Transport of bromide in the Bainsvlei soil: Field experiment and deterministic/stochastic model simulation. I. Continuous water application
Ketema Tilahun A C , J. F. Botha A and A. T. P. Bennie BA Institute for Groundwater Studies, The University of the Free State, PO Box 339, Bloemfontein 9300, Republic of South Africa.
B Department of Soil, Crop, and Climate Sciences, The University of the Free State, PO Box 339, Bloemfontein 9300, Republic of South Africa.
C Corresponding author. Present address: Alemaya University, PO Box 138, Dire Dawa, Ethiopia. Email: ketematilahun@yahoo.com
Australian Journal of Soil Research 43(1) 73-80 https://doi.org/10.1071/SR03014
Submitted: 29 January 2003 Accepted: 20 September 2004 Published: 14 February 2005
Abstract
A field-scale tracer study was carried out in a sandy loam Bainsvlei soil of South Africa. The objectives were to study the leaching of solutes in this soil and analyse the result using deterministic and stochastic solute transport models. A rainfall simulator was used to apply water and solution on an area 100 by 100 cm at a flux rate of 5.41 mm/h. A neutron probe access tube was drilled at the centre of the plot to a depth of 200 cm. Four tensiometers were installed at 30, 45, 90, and 120 cm depths. After steady-state condition was attained, a conservative tracer Br– was then applied as KBr at a rate of 13.5 g Br/m2. Soil samples were taken 10 times at 20-cm depth intervals to a depth of 160 cm and Br– concentration was analysed using ion chromatography. Transport parameters were determined using a convection–dispersion equation (CDE) and the stream tube model (STM).
The average Br– mass recovery was almost 100%. The average pore-water velocity determined from soil water balance was 2.08 cm/h. Pore-water velocities determined with CDE and STM were 2.24 cm/h and 2.20 cm/h, respectively. Bromide velocities of peak concentration and solute centre of mass were 2.05 cm/h and 2.02 cm/h, respectively. Generally, these results indicate that the Br– moved almost as a piston flow in this soil. The deterministic CDE and the stochastic STM performed almost equally well in estimating the transport parameters.
Additional keywords: convection–dispersion equation, CXTFIT, stream tube model.
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