... north of the town of Roland in Story County, Iowa, (Simpkins and Schultz, 199 3) was used as the basis for model inputs and simulation. The Bear Creek watershed is situated within the Des Moines ... Simulation of atrazine fate, leaching and runoff loss As atrazine load into the RBS and the runoff depth from the cornfield increased the atrazine mass loss in runoff leaving the RBS increased ... 199 9; Landa et al., 199 9; Martin and Watts, 199 9; Wu et al., 199 9). In general, the researchers were satisfied with RZWQM performance, but some suggestions were made to improve the model performance....