PESTICIDE REMOBILIZATION in VEGETATIVE FILTER STRIPS USING MESOSCALE MULTI-EVENT EXPERIMENTATION

VFSMOD, a numerical storm-based vegetative filter strip (VFS) design model, calculates pesticide mitigation from runoff through VFS in regulatory long-term ecotoxicological exposure assessments. After each storm, the model calculates degradation in the hiatus period and currently adopts a risk-conservative approach of full remobilization of surface pesticide residues during following storms. For highly-sorbed chemicals, although risk-conservative, this assumption has been shown to be unrealistic and a revised mechanistic modeling approach that produces accurate estimates across a wide range of chemicals is sought.  To test the ability of the revised modeling approach to predict VFS efficacy accurately over time, a mesoscale experiment was designed using triplicated 1.2Lx0.35Wx0.5D m soil boxes with VFS planted on the surface.  The device was instrumented to quantify how different types of pesticides are remobilized from the VFS surface over consecutive rainfall events with a hiatus in between. A rainfall simulator provides uniformly distributed precipitation input at 5-year storm intensity and a lateral inflow spreader provides runoff entering the upper side of the VFS. A chemical tracer is added to the pesticide and sediment inflow suspension and tracked through the system using a longitudinal grid of 12 soil moisture and electrical conductivity sensors, and 4 automatic flow meters at 3 drainage and 1 surface runoff outlets per box. Infiltration and runoff are quantified to close the mass balance.  The use of advanced instrumentation is vital to achieve data with high spaciotemporal resolution for analysis. Due to the complex nature of the VFS environment, system subcomponents are sequentially tested for water traceability. Before the addition of pesticides, the system was tested with water and tracer. Preliminary mass balance results will ensure all water is traceable through the system, which will be essential during later experimentation with pesticides.