METAMODELS AND NONPOINT POLLUTION POLICY IN AGRICULTURE

Complex mathematical simulation models are generally used for quantita tive measurement of the fate of agricultural chemicals in soil. But it is less efficient to use them directly for regional water quality ass essments because of the large number of simulations required to cover the entire region and because the entire set of simulation runs must b e repeated for each new policy. To make regional water quality impact assessment on a timely basis, a simplified technique called metamodeli ng is suggested. A metamodel summarizes the input-output relationships in a complex simulation model designed to mimic actual processes such as groundwater leaching. Metamodels are constructed and validated to predict groundwater and surface water concentrations of major corn and sorghum herbicides in the Corn Belt and Lake States regions of the Un ited States. The usefulness of metamodeling in the evaluation of agric ultural nonpoint pollution policies is illustrated using an integrated environmental economic modeling system. For the baseline scenario, we estimate that 1.2% of the regional soils will lead to groundwater det ection of atrazine exceeding 0.12 mug/L, which compares well with the finding of an Environmental Protection Agency monitoring survey. The r esults suggest no-till practices could significantly reduce surface wa ter concentration and a water quality policy, such as an atrazine ban, could increase soil erosion despite the conservation compliance provi sions.