Influence d'un changement climatique dû à une hausse de gaz à effet de serre sur l'agriculture au quebec

Abstract

This study, using a climate change scenario generated by the Canadian Climate Centre (CCC) general circulation model (GCM) examines the impacts of such a climate change on agriculture in southern Quebec. Using a crop model from the Food and Agriculture Organization (FAO), yield responses of a variety of cereals, legumes, oleaginous and special crops to climate change are analysed and discussed.

Results show that under the 2 × CO₂ climate scenario the growing season would be longer and accumulation of corn heat units and growing degree days would be more important than under actual climate (1961–1990). One of the more important results of this study is that, on the one hand yield of C₃ cereals would be lower and that of C₄ cereals higher in most agricultural regions. On the other hand, the direct fertilisation effect of increased CO₂ is not considered. It must be cautioned however that we can not generalise results obtained for one legume crop to all legumes.     

Lacustrine sedimentation in a semiarid alpine setting: An example from Ladakh, northwestern Himalaya

The Lamayuru lacustrine strata in Ladakh typify many of the carbonate-rich Pleistocene alpine lakes found in the semiarid environment of the northern Himalaya. Created by a 200-m-thick landslide, the lake was in existence by at least 35,000 yr ago, and may have persisted until 500–1000 yr ago. Represented in the center by thin turbidites and laminated muds, the lacustrine sedimentation along the lake margins and low-relief deltas characteristically displays a marked contrast between (1) clastic lenses representing rapid, sporadic, matrix-poor debris flows and periglacial inputs from the alpine slopes and (2) abundant, diverse, shallow-water, biologically dominated carbonate strata, among which organism-rich, chalky beds and oncolithic and encrusted stem-rich strata predominate. Resemblances of the Lamayuru lacustrine strata and their setting to those of former lakes throughout areas north of the Greater Himalayan crest suggest that the alpine, semi-arid environment would favor diversified, spacially restricted carbonate sedimentation punctuated by occasional clastic influxes. Such a depositional regime contrasts strongly with that found immediately south of the Himalayan crest where more humid conditions promote a more continuous clastic influx into intramontane lakes.     

Energy budget for the Sahel surface layer during the ECLATS experiment

The measurements obtained during the ECLATS experiment were used in order to determine the surface energy budget of the Sahel region (Niamey, Niger). This expedition was carried out from November 15 to December 10, 1980, during the dry period. Some data were collected by an instrumented aircraft, from which the turbulent fluxes were obtained in the boundary layer around midday; data were also collected at a surface station in order to estimate the surface energy budget continuously by the profile method. The aircraft measurements show the homogeneity of the vertical fluxes over large areas, allowing generalization to the bushy steppe of the Sahel region. The mean diurnal cycle of the energy budget is characterized by high values of ground heat flux and weak values of latent heat flux (deduced from the balance of the energy budget). This cycle is compared with that of the Koorin expedition, performed in similar conditions (tropical savanna in the dry period). We compare the three midday budgets: during Koorin; during ECLATS, at the ground station, and with the aircraft. The important differences that appear in the net radiative flux are explained by the difference in surface albedo.Ecole des Sciences, Université de Niamey, B.P. 10662 Niamey, Niger.     

Evidence of an early alteration process driven by magmatic fluid in Mururoa volcano

Evidence for a deuteric alteration process induced by a magmatic fluid has been found in the feeder zone of the Mururoa volcano (French Polynesia). Within the dikes, where basaltic glass does not show any evidence of pervasive alteration, vesicles are filled with dioctahedral smectites and calcite, while olivine phenocrysts are replaced by dioctahedral smectites, ankerite and calcite.The ¹³C signature of carbonates, the carbon and H₂O content of the whole rocks and their impoverishment in deuterium are compatible with the presence of magmatic CO₂ during the crystallization of intruding lavas and exclude contamination by seawater. Mass balance calculations on selected thin sections photographs of partly filled up vesicles and replaced olivine crystals, constrain, assuming a closed system interaction, the chemical composition of the initial fluid and the respective amounts of the initial solid phases involved in the alteration process. Thermodynamic modelings using the EQ3/6 software package correctly predict the mineralogic, chemical and isotopic exchanges accompanying alteration, thus validating the closed system assumption. The model which allows prediction of the influence of CO₂ on the alteration products, shows that, above a 0.25 CO₂ mole fraction in the initial fluid, the alteration is entirely controlled by the chemical composition of the initial solid phases. The presence of CO₂ implies the precipitation of dioctahedral smectites and carbonates instead of the magnesian smectites commonly observed in CO₂-free systems.The Mururoa feeder zone shows alteration features typical of a closed system interaction between the basaltic rock and a magmatic fluid in which seawater did not take part.     

The junction of Fensch and Moselle rivers,France; mineralogy and composition of river materials

The Moselle river flows in the north-east of France, from Vosges Mountains to neighboring countries Luxembourg and Germany. One of its tributaries, the Fensch river, drains a highly industrialized watershed, strongly impacted by mining, smelting and surfacing activities. The objective of this work, part of a general research program on Moselle watershed (Zone Atelier Moselle) was to assess the impact of the polluted Fensch river on the global quality of the Moselle river. For that purpose, water, sediments and suspended particulate matter were sampled in both rivers, upstream and downstream the junction. Four main sampling campaigns were carried out, in winter during a flood event and in spring at low water level. On a first step, mineralogical analyses (XRD and FTIR) and chemical analyses (ICP-MS, ICP-AES), were performed on sediments, suspended particulate matters and filtered waters. Major and trace elements concentrations were obtained on two different granulometric fractions (0–2 mm and 0–50 μm) revealing the enrichment in heavy metals of fine particles. From one collecting campaign to another, seasonal variations could be evidenced on suspended matter composition even though major minerals (calcite, quartz and kaolinite) were always present. Furthermore, spatial variations were evidenced for Fensch and Moselle downstream sediments. Thus, very fine-grained sediments, poorly crystallized, displaying at the same time higher metal concentrations and higher organic matter content than in Fensch river material, were collected downstream, in a low hydrodynamic conditions zone, assumed as a preferential sedimentary zone or even as a placer. Strong correlations could be revealed between iron content and contaminant concentrations, confirming the origin of polluted material.