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On the edge of sedimentary basins, karst aquifers can be fed by several water sources from both autogenic and allogenic recharge. In some cases, assessing water origins can be hard and cause some difficulties for water resource management. The main goal of this study is to show the implementation of the mobile sources mixing model approach. More precisely, this research develops how a monitoring method using a multi-proxy approach can be used to quantify waters sources contributions from several origins at the outlets of a karst system. The study site is the Ouysse karst system, located in western France. The site offers the opportunity to understand the mixing processes between allogenic and autogenic water recharges. The karst system covers a 650 km² watershed, and is fed by three different chemical facies: (i) Autogenic water from the direct infiltration on the karstified limestones with high HCO3− values (median: 436 mg.L−1); (ii) Water coming from sinking rivers fed by spring coming from igneous rocks with low mineralization but relatively higher K+ values (median: 4.2 mg.L−1); (iii) Highly mineralized water coming from deep evaporitic layers and feeding another sinking river with very high sulfate concentrations (median: 400 mg.L−1). Sliding window cross-correlation analyses and hydrochemical analyses during a flood event are performed to implement a mobile source mixing model approach. This approach shows significant differences with a simple fixed source mixing model and appears more reliable but requires more time and money to carry out. The results and conclusion of this study will be used for forecasting and managing operational actions for resource management.

International audience; The objective of this work was to explore centrifugal ultrafiltration (UF) to separate and / or preconcentrate natural colloidal particles for their characterization. A soil suspension obtained by batch leaching was used as a laboratory reference sample. It was preconcentrated with concentration factors (CF) varying from 10 to 450. The dimensional analysis of the colloidal phase was carried out by Asymmetric Flow Field-Flow Fractionation (AF4)-multidetection. The colloidal masses were estimated by mass balance of the initial suspension, its concentrates and filtrates. The size-dependent distribution (expressed in gyration radius) and total colloidal mass (especially recovery), as well as chemical composition and concentration (including species partitioning between dissolved and colloidal phases) were determined to assess the effects of UF preconcentration on colloidal particles. The gyration radius of the colloidal particles recovered in these concentrated suspensions ranged from about 20 nm to over 150 nm. Neither de-agglomeration nor agglomeration was observed. However, only (64 ± 4) % (CF = 10) of the colloidal particles initially in the soil suspension were found in the recovered concentrated suspensions, and this percentage decreased as CF increased. The filter membrane trapped all other particles, mainly the larger ones. Whatever the CF, the centrifugal UF did not appear to change the dissolved-colloidal partitioning of certain species (Al, organic carbon); whereas it led to an enrichment of the colloidal phase for others (Fe, U). The enrichment rate was specific to each species (15% for Fe; 100% for U). By fitting the observed trends (i.e. conservation, depletion or enrichment of the colloidal phase in the concentrate) as a function of CF, the colloidal concentrations (total and species) were assessed without bias. This methodology offers a new perspective for determining physicochemical speciation in natural waters, with a methodology applicable for environmental survey or site remediation studies.

International audience; On the edge of sedimentary basins, karst aquifers can be fed by several water origins from both autogenic and allogenic recharge. In some cases, water origin assessment is difficult and issues in water management may arise. The main goal of this study is to understand what controls hydrodynamical and geochemical variations at the outflow of a quite complex and large karst system. More precisely, this study illustrates how a consistent observational setup can be developed, based on a multi-proxy approach that can be used for tracing water origins, evaluating mixing phenomena, and contributions in karst aquifers considering both autogenic and allogenic recharge. The Ouysse karst system (650 km2), located in western France, provides the opportunity of studying water-mixing processes in binary karst systems fed by allogenic and autogenic recharges. Global water chemistry, hydrograph and chemograph analysis during a flood event, and source-mixing calculation were used to evaluate groundwater-flow origins and the contribution of each water type during the studied flood event: (i) karstic water; (ii) evaporite water; (iii) water from igneous-metamorphic rock aquifers. In terms of resource management, the information obtained can be used as a basis of forecasting and management actions.

