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Spatial and Temporal Dynamics of Preferential Bromide Movement towards a Tile Drain

^a Department of Biological & Agricultural Engineering, Texas A&M University, Scoates Hall, College Station, TX 77843-2117
^b Institute of Soil Landscape Research, Leibniz-Centre for Agricultural Landscape and Land Use Research (ZALF), Müncheberg, Germany

View larger version (51K): [in a new window]   Fig. 1. (a) Schematic of the Bokhorst experimental plot, including interpolated groundwater elevations in m above sea level on 25 Mar. 1997. Symbols: piezometer or well location (cross), drain-pipe connected to monitoring station (thick line), drain-pipe ending in trench (hatched line). (b) Time table of the experiment.

View larger version (22K): [in a new window]   Fig. 2. Schematic of the experimental plot: (a) top view, (b) cross-section view.

View larger version (35K): [in a new window]   Fig. 3. Time series of experimental observations: (a) natural rainfall (open bars) and tile drain discharge rates (line), (b) groundwater levels as observed in selected wells, and (c) Br– concentrations in tile drain effluent, and second irrigation events.

View larger version (22K): [in a new window]   Fig. 4. Pressure heads in soil at different depths below the application strip as recorded with tensiometers during the irrigation on Day 97 (25 Mar. 1997), (a) at 1-m lateral distance from the drain and (b) at 5-m lateral distance from the drain.

View larger version (10K): [in a new window]   Fig. 5. Water contents in soil at different depths and distances from the tile drain as recorded with TDR probes during irrigation on Day 97 (25 Mar. 1997). Legend: 1 m; 0.3 m denotes horizontal offset from the drain (1 m) and depth (0.3 m), respectively.

View larger version (32K): [in a new window]   Fig. 6. Spatial distribution of measured Br– concentrations (mg L–1) on Day 68 (24 Feb. 1997) in Transect 1.

View larger version (30K): [in a new window]   Fig. 7. Data and model results using the mobile–immobile model (MIM), the convection dispersion model without (CDM-forward) and with (CDM-inverse) inverse parameter estimation: (a) drain discharge rates, (b) cumulative drain discharge, (c) Br– concentration of the drain effluent during the entire experimental duration, and (d) from 97 to 99 d, as simulated with the MIM for the mobile region (MIM, mobile), immobile region (MIM, immobile), and for the mobile region when only the first Br– application [MIM, mobile (first application)] was considered.

View larger version (41K): [in a new window]   Fig. 8. Spatial Br– concentration distributions in the mobile and immobile regions as obtained with the MIM simulation at different times after the first tracer application.

View larger version (36K): [in a new window]   Fig. 9. Bromide concentrations of the soil solution on Day 140 (7 May 1997) of Transect 2 for (a) observations, (b) forward simulation results for the convection–dispersion model (CDM-forward), and c) inverse simulation results for the convection–dispersion model (CDM-forward).