Movement of Cryptosporidium parvum Oocysts through Soils without Preferential Pathways: Exploratory Test

Groundwater contamination by oocysts of the waterborne pathogen Cryptosporidium parvum is a significant cause of animal and human disease worldwide. Although research has been undertaken in the past to determine how specific physical and chemical properties of soils affect the risk of groundwater contamination by C. parvum, there is as yet no clear conclusion concerning the range of mobility of C. parvum that one should expect in field soils. In this context, the key objective of this research was to determine the magnitude of C. parvum transport in a number of soils, under conditions in which fast and preferential transport has been successfully prevented. C. parvum oocysts were applied at the surface of different soils and subjected to artificial rainfall. Apparently for the first time, quantitative PCR was used to detect and enumerate oocysts in the soil columns and in the leachates. The transport of oocysts by infiltrating water, and the considerable retention of oocysts in soil was demonstrated for all soils, although differences in the degree of transport were observed with soils of different types. More oocysts were found in leachates from sandy loam soils than in leachates from loamy sand soils and the retention of oocysts in different soils did not significantly differ. The interaction of various processes of the hydrologic system and biogeochemical mechanisms contributed to the transport of oocysts through the soil matrix. Results suggest that the interplay of clay, organic matter, and Ca2+ facilitates and mediates the transfer of organic matter from mineral surfaces to oocysts surface, resulting in the enhanced breakthrough of oocysts through matrices of sandy loam soils compared to those of loamy sand soils. Although the number of occysts that penetrate the soil matrix account for only a small percentage of initial inputs, they still pose a significant threat to human health, especially in groundwater systems with a water table not too distant from the soil surface. The results of the research demonstrate a critical need for the simultaneous study of the interaction of various processes affecting oocysts transport in the subsurface, and for its expansion into complex systems, in order to obtain a coherent picture of the behavior of C. parvum oocysts in soils

A new method to trace colloid transport pathways in macroporous soils using X‐ray computed tomography and fluorescence macrophotography

The fast and deep percolation of particles through soil is attributed to preferential flow pathways, and their extent can be critical in the filtering of particulate pollutants in soil. Particle deposition on the pore walls and transport between the pores and matrix modulate the preferential flow of particulate pollutants. In the present research, we developed a novel method of combining fluorescence macrophotography and X‐ray computed tomography (CT) to track preferential pathways of colloidal fluorescent microspheres (MS) in breakthrough experiments. We located accumulations of MS by fluorescence imaging and used them to delimit the deposition structures along the preferential colloid pathways by superimposing these images on the 3‐D pore network obtained from CT. Advection–diffusion with transport parameters from the dual‐porosity equation correlated with preferential pathway features across different soil management techniques. However, management did not influence the morphology of the MS preferential pathways. Preferential flow occurred in only a small fraction of the total pore network and was controlled by pores connected to the soil surface and by matrix density

Evolution of gravity-driven rock slope failure and associated fracturing: Geological analysis and numerical modelling

International audienceAn accurate analysis of fracture and cleavage anisotropies along two landslides in the Argentera massif (French Southern Alps) was performed in order to relate the fracturing mode to the rock slope failure state. The mature La Clapière landslide and the incipient Isola Landslide were investigated. In both cases, the gneissic rock schistosity was found sub-horizontal in the vicinity of the landslides at shallow depths, while it was sub-vertical elsewhere at the massif's scale. In addition to the well known regional tectonic fracture sets, we identified in both cases a new family of vertical valley parallel (VP) fractures. The VP fractures were only observed on the lower part of slopes affected by landslides where schistosity was found sub-horizontal. The VP fractures are clearly related to the decrease in schistosity dip and correspond to 'fold extrado'-like joints. The proximity of the schistosity folds and the associated VP joints to the landslides suggests that they are gravity-driven. The presented 2-D finite-difference models of the slope destabilisation in the La Clapière site shade light on possible mechanisms of the indicated gravity-induced processes. A progressive degradation of the material strength was imposed in these models to simulate the weathering effect which led to inelastic deformation/damage at the lower part of slope. This was followed by the formation of dense sub-vertical deformation bands and then by the initiation of a landslide in the area corresponding to the actual position of the La Clapière landslide. It is suggested that the gravity-induced damage in the lower part of slope increases the permeability and thereby accelerates the weathering that causes a more rapid strength reduction. The latter results in the tilting/folding of pre-existing fabrics and the related VP fracturing. The La Clapière landslide is initiated in the upper part of this zone

