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International audience; Clay translocation is among the most widespread processes in soils. It is generally identified by the presence of clay coatings at the macroscopic or microscopic scales. Nevertheless, several authors demonstrated that clay coatings have different origins, which renders the attribution of individual coatings to a particular process difficult. Therefore, their characterization at the microscopic scale is necessary. Modern synchrotron technics allow mapping of the mineral composition of soil thin sections by X-ray diffraction with a lateral resolution of a few micrometres that is compatible with the size of the clay coatings. However, the use of this technic raises a certain number of technical difficulties when clay minerals and small pixel size are considered. Therefore a preliminary feasibility analysis was performed on soil coating obtained experimentally in a soil column Claude Manté et al. experiment. We developped a mathematical/statistical method to automatically identify and map the minerals present in synchrotron X-ray diffraction maps. This method combines a subtraction of the background signal, an identification of the diffraction peaks and the attribution of the obtained peaks to the different minerals phases. The robustness of the method was tested for the two first steps that were critical. We then showed that most of the minerals present in the considered samples could be identified, including clay minerals and Fe oxides; however, their relative proportions were difficult to estimate within the experimental conditions. As a conclusion, we proposed here a new mathematical method for the data treatment of synchrotron X-ray diffraction. Our study shows that this method could be applied on natural heterogeneous samples with data of poor quality to perform robust qualitative analysis. Moreover, with the recently available fast data acquisition schemes, large amounts of datasets (diffractograms) can be rapidly acquired, and are expected to benefit of the automatic data treatment approach proposed here.

Soil evolution results from both solute and colloid/particle translocation, but their relative importance in terms of soil formation is still under debate. The genesis of albic material in Retisols represents an ideal case to quantify the relative contribution of these two forms of transport in soil evolution since it results from i) clay eluviation, ii) reductive solubilisation of Fe oxides, and possibly iii) silicate hydrolysis. This issue seems particularly challenging in cultivated Retisols in which detailed analysis of the soil solid phases has demonstrated that artificial drainage and liming alter the genetic pathway of albic material both qualitatively and quantitatively.In the present study, we characterised the chemistry (pH, Eh, Al, Si, Fe and Mn) and dynamics of soil water and its evolution with increasing distance from the drain. Rainfall water, soil solution at water saturation in the E&Bt horizon and drainage water were sampled by an open rainfall collector, piezometers located at different distances from the drain, and an automatic water collector located at the main drain outlet, respectively.An element budget at the profile level revealed that only Si was lost from the soil profile while the leaching losses of Al, Fe and Mn were overcompensated by deposition from the atmosphere. The constant Fe/Al concentration ratios in piezometers and drain waters as well as the breakthrough curves at the drain outlet for individual rainfall events suggested that Fe and Al were exported together and mainly in colloidal form. While this was also partly true for Si, a longer tailing of the Si than the Fe and Al breakthrough curves indicated that Si was additionally transported in soluble form. Lastly, the temporal variation of the Mn concentrations was unrelated to that of the other elements, pointing to the predominance of translocation in soluble form. All these results demonstrated that: i) particle/colloidal translocation is more important than translocation in soluble form in a drained Retisol; ii) reductive solubilisation of Fe and Mn oxides still occurred, in spite of the artificial drainage; iii) processes such as wet and dry deposition, dissolution of quartz or ferrolysis also contribute to element budgets in Retisols, at least at some microsites and in some years.

International audience; Purpose: Vertical transfer of solid matter in soils (bioturbation and translocation) is responsible for changes in soil properties over time through the redistribution of most of the soil constituents with depth. Such transfers are, however, still poorly quantified.Materials and methods: In this study, we examine matter transfer in four eutric Luvisols through an isotopic approach based on 137Cs, 210Pb(xs), and meteoric 10Be. These isotopes differ with respect to chemical behavior, input histories, and half-lives, which allows us to explore a large time range. Their vertical distributions were modeled by a diffusion-advection equation with depth-dependent parameters. We estimated a set of advection and diffusion coefficients able to simulate all isotope depth distributions and validated the resulting model by comparing the depth distribution of organic carbon (including 12/13C and 14C isotopes) and of the 0–2-μm particles with the data.Results and discussion: We showed that (i) the model satisfactorily reproduces the organic carbon, 13C, and 14C depth distributions, indicating that organic carbon content and age can be explained by transport without invoking depth-dependent decay rates; (ii) translocation partly explains the 0–2-μm particle accumulation in the Bt horizon; and (iii) estimates of diffusion coefficients that quantify the soil mixing rate by bioturbation are significantly higher for the studied plots than those obtained by ecological studies.Conclusions: This study presents a model capable of satisfactorily reproducing the isotopic profiles of several tracers and simulating the distribution of organic carbon and the translocation of 0–2-μm particles.

