Diet of fishes in a detritus-based sandy lowland brook     

Christian Göcke  Norbert Kaschek  Elisabeth I. Meyer 《Limnologica》2013,43(6):451-459

To assess the trophic relationships of consumers in a sandy lowland brook (Ladberger Mühlenbach, Northrhine-Westphalia, Germany) the fish as well as the benthic communities were sampled monthly over half a year. Analysis of stomach contents of the fishes revealed two different feeding types: detritivores (including only Cyprinidae; foremost roach, Rutilus rutilus and Prussian carp, Carassius auratus gibelio) and benthivores (mostly stone loach, Barbatula barbatula and three-spined stickleback, Gasterosteus aculeatus). The detritivores mainly foraged on detritus, but also benthic invertebrates were found in their stomachs. This latter prey (especially some Trichoptera and Coleoptera, which were selected with a high preference) is strongly associated to hard substrates, only present in the brook as coarse detritus. Benthivore fishes only foraged on benthic invertebrates, mostly Gammaridae and Chironomidae, which were the most dominant elements of the macrozoobenthos. Niche overlap between these two foraging groups was very low, while the within-group overlap was rather high. As food could not be shown to be a limiting factor, a direct competition for food between most of these species in this brook seems most unlikely.  相似文献   

Chemical and K–Ar systematics of a mylonitic mica after natural and experimental interactions with varied fluids     

Norbert Clauer  Yves Mongodin 《Chemical Geology》2012

Flow-through and batch-leaching experiments combining mineralogical, chemical and K–Ar isotopic analyses of mica separates from a mylonitic sample of the Tyndrum faulting system in Scotland (U.K.) were conducted to evaluate and simulate the natural interaction with H₂SO₄-loaded river water at pHs of 3–4. The flow-through experiments with H₂SO₄-loaded and pure deionized water completed by a batch-leaching experiment with 1 M HCl at room temperature had varied effects on soluble mineral phases, such as Fe-sulfates and Ca/Mg-carbonates, that were present in the varied mica size fractions, but none caused the mineralogical and K–Ar characteristics of the mica to differ from separates of the natural environment.Despite the limited number of K–Ar ages, size fractionation of the mylonitic mica identified two generations of mica with different REE patterns. The coarser (2–8 μm) fraction yielded a high La/Yb ratio of 4.3 and crystallized at 359 ± 6 Ma at a temperature of 250–300 °C, probably during a major tectonic-thermal activity. The smaller (< 0.5 μm) fraction yielded a La/Yb ratio of 2.1, a younger K–Ar age at 315 ± 5 Ma and a lower crystallization temperature of about 200 °C.  相似文献   

Diffusion-driven transport in clayrock formations     

Scott Altmann  Christophe Tournassat  Florence Goutelard  Jean-Claude Parneix  Thomas Gimmi  Norbert Maes 《Applied Geochemistry》2012

Clay mineral-rich sedimentary formations are currently under investigation to evaluate their potential use as host formations for installation of deep underground disposal facilities for radioactive waste (e.g. Boom Clay (BE), Opalinus Clay (CH), Callovo–Oxfordian argillite (FR)). The ultimate safety of the corresponding repository concepts depends largely on the capacity of the host formation to limit the flux towards the biosphere of radionuclides (RN) contained in the waste to acceptably low levels. Data for diffusion-driven transfer in these formations shows extreme differences in the measured or modelled behaviour for various radionuclides, e.g. between halogen RN (³⁶Cl, ¹²⁹I) and actinides (^238,235U, ²³⁷Np, ²³²Th, etc.), which result from major differences between RN of the effects on transport of two phenomena: diffusion and sorption. This paper describes recent research aimed at improving understanding of these two phenomena, focusing on the results of studies carried out during the EC Funmig IP on clayrocks from the above three formations and from the Boda formation (HU).  相似文献   

Late Devonian to Early Carboniferous palaeomagnetic poles from the Armorican Massif, France     

Meridee Jones  Rob Van der  Voo Norbert Bonhommet 《Geophysical Journal International》1979,58(2):287-308

