Herbicide Transport in a Restored Riparian Forest Buffer System

"Little is known about the effects of restored riparian forest bufferson transport of herbicides. The effect of a restored riparian forestbuffer system (RFBS) on transport of two herbicides, atrazine andalachlor, was studied during 1993-1994. Herbicides were applied above arestored 3-zone riparian buffer system in April of 1993 and 1994.Bromide was applied as a tracer with the April 1993 herbicideapplication. The buffer system was managed based on USDArecommendations and averaged 38 m in width. The system included a grassbuffer strip immediately adjacent to the application area (zone 3), anarea of planted pines downslope from the grass buffer (zone 2), and anarrow area of planted hardwoods containing the stream channel system(zone 1). Most of the herbicide transport in surface runoff occurredbefore June 30 with about 250 mm of cumulative rainfall after herbicideapplication. During this period of higher herbicide transport, atrazineand alachlor concentrations averaging 12.7 µg L^-1 and 1.3 µg L^-1, respectively, at the field edge were reduced to 0.66 µg L^-1 and 0.06 µg L^-1, respectively, as runoff neared the stream. The effect ofdilution versus other concentration reduction factors (infiltration,adsorption) was estimated for surface runoff using the bromideconcentration data. Concentration reduction was greatest per meter offlow length in the grass buffer adjacent to the field. There was onlyminor transport of herbicides through the buffer system in shallowgroundwater. Average herbicide concentrations were at or belowdetection limits in groundwater near the stream for the entire studyperiod. The restored riparian forest buffer had similar effects onherbicide transport as a mature buffer." [Abstract]

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