International audience; Colloid retention in soils has mainly been studied in model homogeneous porous media, and during single irrigation events. However, in the field, colloidal suspensions flow through a small number of preferential flow paths, and the soil experiences succession of rainfalls, interrupted by dry periods. We therefore performed series of successive rainfalls (21 mm h(-1)) on three decimetric undisturbed luvisol E-horizon cores to systematically study the impact of the rainfall interruption duration (RID) on retention. Successive rains were doped with 0.5 mu m fluorescent microspheres of different colors. Microsphere release at the base of the soil column was monitored by flow cytometry. When preferential macropore flow was preponderant, increasing the RID from 5 to 1200 h led to the retention of up to an additional 27% of the microspheres rained onto the soil. This increased retention was ascribed to a higher absorption of the colloidal suspension into the macropore walls for longer RIDs, when water redistribution far from the macropores was more important. When matrix flow was preponderant, RID effect on retention was overwhelmed and massive microspheres retention was observed. These results are useful to provide guidelines for the safe use of reclaimed water in agriculture, and to estimate the importance of clay translocation (a colloid transfer based soil formation mechanism). (C) 2016 Elsevier B.V. All rights reserved.

International audience; AbstractAmong soil processes governing the clay size fraction distribution with depth, illuviation is not only widespread but also particularly poorly understood. Using a micromorphological approach, this study aims at i) quantifying the intensity of illuviation independently of all other competing soil processes, ii) testing the sensitivity of illuviation to different land uses, and iii) assessing the relative contribution of illuviation to the genesis of textural differentiation. Two Luvisols developed from loess in Northern France were selected: the first under a deciduous forest and the second under conventional agricultural management, both with no change in land use for at least 100 years. In addition to classical mass balance calculations, clay illuviation features such as limpid and dusty clay coatings were used as diagnostic features of the illuviation process and were quantified by a point-counting approach in large thin sections. In the two Luvisols under study illuviation was found to be responsible for 75% and 86% of the textural contrast, respectively in the cultivated soil and the forested one. Illuviation was thus by far the dominant factor causing textural differentiation, even if accessory processes involving the clay size fraction were also at play such as lithological discontinuity, clay neoformation or biological and physical reworking. The recognition of dusty clay coatings considered as an indicator of cultivation in the soil under forest underlines the sensitivity of illuviation to past periods of cultivation and the legacy of anthropedogenesis on the present soil properties. A qualitative change in the nature of the translocated particles without significant changes in the intensity of illuviation was identified in the soil under cultivation in comparison with the soil under forest. These results support the conclusion that illuviation is an active process in soils under present climatic conditions and must no more be considered as a fossil soil process.

International audience; Meteoric Be-10, due to its high affinity with soil and sediment particles, is widely used in geomorphologic and environmental studies attempting to evaluate the soil production/denudation rates or soil ages up to 10(7) years. However, the evolution of the Be-10 distribution as a function of depth is poorly known in soils as revealed by recent reviews (Graly et al., 2010; Willenbring and von Blanckenburg, 2010). In this study, Be-10 concentrations in the bulk and the 0-2 mu m (lutum) granulometric fraction of samples along Luvisols profiles developed from loess in Northern France have been measured. The bulk Be-10 concentrations are significantly higher in one of the three sites, likely reflecting differences in the inherited Be-10 concentrations of the loess parent material as well as in the accumulation rates of the later. However, the bulk Be-10 concentrations along all profiles are significantly correlated with the lutum (0-2 mu m fraction) content, the maximum Be-10 concentrations being evidenced in the Bt-horizon. Dominant adsorption of Be-10 to the lutum has been furthermore corroborated by the mass-balance calculations with as much as 79.8 +/- 9.0% of Be-10 being associated with the lutum. Contrary to the bulk Be-10 concentrations, the lutum Be-10 concentrations showed several maxima coinciding with shifts in the coarse to fine silt ratio. This was interpreted as a change in the loess deposit dynamic. Finally, using numerical modeling approach based on the advection-diffusion equation, an average downward migration of Be-10 by clay translocation was estimated. It ranges from 0.01 to 0.08 cm yr(-1). Inherited Be-10 in the loess parent material represented from 64 to 71% of the total Be-10 content in the simulated soils. Vertical Be-10 distributions and their maximum concentrations in the Bt-horizon thus mainly result from redistribution of the inherited Be-10 by clay translocation and bioturbation. (C) 2014 Elsevier B.V. All rights reserved.