  相似文献   

Ökologische Bewertung von Tieflandbächen des Ladberger Mühlenbach-Systems im Norddeutschen Tiefland, basierend auf der Standorttypie der Trichopterenbiozönosen     

Christian Alecke  Bernd Spnhoff  Norbert Kaschek 《Limnologica》2001,31(4):329-338

In the last few years ecological evaluation of lowland freshwaters was controversely discussed. Due to the fact that most basic information of assessment systems derived from upland streams, the results could not be applied to the lowland situations. Additionally, it is not sufficient for an integral freshwater evaluation only to focus on the stream to show degradation in the tight coupling of running waters and their adjacent landscape. In this study we critically tested a new method, the Standorttypie-Index (STI), to assess lowland streams using caddis-fly communities.

During 1994 and 1996 we investigated the caddisfly community at 15 sampling sites of a river system in the “Westfälische Tieflandbucht” (Northrhine-Westphalia, Germany). As a result we found 72 species belonging to 16 families of the order Trichoptera. The calculation of the “Standorttypie-Index” is based on four defined ecological categories. Although the definitions were inaccurate, each species was classified into one category. In view of stream regulation and streamwidth, we calculated for all study sites the STI of the immature stages, the adults and a combined total STI.

Although there is a correlation between the “Standorttypie-Index” and the state of degradation of the study sites, the separate analysis of larval and adult communities showed that the results easily lead to misinterpretation. The STI of adults devalues the combined total STI of regulated as well as natural study sites. As a consequence, until now it is not possible to evaluate the state of degradation in the coupling of the stream and the adjacent landscape using the STI of the caddis-fly community.  相似文献   

Kinematics of the Galactic halo from horizontal branch stars in the Hamburg/ESO survey     

Christopher Thom  Chris Flynn  Michael S. Bessell  Jyrki Hänninen  Timothy C. Beers  Norbert Christlieb  Dionne James  Johan Holmberg  Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,360(1):354-359

Large samples of field horizontal branch (FHB) stars make excellent tracers of the Galactic halo; by studying their kinematics, one can infer important physical properties of our Galaxy. Here we present the results of a medium-resolution spectroscopic survey of 530 FHB stars selected from the Hamburg/ESO survey. The stars have a mean distance of ∼7 kpc and thus probe the inner parts of the Milky Way halo. We measure radial velocities from the spectra in order to test the model of Sommer-Larsen et al., who suggested that the velocity ellipsoid of the halo changes from radially dominated orbits to tangentially dominated orbits as one proceeds from the inner to the outer halo. We find that the present data are unable to discriminate between this model and a more simple isothermal ellipsoid; we suggest that additional observations towards the Galactic Centre might help to differentiate them.  相似文献   

Studying the migration behaviour of selenate in Boom Clay by electromigration     

Thomas Beauwens  Pierre De Cannire  Hugo Moors  Lian Wang  Norbert Maes 《Engineering Geology》2005,77(3-4):285-293

For the disposal of high-level waste (HLW) in a deep geological formation as Boom Clay, safety assessment studies have shown that long lived ⁷⁹Se is one of the more critical fission products. Therefore, the knowledge of its migration properties (diffusion, retention) through the geological barrier (Boom Clay) is of paramount importance. The migration behaviour of selenium strongly depends on its speciation. Under reducing conditions, selenide would be the dominant species and selenium migration would mainly be controlled by the low solubility of Se(−II)-bearing minerals. However Se species are often found in redox disequilibrium and more oxidized species might also coexist. Therefore, the study of selenate migration requires attention, as it might be the most mobile selenium species in the host rock. Electromigration experiments performed with a ⁷⁵Se-labeled selenate in Boom Clay indicate a high mobility for this species. The apparent diffusion coefficient (D_app) of selenate in Boom Clay is estimated from electromigration experiments performed under different electric fields. Using two independent approaches, the value of D_app for selenate is shown to fall in the range from 1.7×10⁻¹¹ to 6.2×10⁻¹¹ m² s⁻¹. Moreover, no reduction of selenate in Boom Clay was observed.  相似文献   

