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Lesparre N.,Montpellier University | Lesparre N.,University of Liège | Boudin F.,CNRS ENS Geology Laboratory | Champollion C.,Montpellier University | And 7 more authors.
Geophysical Journal International | Year: 2017

Tilt fluctuations can potentially reflect the response of hydrosystems to important rainfall. In this context, long baseline tiltmeters have been installed in an underground tunnel penetrating the Fontaine de Vaucluse karst to study themedium deformation related to solicitations exerted by water infiltrating the hydrosystem. The instruments monitor the tilt as well as its spatial variation. Northward tilts reaching a 1 μrad amplitude are observed consecutively to rainfalls. The tilt amplitude is highly correlated with the Fontaine de Vaucluse outlet flow fluctuations. The measured tilt signal is also relatively homogeneous over a 150 m length. Different types of structure likely to produce such observations are tested in order to identify their location with respect to the tiltmeters, their dimension as well as the amount of water level variation in the structure. Following rainfalls, the infiltration of water modifies the pore pressure, inducing a medium deformation. The hypothesis of a homogeneous surface loading on the Vaucluse plateau is first refuted since the related tilt is much lower than the one measured. The water supplied by rainfalls has to accumulate in discontinuities in order to generate a higher tilt. So, the deformation related to a pressure exerted on a fracture filled by water is assessed. A first study reveals the interest of the tilt homogeneity information that constrains strongly the fracture properties. Thus, the fracture must be located at a distance more than a few hundred metres from the tiltmeters in order to produce a tilt homogeneous in space. If the fracture is initially dry, it must also be filled on a height higher than 150 m consecutive to a rainfall in order to generate a tilt amplitude in the same magnitude as the one measured. Then, we explore the influence of water level variations on the tilt produced by a fracture located at the interface between the saturated and unsaturated zones, which are thereby permanently flooded. Since several parameters of that model satisfactorily explain the field observations, we discuss how simultaneous geodetical observations could provide complementary information that would further constrain the geometry of the structure at the origin of the medium deformation. © The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Bottinelli N.,CAS Nanjing Institute of Soil Science | Bottinelli N.,IRD Montpellier | Zhou H.,CAS Nanjing Institute of Soil Science | Capowiez Y.,UAPV | And 5 more authors.
Biology and Fertility of Soils | Year: 2017

The aim of this study was to investigate the burrowing activity of two earthworm species: the endogeic Drawida sinica and one undescribed Amynthas species incubated in Vertisol and Ultisol presenting different soil organic C content. Because of their contrasting feeding behaviours, we hypothesised that soil type would have a bigger influence on the burrowing activity of the endogeic than the anecic species. Repacked soil columns inoculated with earthworms for 30 days were scanned using X-ray tomography and the compiled images used to characterise the burrow systems. After scanning, the saturated hydraulic conductivity (Ksat) was also measured. The Amynthas species burrows were less numerous (30 vs. 180), more vertically oriented (57 vs. 37°), more connected from the surface to the bottom of the columns (73 vs. 5 cm3) and had a higher global connectivity index (83 vs. 28%) than those of D. sinica. The Ksat was threefold faster in columns incubated with Amynthas and was linked to the volume of percolating burrows (R2 = 0.81). The soil type did not influence Amynthas burrow characteristics. In contrast, there were 30% more D. sinica burrows in the Vertisol than in the Ultisol while other burrow characteristics were not affected. This result suggests that these burrows were more refilled with casts leading to shorter and discontinuous burrows. The Ksat was negatively related to the number of burrows (R2 = 0.44) but was not statistically different between the Vertisol and the Ultisol, suggesting a constant impact of this species on the Ksat. We found that a decrease in the amount of soil organic C by 50% had only a small influence on earthworm burrowing activity and no effect on the Ksat. © 2017 Springer-Verlag GmbH Germany

Baudron P.,Fundacion Instituto Euromediterraneo del Agua | Baudron P.,CIRAD - Agricultural Research for Development | Barbecot F.,GEOTOP UQAM | Barbecot F.,University Paris - Sud | And 6 more authors.
Hydrological Processes | Year: 2014

The development of intense agriculture in semiarid areas modifies intensity and spatial distribution of groundwater recharge by summing irrigation return flow to limited rainfall infiltration. Environmental tracers provide key information, but their interpretation is complicated by more complex groundwater flow patterns. In multilayered aquifers, the real origin of the groundwater samples is hard to assess because of local mixing processes occurring inside long-screened boreholes. We use environmental tracers (14C, 13C, 2H, 18O, 3H) to investigate the long-term evolution of recharge in the five-layer Campo de Cartagena aquifer in South-Eastern Spain, in addition to high-resolution temperature loggings to identify the depth of origin of groundwater. Despite the complex background, this methodology allowed a reliable interpretation of the geochemistry and provided a better understanding of the groundwater flow patterns. The tritium method did not give good quantitative results because of the high variability of the recharge signal but remained an excellent indicator of recent recharge. Nonetheless, both pre-anthropization and post-anthropization recharge regime could be identified and quantified by radiocarbon. Before the development of agriculture, recharge varied from 17mm. year-1 at the mountain ranges to 6mm. year-1 in the plain, whereas the mean annual rainfall is about 300mm. In response to the increase of agricultural activity, recharge fluxes to the plain were amplified and nowadays reach up to 210mm. year-1 in irrigated areas. These values are strengthened by global water budget and local unsaturated zone studies. © 2013 John Wiley & Sons, Ltd.

