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An Evaluation of Three Pesticide Runoff Loading Models¹

ABSTRACT

Three nonpoint source runoff models were tested and compared for their abilities to predict the movement of the pesticides toxaphene and atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-1,3,5-triazine) from a 15.6-ha watershed in the Mississippi Delta region and a smaller watershed in the Southern Piedmont. The three models are the Agricultural Runoff Management (ARM), Continuous Pesticide Simulation (CPS), and the Chemical, Runoff, and Erosion from Agricultural Management Systems (CREAMS). Published data on runoff, erosion, toxaphene, and atrazine runoff were used to test the models. Testing exercises indicated that all models accurately reproduced field data. For the total period of study, model predictions of total runoff differed from field observations by 15% or less. For the CPS and ARM models, predictions of total erosion differed from observations by 6%, whereas CREAMS underpredicted erosion by 25%. All models are within 10% of observations in overland toxaphene loss predictions. Five-year simulations indicated that the models can differ in their predictions of peak events. Sensitivity analysis indicated that ARM can predict higher losses of soluble chemicals than CPS or CREAMS, due to an interflow component unique to the ARM model. Similarly, estimation of a sediment enrichment in the CREAMS model resulted in higher toxaphene loss predictions than the other two models.

Key Words: mathematical simulation • runoff • toxaphene fate and transport

¹ Contribution of the Environmental Research Laboratory, U.S. Environmental Protection Agency, College Station Rd., Athens, GA 30613.

² Agricultural Engineers, EPA Environmental Research Lab.

Received for publication July 21, 1981.