Simulation models are increasingly used to predict effects of conservation practices on transport of pesticides to water bodies. The Agricultural Policy/Environmental eXtender (APEX) model was used to predict the movement of the herbicide, atrazine, from treated fields to Jobos Bay National Estuarine Research Reserve located on Puerto Rico's southeast coast. The objective was to evaluate the sensitivity of APEX to atrazine half-life input values (DT50, time to 50% dissipation) on atrazine in surface runoff. Hydrologic calibration and validation was performed. Atrazine DT50 values were measured in the treated field and adjoining riparian buffer soil and indicated accelerated degradation due to repeated atrazine application. Three scenarios were evaluated: 18-, 55-, and 146-day DT50, representing measured field, measured riparian buffer, and the model default half-life values, respectively. APEX indicated use of the measured field soil atrazine degradation rate (18-day DT50) resulted in 33% lower transport from the field. Findings demonstrated the utility of this model in evaluating atrazine fate and transport, emphasized that use of measured soil dissipation values can improve model accuracy, and that large storm events likely dominate herbicide transport to coastal waters in the region.

APEX sensitivity to atrazine dissipation rate on surface runoff loss within a coastal zone in southeastern Puerto Rico

246th National Meeting (2013)

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