Carriere S.,UAPV | Chalikakis K.,UAPV | Danquigny C.,UAPV | Senechal G.,MIG Pau | Chapelet A.,French National Institute for Agricultural Research
Near Surface Geoscience 2012 | Year: 2012

The structure of karst hydrosystems is complex and the related hydrodynamic functioning mechanism can be highly heterogeneous in both unsaturated and saturated zones. The Low-Noise Underground Laboratory of Rustrel (LSBB) is located in unsaturated zone (UZ) of Fontaine de Vaucluse (FdV) karst hydrosystem. In this way, the LSBB is a unique place to apply surface-based geophysical surveys due to numerous and various geological and hydrogeological knowledge under the investigated zone. We exhibit in this paper complementarity and efficiency of Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR). Both GPR and ERT are well suited for the first phase of our study, in order to characterize the general structure of the investigated chosen zone. GPR results highlight the tectonic features which are also, but less accurately, seen by ERT apparent resistivity maps. ERT 2D inverted results have shown the presence of moderate resistivity zones within the limestone. The provided information allowed carrying out following step of our study to enhance understanding of local karst UZ e.i. apply Magnetic Resonance Sounding (MRS), Gravimetry and Low Frequency Electromagnetics (LF-EM).

Jourde H.,Montpellier University | Mazzilli N.,UAPV | Mazzilli N.,French National Institute for Agricultural Research | Lecoq N.,University of Rouen | And 2 more authors.
Environmental Earth Sciences | Year: 2015

On the basis of the characterization of the different karst subsystems (Soil/Epikarst—Unsaturated Zone—Saturated Zone) and mathematical models developed on specific sites, we propose an adjustable modeling platform of karst for both the simulation of spring discharge at outlets and the analysis of the hydrodynamics of the compartments considered in the model. This platform was developed within the framework of the KARST observatory network initiative from the INSU/CNRS, which aims to strengthen knowledge-sharing and promote cross-disciplinary research on karst systems at the national scale. © Springer-Verlag Berlin Heidelberg 2015.

Capowiez Y.,French National Institute for Agricultural Research | Bottinelli N.,IRD Montpellier | Sammartino S.,UAPV | Michel E.,French National Institute for Agricultural Research | And 2 more authors.
Biology and Fertility of Soils | Year: 2015

Earthworm burrow systems are generally described based on postulated behaviours associated with the three ecological types. In this study, we used X-ray tomography to obtain 3D information on the burrowing behaviour of six very common anecic (Aporrectodea nocturna and Lumbricus terrestris) and endogeic (Aporrectodea rosea, Allolobophora chlorotica, Aporrectodea caliginosa, Aporrectodea icterica) earthworm species, introduced into repacked soil cores for 6 weeks. A simple water infiltration test, the Beerkan method, was also used to assess some functional properties of these burrow systems. Endogeic worms make larger burrow systems, which are more highly branched, less continuous and of smaller diameter, than those of anecic worms. Among the anecic species, L. terrestris burrow systems are shorter (9.2 vs 21.2 m) with a higher number (14.5 vs 23.5) of less branched burrows (12.2 vs 20.2 branches m−1), which are also wider (7.78 vs 5.16 mm) than those of A. nocturna. In comparison, the burrow systems made by endogeic species appeared similar to each other. However, A. rosea burrows were short and narrow, whereas A. icterica had a longer burrow system (15.7 m), more intense bioturbation intensity (refilled macropores or soil lateral compaction around them) and thus a greater number of burrows. Regarding water infiltration, anecic burrow systems were far more efficient due to open burrows linking the top and bottom of the cores. For endogeic species, we observed a linear relationship between burrow length and the water infiltration rate (R2 = 0.49, p < 0.01). Overall, the three main characteristics significantly influencing water infiltration were burrow length, burrow number and bioturbation volume. This last characteristic highlighted the effect of burrow refilling by casts. © 2015, Springer-Verlag Berlin Heidelberg.

Potot C.,University of Nice Sophia Antipolis | Feraud G.,University of Nice Sophia Antipolis | Scharer U.,University of Nice Sophia Antipolis | Barats A.,University of Nice Sophia Antipolis | And 6 more authors.
Journal of Hydrology | Year: 2012

