Sur les possibilités de reconstitutions paléo-environnementales offertes par les andosols des hautes terres tropicales. Exemple des Nilgiri (Inde du Sud) On the possibilities of palaeoenvironmental reconstitution offered by tropical highlands andisols. Example of Nilgiri andisols (South India)

14 pagesInternational audienceEnglish An example, from South India, shows the potentialities offered by the study of high altitude non-allophanic andisols to reconstitute the local palaeoenvironmental history. In this type of soils, organic matter is stabilised in the form of organometallic complexes which migrate downwards very slowly. Compared to the broad signal recorded by peat bogs, the soil organic matter signal appears to be more site-specific that enables precise palaeoenvironmental studies. This application comes just when precise palaeoclimatic reconstitutions are necessary to build reliable climatic models. Français Un exemple, pris en Inde du Sud, montre les potentialités offertes par l'étude d'andosols non-allophaniques d'altitude pour reconstituer l'histoire paléo-environnementale locale. Dans ce type de sol, la matière organique est stabilisée sous forme de complexes organo-métalliques qui ne migrent que très lentement. Comparé au signal général enregistré par les tourbières, le signal retenu par la matière organique paraît beaucoup plus ponctuel et ceci permet des études paléo-environnementales plus précises. Cette application vient à un moment où des reconstitutions paléo-climatiques précises sont nécessaires pour bâtir des modèles climatiques fiables

Advances in characterization of the soil clay mineralogy using X-ray diffraction: from decomposition to profile fitting

International audienceStructural characterization of soil clay minerals often remains limited despite their key influence on soil properties. In soils, complex clay parageneses result from the coexistence of clay species with contrasting particle sizes and crystal-chemistry and from the profusion of mixed layers with variable compositions. The present study aimed at characterizing the mineralogy and crystal chemistry of the < 2 μm fraction along a profile typical of soils from Western Europe and North America (Neo Luvisol). X-ray diffraction (XRD) patterns were nterpreted using i) the combination of XRD pattern decomposition and indirect identification from peak positions commonly applied in soil science and ii) the multi-specimen method. This latter approach implies direct XRD profile fitting and has recently led to significant improvements in the structural characterization of clay minerals in diagenetic and hydrothermal environments. In contrast to the usual approach, the multi-specimen method allowed the complete structural characterization of complex clay parageneses encountered in soils together with the quantitative analysis of their mineralogy. Throughout the profile, the clay paragenesis of the studied Neo Luvisol systematically includes discrete smectite, illite and kaolinite in addition to randomly interstratified illite-smectite and chlorite-smectite. Structural characteristics of the different clay minerals, including the composition of mixed layers, did not vary significantly with depth and are thus indicative of the parent material. The relative proportion of the < 2 μm fraction increased with increasing depth simultaneously with smectite relative proportion. These results are consistent with the leaching process described for Luvisols in the literature

Characteristics of Non-Allophanic Andisols derived from Low Activity Clay Regoliths in Nilgiri Hills (Southern India)

19International audienceLow activity clay soils on old planation surfaces of the tropics are generally considered as stable end points of soil formation. It is therefore surprising to find Andosols on them. We characterised the properties of six profiles representative of these soils in the Western part of Nilgiri Hills (2000–2500 m above mean sea level), Southern India, where the present climatic conditions are cool (mean annual temperature 15°C) and humid (mean annual rainfall 2500 mm). Thick (50–80 cm) dark–reddish brown topsoil overlies strongly desilicated yellowish–red materials. This horizon has andic properties to a sufficient depth and the carbon content requirement of the melanic epipedon to place these soils in the Andisol order. Our data as well as the history of the Nilgiri Hills suggest that the formation of these non-allophanic Andisols result from the succession of two main steps. First, a ‘lateritic' weathering cycle led to the relative accumulation of secondary Al and Fe oxides. Later, the accumulation of organic matter favoured by a more recent climatic change induced complexation by organic acids of Al and Fe oxides, and the production of enough metal–humus complexes to give rise to andic properties. Such soils, in which secondary Al and Fe oxides, generally considered as indicators of an advanced weathering stage, are involved in a new cycle of soil formation, are original Andisols

