Impacts de l’utilisation des eaux polluées en agriculture urbaine sur la qualité de la nappe de Dakar (Sénégal)

L’agriculture urbaine de la région de Dakar est un secteur en plein essor. À cause de la salinisation progressive des eaux de la nappe peu profonde (eaux de Céanes ), des eaux usées brutes sont utilisées pour irriguer les champs. L’objectif de notre étude est d’évaluer la qualité chimique et microbiologique des eaux de la nappe sous-jacentes aux champs irrigués et d’identifier les sources de pollution. Notre travail a été effectué dans les sites de Pikine et de Patte d’Oie.L’analyse de la qualité chimique des eaux d’arrosage a montré qu’à Pikine, la conductivité des eaux de Céanes est plus élevée (4822±2411 µS cm-1) par rapport à celle des eaux usées (3579±1242 µS cm-1 ; p<0.04). Par contre à Patte d’Oie, les eaux d’arrosage sont moins salées (<3000 µS cm-1). La quantité d’azote total de tous les types d’eaux d’arrosage est supérieure à la valeur guide de l’OMS (5-30 mg l-1).Salmonella spp. a été isolée dans 35 % des eaux d’arrosage. Un échantillon d’eaux usées a été positif pour Vibrio cholerae.L’impact des eaux d’irrigation sur la qualité chimique et microbiologique de la nappe d’eau souterraine est fortement influencé par la pluviométrie et est différent selon le site considéré.Ce travail a montré que l’irrigation avec les eaux polluées et l’usage de fumiers organiques peut altérer la qualité de la nappe et constituer des risques pour la santé.In Dakar capital city of Senegal, the urban agriculture is in high expansion. Since the progressive increase of salinity in the local groundwater (Céanes water), raw wastewater is used to water the crops. The objective of this study is to assess chemical and microbiological quality of the groundwater underlying the irrigated plots and to identify the sources of pollution. This work was carried out in the sites of Pikine and Patte d’Oie in Dakar Senegal.Chemical analysis of irrigation water showed that in Pikine, the conductivity of Céanes water was higher (4822±2411 µS cm-1) than those of the wastewater (3579±1242 µS cm-1 ; p<0.04), while at Patte d’Oie it was less salted (<3000 µS cm-1). The quantity of total nitrogen of irrigation water in both sites was higher than the WHO’s threshold (5-30 mg l-1).Salmonella spp. was isolated in 35 % of the irrigation water. One wastewater sample was Vibrio cholerae positive.The impact of irrigation water on the chemical and microbiological quality of the groundwater is strongly influenced by precipitations and is different according to the site considered.This work showed that the use of polluted water and organic manures can spoil the quality of the groundwater and constitute a health threat.Urban agricultur

Tectonics of the Lepontine Alps: ductile thrusting and folding in the deepest tectonic levels of the Central Alps

The Lepontine dome represents a unique region in the arc of the Central and Western Alps, where complex fold structures of upper amphibolite facies grade of the deepest stage of the orogenic belt are exposed in a tectonic half-window. The NW-verging Mont Blanc, Aar und Gotthard basement folds and the Lower Penninic gneiss nappes of the Central Alps were formed by ductile detachment of the upper European crust during its Late Eocene-Early Oligocene SE-directed underthrust below the upper Penninic and Austroalpine thrusts and the Adriatic plate. Four underthrust zones are distinguished in the NW-verging stack of Alpine fold nappes and thrusts: the Canavese, Piemont, Valais and Adula zones. Up to three schistosities S1-S3, folds F1-F3 and a stretching lineation XI with top-to-NW shear indicators were developed in the F1-F3 fold nappes. Spectacular F4 transverse folds, the SW-verging Verzasca, Maggia, Ziccher, Alpe Bosa and Wandfluhhorn anticlines and synclines overprint the Alpine nappe stack. Their formation under amphibolite facies grade was related to late ductile folding of the southern nappe roots during dextral displacement of the Adriatic indenter. The transverse folding F4 was followed since 30Ma by the pull-apart exhumation and erosion of the Lepontine dome. This occurred coevally with the formation of the dextral ductile Simplon shear zone, the S-verging backfolding F5 and the formation of the southern steep belt. Exhumation continued after 18Ma with movement on the brittle Rhone-Simplon detachment, accompanied by the N-, NW- and W-directed Helvetic and Dauphiné thrusts. The dextral shear is dated by the 29-25Ma crustal-derived aplite and pegmatite intrusions in the southern steep belt. The cooling by uplift and erosion of the Tertiary migmatites of the Bellinzona region occurred between 22 and 18Ma followed by the exhumation of the Toce dome on the brittle Rhone-Simplon fault since 18M

