GLEAMS-TC - A 2-COMPARTMENT MODEL FOR SIMULATING TEMPERATURE AND SOIL-WATER CONTENT EFFECTS ON PESTICIDE LOSSES

Many pesticide fate and transport models, including the GLEAMS model, overestimate pesticide degradation during its later stages of residenc e in soil. Except for runoff events shortly after pesticide applicatio n, models using equilibrium sorption kinetics often underestimate sedi ment-transported pesticides. To address concerns about transport of lo w levels of pesticides by runoff to sensitive ecosystems over annual o r longer time cycles, GLEAMS was modified using a two-compartment pest icide-state model and algorithms for adjustment of degradation rates f or temperature and soil water contents. Two pesticide pools, labile an d nonlabile, were linked using first-order kinetics, with the forward and reverse rate constants between these pools as the only two additio nal inputs required for the model, GLEAMS-TC. GLEAMS-TC was calibrated successfully using 3 years of field data, Long-term pesticide persist ence in soil was represented. Comparing model predictions with observe d data, GLEAMS-TC simulated observed pesticide sediment transport, whe reas GLEAMS underestimated observed data by a factor of 4., Sensitivit y to rates of pesticide exchange between the two pools and impact on r unoff losses were demonstrated with 50-year simulations. GLEAMS-TC is a research tool for investigating changes in pesticide state in soils as a function of exposure time, environmental variables, and interrela tionships between pesticide degradation, mobility, and fate and transp ort in the environment.