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Evaluation of Nutrient Modeling by SWAT under Tropical Conditions

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 21-24 February 2010, Universidad EARTH, Costa Rica  701P0210cd.(doi:10.13031/2013.29405)
Authors:   Priscilla Basilio Cardoso Barros Trindade, Luis Felipe Nunes Coutinho, Marco Aurélio Costa Caiado, Conrad Dean Heatwole
Keywords:   SWAT, Brazil, watershed model, tropics, diffuse pollution, nitrogen, phosphorus

SWAT was applied to a small catchment located in the state of Esprito Santo, southeastern Brazil, targeting the verification of its appropriateness to be used to simulate the input of nutrients to tropical water bodies. The catchment was considered to have a single type of soil and be fully planted with corn. Seven fertilization scenarios were simulated. The relative sensitivity of the model to the variation of nutrient application was calculated having the amount of NO3--N, NH4+ -N, and PO4-3-P leaving the catchment as variables of observation. In addition, model output was compared with measured values from highly cropped watershed located in the same Brazilian State. It was observed that SWAT adequately simulated the relationships between monthly rainfall and nutrient output from the watershed. A positive relative sensitivity was observed using the output of NO3--N, NH4+ -N, and PO4-3-P as variables of observation, but model sensitivity was higher for NO3--N and PO4-3-P than for NH4+ -N. Simulated values of NO3--N, NH4+ -N, and PO4-3-P leaving the catchment were significantly higher than the ones measured in the intensely cropped catchments. Besides, a large difference between the simulated and measured ratio of NH4+ -N / NO3--N was observed. We conclude that SWAT should be used carefully when simulating the output of nutrients from tropical catchments, and that a deeper analysis of the model should precede its use in the tropics.

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