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131.
Ecohydrographic constraints on biodiversity and distribution of phytoplankton and zooplankton in coral reefs of the Red Sea,Saudi Arabia 下载免费PDF全文
Benjamin Kürten Hisham S. Khomayis Reny Devassy Saskia Audritz Ulrich Sommer Ulrich Struck Mohsen M. El‐Sherbiny Ali M. Al‐Aidaroos 《Marine Ecology》2015,36(4):1195-1214
An integral concept of ecological research is the constraint of biodiversity along latitudinal and environmental gradients. The Red Sea features a natural example of a latitudinal gradient of salinity, temperature and nutrient richness. Coral reefs along the Red Sea coasts are supported with allochthonous resources such as oceanic and neritic phytoplankton and zooplankton; however, relatively little is known about how the ecohydrography correlates with plankton biodiversity and abundance. In this article we present the biodiversity of phytoplankton and zooplankton in Red Sea coral reefs. Oceanographic data (temperature, salinity), water samples for nutrient analysis, particulate organic matter, phytoplankton and zooplankton, the latter with special reference to Copepoda (Crustacea), were collected at nine coral reefs over ~1500 km distance along the Red Sea coast of Saudi Arabia. The trophic state of ambient waters [as indicated by chlorophyll a (Chl a)] changed from strong oligotrophy in the north to mesotrophy in the south and was associated with increasing biomasses of Bacillariophyceae, picoeukaryotes and Synechococcus as indicated by pigment fingerprinting (CHEMTAX) and flow cytometry. Net‐phytoplankton microscopy revealed a Trichodesmium erythraeum (Cyanobacteria) bloom north of the Farasan Islands. Several potentially harmful algae, including Dinophysis miles and Gonyaulax spinifera (Dinophyceae), were encountered in larger numbers in the vicinity of the aquaculture facilities at Al Lith. Changes in zooplankton abundance were mainly correlated to the phytoplankton biomass following the latitudinal gradient. The largest zooplankton abundance was observed at the Farasan Archipelago, despite high abundances of copepodites, veligers (Gastropoda larvae) and Chaetognatha at Al Lith. Although the community composition changed over latitude, biodiversity indices of phytoplankton and zooplankton did not exhibit a systematic pattern. As this study constitutes the first current account of the plankton biodiversity in Red Sea coral reefs at a large spatial scale, the results will be informative for ecosystem‐based management along the coastline of Saudi Arabia. 相似文献
132.
Soil-Structure Interaction Analysis of Jack-up Platforms Subjected to
Monochrome and Irregular Waves
As jack-up platforms have recently been used in deeper and harsher waters, there has been an increasing demand to understand their behaviour more accurately to develop more sophisticated analysis techniques. One of the areas of significant development has been the modelling of spudcan performance, where the load-displacement behaviour of the foundation is required to be included in any numerical model of the structure. In this study, beam on nonlinear winkler foundation (BNWF) modeling—which is based on using nonlinear springs and dampers instead of a continuum soil media—is employed for this purpose. A regular monochrome design wave and an irregular wave representing a design sea state are applied to the platform as lateral loading. By using the BNWF model and assuming a granular soil under spudcans, properties such as soil nonlinear behaviour near the structure, contact phenomena at the interface of soil and spudcan (such as uplifting and rocking), and geometrical nonlinear behaviour of the structure are studied. Results of this study show that inelastic behaviour of the soil causes an increase in the lateral displacement at the hull elevation and permanent unequal settlement in soil below the spudcans, which are increased by decreasing the friction angle of the sandy soil. In fact, spudcans and the underlying soil cause a relative fixity at the platform support, which changes the dynamic response of the structure compared with the case where the structure is assumed to have a fixed support or pinned support. For simulating this behaviour without explicit modelling of soil-structure interaction (SSI), moment-rotation curves at the end of platform legs, which are dependent on foundation dimensions and soil characteristics, are obtained. These curves can be used in a simplified model of the platform for considering the relative fixity at the soil-foundation interface. 相似文献
133.
