TEM evidence for intracellular accumulation of lead by bacteria in subsurface environments

We monitored near-surface atmospheric fallout (15-cm above ground) and soil solution (at 15, 35 and 55 cm below ground) derived nanoparticles over an 8-month period by collecting the particles directly onto TEM grids in anthropogenically-influenced (vineyard) and pristine (native forest) sites in France. Particle clusters trapped on the grid were selected randomly and individual particles were binned into eight different groups (euhedral clays, weathered clays, salts, oxi-hydroxides, bacteria, non-living organic matter, aggregates and undetermined). Bacteria represent 9–23% of the collected nanoparticle area (ave. 9.4% and 18% for two atmospheric collection sites and ave. 23% for soil infiltration samples). Bacteria were most often associated with non-living organic matter and comprised a variety of morpho-types. Interestingly, 45% of all the bacteria analyzed by transmission electron microscopy and electron dispersive spectroscopy (TEM-EDX) showed the presence of intracellular grains significantly enriched in lead and phosphorus. Intracellular sequestration of Pb into polyphosphate bodies has been observed in the laboratory, but this is the first observation of this phenomenon in a natural environment. Furthermore, this suggests that microbial-bound Pb may be an important transport mechanism in subsurface environments.     

Annual dissolved fluxes from Central Nepal rivers: budget of chemical erosion in the Himalayas

Annual dissolved element fluxes of Himalayan rivers from Central Nepal are calculated using published river discharge and a new set chemical data of rivers, including monsoon sampling. These are used to study the control on chemical erosion of carbonate and silicate over the whole basin. Chemical erosion of carbonate is mainly controlled by the river runoff but it can be limited by the availability of carbonate in limestone-free basin. Chemical erosion of silicate is well correlated to the runoff. However differences between High Himalayan and Lesser Himalayan basins suggest that physical erosion may also play an important control on silicate weathering. To cite this article: C. France-Lanord et al., C. R. Geoscience 335 (2003).     

The impact of land use change on soil water holding capacity and river flow modelling in the Nakambe River, Burkina-Faso

The annual hydrological regime of the Nakambe River shows substantial changes during the period 1955–1998 with a shift occurring around 1970. From 1970 to the mid-1990s, despite a reduction in rainfall and an increase in the number of dams in the basin, average runoff and maximum daily discharges increased. This paper reviews the hydrological behaviour of the Nakambe River from 1955 to 1998 and examines the potential role of land use change on soil water holding capacity (WHC) in producing the counter-intuitive change in runoff observed after 1970. We compare the results of two monthly hydrological models using different rainfall, potential evapotranspiration and WHC data sets. Model simulations with soil WHC values modified over time based upon historical maps of land use, are compared against simulations with a constant value for WHC. The extent of natural vegetation declined from 43 to 13% of the total basin area between 1965 and 1995, whilst the cultivated areas increased from 53 to 76% and the area of bare soil nearly tripled from 4 to 11%. The total reduction in WHC is estimated to range from 33 to 62% depending on the method used, either considering that the WHC values given by the FAO stand for the environmental situation in 1965 or before. There is a marked improvement in river flow simulation using the time-varying values of soil WHC. The paper ends with a discussion of the role of other factors such as surface runoff processes and groundwater trends in explaining the hydrological behaviour of the Nakambe River.     

Using land cover changes and demographic data to improve hydrological modeling in the Sahel

