Influence géomorphologique et structurale des sols sur le report hydrique : Conséquences sur le fonctionnement hydrique des sols et la biomasse en zone soudano-sahélienne

21-22 nov. 2007Cette étude démontre qu'en zone soudano-sahélienne, en année à pluviosité déficitaire, à différentes échelles, plusieurs facteurs physiques, chimiques et anthropiques des sols régissent le report hydrique, part bénéfique du ruissellement représentant "une irrigation naturelle, complémentaire et simultanée à la pluie qui l'a générée en fonction des conditions topographiques et micro morphologiques avec transfert complémentaire de fertilité ". En condition pluviale, l'encroûtement décroissant le long du versant favorise l'infiltration du report hydrique dans les unités de sol en bas de pente. A l'échelle du champ, il est encore maximisé par le micromodelé concave, par une compaction profonde moins forte et par le labour. L'augmentation des nutriments est de 13,4 à 10% et en éléments fins de 16,3 à 12,5% respectivement sous labour et grattage. Cette maximisation du report hydrique provoque un drainage significatif très localement. Sur les périmètres irrigués la salinisation renforce les facteurs de formation des croûtes et le ruissellement, réduisant drastiquement la capacité d'infiltration des sols. Il en résulte une limitation des réserves en eau utile malgré l'irrigation non contraignante. Ceci provoque une sécheresse édaphique. Dans ces deux conditions culturales cette baisse drastique des stocks hydriques due à la formation d'un encroûtement conduit à la réduction voire à l'annulation du rendement des cultures. Ces résultats montrent la difficulté qu'ont les chercheurs à expliquer la complexité du comportement et du fonctionnement hydrique sur l'ensemble d'un versant et à l'intérieur du champ pour comprendre la variabilité des rendements. L'identification, à l'échelle de la parcelle et sur le versant, des causes du ruissellement et du report hydrique et d'en mesurer l'effet sur la modification des stocks hydriques sur de faibles distances est nécessaire pour conceptualiser un aménagement raisonné, innovant et efficace des flux de surface

Mineralogy and ultrastructure of some alteration products of Yamato-86032 meteorite

White products of Yamato-86032 meteorite sample have been studied using linear localization detector method and TEM (powders examination and ultramicrotomed thin-sections). In addition to the mineral phases of the meteorite (olivine, pyroxene, labradorite), calcium sulfate and hydrous minerals have been identified. The observed glassy matrix has high silica content and the alteration products in contact with glass are mainly Fe-Al and Fe-Al-Na-K-S compounds. The presence of these mineral phases suggests that a sulfuric acid alteration has to be involved for the formation of the white products studied

Phytoremediation of polluted soils : recent progress and developments.: Phytostabilisation of a copper contaminated topsoil aided by basic slags: assessment ofCu mobility and phytoavailability

International audiencePurposeBasic slags are alkaline by-products of the steel industry with potential properties to ameliorate nutrient supply and metal stabilisation in contaminated soils. This study aimed at investigating the potential of a P-spiked Link Donawitz slag and a conventional basic slag called Carmeuse for the aided phytostabilisation of a Cu-contaminated soil at a wood treatment site. The effects of basic slag addition on Cu fractionation, mobility and (phyto) availability were assessed.Materials and methodsBoth slags were incorporated at 1 % w/w into the Cu-contaminated soil phytostabilised with Cu-tolerant plants, using either outdoor lysimeters or a field plot. Untreated soil (UNT), amended soils with the P-spiked Link Donawitz slag (PLDS) and the conventional slag (CARM) respectively, and a control soil (CTRL) were sampled, potted and cultivated with dwarf bean. Physico-chemical analysis, determination of total soil elements and a Cu-sequential extraction scheme were carried out for all soils. Physico-chemical characteristics of soil pore water and Cu speciation (rhizon, ion selective electrode and diffusive gradient in thin film (DGT)) were determined. Shoot dry weight yield and leaf ionome (i.e. all inorganic ions present in the primary leaves) of dwarf beans were investigated.Results and discussionThe slag incorporation at only 1 % w/w increased the soil pH from 1.5 to 2 U and electrical conductivity in soil pore water by three times. The residual Cu fraction increased for both slag amended soils compared to the UNT soil by six times in parallel to the decrease of the Cu oxidisable fraction (1.5 times) and to a less extent the reducible fraction. The incorporation of both slags did not reduce the total dissolved Cu concentration in the soil pore water but significantly reduced the real dissolved Cu concentration ca five times, the Cu labile pool as measured by DGT (at least two times) and the Cu phytoavailability. The dwarf bean total biomass was also improved with the slag addition especially for the P-spiked Linz–Donawitz slag.ConclusionsThe addition of both slags in the contaminated soil increased Cu concentration in the residual fraction and thus reduced its potential mobility. Though the total dissolved Cu soil pore water concentration remained identical, its speciation changed as the real dissolved fraction diminished and lowered the Cu bioavailability. The addition of small amount of P-spiked Linz–Donawitz and Carmeuse slags was beneficial for this Cu-contaminated soil in the context of aided phytostabilisation

