Modelling time varying scouring at bed sills     

Matteo Tregnaghi  Andrea Marion  Andrea Bottacin‐Busolin  Simon J. Tait 《地球表面变化过程与地形》2011,36(13):1761-1769

In this paper a modelling approach is presented to predict local scour under time varying flow conditions. The approach is validated using experimental data of unsteady scour at bed sills. The model is based on a number of hypotheses concerning the characteristics of the flow hydrograph, the temporal evolution of the scour and the geometry of the scour hole. A key assumption is that, at any time, the scour depth evolves at the same rate as in an equivalent steady flow. The assumption is supported by existing evidence of geometrical affinity and similarity of scour holes formed under different steady hydraulic conditions. Experimental data are presented that show the scour hole development downstream of bed sills due to flood hydrographs follow a predictable pattern. Numerical simulations are performed with the same input parameters used in the experimental tests but with no post‐simulation calibration. Comparison between the experimental and model results indicates good correspondence, especially in the rising limb of the flow hydrograph. This suggests that the underlying assumptions used in the modelling approach are appropriate. In principle, the approach is general and can be applied to a wide range of environments (e.g. bed sills, step‐pool systems) in which scouring at rapid bed elevation changes caused by time varying flows occurs, provided appropriate scaling information is available, and the scour response to steady flow conditions can be estimated. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Sphalerite oxidation pathways detected by oxygen and sulfur isotope studies     

Claudia Heidel  Marion Tichomirowa  Cornelia Breitkopf 《Applied Geochemistry》2011,26(12):2247-2259

Sphalerite oxidation is a common process under acid-mine drainage (AMD) conditions and results in the release of , Zn and potentially toxic trace metals, which can pollute rivers and oceans. However, there are only a few studies on the mechanisms of aerobic sphalerite oxidation. Oxygen and S isotope investigations of the produced may contribute to the understanding of sphalerite oxidation mechanisms so helping to interpret field data from AMD sites. Therefore, batch oxidation experiments with an Fe-rich sphalerite were performed under aerobic abiotic conditions at different initial pH values (2 and 6) for different lengths of time (2–100 days). The O and S isotope composition of the produced indicated changing oxidation pathways during the experiments. During the first 20 days of the experiments at both initial pH values, molecular O₂ was the exclusive O source of . Furthermore, the lack of S isotope enrichment processes between and sphalerite indicated that O₂ was the electron acceptor from sphalerite S. As the oxidation proceeded, a sufficient amount of released Fe(II) was oxidized to Fe(III) by O₂. Therefore, electrons could be transferred from sphalerite S sites to adsorbed hydrous Fe(III) and O from the hydration sphere of Fe was incorporated into the produced as indicated by decreasing δ¹⁸O_SO4 values which became more similar to the δ¹⁸O_H2O values. The enrichment of ³²S in relative to the sphalerite may also result from sphalerite oxidation by Fe(III).The incorporation of O₂ into during the oxidation of sphalerite was associated with an O isotope enrichment factor ε_SO4–O2 of ca. −22‰. The O isotope enrichment factor ε_SO4–H2O was determined to be ?4.1‰. A comparison with O and S studies of other sulfides suggests that there is no general oxidation mechanism for acid-soluble sulfides.  相似文献   

Burial, crawling and drifting behaviour of the bivalve Macomona liliana in response to common sediment contaminants     

David S. Roper  Marion G. Nipper  Christopher W. Hickey  Michael L. Martin  Mark A. Weatherhead 《Marine pollution bulletin》1995,31(4-12):471-478

To investigate the effect of sediment contamination on the tellinid bivalve Macomona liliana, juvenile shellfish (about 1.3 mm long) were exposed to copper- and zinc-dosed sand, and sediments collected from several contaminated sites. The behavioural responses measured included burial rate, crawling and drifting. In copper-dosed sediment, a significant reduction in the number of shellfish burying after 10 min occurred at 25 mg Cu kg⁻¹ (dry wt). After a 96-h exposure, shellfish crawled away from sediment with 10 mg Cu kg⁻¹ (dry wt), and when a weak current was provided they left this 10 mg Cu kg⁻¹ (dry wt) sediment by drifting. Zinc-dosed sediment slowed burial at 80 mg Zn kg⁻¹ (dry wt), and stimulated crawling and drifting at 40 mg Zn kg⁻¹ (dry wt). Some of the field-collected contaminated sediments slowed burial and stimulated drifting, but none affected crawling. It appears that juvenile drifting induced by sediment contamination could play a role in determining M. liliana distributions.  相似文献   

Arctic warming,moisture increase and circulation changes observed in the Ny-Ålesund homogenized radiosonde record     

Marion?MaturilliEmail authorView author&#;s OrcID profile  Markus?Kayser 《Theoretical and Applied Climatology》2017,127(1-2):1-16

