Seasonal trends in Romanian streamflow          下载免费PDF全文

Marius‐Victor Birsan  Liliana Zaharia  Viorel Chendes  Emilia Branescu 《水文研究》2014,28(15):4496-4505

Mean daily streamflow records from 44 river basins in Romania with an undisturbed runoff regime have been analyzed for trends with the nonparametric Mann‐Kendall test for two periods of study: 1961–2009 (25 stations) and 1975–2009 (44 stations). The statistical significance of trends was tested for each station on an annual and seasonal basis, for different streamflow quantiles. In order to account for the presence of serial correlation that might lead to an erroneous rejection of the null hypothesis, a trend‐free prewhitening was applied to the original data series. The regional field significance of trends is tested by a bootstrap procedure. Changes in the streamflow regime in Romania are demonstrated. The main identified trends are an increase in winter and autumn streamflow since 1961 and a decrease in summer flow since 1975. The streamflow trends are well explained by recent changes in temperature and precipitation that occurred in the last 50 years. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Response of the coccolithophores Emiliania huxleyi and Coccolithus braarudii to changing seawater Mg and Ca concentrations: Mg/Ca, Sr/Ca ratios and δCa, δMg of coccolith calcite     

Marius N. Müller  Ba?ak K?sakürek  Ruth Gutperlet  Ulf Riebesell  Anton Eisenhauer 《Geochimica et cosmochimica acta》2011,75(8):2088-5818

Calcium and magnesium concentrations in seawater have varied over geological time scales. On short time scales, variations in the major ion composition of seawater influences coccolithophorid physiology and the chemistry of biogenically produced coccoliths. Validation of those changes via controlled laboratory experiments is a crucial step in applying coccolithophorid based paleoproxies for the reconstruction of past environmental conditions. Therefore, we examined the response of two species of coccolithophores, Emiliania huxleyi and Coccolithus braarudii, to changes in the seawater Mg/Ca ratio (≈0.5 to 10 mol/mol) by either manipulating the magnesium or calcium concentration under controlled laboratory conditions. Concurrently, seawater Sr/Ca ratios were also modified (≈2 to 40 mmol/mol), while keeping salinity constant at 35. The physiological response was monitored by measurements of the cell growth rate as well as the production rates of particulate inorganic and organic carbon, and chlorophyll a. Additionally, coccolithophorid calcite was analyzed for its elemental composition (Sr/Ca and Mg/Ca) as well as isotope fractionation of calcium and magnesium (Δ^44/40Ca and Δ^26/24Mg). Our results reveal that physiological rates were substantially influenced by changes in seawater calcium rather than magnesium concentration within the range estimated to have occurred over the past 250 million years when coccolithophores appear in the fossil record. All physiological rates of E. huxleyi decreased at a calcium concentration above 25 mmol L⁻¹, whereas C. braarudii displayed a higher tolerance to increased seawater calcium concentrations. Partition coefficient of Sr was calculated as 0.36 ± 0.04 (±2σ) independent of species. Partition coefficient of Mg²⁺ increased with increasing seawater Ca²⁺ concentrations in both coccolithophore species. Calcium isotope fractionation was constant at 1.1 ± 0.1‰ (±2σ) and not altered by changes in seawater Mg/Ca ratio. There is a well-defined inverse linear relationship between calcium isotope fractionation and partition coefficient of Sr²⁺ in all experiments, suggesting similar controls on both proxies in the investigated species. Magnesium isotope ratios were relatively stable for seawater Mg/Ca ratios ranging from 1 to 5, with a higher degree of fractionation in Emiliania huxleyi (by ≈0.2‰ in Δ^26/24Mg). Although Mg/Ca ratios in the calcite of coccolithophores and foraminifera are similar, the former have considerably higher Δ^26/24Mg (by >+3‰), presumably due to differences in calcification mechanisms between the two taxa. These observations suggest, a physiological control over magnesium elemental and isotopic fractionation during the process of calcification in coccolithophores.  相似文献   

Evolution of hillslope soils: The geomorphic theater and the geochemical play     

Kyungsoo Yoo  Beth Weinman  Simon Marius Mudd  Martin Hurst  Mikael Attal  Kate Maher 《Applied Geochemistry》2011

