Sediment | EPFL Graph Search

Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation; if buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification. Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments. Classification Sediment can be classified based on its grain size, grain shape, and co

Study of the microbial communities of core and water samples in a chloroethenes contaminated aquifer

Guillaume Laulan

Widely used in industrial activities, chloroethenes have become common groundwater contaminants. Dehalorespiration is an anaerobic bacterial respiration coupling their sequential degradation to energy production. The interactions between the dehalorespiring bacteria and the other guilds and environmental variables are presumed to influence the dehalorespiration efficiency. Here, water and core samples were extracted from the PCE-contaminated site of Lyss (BE, Switzerland). Bacterial DNA was extracted and the 16S rRNA gene amplified by PCR. Terminal restriction fragment length polymorphism (T-RFLP) was used to assess the diversity of the bacterial communities. Core and groundwater environmental variables were analyzed as well. The T-RFLP profiles and the environmental data obtained were processed using statistical multivariate analysis. Within a period of two months, the bacterial communities remained relatively specific to their respective sampling origins. Communities from the oxic layer shared a similar set of bacterial species whereas piezometers from the anoxic layer had a specific one. The T-RFLP profiles obtained from single depth and multi-level piezometers were clearly distinct, probably due to differences in the pumping flow rates and their associated transport regimes, which can have an impact on i) the sediments extracted from the aquifer, ii) the hydraulic zone reached and iii) a potential selective bacterial adsorption onto the pumping tube wall. Environmental factors related to the groundwater redox state appeared as the major variables influencing the bacterial populations. Bacterial communities from core samples clustered into two distinct sets: i) samples from the strongly reductive silt layer, and ii) samples from the coarser and less reductive layer. Grain size distribution and redox state both had a major influence on the bacterial communities of core samples. Finally, it was shown that microbial populations extracted from groundwater differed from the ones extracted from core material, and thus were not representative of the overall aquifer microbial diversity.

2009

The sediment-contact test using the ostracod Heterocypris incongruens: Effect of fine sediments and determination of toxicity thresholds

Rebecca Bebon

The toxicity test using freshwater ostracods of the species Heterocypris incongruens is a sub-chronic static test that exposes individuals to whole sediments over a period of 6 d, the endpoints being mortality and growth. We tested the hypothesis that endpoints of the sediment bioassay using Heterocypris incongruens are affected by the presence of fine sediment particles by testing control sediment supplied with the commercial test kit with increasing proportions of kaolin clay as a proxy for fines. While mortality was not affected, the results showed that increasing the presence of clay reduced ostracod growth. Based on the variability in growth, a sublethal toxicity threshold of 35% is proposed to distinguish effects due to sediment properties from those due to toxicity. The relevance of this threshold was verified using data from toxicity tests of ambient sediment samples with low levels of contamination. (C) 2016 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2016

Fonctionnement et gestion des aquifères alluviaux de haute altitude

The Haute Sarine alpine valley is located at an average altitude of approximately 1'000 to 1'200 masl. It was formed in its southern part up to the area of Gstaad to the favour of a typical North-South tectonic fault according to the main structures of the Préalpes, then followed normal fault striking East-West to end up on the rock bolt of the Vanel hill. The late and postglacial period was marked by the deposition of glaciolacustrines, glaciofluviatile and flurecent fluviatile sediments which have filled the ice free valley bottom probably starting from a period older than the Bölling-Alleröd interstadial. The depth of this overdeepening varies between 20 and more than 50 m of depth. Drillings which we carried out could document series of typical glaciolacustrine sediments. The implementation of several geophysical survey methods (resistivity, seismic refraction and reflexion, well logs and pumping tests) enabled us to analyse several sources of information which we confronted between them in order to produce a 3D model of the quaternary deposits and their hydrological properties. Most of these sediments are relatively quite permeable and build a free groundwater reservoir that we subdivided into 3 parts. The basin of Gsteig in the south is closed, the valley having been blocked by a massive landslide that probably occurred in several successive stages starting at the first climate improvements. The second part, the basin of Feutersoey has not been retained as a potential important hydrogeologic resource based on our preliminary investigations. The last basin, that of Gstaad-Saanen is the largest and thickest. It is also in this basin that most of the tourist and industrial activities of the area are concentrated. The observation network was established in order to characterize the groundwater flows enabling us at the same time to carry out piezometric measurements and chemical as well as and bacteriological analyses. We also carried out a δ18O isotope analysis campaign. The whole of these approaches highlighted the particular characteristics of the groundwater recharge. The groundwater system is mainly fed by the Sarine and the precipitations infiltration. We also located an underground karstic feeding of evaporitic type. We finally propose a groundwater management and protection concept adapted to the particular situation of the Sarine alluvial mountain aquifer system on both quantitative and qualitative aspects. The high altitude alpine groundwater catchment areas such as the Haute Sarine represent as a whole a quality resource, with high potentials yet to be defined on a larger scale, for example by applying numerical modeling and by organizing and maintaining long term observation networks that will enable us to define a sustainable groundwater resource management within the alpine area.

EPFL2000

Study of the microbial communities of core and water samples in a chloroethenes contaminated aquifer

Guillaume Laulan

2009

Fonctionnement et gestion des aquifères alluviaux de haute altitude

EPFL2000