International audience; The vertical distribution of Cs-137-an artificial fallout radionuclide-is controlled by soil characteristics and processes that may differ among soil groups. The application of a single modelling approach to large number of soil profiles provides an original contribution to the literature and allows for comparison between these different soil groups. In order to quantify Cs-137 migration in soils, we compiled and modelled depth-distributed data documented in the literature published before 2013. The resulting database comprised ninety-nine Cs-137 profiles sampled in 14 soil groups of the World Reference Base (WRB) classification (FAO 1998) under different land uses or covers and collected at various geographical locations in the Northern hemisphere between 1992 and 2007. The Cs-137 profiles were classified in seven different categories according to the shape and location of radiocaesium peak. Depth of the latter ranged between 0 and 12 cm (median of 2 cm) and maximal penetration of cesium reached from 12 to 60 cm. The Cs-137 depth distributions in these soils were fitted using a diffusion-convection equation to allow comparison between different soil groups. Diffusion coefficients ranged from 0.02 to 4.44 cm(2) years(-1) in soils (median of 0.64 cm(2) year(-1)), and convection velocities varied from 0 to 0.74 cm year(-1) (median of 0.1 cm year(-1)). The model underestimated Cs-137 concentrations by a median value of 1.9 % of the total inventory in soil samples collected below a 13-cm depth. Global Cs-137 penetration velocities ranged from 0.05 to 0.76 cm year(-1) (median of 0.28 cm year(-1)) over a 25-year period. Our results showed that modelling Cs-137 depth profile with a diffusion-convection equation allowed estimating the bioturbation and clay translocation velocity in a certain number of soil groups. This quantification is crucial as these processes partially control the development of soil surface characteristics and several soil services.

International audience; Lessivage consists of a substantial vertical transfer of fine particles from an eluvial E-horizon to an illuvial B-11 horizon. It has been described as a major or secondary pedogenetic process for many soil types. However, lessivage fluxes have never been measured because of obvious technical difficulties; thus, lessivage has been poorly quantified, if at all, and has rarely been modelled. For those reasons, the existence of lessivage is somewhat controversial. In this paper, we synthesised existing knowledge about lessivage and particle transfer from the literature and reanalysed data from the literature on particle transfer in soils using laboratory experiments and data from the French soil database. This analysis was performed to estimate (i) the occurrence of lessivage as a major soil forming process; (ii) the quantity of particles that migrate through soils; and (iii) the duration of lessivage in soil, which must be consistent with the mass of particles accumulated in the illuvial B-horizon. We showed that lessivage is responsible for the formation of Luvisols and Albeluvisols in only 1% to 12% of cases. In half of the cases, the current pH of the soil profiles is no longer favourable to lessivage due to agricultural liming practices. We also calculated that lessivage may have occurred over a minimum of 710 to 9100 years in soils developed on loess, a time period long enough to account for the observed accumulations of particles in the B-horizons in 64% of the cases, judging by the quantities of particles that migrate in soils. (C) 2011 Elsevier B.V. All rights reserved

Symposium 1.1.2 Soil morphology and Environment Hazards; In order to better understand the process of morphological degradation and the impact of drainage on this process, morphological evolution of soil volumes was studied using image analysis of decimetric soil monoliths in Albeluvisol sampled along a soil sequence perpendicular to a drain. The geomorphological interrelationships of four different volume types (black, white-grey, pale-brown and ochre) are quantified. Results show that morphological degradation progresses by the progressive transformation of the ochre volume into pale-brown from their inner, around porosity, and their border. Black volume is simultaneously formed by centrifugal condensation of Mn into the ochre volume. As the process goes on, with decreasing distance to the drain, the ochre volume is atomised and the black volume is released into the pale-brown matrix. This pale brown matrix is further transformed into a white-grey volume formed into its core by centripetal evolution.

International audience; Understanding soil evolution requires characterising, quantifying, and modelling the major processes that govern pedogenesis. We proposed to study one of the most widespread processes in soils: lessivage, understood as the vertical transfer of fine particles from a horizon, called eluviated, to another horizon, called illuviated. Lessivage fluxes were never measured to our knowledge due to obvious technical difficulties. In addition, despite its description in many soil types, the existence of this process is somewhat controversial. We designed a laboratory experimental device to imitate the lessivage process and to test the impact i) of extreme events, as heavy rain, and ii) of the structure of the eluviated horizon on lessivage. We used a rainfall generator that allows the examination of the effect of rainfall on soil under controlled conditions. Two climatic modalities were tested: heavy rain on dry soil and small intensity rainfalls on wet soil. We present here the first results of these experiments.

