Ary Bruand

The use of in situ volumetric water content at field capacity to improve the prediction of soil water retention properties

Use of in situ volumetric water content at field capacity to improve prediction of soil water retention properties. Most pedotransfer functions (PTFs) developed over the last three decades to generate water retention characteristics use soil texture, bulk density and organic carbon content as predictors. Despite of the high number of PTFs published, most being class- or continuous-PTFs, accuracy of prediction remains limited. In this study, we compared the performance of different class- and continuous-PTFs developed with a regional database. Results showed that use of in situ volumetric water content at field capacity as a predictor led to much better estimation of water retention properties as compared to using predictors derived from the texture, or the organic carbon content and bulk density. This was true regardless of the complexity of the PTFs developed. Results also showed that the best prediction quality was achieved by using the in situ volumetric water content at field capacity after stratification by texture. Comparison of in situ volumetric water content at field capacity, with the water retained at different matric potentials as measured in the laboratory, showed field capacity to approximate 100 hPa whatever the soil texture. Finally, the lack accuracy of PTFs that do not use the in situ volumetric water content at field capacity as predictor did not appear due to the test soils being unrepresentative of the soils used to develop the PTFs, but were instead related to poor correlations between the predictors used and the water retention properties.

Groundwater Vulnerability and Risk Mapping Based on Residence Time Distributions: Spatial Analysis for the Estimation of Lumped Parameters

Specific vulnerability estimations for groundwater resources are usually geographic information system-based (GIS) methods that establish spatial qualitative indexes which determine the sensitivity to infiltration of surface contaminants, but with little validation of the working hypothesis. On the other hand, lumped parameter models, such as the Residence Time Distribution (RTD), are used to predict temporal water quality changes in drinking water supply, but the lumped parameters do not incorporate the spatial variability of the land cover and use. At the interface between these two approaches, a GIS tool was developed to estimate the lumped parameters from the vulnerability mapping dataset. In this method the temporal evolution of groundwater quality is linked to the vulnerability concept on the basis of equivalent lumped parameters that account for the spatially distributed hydrodynamic characteristics of the overall unsaturated and saturated flow nets feeding the drinking water supply. This vulnerability mapping method can be validated by field observations of water concentrations. A test for atrazine specific vulnerability of the Val d’Orléans karstic aquifer demonstrates the reliability of this approach for groundwater contamination assessment.

Zinc Redistribution in a Soil Developed from Limestone During Pedogenesis

The long-term redistribution of Zn in a naturally Zn-enriched soil during pedogenesis was quantified based on mass balance calculations. According to their fate, parent limestones comprised three Zn pools: bound to calcite and pyritesphalerite grains, bound to phyllosilicates and bound to goethite in the inherited phosphate nodules. Four pedological processes, i.e., carbonate dissolution, two stages of redox processes and eluviation, redistributed Zn during pedogenesis. The carbonate dissolution of limestones released Zn bound to calcite into soil solution. Due to residual enrichment, Zn concentrations in the soil are higher than those in parent limestones. Birnessite, ferrihydrite and goethite dispersed in soil horizon trapped high quantities of Zn during their formation. Afterwards, primary redox conditions induced the release of Zn and Fe into soil solution, and the subsequent individualization of Fe and Mn into Zn-rich concretions. Both processes and subsequent aging of the concretions formed induced significant exportation of Zn through the bottom water table. Secondary redox conditions promoted the weathering of Fe and Mn oxides in cements and concretions. This process caused other losses of Zn through lateral exportation in an upper water table. Concomitantly, eluviation occurred at the top of the solum. The lateral exportation of eluviated minerals through the upper water table limited illuviation. Eluviation was also responsible for Zn loss, but this Zn bound to phyllosilicates was not bioavailable

Concentration and mobility of lithogenic trace metals in soils: significance of anthropogenic lateral redistributions

One of the main current concerns regarding soil quality is the presence of trace metals that constitutes a risk of toxicity for plants and animals [1, 5, 7 and 11]. Trace metals in soils can have either a lithogenic origin when they inherit from the lithosphere or an anthropogenic origin when they result from mans activities (mining, metallurgy of non-ferrous metals, combustion of fossil energy sources, solid waste or sewage sludge) [5]. Recent studies showed that concentration of lithogenic trace metals in soils could not be explained without taking mans activities into account.

