We report a combination of δ¹⁵N-NO₃^- and δ¹⁵N-N₂O values along vertical porewater profiles through a Sphagnum-dominated, high-elevation peat bog. Our objective was to distinguish between N₂O production from NO₃^- via denitrification and N₂O consumption via reduction to N₂. Nitrate-N in runoff was isotopically heavier than NO₃^--N in atmospheric deposition, indicating export of organically-cycled NO₃^-. Constant N₂O concentrations in porewater profiles contrasted with a shift toward higher δ¹⁵N-N₂O values upward. In the 60-30 cm depth interval, a significant negative correlation between δ¹⁵N-NO₃^- and δ¹⁵N-N₂O values was observed. Higher δ¹⁵N values of residual NO₃^- in the deepest peat layer reflected higher rates of NO₃^- reduction. Isotopically heavier N₂O-N at shallower depths corresponded to residual N₂O following partial reduction to N₂.