International audience; Three methods of membrane separation by dead-end, tangential, and centrifugal ultrafiltration (UF) were considered in order to understand the physicochemical phenomena occurring during the preconcentration of the colloidal phase of soil water. The analytical approach used involved dynamic light scattering (DLS), transmission electron microscopy (TEM), determination of total organic carbon (TOC-metry) and mass spectrometry (ICP-MS). The mass amounts of the major components of the colloidal phase, i.e. Al, Fe and total organic carbon (TOC), as well as the mass amount of uranium considered as a trace element of environmental interest, were determined, both in soil water, and in the concentrates (i.e. retentates) and filtrates of this water obtained by the 3 methods tested. Dead-end ultrafiltration led to an enlargement of the size distribution towards larger sizes because of agglomeration/aggregation phenomena. This method also generated enrichment of concentrates, in particular in organic matter. The consequence was that large structures were observed coating or embedding the particles initially present individually dispersed in the test sample. The mass amounts of elements and TOC increased more importantly than expected, which confirmed the enrichment of the concentrates from the dissolved phase probably by sorption on colloidal objects. To a lesser extent similar effects were observed after tangential ultrafiltration. Such phenomena were not observed after centrifugal ultrafiltration. From a practical point of view, both tangential and centrifugal ultrafiltration proved to be both the most practical and the best suited for the preconcentration of soil water sample. Finally, centrifugal ultrafiltration has proved to be the best compromise given the preservation of colloidal particles and method practicality.

International audience; Spatial Variation in the Molecular Composition of Dissolved OrganicMatter from the Podzol Soils of a Temperate Pine ForestEmmanuelle Maria,†Pierre Crançon,‡Gaëtane Lespes,†and Maxime C. Bridoux*,‡†Universitéde Pau et des Pays de l’Adour (UPPA)/CNRS, Laboratoire de Chimie Analytique Bio-Inorganique et Environnement,UMR IPREM 5254, Technopôle Hélioparc, Av. du Président Angot, 64000 PAU, France‡CEA, DAM, DIF, F-91297 Arpajon, France*SSupporting InformationABSTRACT:In podzols, the production and mobilization ofdissolved organic matter (DOM) account for a considerableloss of carbon from the forestfloor. The dynamics of DOM inthe podzol soils of a pine forest result from complexinteractions between water infiltrations, weathering, biologicaltransformation, and retention-mobilization mechanisms. How-ever, little is known about how the molecular composition ofDOM changes spatially in the podzol soil as it moves from theupper horizons (organic (O) and eluvial (E)) to the illuvialhorizon (B(h/s)) to the groundwater. In this study, DOMsamples were collected in the upper (A1) and accumulation(Bh) horizons of a sandy permeable podzol with a hydrologyoccurring exclusively through drainage of shallow water (no surface runoff), as well as from the groundwater. Samples wereconcentrated on a Strata-X-AW solid-phase extraction cartridge and directly infused using electrospray ionization in the negativemode coupled with an LTQ-Orbitrap mass spectrometer. Over 2300 monoisotopic molecular formulas of CHO and CHONwith molecular weights up to 600 Da, assigned mainly to lignin-like compounds (53%), tannins (22%), condensed aromatics(14%), protein-like compounds, lipids (3%), aminosugars/carbohydrates (1%), and unsaturated hydrocarbons, were identifiedin DOM from the upper podzol horizon (A1), indicating that leaching of plant debris dominates the DOM pool released in thesoil seepage waters. Among all molecular formulas detected, 31% were unique to A1, while only 6.9% were only detected in Bhand 12.9% in Gw. Van Krevelen diagrams of these unique formulas clearly highlighted an evolution of the OM molecularcomposition along the podzol soil profile, from the upper horizon, through the accumulation horizon, to the groundwater with ashift from the high-oxygen, plant-derived compounds (tannins-like and lignin-like) to the low-oxygen classes (unsaturated andcondensed hydrocarbon), suggesting a reduction process either microbially mediated or via preferential adsorption of oxygen-functionalized DOM compounds to mineral surfaces

