Search results for "Global changes"
showing 10 items of 533 documents
Analysis of the relationship between start of the rainy season and farmer's sowing strategy in the Niamey area and its impacts on the pearl millet yi…
2009
International audience; Relationship between start of the rainy season and farmer's planting date have been analysed at local scale through in situ daily rainfall records and agronomical measurement provided by on-farm survey at plot scale for 10 villages network located on the mesoscale AMMA-CATCH Niger site during the 2004-2007 rainy seasons. Many classical empirical methods of monsoon onset dectection (e.g. Benoit, Kowal, Sivakumar, Ati, Marteau, Balme, Sultan) and numerical methods based on crop model SARRAH have been compared to the observed farmer's sowing date. Results show that SARRAH and Balme mean onset date are close to sowing date. But spatial and temporal variability of the sow…
Pore fabric geometry inferred from magnetic and acoustic anisotropies in rocks with various mineralogy, permeability and porosity.
2014
14 pages; International audience; he ferrofluid impregnation technique combined with anisotropy of magnetic susceptibility measurements (AMSff) is one of the ways to analyze the 3-D geometry of the pore space in a rock and indirectly to infer the anisotropy of permeability. We applied this method on different types of rocks (sandstones and carbonates) with a range of different porosity values (10-30%) and permeability (1 mD to 1 D). To get additional information on both the pore aspect ratio and the directional anisotropy we used another technique, measuring the anisotropy of P-waves velocity (APV) in dry and water saturated conditions. Comparing between both methods shows that despite the …
Testing a portable laser-induced breakdown spectroscopy system on geological samples.
2012
9 pages; International audience; This paper illustrates the potentialities of a home-made portable LIBS (laser-induced breakdown spectroscopy) instrument in Earth sciences, more particularly in geochemically recognizing (i) tephra layers in lacustrine sediments and (ii) fossilization processes in ammonites. Abundances for selected lines of Al, Ca, Fe, Ti, Ba and Na were determined in lacustrine chalk sediments of the Jura, where the Laacher See Tephra (LST) layer is recorded. A statistical treatment of elemental maps produced from the section of a sedimentary column containing the LST event allows instrumental conditions to be optimized. Accumulating spectra from close shot positions gives …
Importance of denitrifiers lacking the genes encoding the nitrous oxide reductase for N2O emissions from soil
2010
Analyses of the complete genomes of sequenced denitrifying bacteria revealed that approximately 1/3 have a truncated denitrification pathway, lacking the nosZ gene encoding the nitrous oxide reductase. We investigated whether the number of denitrifiers lacking the genetic ability to synthesize the nitrous oxide reductase in soils is important for the proportion of N2O emitted by denitrification. Serial dilutions of the denitrifying strain Agrobacterium tumefaciens C58 lacking the nosZ gene were inoculated into three different soils to modify the proportion of denitrifiers having the nitrous oxide reductase genes. The potential denitrification and N2O emissions increased when the size of ino…
The Bossons glacier protects Europe's summit from erosion
2013
13 pages; International audience; The contrasting efficiency of erosion beneath cold glacier ice, beneath temperate glacier ice, and on ice-free mountain slopes is one of the key parameters in the development of relief during glacial periods. Detrital geochronology has been applied to the subglacial streams of the north face of the Mont-Blanc massif in order to estimate the efficiency of erosional processes there. Lithologically this area is composed of granite intruded at ~303 Ma within an older polymetamorphic complex. We use macroscopic features (on ~10,000 clasts) and U-Pb dating of zircon (~500 grains) to establish the provenance of the sediment transported by the glacier and its subgl…
Comment on "Lethally hot temperatures during the Early Triassic greenhouse".
2013
Sun et al . (Reports, 19 October 2012, p. 366) reconstructed Permian to Middle Triassic equatorial seawater temperatures. After correct temporal positioning of their data points, their presumed trends of temperature changes, and hence their assumption of a one-to-one relationship between putative "lethally hot" seawater temperatures and a disputable equatorial "eclipse" of some organisms, are no longer supported by their data.
Quantifying the contribution of nitrification and denitrification to the nitrous oxide flux using 15N tracers.
2006
8 pages; International audience; Microbial transformations of nitrification and denitrification are the main sources of nitrous oxide (N2O) from soils. Relative contributions of both processes to N2O emissions were estimated on an agricultural soil using 15N isotope tracers (15NH4+ or 15NO3-), for a 10-day batch experiment. Under unsaturated and saturated conditions, both processes were significantly involved in N2O production. Under unsaturated conditions, 60% of N-N2O came from nitrification, while denitrification contributed around 85-90% under saturated conditions. Estimated nitrification rates were not significantly different whatever the soil moisture content, whereas the proportion o…
Climate change and cyclic predator-prey population dynamics in the high Arctic.
2009
The high Arctic has the world's simplest terrestrial vertebrate predator–prey community, with the collared lemming being the single main prey of four predators, the snowy owl, the Arctic fox, the long-tailed skua, and the stoat. Using a 20-year-long time series of population densities for the five species and a dynamic model that has been previously parameterized for northeast Greenland, we analyzed the population and community level consequences of the ongoing and predicted climate change. Species' responses to climate change are complex, because in addition to the direct effects of climate change, which vary depending on species' life histories, species are also affected indirectly due to…
Monitoring soil volume wetness in heterogeneous soils by electrical resistivity. A field-based pedotransfer function.: A field-based pedotransfer fun…
2014
11 pages; International audience; Modern irrigation techniques require accurate, rapid, cost-effective, spatial measurement of soil moisture. Electrical Resistivity Tomography (ERT) meets most of these requirements, but needs to be calibrated for each use because it is very sensitive to differences in soil characteristics. In this study, a pedotransfer function approach is used to remove the need for site-specific calibration, allowing ERT to be used directly to measure soil moisture. The study site was a hillslope vineyard, where eight calcaric-cambisol soil profiles were identified. From 2012 to 2013, 23 000 soil volume wetness measurements were acquired by Time Domain Reflectometry, and …
Isolation and characterisation of Nocardioides sp. SP12, an atrazine-degrading bacterial strain possessing the gene trzN from bulk- and maize rhizosp…
2003
International audience; We report the characterisation of Nocardioides sp. SP12, an atrazine-degrading bacteria isolated from atrazine-treated bulk- and maize rhizosphere soil. Based on 16S rDNA alignment, strain SP12 showed close phylogenic relationships with Nocardioides sp. C157 and Nocardioides simplex. Internal transcribed spacer (ITS) sequences of strain SP12 were longer than those of other Nocardioides sp. and present Ala- and Ile-tRNA unlike Actinomycetales. Nocardioides sp. SP12 presents a novel atrazine catabolic pathway combining trzN with atzB and atzC. Atrazine biodegradation ends in a metabolite that co-eluted in HPLC with cyanuric acid. This metabolite shows an absorption spe…