Spatial heterogeneity of land cover response to climatic change in the Nilgiri highlands (southern India) since the Last Glacial Maximum

25 pagesFourteen hillslope soil profiles were sampled under natural vegetation (i.e., grassland or forest) and plantations in the Nilgiri highlands, southern India. Delta 13C ratios were measured at different depths and 14C ages determined for six profiles. In these highland soils where the turnover rate of organic matter is extremely low, the Δ13C ratios of entire soil profiles have recorded signatures of past land cover. By correlating the data with results previously obtained from peat bogs and with knowledge concerning the history of human settlement, we distinguish three contrasting trajectories of palaeoenvironmental history and landscape change since the Last Glacial Maximum. In the central Nilgiris, between 18 and 10 ka BP, forest expansion occurred due to the conjunction of a wetter climate (the maximum of southwest monsoon-related humidity occurring at ca. 11 ka BP) and higher temperatures; since 10 ka BP, the reversal towards grassland vegetation is attributed to drier conditions. In the western Nilgiris, where strong southwest monsoon winds permanently restrict forest patches to sheltered valley sites, steady but limited expansion of forest from 18 ka BP to the present is recorded and attributed to rising temperatures. The southern and eastern Nilgiris, where the northeast monsoon contributes 20% of the annual rainfall, are the less sensitive to fluctuations in the southwest monsoon. In these areas, rapid and extensive expansion of forest occurred mainly as a consequence of higher temperatures from 18 ka BP to the present. Massive deforestation by Badaga cultivators and Europeans planters followed after the 16th century AD. As a result, and in contrast with the western Nilgiris where the land cover mosaic has remained remarkably stable in the last 18 ka BP, the current landscape differs sharply from the land cover pattern detected by the soil record

Impact of drainage on soil-forming mechanisms in a French Albeluvisol: Input of mineralogical data in mass-balance modelling

International audienceResearch on soil pedogenesis has mainly focused on the long-term soil formation and has most often neglected recent soil evolutions in response to human practices. Such recent soil evolutions are however of considerable interest to study the timing of soil forming processes in response to changes in environmental conditions. In this paper, we model the Albeluvisol evolution in response to agricultural drainage. This was considered as a model case to study the velocity of mineralogical changes in soil as a result of eluviation and redox processes. We used a space-for-time substitution approach in combination with mass balance modelling based on mineralogical data in order to identify and characterise the mineralogical transformations responsible for the recent soil evolution in response to subsurface drainage. This approach allowed demonstrating that the main effects of subsurface drainage are (i) increasing precipitation of Mn oxides and Mn-rich ferrihydrite with decreasing distance to the drain as a result of the change in redox conditions and (ii) increasing loss of clay-sized oxides and smectites due to the enhanced eluviation in the vicinity of the drain. Both processes induce significant matter fluxes in comparison with those that occurred over the long-term soil formation. Nowadays, the precipitation of Mn oxides and Mn-rich ferrihydrite seems to still be active in the studied soil. On the opposite, the eluviation process appears less active than immediately after the drainage network installation, if not totally inactive. It thus demonstrates that some soil processes may have significant impact on the soil mineralogical composition even if they are only active over very short periods of time after a change in environmental conditions

METODOLOGY FOR LATERÍTICS CU-BEARING CLAY MINERALS CHARACTERIZATION

Lateritic material lies over nearly 75% of the Brazilian surface area; but not more than 30% of this material is exploited. The expressive volume of clay minerals associated to the ores is the main reason of this low figure, especially because clay minerals are very complex, most of the time, impossible to concentrate. Under this circumstance, a proper mineral identification and the knowledge of the clay mineral structure are essential for the best mineral processing route choice. This study describes an optimized methodology to characterize a Cu-lateritic ore, mainly composed of Cu-bearing clay minerals. Cations saturations and particle sizes separation, combined with X-ray diffraction, mid infrared spectroscopy and scanning electron microscopy allow concluding that this Cu-lateritic ore is mainly composed of smectites, micas and kaolinite; furthermore, the copper is especially associated to mica and secondarily to smectite

Propriedades físicas de un Argissolo después de 17 años de forestación con Eucalyptus spp