Delay-difference models are intermediate between simple surplus-production models and complicated age-structured models. Such intermediate models are more efficient and require less data than age-structured models. In this study, a delay-difference model was applied to fit catch and catch per unit effort(CPUE) data(1975–2011) of the southern Atlantic albacore(Thunnus alalunga) stock. The proposed delay-difference model captures annual fluctuations in predicted CPUE data better than Fox model. In a Monte Carlo simulation, white noises(CVs) were superimposed on the observed CPUE data at four levels. Relative estimate error was then calculated to compare the estimated results with the true values of parameters α and β in Ricker stock-recruitment model and the catchability coefficient q. α is more sensitive to CV than β and q. We also calculated an 80% percentile confidence interval of the maximum sustainable yield(MSY, 21756 t to 23408 t; median 22490 t) with the delay-difference model. The yield of the southern Atlantic albacore stock in 2011 was 24122 t, and the estimated ratios of catch against MSY for the past seven years were approximately 1.0. We suggest that care should be taken to protect the albacore fishery in the southern Atlantic Ocean. The proposed delay-difference model provides a good fit to the data of southern Atlantic albacore stock and may be a useful choice for the assessment of regional albacore stock. 相似文献
134.
Suman?MajumdarEmail authorView authors OrcID profile Kanan?K.?Datta Raghunath?Ghara Rajesh?Mondal T.?Roy?Choudhury Somnath?Bharadwaj Sk.?Saiyad?Ali Abhirup?Datta 《Journal of Astrophysics and Astronomy》2016,37(4):32
The line-of-sight direction in the redshifted 21-cm signal coming from the cosmic dawn and the epoch of reionization is quite unique in many ways compared to any other cosmological signal. Different unique effects, such as the evolution history of the signal, non-linear peculiar velocities of the matter etc. will imprint their signature along the line-of-sight axis of the observed signal. One of the major goals of the future SKA-LOW radio interferometer is to observe the cosmic dawn and the epoch of reionization through this 21-cm signal. It is thus important to understand how these various effects affect the signal for its actual detection and proper interpretation. For more than one and half decades, various groups in India have been actively trying to understand and quantify the different line-of-sight effects that are present in this signal through analytical models and simulations. In many ways the importance of this sub-field under 21-cm cosmology have been identified, highlighted and pushed forward by the Indian community. In this article, we briefly describe their contribution and implication of these effects in the context of the future surveys of the cosmic dawn and the epoch of reionization that will be conducted by the SKA-LOW. 相似文献
135.
136.
Kaushar Ali Sunil Sonbawane D. M. Chate Devendraa Siingh P. S. P. Rao P. D. Safai K. B. Budhavant 《Journal of Earth System Science》2010,119(6):753-762
Surface snow and lake water samples were collected at different locations around Indian station at Antarctica, Maitri, during December 2004–March 2005 and December 2006–March 2007. Samples were analyzed for major chemical ions. It is found that average pH value of snow is 6.1. Average pH value of lake water with low chemical content is 6.2 and of lake water with high chemical content is 6.5. The Na+ and Cl? are the most abundantly occurring ions at Antarctica. Considerable amount of SO 4 2? is also found in the surface snow and the lake water which is attributed to the oxidation of DMS produced by marine phytoplankton. Neutralization of acidic components of snow is mainly done by NH 4 + and Mg2+. The Mg2+, Ca2+ and K+ are nearly equally effective in neutralizing the acidic components in lake water. The NH 4 + and SO 4 2? occur over the Antarctica region mostly in the form of (NH4)2SO4. 相似文献
137.
A combined hydrologic and hydraulic modeling approach for testing efficiency of structural flood control measures 总被引:3,自引:2,他引:1
The necessity of estimating the degree and spatial extent of positive impacts with regard to protecting communities and properties
through potential flood control projects can be considered one of the main reasons for performing flood modeling. This paper
presents an overall systematic approach based on the simulation of some extreme event conditions, using a hydrological model
to generate the resulting river flows and then using a hydraulic modeling exercise to decide upon floodplain evolution in
the case-study area, Bostanli river basin, which has been under the threat of flooding for many years. The potential serviceability
of the planned Bostanli Dam in the study area was examined by using the HEC-HMS and HEC-RAS modeling tools, both integrated
with GIS functions for spatial operations. The results indicate that the dam construction as planned would have a somewhat
positive impact as a potential flood control measure, since it seems to decrease the flood peaks of 68.9 and 158.7 m3/s (that would potentially be generated by 100- and 500-year storm events under current conditions) to 65.5 and 150.7 m3/s (when the dam is in operation), respectively. However, this seems to contribute little to the overall flood mitigation
performance in the basin. 相似文献
138.
