The geographical valley of the River Cauca in Colombia is characterized by intensive agriculture where sugarcane covers about 200,000 ha (50% of the arable land). Existing monitoring data for 2010 and 2011 showed high levels of the pesticides atrazine and simazine along the river. These herbicides are used in the region for pre-emergence weed control in sugarcane, maize and sorghum crops. The USDA AnnAGNPS model was used to study the fate of atrazine and simazine in the area in order to investigate the dynamics of the pesticides in the watershed and the areas of risk for water contamination. The advantages of using AnnAGNPS include the possibility of using meteorological data from different stations along the catchment as well as spatially-distributed soil and land use information. Spatial information used in the model included elevation data, soils, land use and precipitation data from eight stations along the valley. The watersheds and the stream network were generated by using a critical source area and a minimum source channel length of 600 ha and 2000 m, respectively, generating 1410 cell units and 567 reaches in the catchment. Since the study area did not cover the river source, the model was supplemented by adding upstream measured flow. Preliminary modelling results showed good agreement in the predictions which confirm that the intensive use of pesticides in the Valle del Cauca and the lack of pesticide application control in sugarcane pose a high risk to water bodies in the region which is exacerbated by the lack of monitoring data in the area. Mediacanoa and Guayabal are the areas at higher risk where both observed and predicted concentrations increased considerably compared to other sites. This presentation will give further analysis of the modelling results needed to understand the dynamics of contaminants in the area.

Assessing the fate of atrazine and simazine using the AnnAGNPS model in the geographical valley of the River Cauca in Valle del Cauca, Colombia

248th National Meeting (2014)

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