Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/1999
Publication Date: N/A
Interpretive Summary: A leaching model, PRZM-2, was applied to data from seven research sites that were part of the Management Systems Evaluation Areas program. This was done to test the potential for using this model to estimate the leaching of herbicides below the root zone in the Midwest. Atrazine was selected for this test because it is the herbicide most commonly found in groundwater of the region. The seven sites represent a range of hydrologic conditions that are commonly found in the region. Simulations that ran for 6 years or fewer used site-specific data on soil parameters and factors affecting atrazine decay and movement. Long-term simulations were made using regional soils data and generalized information on factors affecting atrazine decay and movement. The ranking of sites from most leaching to least leaching was generally similar between model results and measured atrazine in groundwater beneath each site. The ranking comparison was better between simulations using generalized input parameters than for simulations using site-specific parameters. The implications of these results are encouraging because they justify the use of PRZM-2 for regional modeling. Modeling is much less expensive than monitoring and will provide a method to evaluate changes in farming practices that include atrazine or similar herbicides.
Technical Abstract: Data from seven Management Systems Evaluation Areas (MSEA) were used to test the sensitivity of the model, PRZM-2, to hydrologic settings common in the Midwest. Long-term simulations using regional and generalized input parameters produced ranks of leaching potential similar to those measured, lending credence to the model's use throughout the region. Atrazine leaching was simulated because it frequently occurs in the region's groundwater. Short-term simulations used site-specific data provided by researchers at each MSEA. Long-term, generalized simulations used data available from regional soil databases and standardized degradation rates and sorption coefficients. Accurate site-specific simulations were precluded by lack of antecedent atrazine concentration data, raising questions about simulation using data sets of less than five years. Ranks of simulated atrazine detections among the study sites were similar to those observed. Generalized, long-term simulations underestimated the occurrence of atrazine for the three sites with small concentrations. Simulations generally overestimated concentrations for four sites with the greatest frequencies of atrazine detection. The long-term simulations using generalized soils data produced concentrations that compared more favorably with observed detection frequencies than did short-term, site-specific simulations. This is encouraging for regional modeling efforts because soil parameters are among the most critical for operating PRZM-2 and many other leaching models.