Relationship between nitrogen isotope ratios of NO3−and N2O in vertical porewater profiles through a polluted rain-fed peat bog

Abstract We report a combination of δ 15 N-NO 3 - and δ 15 N-N 2 O values along vertical porewater profiles through a Sphagnum -dominated, high-elevation peat bog. Our objective was to distinguish between N 2 O production from NO 3 − via denitrification and N 2 O consumption via reduction to N 2 . Nitrate-N in runoff was isotopically heavier than NO 3 − -N in atmospheric deposition, indicating export of organically-cycled N. Constant N 2 O concentrations in porewater profiles contrasted with a shift toward higher δ 15 N-N 2 O values upward. In the 60-30 cm depth interval, a significant negative correlation between δ 15 N-NO 3 - and δ 15 N-N 2 O values was observed. Higher δ 15 N values of residual NO 3 − in the deepest peat layer reflected higher rates of NO 3 − reduction. Isotopically heavier N 2 O-N at shallower depths corresponded to residual N 2 O following partial reduction to N 2 .