A snapshot of soil water composition as an indicator of contrasted redox environments in a hedged farmland plot

While soil water composition has long been recognised as being related to soil type (characteristics of the horizons), the influence of structures resulting from agricultural activities (hedges, ditches, wheel ruts, etc) is still under discussion. This work was undertaken to show that a snapshot of spatial variability of the geochemical characteristics of soil water at the scale of a plot can improve our understanding of soil geochemistry in a farmland setting. We selected a 3 hectare hedged plot located on a hillside, limited by a stream and used as pasture where soils have developed in weathered gneiss. The water depth, electrical conductivity, major ions, temperature, pH, dissolved organic carbon (DOC) content, dissolved oxygen content, fluorescence, alkalinity, Fe(2+), Mn(2+), NO(2)(-), Fe(III) and F(-) contents were measured in 62 auger holes randomly drilled on the site. Four sectors were identified in order to describe the distribution of the main geochemical parameters. Electrical conductivity and some major ions, especially sulphate, had larger concentrations near hedges where oxic conditions prevailed. These features were attributed to the impact of the linear anthropogenic network on the circulation of subsurface soil waters and evapo-transpiration and represent sector I. Dissolved Mn was an indicator of well channelled runoff subsurfaces facilitating the circulation of more highly reducing water (sector III), while DOC probably marked areas drained less well, with a prolonged contact time between soil solutions and organic topsoil horizons (sector II). The presence of dissolved Mn and Fe(II) indicates bottomland anoxic conditions (sector IV). It is concluded that a survey of the chemical composition of soil water may be a direct approach to show the influence of permanent structures on current soil properties and dynamics.

Stock de carbone organique dans des sols de la région aride de Coquimbo (Chili) : conséquences de l’intensité du pâturage sur les parcours caprins

Les stocks de carbone organique ont ete etudies sous deux intensites de pâturage sur parcours par des chevres et compares a une situation temoin au sein de la station experimentale de Las Cardas (region de Coquimbo, Chili). Les resultats montrent que sous pâturage d’intensite moderee (6 unites petits ruminants (UPR)/ha/an), le stock de carbone organique de 0 a 100 cm de profondeur est peu affecte avec 24,3 a 29,3 Mg/ha de carbone organique total contre 31,1 a 42,6 Mg/ha sous vegetation naturelle, ces stocks n’etant pas significativement differents ( P = 0,95) en raison de la variabilite des resultats entre les repetitions. En revanche, sous parcours d’intensite elevee (10 UPR ha /an), le stock de carbone organique n’est plus que de 10,2 a 15,5 Mg/ha. Enfin, dans ces milieux ou il est particulierement difficile d’etudier les stocks de carbone en raison de la charge souvent elevee en elements grossiers, nos resultats indiquent qu’il est possible de predire le stock total du carbone organique des sols a partir de la seule mesure du stock de carbone dans les 30 premiers centimetres (R 2 = 0,89) avec un biais inferieur a 0,1 Mg/ha et une precision de 3,6 Mg/ha.

Détermination de la masse volumique du solide pour un échantillon de sol argileux : validité de la méthode utilisant les propriétés de retrait de l'échantillon remanié sous dessication pneumatique

mdash; Particle density in a clayey soil sample : validity of the method utilising the shrinkage properties of the sample remoulded by air pressure equipment. The particle density value (p,) calculated from the shrinkage curve is lower than that obtained by using a gas pycnometer. This difference is explained by the presence of air trapped inside the sample after subjecting it to pneumatic pressure.