Effects of leaf extracts on glutathione reductase expression, hydrogen peroxide and glutathione contents in the aquatic macrophyte Ceratophyllum demersum     

Sheku Kamara  Stephan Pflugmacher 《Aquatic Sciences - Research Across Boundaries》2008,70(2):204-211

  相似文献   

Melt water driven stream and groundwater stage fluctuations on a glacier forefield (Dammagletscher,Switzerland)          下载免费PDF全文

Jan Magnusson  Florian Kobierska  Stephan Huxol  Masaki Hayashi  Tobias Jonas  James W. Kirchner 《水文研究》2014,28(3):823-836

In many mountain regions, large land areas with heterogeneous soils have become ice‐free with the ongoing glacier retreat. On these recently formed proglacial fields, the melt of the remaining glaciers typically drives pronounced diurnal stream level fluctuations that propagate into the riparian zone. This behaviour was measured on the Damma glacier forefield in central Switzerland with stage recorders in the stream and groundwater monitoring wells along four transects. In spite of the large groundwater stage variations, radon measurements in the near‐stream riparian zone indicate that there is little mixing between stream water and groundwater on daily time scales. At all four transects, including both losing and gaining reaches, the groundwater level fluctuations lagged the stream stage variations and were often damped with distance from the stream. Similar behaviours have been modelled using the diffusion equation in coastal regions influenced by tidal sea level variations. We thus tested the ability of such a model to predict groundwater level fluctuations in proglacial fields. The model reproduced several key features of the observed fluctuations at three of four locations, although discrepancies also arise due to non representative input data and model simplifications. Nevertheless, calibration of the model for the individual transects yielded realistic estimates of hydraulic diffusivities between the stream and groundwater monitoring wells. We conclude that studying diurnal groundwater fluctuations can provide important information about the subsurface hydrology of alpine watersheds dominated by glacier melt. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Relict rock glaciers and protalus lobes in the British Isles: implications for Late Pleistocene mountain geomorphology and palaeoclimate     

Stephan Harrison  Brian Whalley  Edward Anderson 《第四纪科学杂志》2008,23(3):287-304

Many relict rock glaciers and protalus lobes have been described in mountainous areas of the British Isles. This paper reviews their distribution, chronology, supposed origin and development, and places the research within current investigations and knowledge. Rock glaciers and protalus lobes are located in a number of different topographic locations and settings. They developed at the base of steep cliffs following the catastrophic failure of rock faces, at the base of scree slopes following the gradual accumulation of rock debris and in association with glaciers. Protalus lobes probably developed in response to the permafrost creep of talus material while rock glaciers formed through the deformation and sliding of large bodies of buried ice. Rock glaciers probably developed, or were last active, during the Younger Dryas, although the possibility exists that some of these landforms are Dimlington Stadial in age. The development of protalus lobes during the Younger Dryas suggests that precipitation levels were low and permafrost was widespread during this time. The lack of rock glaciers (sensu stricto) in the British Isles compared with other mountain areas is believed to be a consequence of the rock type and relative scarcity of weathered debris for their formation rather than a lack of suitable sites or appropriate environmental conditions. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust   总被引：1，自引：0，他引：1  

Jens Hartmann  Hans H. Dürr  Nils Moosdorf  Michel Meybeck  Stephan Kempe 《International Journal of Earth Sciences》2012,101(1):365-376