At the beginning of the drought in the Sahel in the 1970s and 1980s, rainfall decreased markedly, but runoff coefficients and in some cases, absolute runoff increased. This situation was due to the conversion of the land cover from natural vegetation with a low annual runoff coefficient, to cropland and bare soils, whose runoff coefficients are higher. Unless they are adapted, hydrological conceptual models, such as GR2M, are unable to reproduce this increase in runoff. Despite the varying environmental and climatic conditions of the West African Sahel, we show that it is possible to increase the performance of the GR2M model simulations by elaborating a time‐varying soil water holding capacity and to incorporate this value in the annual maximum amount of water to be stored in reservoir A of the model. We looked for interactions between climate, rural society, and the environment. These interactions drive land‐cover changes in the Sahel, which in turn drive the distribution of rainfall between infiltration, evaporation, and runoff and hence the water resources, which are vital in this region. We elaborated several time series of key indicators linked to these interactions. We then integrated these changes in the runoff conditions of the GR2M model through the maximum value of the reservoir capacity. We calculated annual values of water holding capacity using the annual values of four classes of land cover, natural vegetation, cultivated area, bare soil, and surface water. We then used the hydrological model with and without this time‐varying soil value of A and compared the performances of the model under the two scenarios. Whatever the calibration period used, the Nash–Sutcliffe index was always greater in the case of the time‐varying A time series.     

Measuring runoff by plots at different scales: Understanding and analysing the sources of variation

The decrease of runoff with the increase in area is not a new fact. The scale effect depends on the spatial and temporal variability of different factors, including the surface characteristics and hydrodynamic properties of the soil and the vegetation development. The purpose of our work is to study the relative influence of the sources of variation of runoff from a small Sahelian catchment on several types of soil surfaces features. Plots of different sizes (1, 50 and 150 m²) on cultivated soils and degraded soils (non-cultivated with three different types of crusts) were monitored for two consecutive years. The results show that the runoff coefficients of rainfall events range from 4 to 65% on cultivated soils and 16 to 96% on uncultivated bare and degraded soils. A statistical and dimensionless analysis shows that in degraded environments, the processes generating runoff on plots of 50 and 150 m² are identical and significantly different from the unit plot (1 m²). The decrease in runoff with increasing scale becomes more pronounced when rainfall duration decreases. In cultivated areas, this result is not observed. Additional measurements are needed to better understand the differences in functioning at various scales of observations.     

Lithospheric tectonic structures developed under high-grade metamorphism in the Southern part of Madagascar

Abstract

This paper describes the tectono-metamorphic evolution of a segment of the Precambrian deep crust, in the southern Madagascar island. This crust corresponds to an Archaean basement reworked by a widespread, late panAfrican event (550–580 Ma) during the formation of the Mozambican belt. The finite geometry and associated metamorphism are depicted by satellite imaging, field mapping and P-T estimations using both conventional thermobarometric methods and TWEEQ software program with internally consistent thermodynamic data and uniform set of solution models. The structural pattern developed during high-grade metamorphism shows the juxtaposition of domains with complex fold geometries separated by a 15 km wide ductile shear zone. Within the folded domains, kilometre scale interference patterns associated with strongly dipping metamorphic stretching lineations can be described as superposed folding (F1 and F2 folds). The tight and upright F2 folds result from East-West horizontal shortening. The shear zone is defined by homogeneous orientations of steep foliations, sub-horizontal stretching lineations, and kilometre scale strain gradient. Within the shear zone, we observe dominant non-coaxial criteria at various scales that are consistent with a sinistral strike-slip system during D2 deformation stage. Nevertheless, we have also found in the shear zone, geometries typical of a horizontal shortening. Such a strain pattern is characteristic of transpression tectonics.

The synkinematic metamorphic conditions are estimated on mafic garnetiferous metabasites. Results show that regional transpression tectonics has developed under very high and constant thermal regime (about 800°C). A pressure gap, of about 3 kbar between the domains separated by the shear zone is identified. This implies tectonic coupling of two different structural levels during tranpressive tectonic.     

