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排序方式: 共有407条查询结果,搜索用时 15 毫秒
91.
Joanna Staneva Emil V. Stanev Jörg-Olaf Wolff Thomas H. Badewien Rainer Reuter Burghard Flemming Alexander Bartholomä Karsten Bolding 《Continental Shelf Research》2009
This work deals with analysis of hydrographic observations and results of numerical simulations. The data base includes acoustic Doppler current profilers (ADCP) observations, continuous measurements on data stations and satellite data originating from the medium resolution imaging spectrometer (MERIS) onboard the European Space Agency (ESA) satellite ENVISAT with a spatial resolution of 300 m. Numerical simulations use nested models with horizontal resolutions ranging from 1 km in the German Bight to 200 m in the East Frisian Wadden Sea coupled with a suspended matter transport model. Modern satellite observations have now a comparable horizontal resolution with high-resolution numerical model of the entire area of the East Frisian Wadden Sea allowing to describe and validate new and so far unknown patterns of sediment distribution. The two data sets are consistent and reveal an oscillatory behaviour of sediment pools to the north of the back-barrier basins and clear propagation patterns of tidally driven suspended particulate matter outflow into the North Sea. The good agreement between observations and simulations is convincing evidence that the model simulates the basic dynamics and sediment transport processes, which motivates its further use in hindcasting, as well as in the initial steps towards forecasting circulation and sediment dynamics in the coastal zone. 相似文献
92.
Modelling blue and green water resources availability in Iran 总被引:7,自引:0,他引:7
Knowledge of the internal renewable water resources of a country is strategic information which is needed for long‐term planning of a nation's water and food security, among many other needs. New modelling tools allow this quantification with high spatial and temporal resolution. In this study we used the program Soil and Water Assessment Tool (SWAT) in combination with the Sequential Uncertainty Fitting program (SUFI‐2) to calibrate and validate a hydrologic model of Iran based on river discharges and wheat yield, taking into consideration dam operations and irrigation practices. Uncertainty analyses were also performed to assess the model performance. The results were quite satisfactory for most of the rivers across the country. We quantified all components of the water balance including blue water flow (water yield plus deep aquifer recharge), green water flow (actual and potential evapotranspiration) and green water storage (soil moisture) at sub‐basin level with monthly time‐steps. The spatially aggregated water resources and simulated yield compared well with the existing data. The study period was 1990–2002 for calibration and 1980–1989 for validation. The results show that irrigation practices have a significant impact on the water balances of the provinces with irrigated agriculture. Concerning the staple food crop in the country, 55% of irrigated wheat and 57% of rain‐fed wheat are produced every year in water‐scarce regions. The vulnerable situation of water resources availability has serious implications for the country's food security, and the looming impact of climate change could only worsen the situation. This study provides a strong basis for further studies concerning the water and food security and the water resources management strategies in the country and a unified approach for the analysis of blue and green water in other arid and semi‐arid countries. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
93.
Towards continuous long-term measurements of suspended particulate matter (SPM) in turbid coastal waters 总被引:1,自引:1,他引:0
Thomas H. Badewien Elke Zimmer Alexander Bartholomä Rainer Reuter 《Ocean Dynamics》2009,59(2):227-238
The dynamics of sediment transport in the East Frisian Wadden Sea are important for the coastal zone and for ecosystem functioning.
The tidal inlets between the East Frisian islands connect the back-barrier intertidal flats to the North Sea. Here, concentrations
of suspended particulate matter (SPM) in the water column are highly variable, depending on weather conditions and tides.
In order to estimate the nature and quantity of sediment transport, in situ measurements were carried out at a Time Series
Station in the tidal inlet between the islands of Spiekeroog and Langeoog. This study shows the suitability of multispectral
transmissometry (MST) for obtaining long-term SPM measurements with high resolution. The comparability of this technique to
the standard filter method and the laser diffraction method [laser in situ scattering and transmissometry (LISST)] is demonstrated.
In addition, the Junge coefficients derived from both MST and LISST measurements are compared. A time series of SPM data covering
nearly 4 months is presented. As a major result, the data reveal that a single storm surge can have less impact on SPM dynamics
than longer-lasting gales. This high-resolution long-term data set is very valuable for modelling suspended matter flux. It
also provides background information for studying the influence of SPM dynamics on coastal sediments. 相似文献
94.
95.
