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ARS Home » Southeast Area » Tifton, Georgia » Southeast Watershed Research » Research » Publications at this Location » Publication #289337
Title: Atrazine transport within a coastal zone in Southeastern Puerto Rico: a sensitivity analysis of an agricultural field model and riparian zone management model

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

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2016
Publication Date: 3/22/2016
Citation: Williams, C.O., Lowrance, R.R., Potter, T.L., Bosch, D.D., Strickland, T.C. 2016. Atrazine transport within a coastal zone in Southeastern Puerto Rico: a sensitivity analysis of an agricultural field model and riparian zone management model. Springer International Publishing Switzerland. doi:10.1007/s10666-016-9508-4.

Interpretive Summary: Models that estimate the effects of agricultural conservation practices on water quantity and quality have become increasingly important tools for short- and long-term assessments. In this study, we simulated transport of a herbicide (atrazine) in a portion of the Jobos Bay watershed, Puerto Rico using two models, one for simulating the upland agricultural field and one for simulating the adjacent riparian zone. The model used to simulate upland field outputs was the Agricultural Policy/Environmental eXtender (APEX) model and the model used to simulate riparian functions was the Riparian Ecosystem Management Model (REMM). The field was irrigated with a center pivot system for the first two years of the study and the four quadrants of the field were treated as subareas in the APEX model. The objectives were to evaluate the sensitivity of APEX to atrazine half-life input values and evaluate the effects of a three-zone riparian buffer system on atrazine transport. The study area was part of the Jobos Bay Watershed on the south coast of Puerto Rico. The Jobos Bay watershed is part of the USDA Conservation Effects Assessment Project (CEAP) and the coastal waters are a National Estuarine Research Reserve. APEX was used to simulate inputs of atrazine to REMM and REMM was used to simulate a three zone buffer of grass and trees. Different half-life values used in APEX resulted in up to a 33% difference in atrazine transport with longer half-life (slower pesticide dissipation) leading to greater atrazine transport. The REMM simulated riparian buffer reduced atrazine transport by as much as 77% in surface runoff, 100% in subsurface flow and by as much as 50% in sediment transport. Almost all of the atrazine transport in both APEX and REMM was in dissolved form in surface runoff. Although the buffer was effective at reducing atrazine transport, in a large event due to a tropical storm, there was only a 37% reduction in atrazine transport. REMM simulated that the part of the buffer nearest the field, occupied by perennial grasses, had significantly greater in total atrazine reduction than the part of the buffer further from the field. REMM simulations showed that a 157 m buffer was not significantly more effective in removing atrazine than an 80 m buffer.

Technical Abstract: Water quality models are used to predict effects of conservation practices to mitigate the transport of herbicides 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 atrazine from fields and through a riparian buffer in a coastal watershed in Puerto Rico. The 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 riparian buffer system on atrazine transport. The study area was part of the Jobos Bay Watershed on the south coast of Puerto Rico. The Jobos Bay watershed is part of the USDA Conservation Effects Assessment Project (CEAP) and the coastal waters are a National Estuarine Research Reserve. APEX was used to simulate inputs of atrazine to REMM and REMM was used to simulate a three zone buffer of grass and trees. Different DT50 values used in APEX resulted in up to a 33% difference in atrazine transport with longer DT50 leading to greater atrazine transport. The REMM simulated riparian buffer reduced atrazine transport by as much as 77% in surface runoff, 100% in subsurface flow and by as much as 50% in sediment transport. Almost all of the atrazine transport in both APEX and REMM was in dissolved form in surface runoff. Although the buffer was effective at reducing atrazine transport, in 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 showed that a 157 m buffer was not significantly more effective than an 80 m buffer.