Bilan des transferts verticaux d'eau en zone non-saturée sous climat soudano-sahélien: application à l'estimation de la recharge des nappes

Une estimation précise de la recharge des nappes est indispensable pour une gestion optimale des ressources en eaux souterraines. Plusieurs méthodes ont été mises au point en région soudano-sahélienne pour son évaluation, méthodes conduisant à des résultats très disparates compte tenu de la variabilité des propriétés du milieux et de la conception même des outils d'évaluation utilisés. Le travail présenté est une contribution à l'amélioration de la compréhension de la dyna- mique hydrique à l'échelle d'une parcelle.A partir d'un dispositif de mesure tensio-neutronique installé aussi bien dans le sol non remanié que dans des lysimètres constitués de sols reconstruits sur une profondeur de 7 m, une étude qualitative et quantitative de ces mécanismes d'infiltration et d'évaporation dans les niveaux d'altération des roches cristallines constituant la zone non-saturée, a été menée sur un site expérimental de l'École Inter-États d'Ingénieurs de l'Équipement Rural (EIER) à Ouagadougou (Burkina Faso).Elle a permis de: - localiser et décrire la dynamique de l'eau dans les différentes tranches de sol concernées par les processus d'humectation et d'assèchement; - estimer la profondeur de reprise de l'eau par évaporation et les quantités d'eau mises en jeu à différentes profondeurs; - réévaluer la réserve en eau du sol, c'est-à-dire la lame d'eau qu'il faut restituer au sol avant qu'il y ait recharge, en tenant compte de la profondeur d'échange entre le sol et l'atmosphère. Les résultats montrent que cette réserve, généralement calculée sur des bases agro-pédologiques, est très sous-estimée pour des applications hydrogéologiqueA reliable estimation of the recharge rate of an aquifer is a prerequisite for the efficient management of the groundwater resources. A variety of methods for recharge estimation in Sudano-Sahelian areas are available, but most of them do not take into account all mechanisms of water transfer in the unsaturated zone; as a result, the estimated recharge values for a given region are often dissimilar.Field equipment was used to measure water content and capillary tension at various depths in the unsaturated zone at an experimental site at Ouagadougou, Burkina Faso, in order to study infiltration and evaporation processes. Several water content profiles and water tension profiles were used to determine mass balances and water fluxes. The calculation of the head gradients allows the determination of flow direction.This study, carried out both in deep lysimeters (7 m) and on undisturbed soil over two years, has allowed:- A description of water dynamics at different soil depths.       The soil can be divided into three parts. The water movement (infiltration and evaporation) takes place in the upper part of the soil. Its extension reaches 2.5 m depth. Drainage at this depth could not be measured and can be neglected. Below this zone, the water movements are very slow. The water content is constant over time and is equal to about 22%. The third zone, which lies between 5.5 m and groundwater table (7 m depth) is influenced by the groundwater table fluctuations. - An estimation of the depth at which water can be taken up by evapotranspiration and of the amount of this water at different depths.       This depth is equal to 2.5 to 3 m under our experimental conditions (soil and climatic conditions). At the end of the dry period, about 180 mm water has been extracted from the soil by evaporation: 50 mm from the first meter, 100 mm between 1 m and 2 m depth and 20 mm for the last 50 cm. - A reevaluation of the effective minimum soil capacity by taking into account the soil-plant- atmosphere exchange depth.       The results show that this effective minimum soil capacity, usually calculated on an agricultural basis, is under-estimated for hydrogeologic purposes. The hydrodynamic behavior of the lysimeters and the undisturbed soil are similar. Under the studied climate conditions and soil hydrodynamic properties, groundwater recharge by direct infiltration can be neglected

Leaf Eh and pH: A Novel Indicator of Plant Stress. Spatial, Temporal and Genotypic Variability in Rice (Oryza sativa L.)

A wealth of knowledge has been published in the last decade on redox regulations in plants. However, these works remained largely at cellular and organelle levels. Simple indicators of oxidative stress at the plant level are still missing. We developed a method for direct measurement of leaf Eh and pH, which revealed spatial, temporal, and genotypic variations in rice. Eh (redox potential) and Eh@pH7 (redox potential corrected to pH 7) of the last fully expanded leaf decreased after sunrise. Leaf Eh was high in the youngest leaf and in the oldest leaves, and minimum for the last fully expanded leaf. Leaf pH decreased from youngest to oldest leaves. The same gradients in Eh-pH were measured for various varieties, hydric conditions, and cropping seasons. Rice varieties differed in Eh, pH, and/or Eh@pH7. Leaf Eh increases and leaf pH decreases with plant age. These patterns and dynamics in leaf Eh-pH are in accordance with the pattern and dynamics of disease infections. Leaf Eh-pH can bring new insight on redox processes at plant level and is proposed as a novel indicator of plant stress/health. It could be used by agronomists, breeders, and pathologists to accelerate the development of crop cultivation methods leading to agroecological crop protection

Finite-size scaling analysis of the distributions of pseudo-critical temperatures in spin glasses

Using the results of large scale numerical simulations we study the probability distribution of the pseudo critical temperature for the three-dimensional Edwards-Anderson Ising spin glass and for the fully connected Sherrington-Kirkpatrick model. We find that the behavior of our data is nicely described by straightforward finite-size scaling relations.Comment: 23 pages, 9 figures. Version accepted for publication in J. Stat. Mec

Characterization of a cold battery with iced water and double heat exchanger in a humid mode

The cold battery is a heat exchanger between two fluids, air (secondary fluid) and iced water (primary fluid). The cold battery is composed of two heat exchangers in series, one of which is made up of flat-plate in galvanized steel serving as a reservoir for the iced water and the other one a copper shell-and-tube exchanger with aluminum cooling blades. The two heat exchangers a connected pipe of the same diameter. These pipes will permit the transit of the iced water coming from the flat-plate exchanger by gravitation towards the tubes of the second exchanger. These two heat exchangers are incorporated in a galvanized container coupled with a centrifugal fan for the improvement of the thermal comfort. The water, after passing through the two heat exchangers is stored in an adiabatic reservoir and will serve as a water fountain [1].   The modeling will be done in a humid mode that is the temperature of the surface of the battery is very low compared with the dew temperature of air. The cooling allows the condensation of water vapor [2]. Key words: Battery, Heat exchanger, Temperature, Humidity, Condensation,  Cross flow, Counter flo

Theta Vectors and Quantum Theta Functions

In this paper, we clarify the relation between Manin's quantum theta function and Schwarz's theta vector in comparison with the kq representation, which is equivalent to the classical theta function, and the corresponding coordinate space wavefunction. We first explain the equivalence relation between the classical theta function and the kq representation in which the translation operators of the phase space are commuting. When the translation operators of the phase space are not commuting, then the kq representation is no more meaningful. We explain why Manin's quantum theta function obtained via algebra (quantum tori) valued inner product of the theta vector is a natural choice for quantum version of the classical theta function (kq representation). We then show that this approach holds for a more general theta vector with constant obtained from a holomorphic connection of constant curvature than the simple Gaussian one used in the Manin's construction. We further discuss the properties of the theta vector and of the quantum theta function, both of which have similar symmetry properties under translation.Comment: LaTeX 21 pages, give more explicit explanations for notions given in the tex

Quantification de la biomasse aérienne des palétuviers du genre Rhizophora au Delta du Saloum (Sénégal)

L’étude de la biomasse aérienne des palétuviers a fait l’objet d’un  inventaire dans quatre unités d’échantillonnage. Quinze parcelles  permanentes ont aussi permis d’étudier les effets de certains facteurs dumilieu sur la biomasse. Dans les strates de hauteur moyenne, la biomasse sèche des racines aériennes la plus élevée est de 67 tonnes à l’hectare chez R. mangle. Dans les strates hautes, celle la plus élevée est de 83,3tonnes à l’hectare. Ces deux grandes quantités de biomasse racinaire supportent aussi les biomasses sèches de tiges et autres parties les plus élevées dans la zone. En termes de comparaison, le pic de la biomasse sèche des tiges et autres parties est observé chez R. mangle. Quant à la biomasse racinaire sèche, le pic est noté chez R. racemosa/harisonnii. Dans les strates de hauteur moyenne, la biomasse sèche des tiges et autres parties est en général plus élevée que celle des racines. Dans les strates hautes, ces rapports de biomasse sont inversés. L’analyse de corrélation entre la biomasse racinaire et les facteurs étudiés montre que l’augmentation de celleci est plus liée à la hauteur de submersion qu’au type de sol. Cette augmentation serait le résultat d’une adaptation morphologique des palétuviers aux vasières meubles et à leur  submersion.Mots clés : Biomasse sèche, strates, milieu, racinaire, tiges, autres parties