A Cumulative Vulnerability Index to Account for Interactions of Hydrology, Timing of Application, and Dissipation Kinetics in Annual Atrazine Transport.

Year-to-year dynamics in weather affect both the timing of application and eventual hydrologic transport of pesticides. Further, most pesticides dissipate in the environment, which lessens risk of transport with time after application. Interactions among these three factors – hydrology, timing of application, and dissipation kinetics – render the detection of temporal trends in pesticide transport problematic. It is increasingly important to be able to discern temporal trends in pesticide transport, to judge effectiveness of management practices or simply ascertain whether changes were caused by management or weather. A cumulative vulnerability index (CVI) was developed to account for these three known factors and demonstrated to explain ~70% of inter-annual variation in atrazine load in the Goodwater Creek Experimental Watershed. In this work, the CVI was generalized to explicitly account for variation in watershed size, cropland area, and application rate. Results of tests for additional watersheds in the northeast Missouri claypan region will be presented to demonstrate the performance of the CVI in accounting for variations in land use and application rate. An example of the increased sensitivity of the time trend analysis that is possible when the CVI is used to account for known factors will also be presented.