Coupled kinematic and thermal modelling of collisional orogens: Implications for subsurface geo-resources assessment in the external Dinarides

The thermal evolution of collisional orogens is largely controlled by their kinematic and burial/exhumation history, where sedimentation and erosion rates, as well as shear heating and deep heat flow supply conditions for the temperature distribution, fluid flow and the associated fluid-rock interactions. The aim of our research is to understand this coupled kinematic and thermal evolution to ultimately infer the conditions favourable for subsurface geo-resources. We achieve this aim by means of numerical modelling and its application to one of the best available orogenic indentation examples, which is the Dinarides Mountains chain in Central Europe. Based on the analysis and modelling of an integrated onshore and offshore geological cross-section, we quantified the shortening, erosion/exhumation and sedimentation/burial rates, maturity of potential petroleum source rocks and the gross potential for sustainable geothermal resources. The coupled kinematic/thermal modelling revealed a general pattern of heat flow variations associated with crustal deformations. The hanging-wall and upper parts of the footwalls show increased conductivity and heat flow during episodes of thrusting, whereas the deepest parts of footwalls have lower heat flow values. Fluids are observed to migrate towards the foreland during the latest Cretaceous – Early Oligocene thrusting. The largest amounts of post-Middle Miocene shortening took place in the SE external parts of the orogen, where deep-sourced fluid ascent took place towards the foreland. In this region, significant footwall burial enhanced the maturation of potential source rocks. Modelling results infer a considerable hydrocarbon potential for the Dalmatian unit and the South Adriatic basin. The kinematic and thermal model combined with geothermal well design and well performance calculations infer a viable geothermal energy potential for the Dalmatian and High-Karst units. Results of this novel workflow allowed to quantify the orogenic kinematic and thermal history, and its bearing on conventional and sustainable geo-resources

Timing of the last deglaciation revealed by receding glaciers at the Alpine-scale: impact on mountain geomorphology

International audienceNew Terrestrial Cosmogenic Nuclides (TCN) 10Be ages obtained on glacially polished rocks from the SW Alps (Tinée Valley, France) allow a comparison with ages obtained using similar methods for dating the deglaciation steps after the Last Glacial Maximum on the northern and southern sides of the Alps. The data presented in this study highlight three stages of glacial retreat on the southern flank of the Alps at remarkably similar ages that are 14.9 ± 0.8 10Be ka for the end of Oldest Dryas cold period, 10.9 ± 1.1 10Be ka for the end of Younger Dryas cold period and 8.4 ± 0.9 10Be ka for a late ice retreat stage. Previously published data from the Northern Alps lead also to an age of 15.7 ± 1.0 ka for the Oldest Dryas deglaciation, followed by the Younger Dryas at 11.3 ± 1.0 ka, and a late discrete ice retreat event at 9.7 ± 1.2 ka. The last glacial retreats occur thus simultaneously across the Alps and the deglaciation process was most likely unrelated to variations in latitude or to mountain flank exposition throughout the Alps. This may be ascribed to a relatively rapid climate change. Subsequent mountain slope evolution following the rapid glacier unloading is reflected by landslides and fault reactivation directly following the deglacial period. This temporal coincidence is ascribed to a cause-to-consequence effect of glacial unloading and water infiltration into tectonic and landslide triggering

Inner gorges incision history: A proxy for deglaciation? Insights from Cosmic Ray Exposure dating (10Be and 36Cl) of river-polished surfaces (Tinée River, SW Alps, France)