Exercice de scénarisation hydrologique en Afrique de l’Ouest—Bassin du Bani

Résumé

Les pays sub-sahariens basent principalement leur économie sur l’agriculture pluviale. Les projections démographiques à moyen ou long terme montrent que la pression démographique va s’accroître très fortement. A l’avenir, il faudra soutenir encore plus fortement le développement de stratégies agricoles de ces pays : cela nécessite une meilleure connaissance de leurs ressources en eau futures. Cette connaissance de la ressource en eau dans le futur passe par l’élaboration de scenarios climatiques et hydrologiques qui font intervenir différents acteurs, compétents dans des activités très variées, qu’ils soient scientifiques de divers domaines (climatologues, hydrologues, sociologues, …) mais aussi financiers, politiques, acteurs sociaux et décideurs. Ce processus d’élaboration de scenarios s’accompagne de nombreuses incertitudes, plus ou moins bien maitrisées, avec lesquelles doivent s’accommoder les gestionnaires d’ouvrages et planificateurs d’aménagements régionaux. Illustré par l’exemple du bassin du Bani, affluent du fleuve Niger, ce travail propose une réflexion sur la « scénarisation hydrologique » et la prédétermination des paramètres d’un modèle hydrologique dans un contexte global non stationnaire. Le choix de jeux de paramètres a de nombreux impacts sur les résultats de la scénarisation comme l’estimation de la ressource et la variabilité de cette ressource. Ces deux éléments sont fondamentaux pour qui doit conduire un processus de décision en réponse à une demande de stratégie d’aménagement ou à une demande de stratégie de développement. Nous proposons une méthodologie de détermination des jeux de paramètres se basant sur la construction de plusieurs jeux de paramètres issus de calages glissants, qui permet d’aller dans le sens de ce que de plus en plus de gestionnaires préconisent : ne pas essayer de prévoir le futur mais plutôt des futurs envisageables qui forceront des modèles d’impact, ce qui leur permettra de fournir des éléments de décision afin de s’adapter ou d’adapter des solutions d’aménagement aux conditions de ces futurs.

Editeur Z.W. Kundzewicz; Editeur associé C. Perrin

Citation Paturel, J.-E., 2014. Exercice de scénarisation hydrologique en Afrique de l’Ouest—Bassin du Bani. Hydrological Sciences Journal, 59 (6), 1135–1153. http://dx.doi.org/10.1080/02626667.2013.834340     

Métabasites de la cordillère occidentale d'Équateur,témoins du soubassement océanique des Andes d'Équateur

The building-up of the Andean Range is linked to the subduction of the Pacific lithosphere beneath the South American plate. However, the formation of the Central Andes is marked by continental crustal shortening, whereas accretion and underplating of exotic oceanic terranes occurred in the northern Andes. The study of various magmatic and metamorphic rocks exhumed in the Western Cordillera of Ecuador by Miocene transpressive faults enables us to constrain the nature and thermal evolution of the crustal root of this part of Ecuador. These rocks are geochemically similar to oceanic plateau basalts. The thermobarometric peak conditions of a granulite and an amphibolite indicate temperatures of 800–850?°C and pressures less than 6–9 kbar (lack of garnet). The abnormally high geothermal gradient (≈40?°C?km^?1) is probably due to the activity of the magmatic arc, which developed on the accreted oceanic terranes after Late Eocene times, and may have provoked the re-mobilisation of deeply underplated oceanic material during the genesis of the Neogene to Recent arc. To cite this article: É. Beaudon et al., C. R. Geoscience 337 (2005).     

Influence du Bani sur la variabilité saisonnière et interannuelle de la crue du fleuve Niger dans le delta intérieur au Mali

Le delta intérieur du fleuve Niger est une zone humide sahélienne dont l’inondation dépend de la pluviométrie des bassins supérieurs du fleuve Niger et de son principal affluent, le Bani. La crise climatique qui a débuté en 1970 a très peu influencé les dates de passage des maximums de crue sur le Niger amont et son principal défluent, le Diaka. L’influence par contre est très forte sur le Bani, à la confluence avec le Niger à Mopti et sur le delta aval avec des dates de passages des maximums plus précoces qu’auparavant. Cela est dû à la faiblesse des superficies inondées au cours des années sèches. Pendant les années humides, l’importance des débordements latéraux ralentit la propagation de la crue avec pour conséquence des dates de passages plus tardives des maximums. Par ailleurs pendant les années humides antérieures à 1970 l’importance des débordements latéraux conférait au delta amont un caractère d’autorégulation par écrêtage des crues au niveau de certaines station.