Contributing area and concentration effects on herbicide removal by vegetative buffer strips

Deteriorated water quality due to nonpoint source pollution from herbicides is one of the environmental problems receiving attention this decade. One off-site best management practice (BMP) being suggested to improve water quality is vegetative buffer strips. This study was conducted 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 (simulated to be I5:1 and 30:1) on the efficiency of vegetative buffer strips (12.2 m long) in removing herbicides dissolved in runoff water. Four treatments (2x2 factorial) replicated three times were included in the 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% from plots having a relative area ratio of 30:1 were measured, respectively, for atrazine, metolachlor; and cyanazine. Although the percentage 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 45% from plots having 1.0 mg/L nominal inflow concentration were measured, respectively, for atrazine, metolachlor; and cyanazine. The differences between reductions for the nominal inflow concentrations were significant. Using a bromide tracer it was determined that the major factor in reduction of herbicide transport was infiltration of inflow into the vegetative buffer strips.