A presença de gradiente textural é comum e marcante em Argissolos. O objetivo do trabalho foi estudar a mineralogia das partículas envolvidas no processo de formação de gradiente textural em um solo subtropical do Rio Grande do Sul. Amostras de um Argissolo Vermelho-Amarelo distrófico abrúptico, material parental sedimentar, foram coletadas em duas trincheiras localizadas em distintas posições no relevo da área do departamento de solos da Universidade Federal de Santa Maria. No perfil 1, sob campo nativo e posicionado na meia encosta de uma colina com 9 % declividade, amostras foram coletadas nos horizontes A1, A2, AB e Bt. No perfil 2, sob vegetação espontânea e localizado no topo plano da colina, amostras foram coletadas nos horizontes A1, A2, E e Bt. Atributos químicos foram avaliados sobre a fração de solo menor que 2 mm. Amostras de argila dispersa em NaOH, após serem extraídas, foram submetidas à difração laser, discriminando a distribuição do tamanho de partícula envolvida no processo. A fração menor que 0,2 μm foi extraída, saturada com Ca2+ e submetida à difração de raios X sob os seguintes tratamentos: normal, à temperatura ambiente (N); depois de saturada com etilenoglicol (EG), depois de aquecida a 300 e 550 ºC. Os difratogramas de raios X (N) foram submetidos à modelagem matemática com DecompRX. Ambos os perfis apresentaram gradiente textural. Os teores de argila no horizonte Bt foram 2,9 e 4,4 vezes maiores no perfil 1 e 2 que nos seus respectivos horizontes mais arenosos. Os diagramas de difração laser mostraram enriquecimento no horizonte Bt em partículas de tamanho modal de 0,09 e 0,2 μm. A mineralogia dessa fração apresentou incremento nos horizontes Bt de interestratificados caulinita-esmectita (C-E) em detrimento das fases vermiculita hidróxi-Al entrecamada (VHE) e ilita-esmectita (I-E). Dessa forma, infere-se que o gradiente textural observado no solo está associado ao processo de migração de C-E com partículas de tamanho modal de 0,09 e 0,2 μm. Entretanto, o perfil 2 apresenta indícios de descontinuidade litológica, indicando que o processo de migração de partículas não é o único responsável pela formação de gradiente textural. Texture gradient is a prominent and ubiquitoud feature of Acrisol. The objective of this paper was to study the particle size distribution and mineralogy involved in the formation of the texture gradient of a subtropical soil in Rio Grande do Sul. Soil samples of a Red-Yellow Acrisol, formed on sedimentary parent material, were collected from trenches at two relief positions in an area of the Universidade Federal de Santa Maria, RS, Brazil. Soil samples were collected from profile 1, located on a slope and under natural pasture, in the horizons A1, A2, AB, and Bt and from profile 2, on a hilltop and under spontaneous vegetation, samples were collected in the horizons A1, A2, E, and Bt. Chemical attributes of the < 2 μm fraction were evaluated. The clay fraction (< 2 μm), after NaOH dispersion, was laser-diffracted, to discriminate the size distribution of the particles involved in the process. The < 0.2 μm fraction was separated by centrifugation, Ca2+ saturated and X ray diffracted after the following treatments: control, air-drying at room temperature (N); ethylene-glycol saturation (EG); and heating to 300 and 550 ºC. The raw X ray diffractograms were modelled using DecompRX. A texture gradient was observed in both soil profiles. Clay contents in the Bt horizons of profile 1 and 2 were 2.9 and 4.4 times higher than in the surface horizons. Laser diffraction diagrams of the Bt horizon revealed an enrichment in two modal diameter sizes (0.09 and 0.2 μm). The mineralogy of Bt horizons was composed of high kaolinite-smectite (K-S) amounts in detriment of Al-hydroxy interlayered vermiculite (HIV) and illite-smectite (I-S) clay minerals. It is suggested that the textural gradient in the soil profiles was due to migration of K-S particles with a modal diameter of 0.09 ìm and 0.2 μm. However, there are pieces of evidence pointing out for lithological discontinuity in profile 2, indicating that particle migration was not the only process of texture gradient formation.