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Gomez C.,Montpellier SupAgro | Le Bissonnais Y.,Montpellier SupAgro | Annabi M.,Institute National Of Recherche Agronomique Of Tunisie | Bahri H.,Institute National Of Recherche En Genie Rural Eaux Et Forets | Raclot D.,Montpellier SupAgro

The characterization of soil aggregate stability is an important step for assessing the susceptibility of soil to water erosion. A normalized international method has recently been proposed for estimating soil aggregate stability indexes (ISO/FDIS 10930, 2012), but extensive measurements of the soil aggregate stability for mapping erosion risks on the regional scale remain a fastidious enterprise. This paper explores three different approaches as an alternative to the normalized international measurements. The first, called the PTFs Approach, estimates aggregate stability indexes via elementary soil properties using multiple linear regression. The second one, called the RS Approach, estimates aggregate stability indexes via Laboratory (Lab) Visible-Near Infrared (Vis-NIR) spectra using multivariate linear regressions. The third, called the RS+PTFs Approach first used the Lab Vis-NIR spectra to predict the elementary soil properties using multivariate linear regressions, which are then used to predict the soil aggregate stability indexes using multiple linear regression. These tests were performed on a collection of 113 soil samples from the Mediterranean region of Northern Tunisia. Four soil aggregate stability indexes were considered: three indexes calculated using three disruptive tests that correspond to various wetting conditions and energies, and the fourth index was the mean of the first three. This study shows that Lab Vis-NIR spectroscopy may be used directly in multivariate regression models to estimate two soil aggregate stability indexes (R2 val between 0.52 and 0.57, RPD between 1.47 and 1.61) with accuracy comparable to the multiple linear models in the PTFs Approach. Further investigations on various soil types, especially those for which the soil aggregate stability indexes were strongly correlated to organic carbon content, are encouraged to extend the utility and applicability of Lab Vis-NIR spectroscopy as an alternative method for soil aggregate stability indexes estimates.© 2013 Elsevier B.V. Source

Lagacherie P.,Montpellier SupAgro | Sneep A.-R.,Montpellier SupAgro | Gomez C.,Montpellier SupAgro | Bacha S.,Center National Of Cartographie Et Of Teledetection Cnct | And 3 more authors.

Previous studies have demonstrated that Visible Near InfraRed (Vis-NIR) hyperspectral imagery is a cost-efficient way to map soil properties at fine resolutions (~. 5. m) over large areas. However, such mapping is only feasible for the soil surface because the effective penetration depths of optical sensors do not exceed several millimeters. This study aims to determine how Vis-NIR hyperspectral imagery can serve to map the subsurface properties at four depth intervals (15-30. cm, 30-60. cm, 60-100. cm and 30-100. cm) when used with legacy soil profiles and images of parameters derived from digital elevation model (DEM). Two types of surface-subsurface functions, namely linear models and random forests, that estimate subsurface property values from surface values and landscape covariates were first calibrated over the set of legacy measured profiles. These functions were then applied to map the soil properties using the hyperspectral-derived digital surface soil property maps and the images of landscape covariates as input. Error propagation was addressed using a Monte Carlo approach to estimate the mapping uncertainties.The study was conducted in a pedologically contrasted 300km2-cultivated area located in the Cap Bon region (Northern Tunisia) and tested on three soil surface properties (clay and sand contents and cation exchange capacity). The main results were as follows: i) fairly satisfactory (cross-validation R2 between 0.55 and 0.81) surface-subsurface functions were obtained for predicting the soil properties at 15-30cm and 30-60cm, whereas predictions at 60-100cm were less accurate (R2 between 0.38 and 0.43); ii) linear models outperformed random-forest models in developing surface-subsurface functions; iii) due to the error propagations, the final predicted maps of the subsurface soil properties captured from 1/3 to 2/3 of the total variance with a significantly decreasing performance with depth; and iv) these maps brought significant improvements over the existing soil maps of the region and showed soil patterns that largely agreed with the local pedological knowledge. This paper demonstrates the added value of combining modern remote sensing techniques with old legacy soil databases. © 2013 Elsevier B.V. Source

Sabbahi S.,Institute National Of Recherche En Genie Rural Eaux Et Forets | Sabbahi S.,Laboratoire Microorganismes et Biomolecules Actives | Alouini Z.,Institute National Of Recherche En Genie Rural Eaux Et Forets | Ayed L.B.,Institute National Of Recherche En Genie Rural Eaux Et Forets | And 2 more authors.
Desalination and Water Treatment

The high inactivation of faecal indicators [faecal coliforms (FC), E. coli and faecal streptococci (FS)] using a combination of methylene blue (MB) with natural sunlight or artificial visible light determined on a small scale, was dependent mainly on the MB concentration, its application process and pH. In order to avoid primarily leaching of the compound into the environment and to further understand the MB photosensitization mechanisms, MB should be properly immobilized within resin. The FC and FS were found to be susceptible to the photodynamic action of MB fixed to the support. The mechanism of faecal bacteria inactivation by MB also seems to be a combination of Type I and Type II processes, and the relative efficiency of each of them depends notably on the experimental conditions. In parallel, the MB stability under light "photobleaching" has been studied by optical absorption spectroscopy. It has been shown that it was dependent essentially on pH, nature of the medium (distilled water and secondary wastewater effluent) and time exposure to light. Practically, all of the MB (10 μM) disappeared from effluent, exposed to sunlight, by the end of a 12 h experiment with a bleaching rate from 92 at neutral pH. Kinetic data indicate that the dye photobleaching efficiency can be approximated by pseudo-first-order reaction. © 2010 Desalination Publications. Source

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