Modeling pesticide transport in subsurface drained soils
1994
Thooko, L.W. | Rudra, R.P. | Dickinson, W.T. | Patni, N.K. | Wall, G.J.
Transport of chemicals through the soil profile and crop root zone, and the discharge from subsurface drainage lines into surface water can be a significant source of water pollution. This study measured and simulated subsurface drain outflows and atrazine loads in the subsurface drains from a field site in Ottawa, eastern Ontario, Canada, during 1988 and 1989. Corn was grown for silage at the site, and an H-flume with an automated water sampler was used to monitor temporal changes in quantity and quality of subsurface drain outflows from a 14-ha field site. A drainage simulation model, DRAINMOD, was combined with a chemical transport model, GLEAMS, to simulate the chemical transport of atrazine through the soil into the subsurface drain outflow. The model was calibrated with 1989 field data and compared to measured 1988 data. The calibrated DRAINMOD model predicted subsurface drain outflows for 1988 with a coefficient of determination of 0.40 and a standard error of the estimate, S(y/x), of 0.09 mm. Measured Atrazine concentrations exceeded 6 micrograms/kg on one occasion, but simulated Atrazine concentrations did not exceed 2.5 micrograms/kg. The model underpredicted atrazine mass in the subsurface drain outflows. Spring underpredictions of atrazine mass discharge was due to underprediction of subsurface drain flows while fall underpredictions were due to underpredictions of atrazine concentrations. Effects of temperature on atrazine half life and adsorption constant may be partially responsible for these results. This integrated model of chemical transport with the drainage simulation model provides a useful tool for studying chemical transport through the soil and crop root zone into surface waters.
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