Variabilité structurale et physico-chimique des croûtes superficielles des sols de la vallée du Syr Daria (Kazakhstan)

International audienceToutes les régions arides et semi-arides sont le lieu de nombreux types de croûtes physiques et micro ou cryptobiologiques (Afrique, Israël, Australie, USA, Chili). Les micro horizons durs formés sur la surface du sol sont le résultat de processus naturels principalement l'impact des gouttes de pluies, le ruissellement et le dessèchement et anthropiques tel que l'irrigation et le travail du sol. Une prospection réalisée au Kazakhstan, en 2003, a démontré, pour la première fois l'existence d'un tel encroûtement sur les sols cultivés ou non de la vallée du Syr Daria. L'étude de ces croûtes fait apparaître leur extrême variabilité physique, chimique et microbiologique. Toutefois le milieu spécifique du Kazakhstan conduit à la formation de nombreuses variantes et même à celle de croûtes apparemment spécifiques. L'analyse en composantes principales fait apparaître que seulement 4 variables sont suffisantes pour expliquer la variabilité des sites (longitude, épaisseur et largeur des fentes et couvert végétal). Les trois premiers axes expliquent 92,7% de l'inertie totale des données. Le premier axe, climatique, explique 54,4% de la variance des échantillons et le second, physique, explique 27,7%. Les quatorze échantillons de croûtes étudiés sont très bien classés par ces quatre facteurs physiques, géographiques et biotiques (R=0,90). Les analyses au RX indiquent une forte salinité de ces croûtes qui croit vers l'ouest, à l'exemple des sols. Les images microscopiques (MEB et classique) montrent une forte hétérogénéité structurale avec des micropores variables d'un site à l'autre. Les mesures porosimétrique confirment bien cette variabilité qui traduit les caractéristiques spécifiques de cette région. Cette variabilité des croûtes confère aux champs une variabilité des conditions hydrologiques, géochimiques et d'érodibilité qui devront être prises en compte dans le cadre de réhabilitation des sols des périmètres irrigués comme dans le contrôle d'un pâturage rationnel. Ces premiers résultats montrent que les politiques d'aménagement des périmètres irrigués et des zones de parcours d'élevage doivent intégrer le rôle spécifique des diverses croûtes en fonction de l'importance de leur effet dans la stabilité du milieu. Pour identifier ce rôle, leur étude doit être entreprise de façon systématique car leur présence est généralisée et dominante. Pour ce faire il faut démarrer une étude des mécanismes d'encroûtement et de la salinisation pour la compréhension et la prédiction des processus de ce type de dégradation des différents agro/écosystèmes

Sustainable Irrigated Agricultural Production of Countries in economic Transition: Challenges and Opportunities (A case study of Uzbekistan, Central Asia)

For the fulfillment of the thirsty ambition of self-sufficiency of the Soviets for cotton production, the arid Central Asian region and in particular Uzbekistan has been extensively exploited. In fact, vast tracts of deserts have been converted into irrigated agricultural lands without proper consideration to environment and technical standards. As a result trends in natural resource degradation (soil salinity, desertification, water quality) as well as declining crop yields have dramatically increased. The agricultural sector is the backbone for employment, food security and export revenues of the Central Asian countries. Since the independence of the Central Asian countries (after the breakup of the former Soviet Union) the situation has changed dramatically in terms of institutional, political and technical systems. Political transition, which is defined as a shift from once planned centralized economy to a market-driven one, has introduced 'new' concepts like land tenure, water rights and different kinds of ownership. All of such transformations have impacted the agricultural production in Central Asia. The institutional change can be described as decentralization of the farming systems i.e., transition from the former state collective farms into the smaller forms of private farms. The institutional interventions are aimed to increase agricultural production through improving water management. It is arguable that private production systems are the most effective business driven forces but the situation is quite different in Central Asia due to the irrigated agriculture. The biggest challenge for a sustainable irrigated agricultural production lies in the recent reforms of water management sector in Central Asia and Uzbekistan. The water users associations have been established for replacing the former collective farming systems for irrigation water distribution and maintenance of irrigation infrastructures at on-farm level. The intention of the national government was to shift the operation, maintenance and management of irrigation infrastructures to non government institutions (decentralization). However, these institutions have not fulfilled their promising tasks because of i) a rapid increase of number of private farms along canals; ii) the cropping structure is mosaic with different crop water requirements against the former monoculture; iii) a poor financial, trained and technical capacities of new established institutions; iv) a state ordered agricultural production quota system (for cotton and wheat). This paper analyzes the historical aspects of transformation in the farming production institutions in Central Asia with special focus on Uzbekistan and comprehensively overviews the main current challenges facing the farming system and potential opportunities for reversing the situation

Antimicrobial Activity of Thin Solid Films of Silver Doped Hydroxyapatite Prepared by Sol-Gel Method