A method for estimating vegetation change over time and space     

LI Maihe  Norbert Kr?uchi 《地理学报》2003,13(4):447-454

Plant diversity is used as an indicator of the well-being of vegetation and ecological systems. Human activities and global change drive vegetation change in composition and competition of species through plant invasions and replacement of existing species on a given scale. However, species diversity indices do not consider the effects of invasions on the diversity value and on the functions of ecosystems. On the other hand, the existing methods for diversity index can not be used directly for cross-scale evaluation of vegetation data. Therefore, we proposed a 3-dimensional model derived from the logistic equation for estimating vegetation change, using native and non-native plant diversity. The two variables, based on the current and the theoretical maximum diversity of native plants on a given scale, and the result of the model are relative values without units, and are therefore scale-independent. Hence, this method developed can be used directly for cross-scale evaluations of vegetation data, and indirectly for estimating ecosystem or environmental change.  相似文献   

High-resolution magnetostratigraphy of four sediment cores from the Greenland Sea–I. Identification of the Mono Lake excursion, Laschamp and Biwa I/Jamaica geomagnetic polarity events     

Norbert R. Nowaczyk  Martin Antonow 《Geophysical Journal International》1997,131(2):310-324

High-resolution magnetostratigraphic analysis of three sediment cores from the base of the volcanic seamount Vesteris Banken in the Greenland Basin and one core from the Jan Mayen Fracture Zone revealed records of three pronounced geomagnetic events within the last 200 ka. Dating by stable carbon and oxygen isotope analysis, AMS¹⁴C measurements and biostratigraphic data (foraminifera abundances) yielded ages of 28–27 ka for the Mono Lake excursion, 37–33 ka for the Laschamp event, and 189–179 ka for the Biwa I event. In at least one of the cores the Laschamp event exhibits a full reversal of the local geomagnetic field vector. The same is true of the Biwa I event, documented in one of the cores.  相似文献   

Time dependent deformations during tunnelling and stability of tunnel faces in fine-grained soils under groundwater   总被引：2，自引：2，他引：0  

Roger Höfle  Jochen Fillibeck  Norbert Vogt 《Acta Geotechnica》2008,3(4):309-316

The measures required for driving a tunnel below the groundwater table depend on the permeability of the soil. In coarse-grained, highly permeable soils additional measures, for example compressed-air support combined with a reduction of the permeability of the soil, e.g. induced by grouting, are necessary. Compared to this, it is possible to do without such measures in fine-grained, cohesive soils because of the increased short-term stability of the tunnel face under undrained conditions. In this publication the results of 3-dimensional finite-element calculations are presented to show the influence of the permeability of the soil and also the rate of the tunnel driving on the deformations around the tunnel as well as on the ground surface. The calculated deformations can furthermore be considered as an indicator for the time dependent stability of the tunnel face due to a higher redistribution of stresses and by that an enlargement of the plasticized zone. Usually the stability of the tunnel face is reduced by the presence of water because of the flow of water towards the tunnel. In low permeable soils undrained conditions prevail immediately after an excavation step. In this case relatively high stability-ratios may occur. The stability of the tunnel face will be reduced with increasing time until reaching the lower boundary of possible values, possibly leading to failure. If calculations are done under the assumption of drained conditions, the real stability of the tunnel face during construction may substantially exceed that of the calculated one. On the other hand, if calculations are done for undrained conditions, the effective stability may lie on the unsafe side [10]. There is therefore a big demand to optimize the method of investigating deformations around the tunnel, so as to ensure a safe tunnel excavation on the one hand and to guarantee a cost-effective process on the other. In this paper the tunnelling process is modelled by a step-by-step excavation under atmospheric conditions. The soil is described by a material model which distinguishes between primary and unload-reload stress paths and also accounts for stress-dependent stiffness parameters. The failure criterion is described by the Mohr-Coulomb criterion that considers cohesion, friction angle and angle of dilatancy.  相似文献