CONTRIBUTING AREA AND CONCENTRATION EFFECTS ON HERBICIDE REMOVAL BY VEGETATIVE BUFFER STRIPS

Deteriorated water quality due to nonpoint source pollution from herbi cides is one of the environmental problems receiving attention this de cade. One off-site best management practice (BMP) being suggested to i mprove water quality is vegetative buffer strips. This study was condu cted on a Storden loam soil, under simulated rainfall (6.35 cm/h), to determine the effects of nominal inflow concentration (0.1 and 1.0 mg/ L) and the ratio of drainage area to vegetated buffer strip area (simu lated to be I5:1 and 30:1) on the efficiency of vegetative buffer stri ps (12.2 m long) in removing herbicides dissolved in runoff water. Fou r treatments (2x2 factorial) replicated three times were included in t he study. Three inflow samples (each integrated over 15 min) and nine outflow samples (each integrated over 5 min) were collected from each plot and analyzed for three herbicides. Reductions of 41, 39, and 38% from plots having a relative area ratio of 15:1, and 37, 35, and 34% f rom plots having a relative area ratio of 30:1 were measured, respecti vely, for atrazine, metolachlor; and cyanazine. Although the percentag e of removal decreased for the larger area ratios for each herbicide, the decreases were not significant. Reductions of 29, 30, and 28% from plots having 0.1 mg/L nominal inflow concentration, and 49, 44, and 4 5% from plots having 1.0 mg/L nominal inflow concentration were measur ed, respectively, for atrazine, metolachlor; and cyanazine. The differ ences between reductions for the nominal inflow concentrations were si gnificant. Using a bromide tracer it was determined that the major fac tor in reduction of herbicide transport was infiltration of inflow int o the vegetative buffer strips.