North American rainfall and temperature prediction response to the diversity of ENSO   总被引：1，自引：0，他引：1  

Johnna M. Infanti  Ben P. Kirtman 《Climate Dynamics》2016,46(9-10):3007-3023

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Very high CO2 exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem     

Torbern Tagesson  Jonas Ardö  Idrissa Guiro  Ford Cropley  Cheikh Mbow  Stephanie Horion 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2016,116(2):93-109

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO₂ exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO₂ exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO₂ exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to ?48 μmol CO₂ m^?2 s^?1 and 20 μmol CO₂ m^?2 s^?1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO₂ uptake was high, the annual budget of ?229 ± 7 ± 49 g C m^?2 y^?1 (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost .20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.  相似文献   

Role of energy consumption and economic growth in the spread of greenhouse emissions: empirical evidence from Spain     

Mounir Ben Mbarek  Boutheina Boukarraa  Kais Saidi 《Environmental Earth Sciences》2016,75(16):1161

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Identifying recharge and salinization sources of groundwater in the Oussja Ghar el Melah plain (northeast Tunisia) using geochemical tools and environmental isotopes     

Safouan Ben Ammar  Jean-Denis Taupin  Kamel Zouari  Mohamed Khouatmia 《Environmental Earth Sciences》2016,75(7):606

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Impact of drilling mud on chemistry and microbiology of an Upper Triassic groundwater after drilling and testing an exploration well for aquifer thermal energy storage in Berlin (Germany)     

Simona Regenspurg  Mashal Alawi  Guido Blöcher  Maria Börger  Stefan Kranz  Ben Norden  Ali Saadat  Traugott Scheytt  Lioba Virchow  Andrea Vieth-Hillebrand 《Environmental Earth Sciences》2018,77(13):516

After completion of an exploration well, sandstones of the Exter Formation were hydraulically tested to determine the hydraulic properties and to evaluate chemical and microbial processes caused by drilling and water production. The aim was to determine the suitability of the formation as a reservoir for aquifer thermal energy storage. The tests revealed a hydraulic conductivity of 1–2 E-5 m/s of the reservoir, resulting in a productivity index of 0.6–1 m³/h/bar. A hydraulic connection of the Exter Formation to the overlaying, artesian “Rupelbasissand” cannot be excluded. Water samples were collected for chemical and microbiological analyses. The water was similarly composed as sea water with a maximum salinity of 24.9 g/L, dominated by NaCl (15.6 g/L Cl and 7.8 g/L Na). Until the end of the tests, the water was affected by drilling mud as indicated by the high pH (8.9) and high bicarbonate concentration (359 mg/L) that both resulted from the impact of sodium carbonate (Na₂CO₃) additives. The high amount of dissolved organic matter (>?58 mg/L) and its molecular-weight distribution pattern indicated that residues of cellulose, an ingredient of the drilling mud, were still present at the end of the tests. Clear evidence of this contamination gave the measured uranine that was added as a tracer into the drilling mud. During fluid production, the microbial community structure and abundance changed and correlated with the content of drilling mud. Eight taxa of sulfate-reducing bacteria, key organisms in processes like bio-corrosion and bio-clogging, were identified. It can be assumed that their activity will be affected during usage of the reservoir.  相似文献   

Cool heads for a hot world – Social sciences under a changing sky     

Arun Agrawal  Maria Carmen Lemos  Ben Orlove  Jesse Ribot 《Global Environmental Change》2012,22(2):329-331

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Multivariate analysis of flood characteristics in a climate change context of the watershed of the Baskatong reservoir,Province of Québec,Canada     

M.‐A. Ben Aissia  F. Chebana  T. B. M. J. Ouarda  L. Roy  G. Desrochers  I. Chartier  É. Robichaud 《水文研究》2012,26(1):130-142