Ali Salim Joodi Stanislas Sizaret Stéphane Binet Ary Bruand Patrick Alberic Michel Lepiller 《Hydrogeology Journal》2010,18(2):295-309
Darcy’s law is the equation of reference widely used to model aquifer flows. However, its use to model karstic aquifers functioning with large pores is problematic. The physics occurring within the karstic conduits requires the use of a more representative macroscopic equation. A hydrodynamic model is presented which is adapted to the karstic aquifer of the Val d’Orléans (France) using two flow equations: (1) Darcy’s law, used to describe water flow within the massive limestone, and (2) the Brinkman equation, used to model water flow within the conduits. The flow equations coupled with the transport equation allow the prediction of the karst transfer properties. The model was tested by using six dye tracer tests and compared to a model that uses Darcy’s law to describe the flow in karstic conduits. The simulations show that the conduit permeability ranges from 5?×?10?6 to 5.5?×?10?5?m2 and the limestone permeability ranges from 8?×?10?11 to 6?×?10?10?m2. The dispersivity coefficient ranges from 23 to 53 m in the conduits and from 1 to 5 m in the limestone. The results of the simulations carried out using Darcy’s law in the conduits show that the dispersion towards the fractures is underestimated. 相似文献
139.
Fly ash is a waste by-product obtained from the burning of coal by thermal power plants for generating electricity. When bulk
quantities are involved, in order to arrest the fugitive dust, it is stored wet rather than dry. Fly ash contains trace concentrations
of heavy metals and other substances in sufficient quantities to be able to leach out over a period of time. In this study
an attempt was made to study the leachabilities of a few selected trace metals: Cd, Cu, Cr, Mn, Pb and Zn from two different
types of class F fly ashes. Emphasis is also laid on developing an alternative in order to arrest the relative leachabilities
of heavy metals after amending them with suitable additives. A standard laboratory leaching test for combustion residues has
been employed to study the leachabilities of these trace elements as a function of liquid to solid ratio and pH. The leachability
tests were conducted on powdered fly ash samples before and after amending them suitably with the matrices lime and gypsum;
they were compacted to their respective proctor densities and cured for periods of 28 and 180 days. A marked reduction in
the relative leachabilities of the trace elements was observed to be present at the end of 28 days. These relative leachability
values further reduced marginally when tests were performed at the end of 180 days. 相似文献
140.
Mahnaz Khodami Moussa Noghreyan Ali Reza Davoudian 《Arabian Journal of Geosciences》2010,3(3):257-266
Late Miocene–Pliocene to Quaternary calc-alkaline lava flows and domes are exposed in southeast of Isfahan in the Urumieh Dokhtar magmatic belt in the Central Iran structural zone. These volcanic rocks have compositions ranging from basaltic andesites, andesites to dacites. Geochemical studies show these rocks are a medium to high K calc-alkaline suite and meta-aluminous. Major element variations are typical for calc-alkaline rocks. The volcanic rocks have SiO2 contents ranging between 53.8% and 65.3%. Harker diagrams clearly show that the dacitic rocks did not form from the basaltic andesites by normal differentiation processes. They show large ion lithophile elements- and light rare earth elements (LREE)-enriched normalized multielement patterns and negative Nb, Ti, Ta, and P. Condrite-normalized REE patterns display a steep decrease from LREE to light rare earth elements without any Eu anomaly. These characteristics are consistent with ratios obtained from subduction-related volcanic rocks and in collision setting. The melting of a heterogeneous source is possible mechanism for their magma genesis, which was enriched in incompatible elements situated at the upper continental lithospheric mantle or lower crust. The geochemical characteristics of these volcanic rocks suggested that these volcanic rocks evolved by contamination of a parental magma derived from metasomatized upper lithospheric mantle and crustal melts. 相似文献