International audience; An analytical methodology was developed to characterize the colloidal distribution of trace elements of interest in environmental waters sampled in a same site and enables the different colloidal distributions from waters to be compared. The purpose was to provide consistent information related to the origin and nature of colloids responsible for the transport of trace element(s). The work was motivated by the observed enhanced mobility of uranium in soil. The colloidal size continuum was investigated by a multi-technique approach involving asymmetric flow field-flow fractionation (AF4) coupled with ultraviolet spectroscopy (UV), multi angle light scattering (MALS), and atomic mass spectrometry (ICPMS). To take into consideration the size and shape variability specific to each sample, the size distributions were established from the gyration radii measured from MALS, also considering the size information from standard nanospheres fractionated by AF4. A new parameter called “shape index” was proposed. It expresses the difference in hydrodynamic behavior between analytes and spherical particles taken as reference. Under AF4 diffusion conditions, it can be considered as an evaluator of the deviation from the sphericity of the fractionated analytes. AF4-UV-MALS-ICPMS enabled the dimensional and chemical characteristics of the colloidal size continuum to be obtained. As a “proof of concept”, the developed methodology was applied at a field scale, in a reference study site. In order to have a “dynamic understanding”, the investigation was based on the joint characterization of colloids from surface waters and soil leachates from static and dynamic processes. In the water samples of the study site, the continuum of gyration radius ranged from a few nanometers up to 200 nm. Colloids containing iron, aluminum, and organic carbon were involved in the uranium transport in the soil column and surface waters. The colloidal uranium concentration in the surface water increased from the upstream location (approximately 13 ng (U) L−1) to the downstream location (approximately 60 ng (U) L−1).

Appendix A. Supplementary data : Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.jconhyd.2012.06.004; International audience; This study investigates thermodynamics and kinetics of water-rock interactions in a carbonate aquifer at the watershed scale. A reactive transport model is applied to the unconfined chalk aquifer of the Champagne Mounts (France), by considering both the chalk matrix and the interconnected fracture network. Major element concentrations and main chemical parameters calculated in groundwater and their evolution along flow lines are in fair agreement with field data. A relative homogeneity of the aquifer baseline chemistry is rapidly reached in terms of pH, alkalinity and Ca concentration since calcite equilibrium is achieved over the first metres of the vadose zone. However, incongruent chalk dissolution slowly releases Ba, Mg and Sr in groundwater. Introducing dilution effect by rainwater infiltration and a local occurrence of dolomite improves the agreement between modelling and field data. The dissolution of illite and opal-CT, controlling K and SiO2 concentrations in the model, can be approximately tackled by classical kinetic rate laws, but not the incongruent chalk dissolution. An apparent kinetic rate has therefore been fitted on field data by inverse modelling: 1.5×10−5 molchalkL −1wateryear −1. Sensitivity analysis indicates that the CO2 partial pressure of the unsaturated zone is a critical parameter for modelling the baseline chemistry over the whole chalk aquifer.

The Chalk aquifer of Champagne (France) baseline geochemistry has been determined using a solid solution approach for the modelling of calcite dissolution. The water–rock interactions are modelled by the speciation code CHESS from field data and Ca, Mg and Sr aqueous concentrations in groundwater. The stoichiometries of solid solutions are defined in each stratigraphic unit of the Chalk aquifer from bulk geochemistry and Chalk mineralogy of samples taken from boreholes. The initial mineralisation of water at the bottom of the unsaturated zone and the characterisation of the theoretical evolution of groundwater chemistry along the flow lines associated with incongruent calcite dissolution are calculated from this approach.

Uranium is known to easily form stable complexes with both organic and inorganic ligands in natural aquatic environments. The potential mobility of U(VI), and particularly the role of humic substances, has been investigated for a sandy podzol. Adsorption of U(VI) at equilibrium was experimentally investigated, comparatively for a pure quartz sand as well as a sandy podzolic soil from Landes Gascony, France, containing 0.6 wt. organic matter. Uranium is strongly retained by the bulk soil, mainly due to organic aggregates (

Presented in this paper are measurements from five different laboratories with four different probes to determine the moisture content of sand samples in flight on a geotechnical centrifuge. The sensors are resistivity probes, capacitance probes, TDR sensors and Geiger Müller tubes. Experiments were carried out with a sand-water-air system, resistivity probes and TDR sensors were additionally tested in the sand-water-NAPL system. All probes were fast responding and gave reliable and reproducible results during centrifuge tests at up to 40 g. The work presented in this paper was carried out as part of the NECER programme funded by the European Commission.