International audienceEditor: A. Yin Keywords: river gorges incision CRE 10 Be and 36 Cl dating river polished surfaces 10 Be and 36 Cl Cosmic Ray Exposure (CRE) dating performed on river polished surfaces of river gorges in a mountain-to-sea river system in the French SW Alps highlights transient erosional events involving incision rates >10 mm a −1. These events took place during the last two major deglaciation phases following (1) the Last Glacial Maximum (LGM) at 16–14 ka, (2) the Younger Dryas at 8–11 ka, and during the warm and humid Holocene climatic optimum at 4–5 ka. These periods of high incision rates (3–>30 mm a −1) alternated with periods of low incision rates (<1 mm a −1), which probably correspond to a long-term equilibrium between incision and relative uplift. The Alpine river staircase shape profiles evidence local and transient responses that are ascribed to cumulate disequilibrium after the long-time-spanned glaciations. After each glaciation, rivers rush down to get closer to their equilibrium profile. Incision is amplified both by the sediment discharge due to the erosion of moraines and by landslides triggered by the glacier retreat

Preferential flow systems amended with biogeochemical components: imaging of a two-dimensional study

The vadose zone is a highly interactive heterogeneous system through which water enters the subsurface system by infiltration. This paper details the effects of simulated plant exudate and soil component solutions upon unstable flow patterns in a porous medium (ASTM silica sand; US Silica, Ottawa, IL, USA) through the use of two-dimensional tank light transmission method (LTM). The contact angle (θ) and surface tension (γ) of two simulated plant exudate solutions (i.e., oxalate and citrate) and two soil component solutions (i.e., tannic acid and Suwannee River natural organic matter, SRNOM) were analyzed to determine the liquid–gas and liquid–solid interface characteristics of each. To determine if the unstable flow formations were dependent on the type and concentration of the simulated plant exudates and soil components, the analysis of the effects of the simulated plant exudate and soil component solutions were compared to a control solution (Hoagland nutrient solution with 0.01 M NaCl). Fingering flow patterns, vertical and horizontal water saturation profiles, water saturation at the fingertips, finger dimensions and velocity, and number of fingers were obtained using the light transmission method. Significant differences in the interface properties indicated a decrease between the control and the plant exudate and soil component solutions tested; specifically, the control (θ =  64.5° and γ =  75.75 mN m−1) samples exhibited a higher contact angle and surface tension than the low concentration of citrate (θ =  52.6° and γ =  70.8 mN m−1). Wetting front instability and fingering flow phenomena were reported in all infiltration experiments. The results showed that the plant exudates and soil components influenced the soil infiltration as differences in finger geometries, velocities, and water saturation profiles were detected when compared to the control. Among the tested solutions and concentrations of soil components, the largest finger width (10.19 cm) was generated by the lowest tannic acid solution concentration (0.1 mg L−1), and the lowest finger width (6.00 cm) was induced by the highest SRNOM concentration (10 mg L−1). Similarly, for the plant exudate solutions, the largest finger width (8.36 cm) was generated by the lowest oxalate solution concentration (0.1 mg L−1), and the lowest finger width (6.63 cm) was induced by the lowest citrate concentration (0.1 mg L−1). The control solution produced fingers with average width of 8.30 cm. Additionally, the wettability of the medium for the citrate, oxalate, and SRNOM solutions increased with an increase in concentration. Our research demonstrates that the plant exudates and soil components which are biochemical compounds produced and released in soil are capable of influencing the process of infiltration in soils. The results of this research also indicate that soil wettability, expressed as cosθ1∕2, should be included in the scaling of the finger dimension, i.e., finger width, when using the Miller and Miller (1956) scaling theory for the scaling of flow in porous media

Self-colour anodizing of titanium

Relations between the colours and the electrochemical parameters (current density, quantity of electricity and temperature of the electrolyte) during the anodization of titanium sheets were studied in a 1 M H2SO4 solution. Mathematical theories were developed for the kinetics of growth of the anodic film and for the colours of this film. These theories show that the relation between the growth and the colour of the film is complicated. Nevertheless, it was possible to find experimental conditions that led to uniform and well-defined colours. © 1982.SCOPUS: ar.jinfo:eu-repo/semantics/publishe