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Solute movement through an allophanic soil
G N Magesan1, I Vogeler, B E Clothier
1Forest Research, Private Bag 3020, Rotorua, New Zealand. gujja.magesan@forestresearch.co.nz
Journal of Environmental Quality
|December 17, 2003
Summary
Solute transport in allophanic soils, like Horotiu silt loam, shows bromide (Br) and chloride (Cl) retardation. Transport becomes more uniform with depth, unaffected by intermittent flow, indicating consistent soil properties.
Area of Science:
- Soil Science
- Environmental Science
- Geochemistry
Background:
- Allophanic soils are globally prevalent but under-researched regarding their transport properties.
- Understanding solute movement in these soils is crucial for environmental management and agricultural practices.
Purpose of the Study:
- To investigate the effects of soil water potential and flow regimes on solute transport in allophanic soils.
- To determine the extent of preferential solute transport and its depth dependence.
Main Methods:
- Undisturbed soil columns of Horotiu silt loam were used.
- Breakthrough curves (BTCs) and time domain reflectometry (TDR) were employed to monitor solute (Br and Cl) transport.
- The convection-dispersion equation (CDE) was used to model solute movement.
Main Results:
- No preferential flow was observed under unsaturated conditions, with flow and solute transport becoming more uniform with depth.
- Bromide and chloride exhibited retardation, with retardation values ranging from 1.5 to 1.9.
- Retardation increased with depth (5.0 to 10.0 cm), and intermittent flow did not affect leachate solute concentrations.
Conclusions:
- Allophanic soils like Horotiu silt loam demonstrate solute retardation for Br and Cl.
- Water and solute transport in these soils tend to be uniform with depth, even under intermittent flow conditions.
- Transverse mixing effectively eliminates concentration gradients, suggesting predictable solute behavior in this soil type.