Submitted to: International Congress of Pesticide Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: April 30, 2002
Publication Date: N/A
Technical Abstract: Riparian buffer areas are widely touted for their ability to abate pollutants emerging from agricultural fields. We are studying this abatement process for the pesticides atrazine and metolachlor, using a heavily instrumented site located in Beltsville, Maryland. One of our overall goals in this study was to define the impact of a riparian zone on the transport and fate of pesticides. After much study of the the varying composition of pesticides in a first-order stream that drains the region, it was determined that large pulses of pesticide inputs occurred after spray application and that these pulses coincided with rain events. Careful examination of the composition of these samples indicated that even without field runoff, parent compounds were dominant in the pulse periods. The source of these pesticides appears to be linked to washoff from the canopy of the trees growing within the buffer area. We obtained samples of event-based wet deposition both within and outside of the tree canopy, as well as tree stemflow. Examination of residues in each type of rain collection demonstrated clear differences in the composition of parent compounds and degradates in the samples. A significant proportion of total atrazine (parent + degradates) in stemflow was measured as hydroxy atrazine (43.9%), and a significant proportion of metolachlor (parent + degradates) measured in through-fall was recovered as metolachlor ethane sulfonic acid (26.3%). The parent compound concentration was suprisingly high in the stemflow collection (45%), relative to the throughfall, especially considering that the bulk of rain actually reaching the ground in a hardwood forest system is throughfall (95-97%).