How and how fast do hillslope soils form as the landscape’s morphology changes over time? Here results are shown from an ongoing study that simultaneously examines the morphologic and geochemical evolution of soil mantled hillslopes that have been exposed to distinctively different denudation history. In Northern Sierra Nevada, California, the authors are investigating a tributary basin to the Middle Fork Feather River. A major incision signal from the river is well marked in a knickpoint within the tributary basin which stretches from its mouth to the Feather River at an elevation of ～700 m to the plateau at an elevation of ～1500 m. Hillslopes are significantly steeper below the knickpoint. The area’s total denudation rates are currently being constrained using cosmogenic radio nuclides, but a previous study suggested an order of magnitude difference in total denudation rates below and above the knickpoint. When compared with topographic attributes calculated from LIDAR data, physical erosion rates can be modeled as a linear function of ridge top curvature. Surprisingly, over the wide range of total denudation rates, soil thicknesses do not vary significantly until a threshold point where soil mantled landscapes abruptly shift to bedrock dominated landscapes. Bioturbation by tree falls appear to buffer soil thickness over the wide range of physical soil erosion rates. From three hillslopes with different physical erosion rates, the concentrations of Zr, which were considered conserved during dissolution and leaching, were determined and used as a proxy for the degree of mass losses via chemical denudation. There is a general trend that colluvial soils along the hillslopes with lower physical erosion rates are enriched in fine size fractions, Zr, and pedogenic crystalline Fe oxides. Likewise, the saprolites show greater degrees of chemical denudation at the sites above the knickpoint, presumably because of the saprolites’ longer turnover time in the slowly eroding landscapes. In the two steep hillslopes below the knickpoint, no significant or systematic topgraphic trends were found for soil geochemistry. However, soils show increasing Zr enrichment in the downslope direction in the hillslope above the knickpoint, which suggests a critical denudation rate beyond which soils’ turnover time is too short to develop a geochemical catena. As detailed CRN-based soil production rates and catchment scale denudation rates are acquired, the data will be combined with a mass balance model to calculate the rates of chemical denudation and weathering in soils and saprolites along the denudation gradient.  相似文献   

Consequences of Water Level Drops for Soft Sediment Deformation and Vertical Fluid Leakage     

Christian Hermanrud  Jon Marius Venstad  Joe Cartwright  Lars Rennan  Kristine Hermanrud  Hege M. Nordgård Bolås 《Mathematical Geosciences》2013,45(1):1-30

Both water level drops and erosion have previously been suggested as causes of fluid overpressures in the subsurface. Quantification of the relevance of these processes to supra-lithostatic fluid pressure formation with a wide selection of input parameters is lacking, and thus desired. The magnitudes and drop times that are required for water level drops to result in supra-lithostatic pore pressures in a variety of situations are calculated. Situations with pore fluids consisting of water, water with dissolved methane, water with a gas hydrate layer and dissolved methane in the underlying sediments, and water with dissolved methane, a gas hydrate layer, and free gas accumulation below the hydrate layer are separately addressed. The overpressure formation from reservoir gas expansion is also simulated. The simulation results demonstrate that high fluid overpressures can develop in a rock as a response to a water level drop without the presence of gas, provided that the rock has a sufficiently low compressibility. The contribution to fluid overpressuring is however dramatically increased if the pore water is saturated with methane prior to the water level drop, and is further amplified by the presence of gas hydrates and free gas accumulations beneath such hydrates. Gas expansion in reservoirs should be expected to significantly increase the fluid overpressures in shallow, sealed pressure compartments that experience erosion or water level drops, even if the water level drop duration exceeds one million years. Enough relationships between the calculated overpressure formation and the main controlling factors are provided in order to enable readers to make inferences about a variety of geological settings. Analyses of simulation results prompt us to suggest that pockmarks are likely to be triggered by gas expansion in vertical fluid migration pathways, that the giant craters at the seabed west of Albatross South in the Barents Sea result from hydrate dissociation, and that overpressure build-up due to gas expansion has contributed to reservoir overpressuring in many eroded basins, including the Hammerfest Basin in the Barents Sea.  相似文献   

Towards Geospatial Queries in a Semantic Digital Library for 3D Data     

Ioan Marius Bilasco  Jérôme Gensel  Marlène Villanova-Oliver  Hervé Martin 《Transactions in GIS》2007,11(3):337-353

