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

item WILLIAMS, CANDISS - Natural Resources Conservation Service (NRCS, USDA)
item Potter, Thomas
item Lowrance, Robert
item Williams, Randall
item Bosch, David - Dave
item Strickland, Timothy - Tim

Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/27/2013
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Simulation models are increasingly used to predict effects of conservation practices on transport of pesticides to water bodies. We used two models - the Agricultural Policy/Environmental eXtender (APEX) and the Riparian Ecosystem Management Model (REMM) to predict the movement of the herbicide, atrazine, from treated fields through a vegetated buffer to Jobos Bay National Estuarine Research Reserve located on Puerto Rico’s southeast coast. Models were used in series with APEX simulated edge-of-field outputs routed through a grass-forest buffer using REMM. Objectives were to evaluate the sensitivity of APEX to atrazine half-life input values (DT50, time to 50% dissipation) and evaluate the effects of a three-zone buffer system on atrazine transport. The study was part of the USDA Conservation Effects Assessment Project (CEAP). Atrazine DT50 values were measured in both field and buffer soils demonstrated accelerated enhanced degradation in field soil due to repeated atrazine application. APEX indicated use of the measured field soil atrazine degradation rate resulted in 33% lower transport from the field. REMM simulations indicated that the buffer system had the potential to reduce atrazine transport by 77% in surface runoff, 100% in subsurface flow and by as much as 50% in sediment transport for the entirety of the study. Almost all atrazine transport in APEX and REMM was in dissolved form in surface runoff. Although REMM indicated that the buffer was effective at reducing atrazine transport, during a large event due to a tropical storm, there was only a 37% reduction in atrazine transport. The REMM simulated Zone 3 (perennial grasses) of the buffer was significantly (p<0.001) greater in total atrazine reduction (56%) compared to zones 1 and 2 (forest). REMM simulations also showed that a 157 m buffer was not significantly more effective than an 80 m buffer. Findings demonstrated the utility of these models in evaluating atrazine fate and transport, emphasize 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.