RESUMO
Substantial questions remain about the time required for groundwater nitrate to be reduced below 10 mg L(-1) following establishment of vegetated riparian buffers. The objective of this study was to document changes in groundwater nitrate-nitrogen (NO3-N) concentrations that occurred within a few years of planting a riparian buffer. In 2000 and 2001 a buffer was planted adjacent to a first-order stream in the deep loess region of western Iowa with strips of walnut and cottonwood trees, alfalfa and brome grass, and switch grass. Non-parametric statistics showed significant declines in NO3-N concentrations in shallow groundwater following buffer establishment, especially mid 2003 and later. The dissolved oxygen generally was >5 mg L(-1) beneath the buffer, and neither NO3-N nor DO changed significantly under a non-buffered control area. These short-term changes in groundwater NO3-N provide evidence that vegetated riparian buffers may yield local water-quality benefits within a few years of planting.