The terrestrial surface, the “skin of the earth”, is an important interface for global (geochemical) material fluxes between major reservoirs of the Earth system: continental and oceanic crust, ocean and atmosphere. Because of a lack in knowledge of the geochemical composition of the terrestrial surface, it is not well understood how the geochemical evolution of the Earth’s crust is impacted by its properties. Therefore, here a first estimate of the geochemical composition of the terrestrial surface is provided, which can be used for further analysis. The geochemical average compositions of distinct lithological classes are calculated based on a literature review and applied to a global lithological map. Comparison with the bulk composition of the upper continental crust shows that the geochemical composition of the terrestrial surface (below the soil horizons) is significantly different from the assumed average of the upper continental crust. Specifically, the elements Ca, S, C, Cl and Mg are enriched at the terrestrial surface, while Na is depleted (and probably K). Analysis of these results provide further evidence that chemical weathering, chemical alteration of minerals in marine settings, biogeochemical processes (e.g. sulphate reduction in sediments and biomineralization) and evaporite deposition are important for the geochemical composition of the terrestrial surface on geological time scales. The movement of significant amounts of carbonate to the terrestrial surface is identified as the major process for observed Ca-differences. Because abrupt and significant changes of the carbonate abundance on the terrestrial surface are likely influencing CO₂-consumption rates by chemical weathering on geological time scales and thus the carbon cycle, refined, spatially resolved analysis is suggested. This should include the recognition of the geochemical composition of the shelf areas, now being below sea level.  相似文献   

Earthquakes in Switzerland and surrounding regions during 2011     

Nicholas Deichmann  John Clinton  Stephan Husen  Benjamin Edwards  Florian Haslinger  Donat F?h  Domenico Giardini  Philipp K?stli  Urs Kradolfer  Stefan Wiemer 《Swiss Journal of Geoscience》2012,105(3):463-476

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2011. During this period, 522 earthquakes and 92 quarry blasts were detected and located in the region under consideration. With a total of only 10 events with M _L????2.5, the seismic activity in the year 2011 was far below the average over the previous 36?years. Most noteworthy were the earthquake sequence of Sierre (VS) in January, with two events of M _L 3.3 and 3.2, the M _L 3.3 earthquake at a depth of 31?km below Bregenz, and the M _L 3.1 event near Delémont. The two strongest events near Sierre produced shaking of intensity IV.  相似文献   

Latent Variable Modeling for Integrating Output from Multiple Climate Models     

William F. Christensen  Stephan R. Sain 《Mathematical Geosciences》2012,44(4):395-410

Numerical models of atmosphere–ocean circulation are widely used to understand past climate and to project future climate change. Although the same laws of physics, chemistry, and fluid dynamics govern any general circulation model, each model’s formulations and parameterizations are different, yielding different projections. Notwithstanding, models within an ensemble will have varying degrees of similarity for different outputs of interest. Multi-model ensembles have been used to increase forecast skill by using simple or weighted averages where weights have been obtained by considering factors such as estimated model bias and consensus with other models (Giorgi and Mearns, J. Clim. 15:1141–1158, 2002, Geophys. Res. Lett. 30:1629–1632, 2003; Tebaldi et al., Geophys. Res. Lett. 31:L24213, 2004, J. Clim. 18:1524–1540, 2005). This paper considers an alternative view of multi-model ensembles. For use with the North American Regional Climate Change Assessment Program (NARCCAP), multivariate statistical models are employed to characterize modes of similarity within the members of an ensemble. Specifically, we propose a spatially-correlated latent variable model which facilitates the exploration of when, where, and how regional climate models are similar, and what factors best predict observed locations of model convergence.  相似文献   

Radius and limb topography of Mercury obtained from images acquired during the MESSENGER flybys     

Jürgen Oberst  Stephan Elgner  F. Scott Turner  Mark E. Perry  Robert W. Gaskell  Maria T. Zuber  Mark S. Robinson  Sean C. Solomon 《Planetary and Space Science》2011,59(15):1918-1924

Analysis of images obtained by the MESSENGER spacecraft during its three flybys of Mercury yields a new estimate for the planet's mean radius of 2439.25±0.69 km, in agreement with results from Mariner 10 and Earth-based observations, as well as with MESSENGER altimeter and occultation data. The mean equatorial radius and polar radius are identical to within error, suggesting that rotational oblateness is negligible when compared with other sources of topography. This result is consistent with the small gravitational oblateness of the planet. Minor differences in radius obtained at different locations reflect regional variations in topography. Residual topography along three limb profiles has a dynamic range of 7.4 km and a root-mean-square roughness of 0.8 km over hemispherical scales. Following MESSENGER's entry into orbit about Mercury in March 2011, we expect considerable additional improvements to our knowledge of Mercury's size and shape.  相似文献   

