Brazil’s diverse agricultural landscape poses challenges to assess the impact of agricultural chemicals due to the differences in climate, unique soils, and agricultural management practices across the country. The aim of this project was to determine areas in Brazil that are currently under soybean production and potentially vulnerable to surface water runoff. Potential vulnerable areas were determined by conducting a GIS overlay of soils, climate, and topography data within likely soybean production areas. Potential vulnerable areas were defined as areas having soils with high levels of clay and rainfall with steep slopes, soils low in water holding capacity, and/or poor drainage. The results from this assessment can be used to select potential vulnerable areas for detailed exposure modeling using regulatory accepted environmental fate models. The municipalities with the highest soybean production are located in Mato Grosso (Central Brazil), Paraná, Santa Catarina and Rio Grande Do Sul in southern Brazil. The lowest runoff index was calculated to be 11 and the highest 35. Areas with lower runoff potential are found throughout Brazil and are more prevalent than high runoff potential areas. When the runoff index dataset is filtered to the soybean production areas, regions in Santa Catarina, Paraná and Goiás all have areas with a high (&gt;27) runoff index. This indicates that compared to other soybean producing regions, these areas are more likely to be vulnerable to runoff. Only 9.24% of the soybean regions fall in the highest runoff vulnerability class, having an index of 27 or greater. The majority, 70.66%, of the areas fall within the median range of vulnerability (index 16 – 26). The frequency distribution chart of runoff vulnerability indices shows a bi-modal distribution. The theoretical highest vulnerability value of 42 was never reached in this assessment.

Using GIS overlay methods to determine vulnerable surface water areas in Brazil

ACS Fall 2021

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