Technical Abstract: Riparian ecosystems, through their unique positions in the agricultural landscape and ability to influence nutrient cycles, have the potential to mitigate nutrient loading to surface and ground waters. The purpose of this study was to determine the fate of NO3 in shallow ground water moving along a lateral flowpath from a grass seed cropping system through an undisturbed herbaceous riparian area. Soil A (30-45 cm) and C horizon (135-150 cm) NO3 and dissolved oxygen concentrations were significantly higher in the cropping system than the adjacent riparian area. Nitrate concentrations in both horizons of the riparian soil were consistently close to the detection limit (0.05 mg N L-1) while cropping system concentrations ranged from 1 to 12 mg N L-1. Riparian soil water Cl data suggested that some dilution of NO3 occurred from seasonal recharge by precipitation. However, a sharp decrease in the NO3/Cl ratios as water moved into the riparian area from the cropping system indicated that dilution of NO3 concentrations from upwelling or divergence along the lateral flowpath did not likely occur. The riparian area A horizon soil water had higher soluble organic carbon than the cropping system and has also been shown to support higher soil microbial biomass so that when the riparian soil became saturated, available electron donors (O2, NO3) were rapidly reduced. Carbon limitations in the cropping system likely led to microbial respiration using primarily O2 and to a lesser degree NO3. Data suggested that a riparian area width of 17m was sufficient for soil water NO3 removal from this landscape.