Haar wavelets as a tool for the statistical characterization of variability     

Ryan Price  Stephane Vincent  Stephan LeBohec   《Astroparticle Physics》2011,34(12):871-877

  相似文献   

High‐Precision Fe and Mg Isotope Ratios of Silicate Reference Glasses Determined In Situ by Femtosecond LA‐MC‐ICP‐MS and by Solution Nebulisation MC‐ICP‐MS     

Martin Oeser  Stefan Weyer  Ingo Horn  Stephan Schuth 《Geostandards and Geoanalytical Research》2014,38(3):311-328

In this study, a technique for high precision in situ Fe and Mg isotope determinations by femtosecond‐laser ablation‐multi collector‐ICP‐MS (fs‐LA‐MC‐ICP‐MS) was developed. This technique was employed to determine reference values for a series of common reference glasses that may be used for external standardisation of in situ Fe and Mg isotope determinations in silicates. The analysed glasses are part of the MPI‐DING and United States Geological Survey (USGS) reference glass series, consisting of basaltic (BIR‐1G, BCR‐2G, BHVO‐2G, KL2‐G, ML3B‐G) and komatiitic (GOR128‐G and GOR132‐G) compositions. Their Fe and Mg isotope compositions were determined by in situ fs‐LA‐MC‐ICP‐MS and by conventional solution nebulisation multi‐collector ICP‐MS. We determined δ⁵⁶Fe values for these glasses ranging between ‐0.04‰ and 0.10‰ (relative to IRMM‐014) and δ²⁶Mg values ranging between ‐0.40‰ and ‐0.15‰ (relative to DSM‐3). Our fs‐LA‐MC‐ICP‐MS results for both Fe and Mg isotope compositions agreed with solution nebulisation analyses within analytical uncertainties. Furthermore, the results of three USGS reference glasses (BIR‐1G, BHVO‐2G and BCR‐2G) agreed with previous results for powdered and dissolved aliquots of the same reference materials. Measurement reproducibilities of the in situ determinations of δ⁵⁶Fe and δ²⁶Mg values were usually better than 0.12‰ and 0.13‰ (2s), respectively. We further demonstrate that our technique is a suitable tool to resolve isotopic zoning in chemically‐zoned olivine crystals. It may be used for a variety of different applications on isotopically‐zoned minerals, e.g., in magmatic or metamorphic rocks or meteorites, to unravel their formation or cooling rates.  相似文献   

Chromium oxidation by manganese (hydr)oxides in a California aquifer     

Kuria Ndung’u  Stephan Friedrich  Ana R. Gonzalez  A. Russell Flegal 《Applied Geochemistry》2010

There are increasing concerns with elevated levels of Cr(VI) in the environment because it is a strong oxidant, corrosive, and carcinogenic. The concerns extend to the presence of Cr(VI) in many aquifers in California and elsewhere, where relatively high levels have been attributed to both industrial pollution and natural processes. The authors have, therefore, determined if natural redox processes contribute to the presence of high Cr(VI) concentrations (6–36 μg L⁻¹) in an aquifer in central California relative to non-detectable concentrations (<0.1 μg L⁻¹) in an adjacent aquifer. Specifically, the distribution and the redox speciation of dissolved (<0.45 μm) Cr have been compared with those of particulate Mn and Fe oxy-hydroxides in sediments, using X-ray absorption spectroscopy at the Mn and Fe L-edges. The analyses show a correlation between the presence of dissolved Cr(VI) and Mn (hydr)oxide minerals, which are the only common, naturally occurring minerals known to oxidize Cr(III) in laboratory experiments. This covariance substantiates the results of those experiments and previous field studies that indicate natural oxidation mechanisms might account for the relatively high levels of Cr(VI) in the study site, as well as for elevated concentrations in other aquifers with similar biogeochemical conditions.  相似文献