DENITRIFICATION IN SEDIMENT DETERMINED FROM NITROGEN ISOTOPE PAIRING

A new method for accurate and easy measurement of denitrification in sediments is presented. The water overlying intact sediment cores was enriched with (NO3-)-N-15 which mixed with the (NO3-)N-14 of the natural sources of NO3-. The formation by denitrification of single-labeled (NN)-N-14-N-15 and double-labeled (NN)-N-15-N-15 dinitrogen pairs was measured by mass spectrometry after a few hours incubation. Total denitrification including the formation of unlabeled (NN)-N-14-N-14 dinitrogen could be calculated assuming random isotope pairing by denitrification of the uniformly mixed NO3- species. In contrast to previous approaches, by this method it is possible to measure denitrification of both NO3- diffusing from the overlying water and NO3- from nitrification within the sediment.