HR: 1340h
AN: H33B-0462    [Abstracts]
TI: Non-Equilibrium and Two-Dimensional Flow Field Effects on Bromide Transport at a Tile-Drained Field Site
AU: * Koehne, S
EM: mskoehne@mailblocks.com
AF: University of Rostock, Institute of Land Use, Justus-von-Liebig Weg 6 , Rostock, 18059 Germany
AU: Lennartz, B
EM: Bernd.Lennartz@auf.uni-rostock.de
AF: University of Rostock, Institute of Land Use, Justus-von-Liebig Weg 6 , Rostock, 18059 Germany
AU: Koehne, J M
EM: mkoehne@cora.tamu.edu
AF: Texas A@M University, Department of Biological and Agricultural Engineering, Scoates Hall 140, College Station, TX 77843 United States
AU: Simunek, J
EM: jsimunek@ucr.edu
AF: University of California Riverside, Department of Environmental Sciences, A135 Bourns Hall, Riverside, CA 92521 United States
AB: Systematically tile drained field sites have been recognized as one major source for surface water contamination with agrochemicals. To study the effects of tile drainage and physical non-equilibrium on solute transport in structured soil, bromide (Br-) transport experiments were carried out on three plots (N2, N4, and N8) with different tile drain spacings (16, 18, and 12 m, respectively) and depths (128, 101, and 96 cm) at the Infeld experimental field site (North-West Germany). Tile drain outflow along with Br- concentrations were monitored over a half-year period. For all three plots, the observed Br- concentrations fluctuated around low levels below 8 mg/l during the experiment without showing a distinct concentration maximum. Experimental observations of the N4 plot were analyzed using one- and two-dimensional (1D and 2D, respectively) single- and dual-porosity (SPM and MIM, respectively) model approaches. All SPM and MIM parameters were obtained from independent measurements, except for the calibrated MIM water and solute transfer coefficients. Water flow and Br- transport were then predicted for the N2 and N8 plots using the N4 model parameters. Measured low-level Br- concentrations could only be consistently calibrated (N4) and predicted (N2 and N8) using the 2D-MIM approach, while the 1D-MIM, 2D-SPM, and 1D-SPM approaches (in this order) increasingly deviated from the experimental data. SPM approaches yielded unrealistically high Br- peaks. MIM simulations suggested that solute transfer into the immobile region represented more than 60 % of the surface applied Br-, thus effectively reducing Br- peak concentrations in the drain effluent. Model simulations further suggested that the two-dimensional flow field induced by tile drains caused dispersion and dilution of the Br- observed in the drainage effluent. This study showed that both the 2D flow field and physical non-equilibrium transport should be explicitly accounted for in physically based model simulations of solute transport in tile-drained structured field soils.
DE: 5139 Transport properties
DE: 3210 Modeling
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting