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Perga M.-E.,French National Institute for Agricultural Research | Desmet M.,National School of Public Works | Desmet M.,University of Tours | Enters D.,University of Bremen | And 2 more authors.
Limnology and Oceanography | Year: 2010

We reconstructed the changes in the planktonic food web of an oligotrophic subalpine lake over the past century, combining paleoecological methods and historical monitoring data. Analyses of organic matter δ 15N from sediment cores show that nutrient enrichment started in the 1910s and intensified from the 1930s. Subsequent changes in sediment organic carbon content and accumulation rates, carotenoid pigment concentrations, organic matter δ 13C, and cladoceran subfossil remains show that excess nutrient inputs triggered bottom-up-driven increases in lake primary production, as well as in Daphnia abundance. Daphnia size, however, started to decrease in the late 1930s, indicating an increasing size-selective predation from zooplanktivorous whitefish populations (Coregonus lavaretus) that had been fostered by stocking and increased food availability. Whitefish predation is likely to have indirectly facilitated the establishment of Bosmina longirostris. With decreasing nutrient concentrations, Daphnia abundance decreased, but their size declined, presumably due to an ongoing size-selective predation. At this same time, Bosmina abundance doubled as a likely result of released interspecific competition from smaller Daphnia. δ 15N analyses on subfossil cladoceran remains revealed that these changes in cladoceran community structure were accompanied by major changes in the food web. In spite of successful measures to reduce nutrient inputs from the late 1960s and reduced primary production, anoxia still occurs every summer at the lake bottom. These patterns are the consequence of a still relatively high export of phytoplankton-derived organic matter to the sediment as a result of strong top-down effects on the planktonic food chain. © 2010, by the American Society of Limnology and Oceanography, Inc.

Remki B.,University of La Rochelle | Remki B.,National School of Public Works | Abahri K.,University of La Rochelle | Tahlaiti M.,University of La Rochelle | Belarbi R.,University of La Rochelle
International Journal of Thermal Sciences | Year: 2012

The main objective of this work is to present the impact of atmospheric pressure gradient on the hygrothermal transfers in porous material. In this way, a mathematical model described by driving forces of temperature, moisture content and total pressure gradient has been addressed. The non-linear partial differential equations are defined through the balance equations of mass and energy development. After that, a numerical implementation focused on the wood drying behavior is treated for one dimensional Fourier boundary conditions. In order to evaluate the pressure sensitivity, temperature and moisture content profiles are presented and compared to the ones obtained by the classical models [15,16]. Results show that the atmospheric pressure gradient may cause significant influence on the hygrothermal behavior of the porous materials especially for wood process. A significant effect, up to 15%, on moisture content profile distribution is observed. © 2012 Elsevier Ltd. All rights reserved.

Oyebog S.A.,University of Buea | Ako A.A.,Hydrological Research Center Yaounde | Nkeng G.E.,National School of Public Works | Suh E.C.,University of Buea
Journal of Geochemical Exploration | Year: 2012

In this study, 8 bottled water brands sold in Cameroon were analyzed for 76 elements/parameters by ICP-MS, IC, titration and mass spectrometric methods. This was to investigate the geochemical characteristics of the bottled waters in order to identify the main hydro geochemical processes controlling their chemical content. A comparison of the element concentrations and the legal limits for both bottled and tap water (Cameroon, EU, US EPA, WHO) shows that Aluminium concentration in three brands is above the lower guideline value set by EPA with very high lead concentration (6.4μg/l) in one brand. Various water quality classification systems were used in to characterize the different bottled water types. Piper diagram was used to establish that dominant chemical types of the bottled water brands are Ca-HCO 3, Ca-Mg-HCO 3, Ca-Na-Mg-HCO 3, Na-HCO 3 and Na-Mg-HCO 3. Application of R-Mode factor analysis to the data set allowed the determination of the possible relationship between the distribution of individual elements and lithology or other surface enrichment phenomena. In particular waters draining through volcanic rocks are enriched in elements such as As, B, Br -, Cl -, Cs, F, K, Li, Na, NO 3 -, PO 4 3-, Rb, Sc, SiO 2, Sr, Te, Ti, and V. One of the three R-Mode factor analysis associations, recognized as being representative of elements analyzed shows high nitrate and Pb loadings along with As, PO 4 3- and Zn. The latter association probably reflects a sign of anthropogenic contribution in the volcano-sedimentary aquifers of the study area. Q-Mode hierarchical cluster analysis established four major groups amongst the bottled water brands. Stable water isotopes (δD and δO 18) established that the recharge origin of the bottled waters and other groundwaters of the study area is meteoric. © 2011 Elsevier B.V.

Gress J.C.,National School of Public Works
5th Asia-Pacific Conference on Unsaturated Soils 2012 | Year: 2012

Using the simple filter paper test, controlling at the same time the variation of void index, we have a good assessment of the law of the variation of void index with suction or of the swelling pressure, if displacement is not possible. We also show how this test allows knowing of in situ variation of soil stiffness, with moisture content.

Belabdelouahab F.,National School of Public Works | Trouzine H.,University Djilali Liabes
Physics Procedia | Year: 2014

Currently engineers seeking to improve the characteristics of soils used for the construction of earthworks, with innovations developed from ideas, products or processes of original construction, the land army is an early example particularly successful but there are many other processes as well as other Pneusol processes more or less known to sometimes use bulky industrial wastes, while fitting well into the existing environment. In this paper, we discuss a particular research work within the framework of environmental protection and sustainable development, led to the realization of the recovery and reuse of used tires in the construction of works civil engineering. The main objective of this paper is to present the results of studies in Algiers on ENSTP " Pneusol reducing the thrust" on a scale model on the study of a retaining wall reinforced by a simulation tablecloths tires, and the results of particular research enterprise at the University Djillali Liabes of Sidi Bel Abbes, on an experimental campaign on the Pneusol under expansive soil foundations. Topics will also present the projects carried out in Algeria, as the pilot of stability of a slope to Pneusol in Bousmail (2005), then another item of protection against landslides in Bejaia (2006), from the project of Africa in Mostaganem (2007), concerning the stability of an embankment on the RN11 road, and the conduct of a small dike protection technology Pneusol in Blida (2008), and in 2010 the stability of a landslide in Miliana. © 2014 Elsevier B.V.

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