2 results for Prado, B

  • Quantifying fluorescent tracer distribution in allophanic soils to image solute transport

    Duwig, C; Delmas, PJ; mueller, K; Prado, B; Kevin, R; Morin, H; Woodward, Alexander (2008)

    Journal article
    The University of Auckland Library

    The accurate prediction of solute transport through soils is a necessity to counter the worldwide degradation of aquifers. Dye tracers are widely used to visualize active flow paths in cross-sections of soil, but methods previously proposed to map concentrations have been very costly, demanding, or of coarse resolution and not always applicable in dark allophanic soils. We have developed a cheap and fairly easy experimental procedure and used multiple regression to map dye concentrations in two dimensions. We tested the method using the fluorescent dye, pyranine, in intact cores of an allophanic soil. The method requires a calibration step, which we made using eight dye concentrations. The main difficulty was to mix the soil homogeneously with the dye and to pack it evenly before acquisition of the images. The pyranine was infiltrated in soil cores under unsaturated conditions: its distribution on the vertical core faces was highly heterogeneous with fingered penetration. The maps of dye concentration obtained from each core section achieved fine spatial resolution (e.g. 0.25 mm 2 per pixel) and satisfactory dye concentration localization and estimation. We could achieve better spatial resolution by sectioning the soil cores at finer intervals, and estimate the dye concentration more accurately by improving the correction for illumination variations.

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  • Image Processing-based study of soil porosity and its effect on water movement through Andosol intact columns

    Prado, B; Duwig, C; Marquez, J; Delmas, Patrice; Etchevers, J; Moralez, P (2009)

    Journal article
    The University of Auckland Library

    The soil pore network and marcoporosity are important factors affecting water and solute transport. The transfer of contaminants to water resources is of particular importance in the Valle de Bravo watershed as it provides 10% of the drinking water for the 20 million inhabitants of Mexico City. This watershed is composed mainly of Andosols with unique mineralogical and physical characteristics. Soil porosity is usually examined on thin sections, using various image analysis techniques. We propose a novel methodology combining image analysis and a displacement experiment to study relationships between soil structure and water tracer transport parameters. H2 18 O displacement experiments were conducted through intact soil columns sampled at three depths from a representative cultivated Andosol pro???le. The soil structure and pore characteristics were obtained by image analysis on thin sections obtained from each column at the end of the displacement experiment. The total 2D porosity (for pores larger than 50 mm) varied from 80% of the total section area in the topsoil to around 60% in the subsoil. Tubular pores were the most abundant in the soil pro???le, but ploughing of the topsoil had destroyed sections of these pores and replaced them with packing pores. Water transport in the intact subsoil columns was always in physical non-equilibrium, showing the existence of preferential ???ow pathways. In the topsoil, one column out of three showed no preferential ???ow, demonstrating that soil ploughing also homogenised pore connections. Pore connectivity was larger in the ploughed topsoil than in their deeper soil horizon counterparts. Our methodology offers a 2D quantitative characterisation of the macroporous network at 50 mm resolution and the determination of water transport parameters on the same intact soil samples. 3D characterisation of soil porosity using X-ray computed tomography (CT) gives a better picture of pore connection but usually has lower spatial resolution and a larger cost.

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