Quantifying fluorescent tracer distribution in allophanic soils to image solute transport

Abstract

International audienceThe 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 mm2 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

Sorption of Uranine on Forest Soils

“…Recently, concentrations of dyes have been evaluated to elucidate subsurface flux (Aeby et al 1997, Forrer et al 2000, in addition to the more traditional assessment of stained and unstained portions of soil profiles. In the past decade fluorescent dyes were also proposed as staining tracers and methods for quantifying tracer concentrations (Aeby et al 2001, Vanderborght et al 2002, Duwig et al 2008. While such techniques require more complicated equipment, they provide better possibilities to quantify vadose zone preferential flow, especially in dark (Duwig et al 2008) and heterogeneous soils where Brilliant Blue is difficult to detect or that would require very complex calibrations.…”

Criteria for selecting fluorescent dye tracers for soil hydrological applications using Uranine as an example

“…Compared to common dyes, fluorescent substances have several distinct advantages: (1) they are visible in soils of different colors, even very dark soils (Duwig et al, 2008;Hangen et al, 2004); (2) two or more fluorescent dyes with separated excitation and emission wavelengths can be used simultaneously (Aeby et al, 2001;Vanderborght et al, 2002); and (3) they allow examination of soil profiles at any wavelength different from the excitation range of the staining dye being employed. Different fluorescent dyes have been used as staining substances, including Pyranine (Duwig et al, 2008), Rhodamines (McNeil et al, 2006), Sulforhodamine B, Brilliant Sulfoflavine, and Oxazine 170 (Aeby et al, 2001;Vanderborght et al, 2002). To the best of our knowledge, however, no criteria have been established for selecting fluorescent tracers for soil staining, and no comparison of dye properties that are significant for soil staining has been reported.…”

“…Evaluations of Brilliant Blue (BB) dye concentrations in a natural soil profile enabled quantification of the subsurface flux (Aeby et al, 1997;Forrer et al, 2000), in addition to more traditional assessments of stained and unstained portions of soil profiles. In the past decade fluorescent dyes have been proposed as staining tracers while methods for quantifying tracer concentrations were developed concurrently (Aeby et al, 2001;Duwig et al, 2008;Vanderborght et al, 2002). Compared to common dyes, fluorescent substances have several distinct advantages: (1) they are visible in soils of different colors, even very dark soils (Duwig et al, 2008;Hangen et al, 2004); (2) two or more fluorescent dyes with separated excitation and emission wavelengths can be used simultaneously (Aeby et al, 2001;Vanderborght et al, 2002); and (3) they allow examination of soil profiles at any wavelength different from the excitation range of the staining dye being employed.…”

“…In the past decade fluorescent dyes have been proposed as staining tracers while methods for quantifying tracer concentrations were developed concurrently (Aeby et al, 2001;Duwig et al, 2008;Vanderborght et al, 2002). Compared to common dyes, fluorescent substances have several distinct advantages: (1) they are visible in soils of different colors, even very dark soils (Duwig et al, 2008;Hangen et al, 2004); (2) two or more fluorescent dyes with separated excitation and emission wavelengths can be used simultaneously (Aeby et al, 2001;Vanderborght et al, 2002); and (3) they allow examination of soil profiles at any wavelength different from the excitation range of the staining dye being employed. Different fluorescent dyes have been used as staining substances, including Pyranine (Duwig et al, 2008), Rhodamines (McNeil et al, 2006), Sulforhodamine B, Brilliant Sulfoflavine, and Oxazine 170 (Aeby et al, 2001;Vanderborght et al, 2002).…”

Eine Methode zur Bestimmung des Fliessverhaltens von flüssigem Wasser im Holz während des Trocknens unter Anwendung eines fluoreszierenden Farbstofftracers

“…Tracing the liquid water flow with a dye solution had been used earlier especially in soil science to visualize flow paths of water in aquifers (Atkinson 1978;Duwig et al 2008). In living trees, dye tracers have been used to investigate the sap flow along the trunk (Edwards and Booker 1984;Zimmermann 1983).…”