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 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 N. 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.