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Heterogeneity in hedonic modelling of house prices: looking at buyers’ household profiles   总被引：2，自引：0，他引：2  

Yan Kestens  Marius Thériault  François Des Rosiers 《Journal of Geographical Systems》2006,8(1):61-96

This paper introduces household-level data into hedonic models in order to measure the heterogeneity of implicit prices regarding household type, age, educational attainment, income, and the previous tenure status of the buyers. Two methods are used for this purpose: a first series of models uses expansion terms, whereas a second series applies Geographically Weighted Regressions. Both methods yield conclusive results, showing that the marginal value given to certain property specifics and location attributes do vary regarding the characteristics of the buyer’s household. Particularly, major findings concern the significant effect of income on the location rent as well as the premium paid by highly-educated households in order to fulfil social homogeneity.  相似文献   

Electrons in the solar corona     

Dollfus  Audouin  Laffineur  Marius  Mouradian  Zadig 《Solar physics》1974,38(2):367-376

We discuss a model for the formation of the chromospheric Ca ii K line which does not make the usual assumption of complete redistribution. Using a physically reasonable scattering model, we find significant departures due to the frequency dependence of the line source function, particularly in the relative intensity and centre-to-limb behaviour of the K₁ parts of the line and in the asymmetry produced by differential velocity fields. We conclude that the frequency dependence of the K line source function must be considered in quantitative models for the formation of the K line.  相似文献   

Spatio‐Temporal Object‐Oriented Data Model for Disaggregate Travel Behavior     

Ali Frihida  Danielle J. Marceau  Marius Thriault 《Transactions in GIS》2002,6(3):277-294

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A simple gibbsite analyzer for rapid field determination of the available alumina content in bauxites     

Marius J. van Essen  Johannes A. C. Heynen  Adriaan H. van der Veen  Gerrit H. Vonkeman 《Mineralium Deposita》1971,6(1):41-48

A portable gibbsite analyzer suited for field operation and intended for rapid determination of available alumina is described. The available alumina content is calculated from the relative weight loss caused by the dehydration of gibbsite. More than 100 samples of gibbsite-containing bauxites of different origin, were analyzed with this apparatus. The results always appeared to be correct within 10% of the actual content. In the laboratory, an accuracy of ±2.60% gibbsite, and a reproducibility of ±1.87% gibbsite, both at the 95% confidence interval, could be achieved. The apparatus can be used under tropical conditions. Its weight is 13 kg. It can be fed from a motor-driven generator weighing 18 kg. The duration of a single analysis in the field is 30–40 minutes. In the laboratory about 25 analyses can be performed within 8 hours. The apparatus can be handled by an untrained operator. One operator can run at least two analyzers at a time. The complete set-up, including the generator, costs less than US $ 1500.

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Zusammenfassung Ein tragbarer Apparat für die Gibbsit Bestimmung im Freien wird beschrieben. Der Gibbsitgehalt wird berechnet aus dem Gewichtsverlust während der Entwässerung. Für Gibbsit-haltige Bauxite, die mit diesem Apparat analysiert sind, wurden Resultate gefunden, die immer weniger als 10% vom richtigen Gehalt abwichen. Im Labor konnte eine Genauigkeit von ±2.60% Gibbsit und eine Reproduzierbarkeit von ±1.87% Gibbsit, beide mit einer Wahrscheinlichkeit von 95%, erreicht werden. Der Apparat ist ausgerüstet für den Gebrauch in den Tropen. Er wiegt 13 kg und kann von einem durch einen Benzinmotor angetriebenen Generator gespeist werden. Der Generator hat ein Gewicht von 18 kg. Eine einzige Bestimmung im Freien dauert 30–40 Minuten. Im Labor können etwa 25 Bestimmungen innerhalb von 8 Stunden gemacht werden. Ein Mann kann mindestens zwei Apparate zugleich beobachten. Apparat und Generator kosteten weniger als US $ 1500.

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Retrieval of effective cloud field parameters from radiometric data     

Paulescu  Marius  Badescu  Viorel  Brabec  Marek 《Theoretical and Applied Climatology》2018,132(1-2):437-450

Theoretical and Applied Climatology - This study presents evaluation of the ability of Rossby Centre Regional Climate Model (RCA4) driven by nine global circulation models (GCMs), to skilfully...  相似文献