The recording of floods and earthquakes in Lake Chichój, Guatemala during the twentieth century

Laguna Chichój (Lake Chichój) is the only deep permanent lake in the central highlands of Guatemala. The lake is located in the boundary zone between the North American and Caribbean plates. The lake has been struck by devastating earthquakes and tropical cyclones in historical times. We investigated the imprint of twentieth century extreme events on the sedimentary record of this tropical lake using a bathymetric survey of the lake, coring the lake floor, and providing a chronology of sediment accumulation. The lake occupies a series of circular depressions likely formed by the rapid dissolution of a buried body of gypsum. 210Pb and 137Cs inventories and varve counting indicate high rates of sedimentation (1-2cmyear−1). The annually layered sediment is interrupted by turbidites of two types: a darker-colored turbidite, enriched in lake-derived biogenic constituents, and interpreted as a seismite, and a lighter-colored type, enriched in catchment-derived constituents, interpreted as a flood layer. Comparison of our 137Cs-determined layer ages with a catalog of twentieth century earthquakes shows that an earthquake on the Motagua fault in 1976 generated a conspicuous darker-colored turbidite and slumped deposits in separate parts of the lake. The entire earthquake inventory further reveals that mass movements in the lake are triggered at Modified Mercalli Intensities higher than V. Tropical cyclonic depressions known to have affected the lake area had limited effect on the lake, including Hurricane Mitch in 1998. One storm however produced a significantly thicker flood layer in the 1940s. This storm is reportedly the only event to have generated widespread slope failures in the lake catchment. It is thus inferred that abundant landsliding provided large amounts of concentrated sediment to the lake, through hyperpycnal flows

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Die ältesten Giltsteinöfen des Wallis - Recherchen zu einer Innovation im Spätmittelalter und in der frühen Neuzeit

Stubenöfen aus Gilt-oder Speckstein sind in den Regionen rund um den Gotthard verbreitet und im Wallis, seit dem 16. Jahrhundet fassbar. Sie werden in zahlreichen kulturhistorischen und ethnografischen Inventaren und Studien beschreiben und haben eine regionaltypische, emblematische Bedeutung. Dabei erhob sich immer wieder die Frage, wann genau diese Oefen, die einen markanten Fortschritt des Wohnens ermöglichten (rauchfreier Wohnraum), in unseren Breitengraden "erfunden" worden seien. In dieser Studie werden gut 25 frühe, gut erhaltene Giltsteinöfen im Detail dokumentiert und mit scheinbar früheren aus andern Gesteinen gemauerten Oefen aus dem Wallis, Uri, Tessin etc. verglichen. Das älteste erhaltene Exemplar ist zweistöckig rund und trägt die Jahrezahl 1497 und stammt aus der Gegend von Sion. In dieser Zeit scheint man von den horizontal aus kleinern variablen Feldsteinen gemauerten Oefen zu den typisch neuzeitlichen Gilsteinöfen aus grossen, mit Eisenklammern zusammengehaltenen Giltsteinplatten übergegangen zu sein, die aus zahlreichen regionalen Steinbrüchen stammten