The Makran accretionary complex shows a distinct bottom-simulating reflector, indicating a thick gas-hydrate-bearing horizon
between the deformational front and about 1350 m water depth which seals off the upward flow of gas-charged fluids. A field
of presently inactive mud diapirs with elevations up to 65 m was discovered in the abyssal plain seawards of the deformation
front, suggesting that in the past conditions were favorable for periodic but localized vigorous mud diapirism. Regional destabilization
of the gas hydrate leading to focused flow was observed where deep-penetrating, active faults reach the base of the gas-hydrate
layer, as in a deeply incised submarine canyon (2100–2500 m water depth). At this location we discovered seeps of methane
and H2S-rich fluids associated with chemoautotrophic vent faunas (e.g., Calyptogena sp.). Driven by the accretionary wedge dynamics, the landward part of the gas-hydrate layer below the Makran margin is being
progressively uplifted. Due to reduced hydrostatic pressure and rising ocean bottom-water temperatures, gas hydrates are progressively
destabilized and dissociated into hydrate water, methane and H2S. Sediment temperatures lie outside the methane stability field wherever water depth is less than 800 m. Above this depth,
upward migration of fluids to the seafloor is unimpeded, thus explaining the abundance of randomly distributed gas seeps observed
at water depths of 350 to 800 m.
Received: 14 June 1999 / Revision accepted: 6 February 2000 相似文献
Stochastic Environmental Research and Risk Assessment - Drought is considered to be one of the most devastating natural hazards, causing widespread environmental and social damage in many parts of... 相似文献
A new seismic hazard model for Cairo, the capital city of Egypt is developed herein based on comprehensive consideration of uncertainties in various components of the probabilistic seismic hazard analysis. The proposed seismic hazard model is developed from an updated catalogue of historical and instrumental seismicity, geodetic strain rates derived from GPS-based velocity-field of the crust, and the geologic slip rates of active faults. The seismic source model consists of area sources and active faults characterised to forecast the seismic productivity in the region. Ground motion prediction models are selected to describe the expected ground motion at the sites of interest. The model accounts for inherent epistemic uncertainties of statistical earthquake recurrence; maximum magnitude; ground motion prediction models, and their propagation toward the obtained results. The proposed model is applied to a site-specific hazard analysis for Kottamiya, Rehab City and Zahraa-Madinat-Nasr (hereinafter referred to as Zahraa) to the East of Cairo (Egypt). The site-specific analysis accounts for the site response, through the parameterization of the sites in terms of average 30-m shear-wave velocity (Vs30). The present seismic hazard model can be considered as a reference model for earthquake risk mitigation and proper resilience planning. 相似文献
This study was conducted to evaluate the effect of replacing soybean meal (SBM) by low protein floc meal (LPFM; 24% CP) in tilapia diets on growth performance, feed utilization and fish chemical composition. Three isonitrogenous and isocaloric diets were formulated; control diet (C; without LPFM), FM 25 (25% of SBM protein was substituted by LPFM) and FM 50 (50% of SBM protein was substituted by LPFM). Nine 55l circular plastic tanks were stocked by 12 fish to form three experimental groups. No differences in tilapia performance were observed between the control and the FM 25 diet. Chemical composition of fish did not differ significantly among treatments except for protein and selenium contents where the highest values were recorded in the control treatment. The highest mineral content was recorded in floc collected from the control tanks, while calcium content showed its highest value in floc collected from FM 50 effluent. These data indicate that replacing soybean meal with LPFM up to 25%, had no negative effect on growth performance and potentially may improve the system sustainability. Meanwhile, the adverse effect of more inclusion of LPFM in tilapia diet may be attributed to the higher content of ash. In other word, minerals seem to cause more energy utilization in fish fed floc meal since it is needed to maintain osmotic homeostasis.
This study was conducted to evaluate the ef fect of replacing soybean meal(SBM) by low protein ?oc meal(LPFM; 24% CP) in tilapia diets on growth performance, feed utilization and ?sh chemical composition. Three isonitrogenous and isocaloric diets were formulated; control diet(C; without LPFM),FM 25(25% of SBM protein was substituted by LPFM) and FM 50(50% of SBM protein was substituted by LPFM). Nine 55 l circular plastic tanks were stocked by 12 ?sh to form three experimental groups.No dif ferences in tilapia performance were observed between the control and the FM 25 diet. Chemical composition of ?sh did not dif fer signi?cantly among treatments except for protein and selenium contents where the highest values were recorded in the control treatment. The highest mineral content was recorded in ?oc collected from the control tanks, while calcium content showed its highest value in ?oc collected from FM 50 e ? uent. These data indicate that replacing soybean meal with LPFM up to 25%, had no negative ef fect on growth performance and potentially may improve the system sustainability. Meanwhile, the adverse ef fect of more inclusion of LPFM in tilapia diet may be attributed to the higher content of ash. In other word,minerals seem to cause more energy utilization in ?sh fed ?oc meal since it is needed to maintain osmotic homeostasis. 相似文献
The Egyptian government is replacing the existing Naga Hammadi barrage, located across the Nile River some 450 km south of
Cairo, with the New Naga Hammadi barrage (NNHB) to incorporate a hydropower plant and to improve conditions for river traffic.
The new structure will lead to an increase in river water levels, both locally near the new barrage and upstream. The rise
in river water levels will in turn result in changes in groundwater levels in the aquifer system up and downstream of the
barrages. In this paper, an area is chosen, which is expected to suffer from a high groundwater table after the construction
of the NNHB, to investigate the problem and propose alternatives for lowering the groundwater levels. The study area is a
village called Bakhaness, with an area of 588 ha. It is located some 1.5 km upstream of the NNHB. A computer model (MicroFEM)
has been used to simulate the groundwater conditions before and after construction of the NNHB. Alternatives for lowering
the groundwater table are proposed, simulated and evaluated. The systems, which are assessed are a municipal sewer system,
a system of perforated pipes in urban areas, and tile drainage with different values of efficiency in agricultural areas. 相似文献
The Domingos Petrolini Swamp, located on the Southern Coastal Plain of Rio Grande do Sul, near the town of Rio Grande, constitutes an ample holocene lagoonal deposit. Events related to the holocene transgression and their diverse phases of glacial-eustatic ocillations were found through palynological analysis. Bases on these palynological data, four distinct phases to the paleoenvironmental evolution of the ecosystem were identified. It has also shown a transgressive restricted marine sequence on the base, which suggests the existence of a coastal brackish lagoon or a marisme type of environment. Later, there was a gradation for continentality conditions along with a scarce pollinical record. The third phase is characterized by the presence of marine components and halophyte vegetation, showing another transgressive event in that place. Lastly, the end of direct marine influence over the swamp was recorded and also the vegetation development as it appears these days. 相似文献