The interannual variability of precipitation and temperature is derived from all runs of the Intergovernmental Panel on Climate Change (IPCC) fourth Assessment Report (AR4)-based two Atmospheric Oceanic General Circulation Model (AOGCM) simulations, over Pakistan, on an annual basis. The models are the CM2.0 and CM2.1 versions of Geophysical Fluid Dynamics Laboratory (GFDL)-based AOGCM. Simulations for a recent 22-year period (1979–2000) are validated using Climate Research Unit (CRU) and NCEP/NCAR datasets over Pakistan, for the first time. The study area of Pakistan is divided into three regions: all Pakistan, northern Pakistan, and southern Pakistan. Bias, root mean square error, one sigma standard deviation, and coefficient of variance are used as validation metrics. For all Pakistan and northern Pakistan, all three runs of GFDL-CM2.0 perform better under the above metrics, both for precipitation and temperature (except for one sigma standard deviation and coefficient of variance), whereas for southern Pakistan, third run of GFDL-CM2.1 perform better expect for the root mean square error for temperature. A mean and variance-based bias correction is applied to bias in modeled precipitation and temperature variables. This resulted in a reduced bias, except for the months of June, July, and August, when the reduction in bias is relatively lower.  相似文献   

Biogéographie des ammonites jurassiques et reconstitution palinspastique de la Téthys     

Jean-Louis Dommergues  Didier Marchand  Jacques Thierry 《Geodinamica Acta》2013,26(4-5):273-281

Résumé

— La distribution géographique des ammonites jurassiques est régie par deux causes fondamentales : l’écologie et l’histoire évolutive (événements vicariants). L’analyse conjointe de ces deux facteurs permet de reconnaître : d’une part des taxons dont la distribution est essentiellement contrôlée par des contraintes écologiques (Phylloce-ratinae et Lytoceratinae, liés à des environnements océaniques profonds; Clydoniceratidae et Proplanulitinae liés à des plates-formes assez superficielles); d’autre part des taxons dont l’histoire évolutive est associée à des événements vicariants (Ammonitina liasiques euro-boréales et Cardioceratidae-Kosmoceratidae boréaux du Jurassique moyen).

Les exemples développés ici permettent d’analyser en terme de paléobiogéographie la position de l’Europe centro-méridionale (Bulgarie, Hongrie, Roumanie) incluse au Jurassique dans la bordure nord-téthy-sienne. Il est montré que Phylloceratinae et Lytoceratinae sont très abondants dans les régions supposées profondes à cette époque (sphéno-chasme des monts d’Apuseni, sillon Dobrogeo-Caucasien), alors qu’elles sont très rares sur la plate-forme moësienne. La même remarque est valable pour les plates-formes moyennes-orientales de la marge sud (Israël, Arabie Saoudite).

Lorsque l’on tente d’établir des reconstructions palinspastiques basées sur la paléobiogéographie, on constate que les taxons qui ont une histoire évolutive originale fournissent de meilleures informations paléogéographiques que les formes ubiquistes ou celles à préférences écologiques accusées. Les données brutes de répartition des faunes d’ammonites ne sont donc pas des arguments absolus pour corroborer les reconstructions. Les analyses fauniques, conduites avec une approche qualitative et quantitative, doivent tenir compte de données extra-biologiques telles que la distribution des faciès et des unités structurales; enfin, le niveau d’intervention — local, régional, global — conditionne fortement les possibilités d’interprétation des résultats.  相似文献   

Catchments as reactors: a comprehensive approach for water fluxes and solute turnover   总被引：1，自引：1，他引：0  

Peter Grathwohl  Hermann Rügner  Thomas Wöhling  Karsten Osenbrück  Marc Schwientek  Sebastian Gayler  Ute Wollschläger  Benny Selle  Marion Pause  Jens-Olaf Delfs  Matthias Grzeschik  Ulrich Weller  Martin Ivanov  Olaf A. Cirpka  Ulrich Maier  Bertram Kuch  Wolfgang Nowak  Volker Wulfmeyer  Kirsten Warrach-Sagi  Thilo Streck  Sabine Attinger  Lars Bilke  Peter Dietrich  Jan H. Fleckenstein  Thomas Kalbacher  Olaf Kolditz  Karsten Rink  Luis Samaniego  Hans-Jörg Vogel  Ulrike Werban  Georg Teutsch 《Environmental Earth Sciences》2013,69(2):317-333

Sustainable water quality management requires a profound understanding of water fluxes (precipitation, run-off, recharge, etc.) and solute turnover such as retention, reaction, transformation, etc. at the catchment or landscape scale. The Water and Earth System Science competence cluster (WESS, http://www.wess.info/) aims at a holistic analysis of the water cycle coupled to reactive solute transport, including soil–plant–atmosphere and groundwater–surface water interactions. To facilitate exploring the impact of land-use and climate changes on water cycling and water quality, special emphasis is placed on feedbacks between the atmosphere, the land surface, and the subsurface. A major challenge lies in bridging the scales in monitoring and modeling of surface/subsurface versus atmospheric processes. The field work follows the approach of contrasting catchments, i.e. neighboring watersheds with different land use or similar watersheds with different climate. This paper introduces the featured catchments and explains methodologies of WESS by selected examples.  相似文献   

