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31.
Streambed hydraulic conductivity (K) and vertical K (K v) are key controls on groundwater and surface water exchange and biogeochemical fluxes through the hyporheic zone, but drivers of transient hydraulic properties in different fluvial environments are poorly understood. This study combines hydrogeology, geophysics, and sedimentology to reveal mechanisms of K and K v transience in the upper 0.5 m of a sandy streambed during low discharge. Hydraulic tests (44 slug tests, 130 falling-head permeameter tests) and 130 grain-size analyses were repeated three times over 8 weeks on a 1,200 m2 grid spanning: (a) a channel with continuously flowing water and mobile bed load; (b) an adjacent mid-channel bar that was stationary and infrequently submerged. Aerial photographs and ground-penetrating radar show scour and complete reworking of fluvial sediments in the channel. Bar sediments below the water table remained immobile, but infrequent flows of moderate discharge reworked the uppermost few centimetres of the bar top. Despite differences in sediment mobility and stream flow characteristics across environments, K and K v exhibited order-of-magnitude differences in spatial heterogeneity and temporal variability in both the channel and bar. Mean K and K v values in the channel were comparatively stable over time. In the immobile bar, mean K declined 20% and K v declined 26% after increased discharge temporarily inundated the bar. Grain-size distributions were steady across both environments over time, but repeat geophysical surveys of the bar show a decrease in electrical conductivity, likely from porosity reduction. These findings suggest that sediment dynamics and stream flow characteristics in different streambed environments are important drivers of K transience during low discharge conditions. Specifically, pore clogging can be an important mechanism of transience over short durations (weeks to months) in immobile sediments subject to infrequent flows and minor reworking. 相似文献
32.
Wilhelm Vischer 《Aquatic Sciences - Research Across Boundaries》1941,9(1-2):108-127
Ohne Zusammenfassung
mit 43 Abbildungen 相似文献
33.
34.
Wilhelm Bierther 《International Journal of Earth Sciences》1948,35(2):106-115
Ohne Zusammenfassung 相似文献
35.
Wilhelm Salomon-Calvi 《International Journal of Earth Sciences》1932,23(5):283-288
Ohne ZusammenfassungViele der im folgenden verwerteten Angaben verdanke ich Frau Prof. Drevermann und Herrn Prof. Dr.Rudolf Richter. Einiges habe ich von ihnen wörtlich übernommen. 相似文献
36.
W. Salomon Wilckens Steinmann Wilhelm Salomon Donath 《International Journal of Earth Sciences》1928,19(5):425-432
Ohne Zusammenfassung 相似文献
37.
A quiescent polar crown prominence was observed at Meudon in Hα and Ca ii lines, and by EIT and SUMER on board SOHO in UV
lines from 9 to 10 March 1996. SUMER observed the prominence continuously in a scanning mode between 21:40 UT on 9 March,
and 18:13 UT on 10 March, in the nitrogen line N v (λ1238) with a 1 arc sec2 resolution. Altogether 190 prominence images (121×108 pixels) were obtained. These are presented in a movie. The prominence
is highly dynamic. Large-scale features, such as mixed loop systems and dark cavities are changing on time scales of a few
hours. Filamentary structure is evident and is changing within a few frames of the movie. A lifetime of 20–25 min for the
fine structure has been found by the autocorrelation method. We have statistically analysed the three moments of the N v line
in the prominence: line intensity, Doppler shift and linewidth, in the context of a multiple-thread model. We find that the
data are consistent with a model where the prominence is assumed to be an ensemble of small threads. In the brightest parts
of the prominence it is possible that there are many unresolved threads (15–20) along the line of sight with diameters smaller
than a few hundred kilometers. The filling factor is probably very small and in that case the structures occupy only a fraction
of the volume.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005151015043 相似文献
38.
