Pesticide Transport With Surface Runoff and Subsurface Drainage Through a Vegetative Filter Strip

Vegetative filter strips (VFS) have become an established best management practice during the last 25 years. Thisstudy examined the effectiveness of VFS of brome grass in central Iowa for reducing the mass transport of sediment andpesticides (atrazine, acetochlor, and chlorpyrifos) with surface runoff under natural rainfall conditions. Measurements ofpesticide concentrations in water from a single subsurface drain under the plots were also made. Overall results showed thatmany factors affect pesticide transport, such as rainfall timing and intensity, hydrology, sourcetoVFS area ratios, and theadsorption properties of pesticides in VFS inflow. Two primary mechanisms (inflow water infiltration and sedimentdeposition) had a significant effect on pesticide passage through VFS. Sediment deposition increased with decreased flowvolume and velocity, and was considerably higher for the 15:1 arearatio plots than for the 45:1 plots; this in turn aided inthe reduction of transport of pesticides adsorbed to sediment. Reductions in atrazine and acetochlor transport were primarilycontrolled by the infiltration efficiency of the VFS, as they are moderately adsorbed, and the major portion of these pesticidesmoved in solution in the surface runoff water phase. Chlorpyrifos was highly adsorbed to the sediment, making sedimentdeposition in the VFS equally, if not more, important than infiltration for mass removal. The herbicides (atrazine andacetochlor) had low to moderate adsorption characteristics and moved primarily in the runoff water phase. Data collectedfor the subsurface drainage from the tile line showed that there were measurable concentrations of the moderately adsorbedherbicides in the tile flow at the time surface runoff was taking place; however, concentrations of the more strongly adsorbedchlorpyrifos were below detection. The statistical difference was most prominent in the event with the smallest runoff volume.This showed that at lower flow rates, VFS can effectively reduce runoff, sediment, and pesticide transport from cropland.