A expressiva expansão do setor florestal no Brasil tem dado evidencia a estudos que direcionam suas ações de investigação para a preservação e utilização racional dos recursos naturais. A pesquisa tem demonstrado que mudanças no uso do solo, alteram as suas condições pedoambientais. Sendo assim, o presente estudo teve como objetivo principal investigar ações antrópicas de longa duração sobre área do bioma Pampa no Rio Grande do Sul: Efeito nos atributos físicos de solo com substituição do uso sob campo para o uso do solo com florestamento comercial de Eucalyptus spp. Amostras de um Argissolo Vermelho Distrófico foram coletadas em horto florestal, em triplicata e em cinco profundidades e também foi coletado um solo de controle, vegetado com campo natural. Não houve alteração na distribuição granulométrica do solo. Após 17 anos de florestamento foi observado um incremento no teor de hematita nos solos da floresta e rizosfera da floresta, aumento nos valores da suscetibilidade magnética e diminuição da área superficial específica das partículas em profundidade.The significant expansion of the forestry sector in Brazil has given evidence to studies that direct its research actions towards the preservation and rational use of natural resources. Research has shown that changes in land use alter its pedoenvironmental conditions. Therefore, the present study aimed to investigate long-term anthropic actions on the Pampa biome area in Rio Grande do Sul: Effect on physical properties of soil with substitution of use under natural pasture for use of commercial forestation of Eucalyptus spp. Samples of an Ultisol (Argissolo Vermelho Distrófico, SiBCS) were collected in a planted forest, in triplicate and at five depths, and a control soil, vegetated with a natural pasture, was also collected. There was no change in the particle size distribution of the soil. After 17 years of forestation, an increase in the hematite content was observed in the forest bulk soil and the rhizospheric soil, an increase in the values of magnetic susceptibility and a decrease in the specific surface area of the particles in depth.La importante expansión del sector forestal en Brasil ha evidenciado estudios que orientan sus acciones de investigación hacia la preservación y uso racional de los recursos naturales. La investigación ha demostrado que los cambios en el uso de la tierra alteran sus condiciones pedológicas. Por lo tanto, el presente estudio tuvo como objetivo investigar las acciones antrópicas a largo plazo en el área del bioma Pampa en Rio Grande do Sul: Efecto sobre los atributos físicos del suelo con sustitución de uso bajo campo por uso de tierra con forestación comercial de Eucalyptus spp. Se recolectaron muestras de un Argissolo Vermelho Distrófico (SiBCS) en un huerto forestal, por triplicado para cinco profundidades, y también se recogió un suelo control, vegetado con un campo natural. No hubo cambios en la distribución granulométrica del suelo. Después de 17 años de forestación, se observó un aumento en el contenido de hematites en los suelos forestales y la rizosfera del bosque, un aumento en los valores de susceptibilidad magnética y una disminución en la ASE de las partículas en profundidad

Dynamique du piégeage des micropolluants métalliques au sein des zones humides artificielles traitant des eaux pluviales urbaines strictes : Etude de cas à Strasbourg, Moulins-lès-Metz et Leuville-sur-Orge

Colloque avec actes et comité de lecture. internationale.International audienceStormwater constructed wetlands (SCW) in Strasbourg (Alsace, France), Moulin-lès-Metz (Lorraine, France), and Leuville-sur-Orge (Ile-de-France, France) receive and treat exclusively runoffs from urban catchments but with different soil uses. Made up of sedimentation ponds and a vertical subsurface flow constructed wetland, the treatment facilities lead to trap several trace metal pollution. Each site belongs to different hydroclimatic areas (modified oceanic, modified continental and semi-continental) and was designed for different purposes (watercourse protection in Strasbourg and in Leuville-sur-Orge, protection of drinking water wells in Moulins-lès-Metz). The aim of this study is to explore trace metals (Cd, Cu, Pb and Zn) behaviours in these SCW. We investigated trace metal trapping by determining concentrations in the systems compartments (filters media and plants). Then trace metal speciation was determined through sequencial extractions of the sediment and filter media. This allowed to determine their forms in soils and to anticipate their behaviour during physical and chemical condition changes. This study permits to obtain first results for the metals stability, to highlight a decrease of the concentrations through the SCW depth (from surficial sediment to clean filter media) and to observe a negligible metal trap in plants (mainly in roots)