cited By 3; International audience; The mobility and colloidal migration of uranium were investigated in a soil where limited amounts of anthropogenic uranium (depleted in the 235U isotope) were deposited, adding to the naturally occurring uranium. The colloidal fraction was assumed to correspond to the operational fraction between 10kDa and 1.2μm after (ultra)filtration. Experimental leaching tests indicate that approximately 8-15% of uranium is desorbed from the soil. Significant enrichment of the leachate in the depleted uranium (DU) content indicates that uranium from recent anthropogenic DU deposit is weakly bound to soil aggregates and more mobile than geologically occurring natural uranium (NU). Moreover, 80% of uranium in leachates was located in the colloidal fractions. Nevertheless, the percentage of DU in the colloidal and dissolved fractions suggests that NU is mainly associated with the non-mobile coarser fractions of the soil. A field investigation revealed that the calculated percentages of DU in soil and groundwater samples result in the enhanced mobility of uranium downstream from the deposit area. Colloidal uranium represents between 10% and 32% of uranium in surface water and between 68% and 90% of uranium in groundwater where physicochemical parameters are similar to those of the leachates. Finally, as observed in batch leaching tests, the colloidal fractions of groundwater contain slightly less DU than the dissolved fraction, indicating that DU is primarily associated with macromolecules in dissolved fraction. © 2013 Elsevier Ltd.

International audience; The migration of uranium from polluted soil has been investigated in the field, and through modelling of thermodynamics and kinetics of uranium-water-rock interactions. Field monitoring following surface contamination by uranium deposits revealed up to 5 m deep uranium migration in soil and chalk substrate, as well as uranium concentrations in groundwater significantly higher than the geochemical background. Such observations can hardly be explained by a pure reactive transport dominated by reversible adsorption of uranium onto mineral phases. Therefore, a reactive transport model using the HYTEC code has been developed to better assess uranium migration through soil to the carbonate aquifer. Reactive transport modelling shows that adsorption of U (VI) at equilibrium on goethite at pH 7 is responsible for strong immobilization of uranium in the soil and carbonate matrix, matching uranium concentration profiles observed in boreholes. Simulations considering highly mobile ternary complex Ca2UO2(CO3)3(aq) in the aqueous phase cannot account alone for the rapid migration of uranium through the unsaturated zone. Without a mobile colloidal phase, the model clearly underestimates the concentration of aqueous U(VI) that reached groundwater underneath polluted soils.

International audience; s u m m a r y Water–rock interactions are major processes that control the solute transfer (from natural or anthropo-genic sources) in aquifers. In carbonate aquifers, these water–rock interactions are mainly characterised by the incongruent dissolutions of carbonates. The in situ quantification of these reactions is few studied. In the present paper, we provide a new quantification of the kinetic rates of simultaneous incongruent dissolution of composite carbonate and dolomite in a Chalk aquifer. The approach is based on a mass-balance model used to calculate the rates of mineral dissolution and precipitation along a 500 m to 4 km flow path starting at the groundwater divide line. The groundwater transfer times between the groundwater divide line and the wells are calculated thanks to flow and transport modelling, used in a backward particle tracking mode. The uncertainties on porosity, dispersivity and transmissivity are taken into account. The rates are found ranging between 1.5 Â 10 À5 and 1.5 Â 10 À4 mol C5 chalk L À1 w yr À1 for the composite carbonate dissolution, between 1.0 Â 10 À7 and 3.0 Â 10 À6 mol dolomite L À1 w yr À1 for the dolomite dissolution and between 1.0 Â 10 À5 and 1.5 Â 10 À4 mol calcite L À1 w yr À1 for the calcite precipitation. The results highlight the importance of physical and geological properties of the aquifer.

International audience; The transport of uranium through a sandy podzolic soil has been investigated in the field and in column experiments. Field monitoring, numerous years after surface contamination by depleted uranium deposits, revealed a 20 cm deep uranium migration in soil. Uranium retention in soil is controlled by the < 50 µm mixed humic and clayey coatings in the first 40 cm i.e. in the E horizon. Column experiments of uranium transport under various conditions were run using isotopic spiking. After 100 pore volumes elution, 60% of the total input uranium is retained in the first 2 cm of the column. Retardation factor of uranium on E horizon material ranges from 1300 (column) to 3000 (batch). In parallel to this slow uranium migration, we experimentally observed a fast elution related to humic colloids of about 1-5% of the total-uranium input, transferred at the mean porewater velocity through the soil column. In order to understand the effect of rain events, ionic strength of the input solution was sharply changed. Humic colloids are retarded when ionic strength increases, while a major mobilization of humic colloids and colloid-borne uranium occurs as ionic strength decreases. Isotopic spiking shows that both 238U initially present in the soil column and 233U brought by input solution are desorbed. The mobilization process observed experimentally after a drop of ionic strength may account for a rapid uranium migration in the field after a rainfall event, and for the significant uranium concentrations found in deep soil horizons and in groundwater, 1 km downstream from the pollution source.