Estimating atrazine leaching in the Midwest

Data from seven Management Systems Evaluation Areas (MSEA) were used to tes t the sensitivity of a leaching model, Pesticide Root Zone Model-a, to a va riety of hydrologic settings in the Midwest. Atrazine leaching was simulate d because it was prevalent in the MSEA studies and is frequently detected i n the region's groundwater. Short-term simulations used site-specific soil and chemical parameters. Generalized simulations used data available from r egional soil databases and standardized variables. Accurate short-term simu lations were precluded by lack of antecedent atrazine concentrations in the soil profile and water, suggesting that simulations using data for less th an five years underestimate atrazine leaching. The seven sites were ranked in order of atrazine detection frequency (concentration > 0.2 mu g L-1) in soil water at 2 m depth in simulations. The rank order of the sites based o n longterm simulations were similar to the ranks of sites based on atrazine detection frequency from groundwater monitoring. Simulations with Map Unit Use File (MUUF) soils data were more highly correlated with ranks of obser ved atrazine detection frequencies than were short-term simulations using s ite-specific soil data. Simulations using the MUUF data for soil parameters were sufficiently similarity to observed atrazine detection to allow the c redible use of regional soils data for simulating leaching with PRZM-2 in a variety of Midwest soil and hydrologic conditions. This is encouraging for regional modeling efforts because soil parameters are among the most criti cal for operating PRZM-2 and many other leaching models.