheric transparency of eight nights at Helwan Observatory site during autumn period of 1987 have been determined using the yellow filter GG5. The prevailing atmospheric transmission extends to 58%. A comparison with previous values obtained with the same filter and site during autumn period of 1963 shows a considerable decrease at the present years in the clear air transmission of the site of Helwan. This can be attributed to the aerosol pollution of the site caused mainly by the increase of the industrial centers at Helwan Zone. Clear air atmospheric transparency values at the beginning of winter season and at spring season are also given.  相似文献