Transports fluviaux de matières dissoutes et particulaires sur un bassin versant en région tropicale : le bassin amont du Niger au cours de la période 1990-1993

Entre janvier 1990 et juillet 1993, 85 échantillons ont été prélevés sur les eaux du Niger à la station de Bamako (Mali). A partir des analyses effectuées et des données de débits disponibles sur cette période particulièrement sèche, ont pu être calculés les flux spécifiques pour les différentes espèces dissoutes (par ordre décroissant : HCO3 > SiO2 >> COD > Na > Ca > K > Mg >> Cl > SO4 >> Fe > Al) et le flux spécifique des matières en suspension. Le flux spécifique de TDS, caractéristique de l'intensité de l'altération chimique, est de 8 t/km2/an, alors que le flux de TSS, représentatif de la vitesse de l'érosion mécanique, est de 5 t/km2/an. Ces flux de matières dissoutes et particulaires sont ensuite comparés à ceux de 16 bassins fluviaux d'Afrique tropicale. On a pu enfin déterminer des relations TDS-drainage et TSS-drainage caractéristiques de cette zone tropicale. (Résumé d'auteur

Suspended sediment load and mechanical erosion in the Senegal basin : estimation of the surface runoff concentration and relative contributions of channel and slope erosion

Cette étude a pour but de mieux cerner les mécanismes d'acquisition de la charge solide et de l'évolution de l'érosion dans le bassin du fleuve Sénégal de 1979 à 1984. L'estimation annuelle du volume ruisselé permet de quantifier les différentes composantes de l'hydrogramme de crue et de préciser ses relations avec les concentrations de MES. Au cours de la période sèche étudiée, le début moyen annuel 330 m3/S ne représente que 46 % du module interannuel de 1903 à 1984. A l'exutoire du bassin versant le flux moyen particulaire s'élève à 1,9 millions de tonnes/an. L'érosion des versants est quatre fois supérieure à celle des berges de la vallée alluviale. (Résumé d'auteur

SciPy 1.0: fundamental algorithms for scientific computing in Python.

SciPy is an open-source scientific computing library for the Python programming language. Since its initial release in 2001, SciPy has become a de facto standard for leveraging scientific algorithms in Python, with over 600 unique code contributors, thousands of dependent packages, over 100,000 dependent repositories and millions of downloads per year. In this work, we provide an overview of the capabilities and development practices of SciPy 1.0 and highlight some recent technical developments

Distribution and origin of lead in stream sediments from small agricultural catchments draining Miocene molassic deposits (SW France)

International audienc

Physical and chemical weathering rates and CO2 consumption in a tropical lateritic environment : the upper Niger basin

The chemical composition of Niger river water measured bimonthly at Bamako (Mali) during the period 1990-1992 provides an estimate of present weathering rates in the upper Niger basin. The dominant weathering process is kaolinite formation ("monosiallitization"). However, seasonal variations promote gibbsite formation in the rainy season (September) and smectite development in the dry season (May). The results show that lateritic profiles continue to develop even during very dry episodes. The rate of profile development, calculated as the difference between the chemical weathering rate at the base of the soil profile and mechanical erosion rate at the soil surface, is about 1.3 to 3.7 m/Myr. A comparison between 43 river basins of the world shows that, for similar runoff, the CO2 flux consumed by silicate weathering is about two times lower in lateritic areas than in nonlateritic zones. (Résumé d'auteur

Origin, distribution, and behaviour of rare earth elements in river bed sediments from a carbonate semi-arid basin (Tafna River, Algeria)

International audienceThe behaviour and sources of rare earth elements (REE) in river sediments were investigated at ten stations and two dams of the Tafna basin (Northern Algeria) during contrasting hydrological conditions and using a combination of normalisation procedures, REE anomalies, various REE ratios, and multivariate statistical analysis. The ranking and REE concentrations were in the range of other carbonated areas. The classical fractionation of the heavy REE(HREE) erosion pattern, evidenced from upstream to downstream by the La/Yb or Sm/Yb ratios, was disturbed by the presence of dams, which retained the light REE (LREE) in particular. The hydrological conditions, particle size, and geochemical characteristics controlled the REE patterns. The LREE were associated with clay minerals and HREE with coarse silts, whereas carbonate and particulate organic carbon (POC) did not influence the transport downstream. The total concentration of REE in sediments was not strongly affected by anthropogenic inputs from various sources (industrial activities, and domestic or medical wastes). Indeed, some LREE enrichment and anomalies were detected at a few stations and locally for Gd, Tb, and Yb. However, the anthropogenic contribution can partially be hidden by dilution due to particle erosion. High flow increased the LREE and MREE enrichment and LREE/HREE fractionation in some places due to erosion processes and an-thropic influences (dam releases and local wastes inputs). Middle REE (MREE) and HREE were the most ex-tractable elements unlike LREE (which are the most concentrated), particularly during high water conditions. Finally, the REE demonstrated the impact of natural processes (hydrological, geochemical, and physical) and some anthropogenic disturbances (waste inputs, fertilisers, and dams). This might inspire to develop such investigations in other similar semi-arid basins undergoing various pressures. The use of local bedrock as a reference and a set of geochemical and statistical tools, is recommended