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Comparison of Pesticide Transport Processes in Three Tile-Drained Field Soils Using HYDRUS-2D

Arnaud Boivin^a,c,*, Jirka imnek^b, Michel Schiavon^c and Martinus Th. van Genuchten^a

^a USDA-ARS, George E. Brown, Jr., Salinity Lab., 450 West Big Springs Rd., Riverside, CA 92507
^b Dep. of Environmental Sciences, Univ. of California, Riverside, CA 92521
^c Laboratoire Sols et Environnement, UMR INPL-ENSAIA/INRA, 2 Avenue de la Forêt de Haye, B.P. 172, 54505 Vandoeuvre-lès-Nancy Cedex, France

View larger version (31K): [in a new window]   Fig. 1. Schematics of the layouts of the tile drainage systems at the Villey, Bouzule-1, and Bouzule-2 experimental sites.

View larger version (66K): [in a new window]   Fig. 2. Distribution of different soil horizons in the transport domain representing half the drain spacings at the Villey sandy loam site, the Bouzule-1 silt loam site, and the Bouzule-2 silty clay site.

View larger version (37K): [in a new window]   Fig. 3. Daily precipitation rates (solid bars) and temperatures (lines) recorded by the Météo France meteorological station in Toul (adjacent to the Villey site) and the INRA meteorological station at Champenoux (adjacent to the two Bouzule sites) during the experiments. The two vertical arrows indicate the times of bentazone application.

View larger version (41K): [in a new window]   Fig. 4. Finite element grid for the transport domain representing half the drain spacing of the modeled silty clay (Bouzule-2) site. The grid consisted of 2298 triangular elements and 1237 nodes.

View larger version (31K): [in a new window]   Fig. 5. Observed and simulated (a) instantaneous and (b) cumulative tile drain discharge rates, (c) bentazone concentrations in the drainage water, (d) daily amounts of bentazone exported with the drainage water, and (e) the cumulative amount of bentazone exported for the Villey sandy loam site. Solute transport simulations were performed with both the advection–dispersion equation (ADE) and the mobile–immobile nonequilibrium transport model (MIM).

View larger version (41K): [in a new window]   Fig. 6. Observed and simulated (a) instantaneous and (b) cumulative tile drain discharge rates, (c) bentazone concentrations in the drainage water, (d) daily amounts of bentazone exported with the drainage water, and (e) the cumulative amount of bentazone exported for the Bouzule-1 silt loam site. Drain discharge calculations were carried using three values of the saturated hydraulic conductivity (Ks) of the bottom layer 5 (Fig. 2b). Solute transport simulations were performed with the mobile–immobile nonequilibrium transport model (MIM) using three values of the mass transfer coefficient (s).

View larger version (36K): [in a new window]   Fig. 7. Observed and simulated (a) instantaneous and (b) cumulative tile drain discharge rates, using the standard van Genuchten–Mualem (VGM) and the modified van Genuchten–Mualem (MVGM) hydraulic functions; (c) bentazone concentrations in the drainage water; (d) daily amounts of bentazone exported with the drainage water; and (e) the cumulative amount of bentazone exported for the Bouzule-2 silty clay site. Solute transport simulations were performed with both the advection–dispersion equation (ADE) and the mobile–immobile nonequilibrium transport model (MIM).