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101.
Understanding the time‐varying importance of different uncertainty sources in hydrological modelling using global sensitivity analysis 下载免费PDF全文
Simulations from hydrological models are affected by potentially large uncertainties stemming from various sources, including model parameters and observational uncertainty in the input/output data. Understanding the relative importance of such sources of uncertainty is essential to support model calibration, validation and diagnostic evaluation and to prioritize efforts for uncertainty reduction. It can also support the identification of ‘disinformative data’ whose values are the consequence of measurement errors or inadequate observations. Sensitivity analysis (SA) provides the theoretical framework and the numerical tools to quantify the relative contribution of different sources of uncertainty to the variability of the model outputs. In traditional applications of global SA (GSA), model outputs are aggregations of the full set of a simulated variable. For example, many GSA applications use a performance metric (e.g. the root mean squared error) as model output that aggregates the distances of a simulated time series to available observations. This aggregation of propagated uncertainties prior to GSA may lead to a significant loss of information and may cover up local behaviour that could be of great interest. Time‐varying sensitivity analysis (TVSA), where the aggregation and SA are repeated at different time steps, is a viable option to reduce this loss of information. In this work, we use TVSA to address two questions: (1) Can we distinguish between the relative importance of parameter uncertainty versus data uncertainty in time? (2) Do these influences change in catchments with different characteristics? To our knowledge, the results present one of the first quantitative investigations on the relative importance of parameter and data uncertainty across time. We find that the approach is capable of separating influential periods across data and parameter uncertainties, while also highlighting significant differences between the catchments analysed. Copyright © 2016 The Authors. Hydrological Processes. Published by John Wiley & Sons Ltd. 相似文献
102.
The uptake of Eu(III) by crystalline calcium silicate hydrate (C-S-H) phases 11 Å tobermorite and xonotlite has been investigated by the combined use of time-resolved laser fluorescence spectroscopy (TRLFS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Eu(III) doped tobermorite and xonotlite samples with varying metal loading (0.4, 7 and 35 μmol Eu/g solid phase) and reaction time (1-570 days) were investigated. The structural environment of Eu(III) taken up by tobermorite and xonotlite was found to depend on both parameters.At high Eu(III) loading (7 μmol Eu/g solid phase), TRLFS data indicated presence of three Eu(III) species with different fluorescence lifetimes after 1 day reaction time. The emission lifetimes deduced for the different species correspond to ∼4.7, ∼1 and 0 water molecules in the first coordination sphere, thus suggesting the presence of one surface species forming an inner-sphere surface complex and two species incorporated in the crystal structure. After longer contact times (90 days, 570 days), the surface species was not observed. At the lower Eu(III) loading (0.4 μmol Eu/g solid phase) and reaction times between 1 and 310 days only two Eu(III) species with ∼1-2 and 0 water molecules were detected, corresponding to Eu(III) being incorporated in the crystal structure. The results from EXAFS showed that the distances between Eu(III) and neighboring Ca and Si atoms in Eu(III) doped tobermorite increase after prolonged reaction time. Furthermore, the number of neighboring Ca and Si atoms was found to increase with time. This study demonstrates that binding into the structure of 11 Å tobermorite and xonotlite is the dominant mode of Eu(III) immobilization after long reaction time. This finding is essential for an overall assessment of the safe disposal of actinides in deep geological repositories for radioactive waste, as incorporation into the crystal structure suggests long-term immobilization in the repository environment. 相似文献
103.
Christina Perdikouri Thorsten Geisler Burkhard C. Schmidt 《Geochimica et cosmochimica acta》2011,75(20):6211-6224
The experimental replacement of aragonite by calcite was studied under hydrothermal conditions at temperatures between 160 and 200 °C using single inorganic aragonite crystals as a starting material. The initial saturation state and the total [Ca2+]:[CO32−] ratio of the experimental solutions was found to have a determining effect on the amount and abundance of calcite overgrowths as well as the extent of replacement observed within the crystals. The replacement process was accompanied by progressive formation of cracks and pores within the calcite, which led to extended fracturing of the initial aragonite. The overall shape and morphology of the parent aragonite crystal were preserved. The replaced regions were identified with scanning electron microscopy and Raman spectroscopy.Experiments using carbonate solutions prepared with water enriched in 18O (97%) were also performed in order to trace the course of this replacement process. The incorporation of the heavier oxygen isotope in the carbonate molecule within the calcite replacements was monitored with Raman spectroscopy. The heterogeneous distribution of 18O in the reaction products required a separate study of the kinetics of isotopic equilibration within the fluid to obtain a better understanding of the 18O distribution in the calcite replacement. An activation energy of 109 kJ/mol was calculated for the exchange of oxygen isotopes between [C16O32−]aq and [H218O] and the time for oxygen isotope exchange in the fluid at 200 °C was estimated at ∼0.9 s. Given the exchange rate, analyses of the run products imply that the oxygen isotope composition in the calcite product is partly inherited from the oxygen isotope composition of the aragonite parent during the replacement process and is dependent on access of the fluid to the reaction interface rather than equilibration time. The aragonite to calcite fluid-mediated transformation is described by a coupled dissolution-reprecipitation mechanism, where aragonite dissolution is coupled to the precipitation of calcite at an inwardly moving reaction interface. 相似文献
104.
This paper investigates by means of several large eddy simulations how the channel aspect ratio affects the transport and settling of suspended sediments. The numerical method is successfully validated using data of a physical experiment of fine sediment net deposition in an open channel flow. The channel aspect ratio, A, is known to be the determining factor for the development, strength and distribution of the turbulence‐driven secondary flow, and it is demonstrated that A influences the primary flow, turbulence quantities and the transport and fate of fine sediments. The secondary flow locally supports or hinders the falling of fine sediment particles in a turbulent flow, which results in a non‐uniform deposition of fine sediments over the cross‐section. While the channel aspect ratio has a large influence on the distribution of suspended sediments within the cross‐section, its effect on the cross‐sectional averaged deposition is negligibly small. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
105.
Abstract This paper examines the potential effects of urbanization on streamflow in Maine, USA, from 1950 to 2000. The study contrasts nine watersheds in southern Maine, which has seen steady urban growth over the study period, with nine rural watersheds from northern Maine. Historical population data and current land cover data are used to develop an urbanization score for each watershed. Trends in watershed urbanization over the study period are compared to trends in ecologically relevant streamflow characteristics. The results indicate that trends in northern, rural watersheds are much more consistent than the trends in the southern watersheds. Additionally, trends in the southern watersheds are inconsistent with the hydrological characteristics observed in urban watersheds elsewhere, likely due to the comparatively low level of current urban development in Maine's urban watersheds. Our study suggests that urban areas in Maine have not yet reached an urbanization threshold where streamflow impacts become consistently detectable. Editor Z.W. Kundzewicz Citation Martin, E.H., Kelleher, C., and Wagener, T., 2012. Has urbanization changed ecological streamflow characteristics in Maine (USA)? Hydrological Sciences Journal, 57 (7), 1337–1354. 相似文献
106.
Thorsten Wagener 《水文研究》2007,21(23):3233-3236
107.
Thorsten Beitter Thomas Wagner Gregor Markl 《Contributions to Mineralogy and Petrology》2008,156(6):689-707
In this study, we have investigated the formation of quartz–kyanite veins of the Alpe Sponda, Central Alps, Switzerland. We
have integrated field observations, fluid inclusion and stable isotope data and combined this with numerical geochemical modeling
to constrain the chemical processes of aluminum transport and deposition. The estimated P–T conditions of the quartz–kyanite
veins, based on conventional geothermometry (garnet–biotite, white mica solvus and quartz–kyanite oxygen isotope thermometry)
and fluid inclusion data, are 550 ± 30°C at 5.0 ± 0.5 kbar. Geochemical modeling involved construction of aqueous species
predominance diagrams, calculation of kyanite and quartz solubility, and reaction–path simulations. The results of the modeling
demonstrate that (1) for the given chemical composition of the vein-forming fluids mixed Al–Si aqueous species are dominant
in transporting Al, and that (2) fluid cooling along a small temperature gradient coupled with a pH decrease is able to explain
the precipitation of the quartz–kyanite assemblages in the proportions that are observed in the Alpe Sponda veins. We conclude
that sufficient amounts of Al can be transported in typical medium- to high-grade regional metamorphic fluids and that immobile
behavior of Al is not very likely in advection–dominanted fluid–rock systems in the upper and middle crust. 相似文献
108.
109.
Aneesh Soman Thorsten Geisler Frank Tomaschek Marion Grange Jasper Berndt 《Contributions to Mineralogy and Petrology》2010,160(6):909-930
A natural, altered zircon crystal from an alkaline pegmatite from the Zomba–Malosa Complex of the Chilwa Alkaline Province
in Malawi has been studied by a wide range of analytical techniques to understand the alteration process. The investigated
zircon shows two texturally and chemically different domains. Whereas the central parts of the grain (zircon I) appear homogeneous
in backscattered electron images and are characterised by high concentrations of trace elements, particularly Th, U, and Y,
the outer regions (zircon II) contain significantly less trace elements, numerous pores, and inclusions of thorite, ytttrialite,
and fergusonite. Zircon II contains very low or undetectable concentrations of non-formula elements such as Ca, Al, and Fe,
which are commonly observed in high concentrations in altered radiation-damaged zircon. U–Pb dating of both zircon domains
by LA-ICPMS and SHRIMP yielded statistically indistinguishable U–Pb weighted average ages of 119.3 ± 2.1 (2σ) and 118 ± 1.2
(2σ) Ma, respectively, demonstrating that the zircon had not accumulated a significant amount of self-irradiation damage at
the time of the alteration event. Electron microprobe dating of thorite inclusions in zircon II yielded a Th–U-total Pb model
age of 122 ± 5 (2σ) Ma, supporting the age relationship between both zircon domains. The hydrothermal solution responsible
for the alteration of the investigated zircon was alkaline and rich in CO3
2−, as suggested by the occurrence of REE carbonates and CO2-bearing fluid inclusions. The alteration of the crystalline, trace element-rich zircon is explained by an interface-coupled
dissolution-reprecipitation mechanism. During such a process, the congruent dissolution of the trace element-rich parent zircon
I was spatially and temporally coupled to the precipitation of the trace element-poor zircon II at an inward moving dissolution-precipitation
front. The driving force for such a process was merely the difference between the solubility of the trace element-rich and
-poor zircon in the hydrothermal solution. The replacement process and the occurrence of mineral inclusions and porosity in
the product zircon II is explained by the thermodynamics of solid solution-aqueous solution systems. 相似文献
110.
Thomas S. Kruijer Peter Sprung Thorsten Kleine Ingo Leya Rainer Wieler 《Meteoritics & planetary science》2013,48(12):2597-2607
Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility‐controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of 113Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd‐Pt‐W isotope results from this study thus demonstrate that the relative magnitude of neutron capture‐induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites. 相似文献