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| Titel |
Imaging and quantification of preferential solute transport in an undisturbed soil |
| VerfasserIn |
John Koestel, Mats Larsbo |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094926
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| Publikation (Nr.) |
 EGU/EGU2014-10361.pdf |
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| Zusammenfassung |
| Despite significant advances during the last decades there are still many processes related to
non-equilibrium flow and transport in macroporous soil that are far from being completely
understood. The use of 3-D X-ray for imaging time-lapse 3-D solute transport has
a large potential to help advance the knowledge in this field. We visualized the
transport of a potassium iodide tracer (20 mg iodine ml-1 H2O) front through a small
undisturbed soil column (height 3.8 cm, diameter 6.8cm) under steady-state hydraulic
conditions using an industrial X-ray scanner. Following an elaborate and time-costly
illumination correction approach we yielded a series of seventeen 3-D difference images
of density-changes with respect to the start of the tracer application. The spatial
resolution was approximately 0.196 mm in all directions. The noise level varied
between 3% and 8% of the maximally expected density changes. We related the
time-lapse images to iodine concentrations using a linear calibration relationship.
The electrical conductivity, assumed proportional to the iodide concentration, was
measured in the effluent solution during the experiment. Eighty-five percent of the
applied iodine mass was recovered in the effluent and inside the column. The solute
transport through the soil predominantly took place within two cylindrical macropores,
by-passing more than 90% of the bulk soil volume during the entire experiment.
From these macropores the solute diffused into the surrounding soil matrix. We
illustrated the properties of the investigated solute transport by comparing it to a 1-D
convective-dispersive transport in terms of 1-D resident concentration profiles and to dilution
indices, here used as estimates of preferential transport. We, furthermore, showed that
the tracer diffusion from one of the macropores into the soil matrix could not be
fitted with a cylindrical diffusion equation. We are positive that similar studies will
help establishing links between soil structure and solute transport processes and
may lead to improvements in models for solute transport through undisturbed soil. |
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