Three node-centered finite volume discretizations for multiphase porous media flow are presented and compared. By combination
of these methods two additional discretization methods are generated. The ability of these schemes to describe flows at textural
interfaces of different geologic formations is investigated. It was found that models with nonzero-entry pressures for the
capillary pressure-saturation relationship in conjunction with the Box discretization may give rise to spurious oscillations
for flows around low permeable lenses. Furthermore, the applicability and sensitivity of the discretization methods with regard
to the used computational grids is discussed. The schemes are used for the numerical study of two-phase flow in porous media
with zones of different material properties.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
96.
97.
Rainer Grün Maxime Aubert Marie-Hélène Moncel 《Geochimica et cosmochimica acta》2008,72(21):5278-5290
We have mapped U (238U) and Th (232Th) elemental concentrations as well as U-series isotope distributions in a Neanderthal tooth from the Middle Palaeolithic site of Payre using laser ablation ICP-MS. The U-concentrations in an enamel section varied between 1 and 1500 ppb. The U-concentration maps show that U-migration through the external enamel surface is minute, the bulk of the uranium having migrated internally via the dentine into the enamel. The uranium migration and uptake is critically dependent on the mineralogical structure of the enamel. Increased U-concentrations are observed along lineaments, some of which are associated with cracks, and others may be related to intra-prismatic zones or structural weaknesses reaching from the dentine into the enamel. The uranium concentrations in the dentine vary between about 25,000 and 45,000 ppb. Our systematic mapping of U-concentration and U-series isotopes provides insight into the time domain of U-accumulation. Most of the uranium was accumulated in an early stage of burial, with some much later overprints. None of the uranium concentration and U-series profiles across the root of the tooth complied with a single stage diffusion-adsorption (D-A) model that is used for quality control in U-series dating of bones and teeth. Nevertheless, in the domains that yielded the oldest apparent U-series age estimates, U-leaching could be excluded. This means that the oldest apparent U-series ages of around 200 ka represent a minimum age for this Neanderthal specimen. This is in good agreement with independent age assessments (200-230 ka) for the archaeological layer, in which it was found.The Th elemental concentrations in the dental tissues were generally low (between about 1 and 20 ppb), and show little relationship with the nature of the tissue. 相似文献
98.
Corrosion-induced gas generation in a nuclear waste repository: Reactive geochemistry and multiphase flow effects 总被引:1,自引:0,他引:1
Corrosion of steel canisters, stored in a repository for spent fuel and high-level nuclear wastes, leads to the generation and accumulation of H2 gas in the backfilled emplacement tunnels, which may significantly affect long-term repository safety. Previous studies have used H2 generation rates based on the volume of the waste or canister material and the stoichiometry of the corrosion reaction. However, Fe corrosion and H2 generation rates vary with time, depending on factors such as amount of Fe, water availability, water contact area and aqueous and solid chemistry. To account for these factors and feedback mechanisms, a chemistry model was developed related to Fe corrosion, coupled with two-phase (liquid and gas) flow phenomena that are driven by gas-pressure buildup associated with H2 generation and water consumption. Results indicate that by dynamically calculating H2 generation rates based on a simple model of corrosion chemistry, and by coupling this corrosion reaction with two-phase flow processes, the degree and extent of gas-pressure buildup could be much smaller compared to a model that neglects the coupling between flow and reactive transport mechanisms. By considering the feedback of corrosion chemistry, the gas pressure increases initially at the canister, but later decreases and eventually returns to a stabilized pressure that is slightly higher than the background pressure. The current study focuses on corrosion under anaerobic conditions for which the coupled hydrogeochemical model was used to examine the role of selected physical parameters on H2 gas generation and corresponding pressure buildup in a nuclear waste repository. The developed model can be applied to evaluate the effect of water and mineral chemistry of the buffer and host rock on the corrosion reaction for future site-specific studies. 相似文献
99.
Dipl. Ing. Dr. Rainer Knickmeyer Staatl. gepr. Lebensmittelchem. Oliver Landgraff Prof. Dr. Hans Steinhart 《Ocean Dynamics》1990,43(6):289-309
The content and distribution of ΣPCB (as the sum of 24 individual components), HCB and p,p′-DDE was determined in sediments
taken from the North Sea during two seasons.
The mass-balance of aromatic organochlorine compounds in the upper 2 cm of sediments is calculated and dicussed in relation
to pollutant dispersal. 相似文献
100.
Cr(III) sorbed at the solid/water interface of latex and hectorite was studied by ESR spectroscopy in the presence of different inorganic ligands. The ESR spectra of the surface obtained in the presence of selenite, phosphate and fluoride can be explained in terms of ternary surface complex formation. This is contrasted by the behaviour of sulfate and selenate ions which were found to have no effect on the ligand field of Cr(III), either in the adsorbed state or in solution. 相似文献