Effect of grass buffer strips on nitrate export from a tile-drained field site

Initial nitrate concentrations in the shallow groundwater entering the buffer strip were up to 98 mg L−1, with median values ranging between 2 and 36 mg L−1. Within the buffer strip, these concentrations decreased by 56-98 %. We assume that this reduction was caused by denitrification processes in two study years and dilution after snowmelt in the third year. The width of the buffer strip did not have any influence on the nitrate reduction. Presumably, site characteristics and the hydraulic conductivity are of greater importance. The groundwater nitrate load was reduced by the buffer strip, but the contribution of the groundwater to total ditch nitrate load was minor. We conclude that possible positive effects of buffer strips on groundwater quality do not ameliorate surface water quality at tile-drained field sites.