Groundwater occurrence in cold environments: examples from Nunavik,Canada     

Jean-Michel Lemieux  Richard Fortier  Marie-Catherine Talbot-Poulin  John Molson  René Therrien  Michel Ouellet  David Banville  Marion Cochand  Renaud Murray 《Hydrogeology Journal》2016,24(6):1497-1513

Water availability and management issues related to the supply of drinking water in northern communities are problematic in Canada. While rivers and lakes are abundant, they are vulnerable to contamination and may become dry in winter due to freezing. Groundwater can often provide a more secure and sustainable water source, however its availability is limited in northern Canada due to the presence of permafrost. Moreover, the exploitation of northern aquifers poses a dual challenge of identifying not only permafrost-free areas, but also permeable areas which will allow groundwater recharge and exploitation. Suitable aquifers are not as common in northern Canada since the shallow subsurface is mostly composed of low-permeability crystalline rocks or unconsolidated sediments of glacial origin that are highly heterogeneous. In order to investigate groundwater occurrence and associated geological contexts in Nunavik (northern Quebec, Canada), along with exploring how these resources will evolve in response to climate change, field and compilation work were conducted in the surroundings of the four villages of Salluit, Kuujjuaq, Umiujaq and Whapmagoostui-Kuujjuarapik. These villages are located in different permafrost zones, ranging from continuous to discontinuous, as well as in different geological environments. It was found that despite the ubiquitous presence of permafrost, unfrozen aquifers could be identified, which suggests that groundwater may be available as a source of drinking water for small communities. Expected climate change, with predicted permafrost thawing and increases in temperature and precipitation, should enhance groundwater availability and may contribute to a more secure source of drinking water for northern communities.  相似文献   

Inland aeolian deposits of south‐west France: facies,stratigraphy and chronology     

Pascal Bertran  Mark D. Bateman  Marion Hernandez  Norbert Mercier  Dominique Millet  Luca Sitzia  Jean‐Pierre Tastet 《第四纪科学杂志》2011,26(4):374-388

Archaeological investigations undertaken along a proposed highway together with the compilation of available geological and pedological data made it possible to give a first overview of the distribution of Pleistocene aeolian deposits in south‐west France. A chronological framework for deposition has been obtained using both radiocarbon (n = 24) and luminescence (n = 26) dating. It shows that aeolian transport was very active during the Late Pleniglacial, between 15 and ～23 ka, leading to sand emplacement over a 13 000‐m² area at the centre of the basin. The Pleniglacial coversands are typified by extensive fields of small transverse to barchanoid ridges giving way to sandsheets to the east. Subsequent aeolian phases, at ca. 12 ka (Younger Dryas) and 0.8–0.2 ka (Little Ice Age), correspond to the formation of more localized and higher, mainly parabolic dunes. At the southern and eastern margins of the coversand area, aeolian dust accumulated to form loess deposits, the thickness of which reaches ～3 m on the plateaus. Luminescence dates together with interglacial‐ranking palaeoluvisols between the loess units clearly indicate that these accumulations built up during the last two glacial–interglacial cycles. The chronology of sand and loess deposition thus appears to be consistent with that already documented for northern Europe. This suggests that it was driven by global climate changes in the northern hemisphere. The relatively thin aeolian deposits (and particularly loess) in south‐west France is thought to reflect both a supply‐limited system and a moister climate than in more northern and continental regions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Absolute calibration of a photoelectric condensation nucleus counter at low values of nucleus concentration     

Marion B. Emmanuel  Patrick Squires 《Pure and Applied Geophysics》1969,72(1):268-283

Summary A new absolute condensation nucleus counter was constructed to investigate the accuracy of the calibration widely used with the Pollak-Nolan photoelectric condensation nucleus counter. An attempt was made to standardize the conditions affecting calibration and, using the new counter, to recalibrate the photoelectric counter at values of extinction less than 16%.Over this extinction range, the present work indicates nucleus concentrations which are higher by about 30% than those given by the calibration ofPollak andMetnieks [8]³). In view of the great natural variability of Aitken nucleus concentrations, this discrepancy, if real, is of little meteorological importance.  相似文献   

A Gibbs–Pitzer function for high-salinity seawater thermodynamics     

Rainer Feistel  Giles M. Marion   《Progress in Oceanography》2007,74(4):515-539

A high-salinity Gibbs function for seawater is derived from Pitzer equations of the sea salt components, in conjunction with the 2003 Gibbs function of seawater for low salinities. Various properties, computed from both formulations by thermodynamic rules, are compared with each other, and with high-salinity measurements. The new Gibbs–Pitzer function presented in this paper is valid in the range 0–110 g kg⁻¹ in absolute salinity, −7 to +25 °C in temperature, and 0–100 MPa in applied pressure. The formulation is expressed in the International Temperature Scale 1990 (ITS-90), and is consistent with the International Standard for Fluid Water (IAPWS-95), and with the 2005/2006 equations of state of ice Ih.  相似文献