In this work, the preparation and characterization of silver doped hydroxyapatite thin films were reported and their antimicrobial activity was characterized. Silver doped hydroxyapatite (Ag:HAp) thin films coatings substrate was prepared on commercially pure Si disks by sol-gel method. The silver doped hydroxyapatite thin films were characterized by various techniques such as Scanning electron microscopy (SEM) with energy Dispersive X-ray attachment (X-EDS), Fourier transform infrared spectroscopy (FT-IR), and glow discharge optical emission spectroscopy (GDOES). These techniques have permitted the structural and chemical characterisation of the silver doped hydroxyapatite thin films. The antimicrobial effect of the Ag:HAp thin films on Escherichia coli and Staphylococcus aureus bacteria was then investigated. This is the first study on the antimicrobial effect of Ag:HAp thin films obtained by sol-gel method. The results of this study have shown that the Ag:HAp thin films with xAg=0.5 are effective against E. coli and S. aureus after 24 h

Sedimentation of reservoirs in Uzbekistan: a case study of the Akdarya Reservoir, Zerafshan River Basin

International audienceThe major rivers of Central Asia (Amu Darya, Syr Darya and Zerafshan) are turbid watercourses. Thus many man-made water reservoirs are affected by high sedimentation rates. It is of strategic importance to rationally quantify available water resources in existing reservoirs to ensure a guaranteed water supply to the different water users. Recent drought years and physical deterioration of hydraulic structures urged authorities to re-estimate the water availability in reservoirs of Uzbekistan for the sustainable use of the scarce water resources and safe operation of hydraulic infrastructure. This paper presents the results after the application of a geostatistical approach to assess the water resources availability in the Akdarya reservoir of Uzbekistan. The geostatistical approach creates digital surfaces that represent relatively accurate reservoir bottom conditions and support automated reservoir volumes and surface areas calculations. This in turn significantly reduces time, work load and financial burdens for sedimentation survey projects

Facts and Perspectives of Water Reservoirs in Central Asia: A Special Focus on Uzbekistan

International audienceThe political transformation of the Central Asian region has induced the implosion of the interconnected physical hydraulic infrastructure and its institutional management systems. Land-locked Central Asian countries with their climatic conditions and transboundary water resources have been striving to meet their food security, to increase the agricultural production, to sustain the energy sectors and to protect the environment. The existing water reservoirs are strategic infrastructures for irrigation and hydropower generation. The upstream countries (Tajikistan and Kyrgyzstan) favor the reservoirs operation for energy supply while the downstream countries (Uzbekistan, Turkmenistan and Kazakhstan) push on the irrigation use. This paper overviews the current challenges and perspectives (technical, institutional and legal regulations) of man-made water reservoirs in Central Asia with special focus on Uzbekistan

Experimental alteration of a meteoritic model-glass in different media

A meteoritic model-glass has been altered under oxidizing conditions in different media (water and sulfuric acid) at 80℃ and 0℃. The reactions were followed by analysis of solutions and solids (XRD, FTIR, SEM, TEM). After reaction, all the elements were detected in solution, at different levels of concentration related to the medium. The most aggressive media were sulfuric acid at pH 1 for 80℃ and 0℃ runs. In such alteration conditions, the surface of the solid evolved rapidly according to the temperature. At 80℃, one noticed the development of a Si-rich layer containing calcium and sulfate ions which combined to form gypsum. At 0℃, only smooth surface with etch pits and scarce gypsum crystals were observed. In contact with glass, ultramicrotomed thin-sections studied by TEM revealed the presence of two kinds of products : Fe-Al silicate phases (in deionized water and H_2SO_4 solution with pH_4) and a high-silica content layer (H_2SO_4 solution with pH1,at 80℃)

Geostatistical approach for the assessment of the water reservoir capacity in arid regions: a case study of the Akdarya reservoir, Uzbekistan

International audienceThe paper presents the results of a new geostatistical approach to generate bathymetric surface models from point measurement converted into continuous contour surfaces of reservoir bottoms in Uzbekistan. Sedimentation of reservoirs raises engineering, environmental and economical issues for the communities around the world in areas affected by a strong water deficit. Because of Uzbekistan's arid climatic conditions, and uneven spatial and temporal water resources distribution, responsive and innovative water availability assessment surveys of all major water reservoirs are required. Bathymetric surveying is a traditional method that is carried out for the estimation of reservoir volumes and surface areas of the corresponding reservoir stages in order to assess the water availability. Volume and surface area differences derived from multiple surveys of a reservoir provide storage loss estimates over time due to sedimentation. However, two main factors, such as intensive field data measurement and post data-processing, often limit the frequency of these surveys. Alternatively, innovative depth measurement technologies coupled with contouring and surface mapping programs provide automated reservoir volume and surface area calculations. This significantly reduces time, workload and financial burdens for reservoir sedimentation projects. This research proposes the use of geostatistical approach to assess the reservoir sedimentation in the Akdarya reservoir of Uzbekistan. The geostatistical approach includes (semi-) variogram analysis and interpolation (kriging and simulations--turning bands) techniques predicting values at unsampled locations for generating digital bathymetric surface models of reservoir bottom conditions in order to calculate the volume and surface area at a given water elevation. The simulation enables to have range of reservoir volumes and surface areas with the same probability, in comparison to the kriging and traditional methods. This gives a real estimation of the resource availability for water operators to manage natural resources and hydraulic infrastructure in a sustainable manner