FerryBox - Application of continuous water quality observations along transects in the North Sea 总被引:3,自引:2,他引:1
In 2002, the Helmholtz-Zentrum Geesthacht, Germany, started to use FerryBox-automated monitoring systems on Ships of Opportunity
to continuously record standard oceanographic, biological and chemical in situ data in the North Sea. The present study summarises
the operational experience gathered since the beginning of this deployment and reflects on the potential and limits of FerryBox
systems as a monitoring tool. One part relates to the instrumental performance, constancy of shipping services, and the availability
and quality of the recorded in situ data. The other considers integration of the FerryBox observations in scientific applications
and routine monitoring campaigns. Examples are presented that highlight the added value of the recorded data for the study
of both long- and short-term variability in water mass stability, plankton communities and surface water productivity in the
North Sea. Through the assessment of technical and scientific performance, it is evident that FerryBoxes have become a valuable
tool in marine research that helps to fill gaps in coastal and open ocean operational observation networks. 相似文献
39.
Katharina?Marquardt Elena?Petrishcheva Emmanuel?Gardés Richard?Wirth Rainer?Abart Wilhelm?Heinrich 《Contributions to Mineralogy and Petrology》2011,162(4):739-749
Yb-Y inter-diffusion along a single grain boundary of a synthetic yttrium aluminium garnet (YAG) bicrystal has been studied
using analytical transmission electron microscopy (ATEM). To investigate the diffusion, a thin-film containing Yb as the diffusant
was deposited perpendicular to the bicrystal grain boundary by pulsed laser deposition (PLD). Structural properties and their
change with time in both the diffusant source and the grain boundary are reported. The diffusion profiles are incorporated
in a numerical diffusion model, which is applied to determine the grain boundary diffusion coefficient, D
gb
, at 1.723 K it is equal to 3 × 10−15 m2/s. We find that grain boundary diffusion is 4.85 orders of magnitude faster than volume diffusion, which was determined from
the same diffusion experiment. This result is discussed in the context of special versus general grain boundaries. Finally,
we successfully tested the capability of synchrotron-based nano-X-ray fluorescence analysis to map micro-chemical patterns
in two dimensions with sub-micrometre resolution. 相似文献
40.
Bastian Joachim Emmanuel Gardés Rainer Abart Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2011,161(3):389-399
Growth rates of monomineralic, polycrystalline åkermanite (Ca2MgSi2O7) rims produced by solid-state reactions between monticellite (CaMgSiO4) and wollastonite (CaSiO3) single crystals were determined at 0.5 GPa dry argon pressure, 1,000–1,200°C and 5 min to 60 h, using an internally heated pressure vessel. Inert Pt-markers, initially placed at the monticellite–wollastonite interface, indicate symmetrical growth into both directions. This and mass balance considerations demonstrate that rim growth is controlled by transport of MgO. At 1,200°C and run durations between 5 min and 60 h, rim growth follows a parabolic rate law with rim widths ranging from 0.4 to 16.3 μm indicating diffusion-controlled rim growth. The effective bulk diffusion coefficient \( D_{\text{eff,MgO}}^{\text{Ak}} \) is calculated to 10?15.8±0.1 m2 s?1. Between 1,000°C and 1,200°C, the effective bulk diffusion coefficient follows an Arrhenius law with E a = 204 ± 18 kJ/mol and D 0 = 10?8.6±1.6 m2 s?1. Åkermanite grains display a palisade texture with elongation perpendicular to the reaction interface. At 1,200°C, average grain widths measured normal to elongation, increase with the square root of time and range from 0.4 to 5.4 μm leading to a successive decrease in the grain boundary area fraction, which, however, does not affect \( D_{\text{eff,MgO}}^{\text{Ak}} \) to a detectible extent. This implies that grain boundary diffusion only accounts for a minor fraction of the overall chemical mass transfer, and rim growth is essentially controlled by volume diffusion. This is corroborated by the agreement between our estimates of the effective MgO bulk diffusion coefficient and experimentally determined volume diffusion data for Mg and O in åkermanite from the literature. There is sharp contrast to the MgO–SiO2 binary system, where grain boundary diffusion controls rim growth. 相似文献