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This article in SSSAJ

  1. Vol. 74 No. 4, p. 1084-1091
     
    Received: Aug 3, 2009


    * Corresponding author(s): mette.laegdsmand@agrsci.dk
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doi:10.2136/sssaj2009.0285

Multitracer and Filter-Separated Half-Cell Method for Measuring Solute Diffusion in Undisturbed Soil

  1. Mette Laegdsmand *a,
  2. Per Moldrupb and
  3. Per Schjønninga
  1. a Dep. of Agroecology and Environment, Faculty of Agricultural Sciences, Aarhus Univ., PO Box 50, DK-8830 Tjele, Denmark
    b Section of Environmental Engineering, Dep. of Biotechnology, Chemistry and Environmental Engineering, Aalborg Univ., Sohngårdsholmsvej 57, DK- 9000 Aalborg, Denmark

Abstract

Solute diffusion controls important processes in soils: plant uptake of nutrients, sorption–desorption processes, degradation of organic matter, and leaching of radionuclides through clay barriers. We developed a new method for measuring the solute diffusivity (solute diffusion coefficient in the soil relative to water) in intact soil samples (the Multiple Tracer, Filter Separated half-cell method using a Dynamic Model for parameter estimation [MT-FS-DM]). The MT-FS-DM method consists of half-cell diffusion of two pairs of counterdiffusing anionic tracers and a parameter estimation scheme that allows diffusion coefficients for tracers in the two half-cells to be estimated on the basis of two concentration profiles in each sample. The parameter estimation scheme uses a fully dynamic (time-resolved) simulation model. From sensitivity and uncertainty analyses of the dynamic model, we found that the MT-FS-DM method provided reliable results. We compared diffusivities measured on a sandy loam soil using the MT-FS-DM method with diffusivities from six sandy loam test soils from the literature. The new method can be used to estimate solute diffusivity in intact structured soil and provides a more confident estimate for solute diffusion due to the use of two tracer profiles in the same soil sample. Especially when we are interested in determining the diffusivity of a single intact soil sample, such as when relating solute diffusivity to other properties of the soil (e.g., microbial activity), this method will be an improvement over existing methods.

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