The analysis of the impact of climate change (CC) on flood peaks has been the subject of several studies. However, a flood is characterized not only by its peak, but also by other characteristics such as its volume and duration. Little effort has been directed towards the study of the impact of CC on these characteristics. The aim of the present study is to evaluate and compare flood characteristics in a CC context, in the watershed of the Baskatong reservoir (Province of Québec, Canada). Comparisons are based on observed flow data and simulated flow series obtained from hydrological models using meteorological data from a regional climate model for a reference period (1971–2000) and a future period (2041–2070). To this end, two hydrological models HSAMI and HYDROTEL are considered. Correlations, stationarity, change‐points, and the multivariate behaviour of flood series were studied. The results show that, at various levels, all flood characteristics could be affected by CC. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Study of bond stress–slip relationship and radial dilation in prestressed concrete     

José Mª Benítez  J.C. Gálvez  M.J. Casati 《国际地质力学数值与分析法杂志》2013,37(16):2706-2726

This paper presents two test procedures for evaluating the bond stress–slip and the slip–radial dilation relationships when the prestressing force is transmitted by releasing the steel (wire or strand) in precast prestressed elements. The bond stress–slip relationship is obtained with short length specimens, to guarantee uniform bond stress, for three depths of the wire indentation (shallow, medium and deep). An analytical model for bond stress–slip relationship is proposed and compared with the experimental results. The model is also compared with the experimental results of other researchers. Since numerical models for studying bond‐splitting problems in prestressed concrete require experimental data about dilatancy angle (radial dilation), a test procedure is proposed to evaluate these parameters. The obtained values of the radial dilation are compared with the prior estimated by numerical modelling and good agreement is reached. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Comment On: 'Early Silurian Palaeolatitude of the Springdale Group Redbeds of Central Newfoundland: A Palaeomagnetic Determination With A Remanence Anisotropy Test For Inclination Error' By J. P. Hodych and K. L. Buchan     

John Stamatakos  Rob Van Der  Voo  Ben Van Der  Pluijm  Stephen Potts  Trond Torsvik 《Geophysical Journal International》1994,119(3):1009-1013

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Marble mylonites in the Bancroft shear zone, Ontario, Canada: microstructures and deformation mechanisms     

van der Pluijm Ben A. 《Journal of Structural Geology》1991,13(10)

Mylonitization of medium-grade marbles in the Bancroft shear zone, Ontario, Canada, is characterized by decreasing grain-size of both calcite and graphite, and a variety of textures. Calcite grain-sizes vary from several millimeters in the protolith, to 50–200 μm in mylonite, to <30 μm in ultramylonite. Corresponding calcite grain shapes are equant in the protolith, elongate in protomylonite (first-developed dimensional preferred orientation), equant in coarse mylonite, elongate in fine mylonite (second-developed dimensional preferred orientation) and generally equant in ultramylonite, which suggests that external energy (applied stress) that tends to elongate grains competed with internal energy sources (e.g. distortional strain) that favor equant shapes. Graphite grain-size changes from several millimeters to centimeters in the protolith to submicroscopic in ultramylonite. In the mylonitic stages, graphite is present as dark bands, while in the ultramylonitic stage it is preserved as a fine coating on calcite grains.Based on textural evidence, twinning (exponential creep; regime I), dynamic recrystallization (power law creep; regime II) and possibly grain boundary sliding superplasticity (regime III) are considered the dominant deformation mechanisms with increasing intensity of mylonitization; their activity is largely controlled by calcite grain-size. Calcite grain-size reduction occurred predominantly by the process of rotation recrystallization during the early stages of mylonitization, as indicated by the occurrence of core and mantle or mortar structures, and by the grain-size of subgrains and recrystallized grains. Grain elongation in S-C structures indicates the activity of migration recrystallization; these structures are not the result of flattening of originally equant grains. Differential stress estimates in coarse mylonites and ultramylonites, based on recrystallized grain-size, are 2–5 and 14–38 MPa, respectively. Initial grain-size reduction of graphite occurred by progressive separation along basal planes, analogous to mica fish formation in quartzo-feldspathic mylonites.Calcite-graphite thermometry on mylonitic and ultramylonitic samples shows that the metamorphic conditions during mylonitization were 475 ± 50°C, which, combined with a differential stress value of 26 MPa, gives a strain rate of 1.2 x 10⁻¹⁰s⁻¹ based on constitutive equations; corresponding displacement rates are <38 mmyr⁻¹.  相似文献