Mathematical model for a fate of atrazine in water and sediment in the Khlong I Tao watershed, Thailand
2008
Pitiyont, B., Kasetsart Univ., P.O. Box 1072, Bangkok 10903 (Thailand). Dept. of Environmental Science | Saengpan, S., Kasetsart Univ., Bangkok 10900 (Thailand). Center of Sustainable land Use and Natural Resource Management | TangTam, N., Kasetsart Univ., Bangkok 10900 (Thailand). Faculty of Forestry
The fate of atrazine in water and sediment of the Khlong I Tao Sub-watershed, was studied from July 2004 to March 2005. About 75% of the area had been applied with Atrazine 90% WG at a rate of 2.25-3.75 kg/ha (360-600 g/rai) once a year to eliminate pre-emergence weeds. Stream water and sediment samples were collected 14 times at the outlet of the sub-watershed area for atrazine analysis. The atrazine concentrations in the water and sediment were found to be in the range of 0.03 to 4.4 ppb and 1 to 179 ppb, respectively. About 29% of the water samples exceeded the 2 ppb maximum allowable concentration in drinking water as defined by WHO (2003). Residue and rainfall data were used to develop a mathematical model for atrazine reflecting herbicide runoff in the watershed area. Elements of the model include the atrazine content accumulated in the watershed area before a specific rainfall day (delta ATZ supi-1), the number of days after atrazine application (D) and daily rainfall (R). Regarding the model developed, the atrazine content (%) which was carried out of the watershed area per atrazine content which was accumulated in the watershed area (ATZR) can result to the mathematical model in terms of regression model: Atrazine=63.322 + 2.402E-05D-4.462E-05R-2.745E-05deltaATZsubi-1; R2=0.964 based on storm events which occurred during the period of investigation. Using the ATZR model, the atrazine application rate for maize cultivation within the Khlong I Tao sub-watershed that can reduce atrazine concentrations in the stream water to near the drinking water standards at 43 days after application has been determined to be 2.305 kg a.i./ha.
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