Validating GLEAMS with Field Data for Fenamiphos and Its Metabolites

Abstract
The GLEAMS (ground water loading effects of agricultural management systems) model was modified to simulate the generation and degradation of pesticide metabolites. Translocation of the metabolites within and through the root zone is considered. The modifications have been verified and preliminary validation has been made using field data. The paper presents the model concepts for metabolite generation and degradation. Results of model simulations for fenamiphos metabolite concentrations in the root zone are compared with observed concentrations from a research location in the Georgia coastal plain. These additions to GLEAMS will be helpful to model users working with those nonvolatile pesticides that have toxic metabolites with mobility and persistence characteristics differing from those of the parent compounds. Soil samples are taken periodically during the cropping season at depths corresponding to the GLEAMS model computational layers. The samples are analyzed for fenamiphos and its metabolites for comparison with model simulations. Field observations of metabolite mobility and persistence are compared with limited data in published literature.