Dissolved trace and major elements, organic carbon and Pb-Sr-O isotopes have been investigated in surface and groundwater of the Var River Valley (SE France), including alluvial, conglomerate and limestone aquifers, as well as surface water. Boxplots and cumulative frequency distribution diagrams define chemical characteristics of each water group and distinguish between natural and anthropogenic range of concentrations.Low concentration of trace elements, statistical analysis of data and Pb isotopic ratios demonstrate that the measured baseline quality is close to the natural background, mainly influenced by water/rock interaction. Pb and Sr isotopes evidence specific primitive end members, buffering these two elements through leaching late Paleozoic rocks, strongly depleted in U and Rb since their formation. Arsenic undergoes geochemical processes such as sorption on clay minerals of the alluvial deposits. Sr isotopic ratios and high SO42-, Sr and Li contents show that Permo-Triassic sediments including evaporites strongly imprint surface waters and alluvial groundwaters. Limestone and conglomerate aquifers are mainly influenced by carbonate minerals, but may be locally affected by evaporite dissolution. High dissolved silica is also specific to conglomerate groundwaters. Limestone and conglomerate groundwaters are characterised by low and heterogeneous trace element compositions that may result from various residence times and rock compositions related to different sampling depth.Even if water quality is generally good for most of the investigated elements, pollution by agricultural activity (fertilisers and pesticides) in the alluvial and some limestone groundwaters has been demonstrated by high NO3- and Br - contents. Br - is suspected to originate from methyl bromide fertiliser. In conglomerate aquifers, NO3- contents may reach high levels, probably due to both agriculture and residential waste pollution. Despite the industrialization in the Low Var Valley, no significant metallic contamination could be detected and therefore, for trace elements, given parameters (min, max and median values) can be used as a baseline guide to detect future contamination. © 2012 Elsevier B.V..

Henry S.,University of Oxford | Pozzo Di Borgo E.,UAPV | Cavaillou A.,French National Institute for Agricultural Research | Cavaillou A.,French National Center for Scientific Research
Review of Scientific Instruments | Year: 2013

SQUIDs can be used to monitor the three vector components of the geomagnetic field to a high precision at very low frequencies, yet as they are susceptible to external interference, the accuracy to which they can track changes in the dc field over long periods has been unclear. We have carried out simultaneous measurements of the geomagnetic field recorded using two independent 3-axis SQUID magnetometers at the Laboratoire Souterrain à Bas Bruit (LSBB). We demonstrate a technique to take the difference between a linear transform of the three signals from one magnetometer, and a reference signal from the other, in order to account for any difference in alignment and calibration, and track local signals at a sub-nT level. We confirmed that both systems tracked the same signal with an RMS difference as low as 56pT over a period of 72 h. To our knowledge this is the first such demonstration of the long term accuracy of SQUID magnetometers for monitoring geomagnetic fields. © 2013 American Institute of Physics.

Capowiez Y.,French National Institute for Agricultural Research | Dittbrenner N.,French National Institute for Agricultural Research | Dittbrenner N.,University of Tübingen | Rault M.,UAPV | And 3 more authors.
Environmental Pollution | Year: 2010

There is currently a lack of ecotoxicity tests adapted to earthworm species of higher ecological relevance and whose endpoints could be directly related to their ecological role in the soil. We propose a new and relatively simple ecotoxicity test based on the estimation of cast production (CP) by Lumbricus terrestris under laboratory conditions. CP was found to be linearly correlated to earthworm biomass and to be greatly influenced by soil water content. Azinphos-methyl had no effect on CP at all the concentrations tested. Significant decreases were observed at the normal application rate for other pesticides with (imidacloprid, carbaryl, methomyl) or without (ethyl-parathion and chlorpyrifos-ethyl) a clear concentration-effect response. For the highest concentration tested, reduction in CP varied between 35 and 67%. CP is straightforward and rapidly measured and ecologically meaningful. We thus believe it to be of great use as an endpoint in ecotoxicity testing. © 2009 Elsevier Ltd. All rights reserved.

Carriere S.D.,UAPV | Chalikakis K.,UAPV | Senechal G.,UPPA FR 2952 IPRA | Danquigny C.,UAPV | Emblanch C.,UAPV
Journal of Applied Geophysics | Year: 2013

This paper highlights the efficiency and complementarity of a light package of geophysical techniques to study the structure of karst Unsaturated Zone (UZ) in typical Mediterranean environment where soil cover is thin or absent. Both selected techniques, 2D Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT), are widely used in environmental studies and their application is accessible for a lot of scientists/engineers. However, GPR or ERT alone is not able to provide an enhanced characterization of geological features in karst media. In the present study, GPR results supply a near surface high resolution imaging and thus can provide relevant geological information such as stratifications and fractures. Despite the quality of the results GPR's investigation depth remains limited to around 12. m. Apparent and inverted resistivity provided by ERT surveys shows strong lateral and vertical variations. These variations can inform about general geological structuring and feature orientation. ERT is able to prospect down to 40. m but it's a low resolution integrative technique. In the study area the investigated limestone is a commonly electrical resistive formation (more than 2000 Ω.m). However deeper than 5-7. m, the ERT profiles reveal several zones of moderate resistivity (around 900. Ω.m). In these zones a stratification change corresponding to slanted bedding is clearly identified by GPR results. The combination of both GPR and ERT results can allow a well-established geological interpretation. These moderate resistivity zones with slanted beddings can explain the presence of a perennial water flow point 35. m below the surface of the studied site within the underground gallery of the Low-Noise Underground Laboratory (LSBB). © 2013 Elsevier B.V.

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