Denitrification in sediment determined from nitrogen isotope pairing

Abstract

A new method for accurate and easy measurement of denitrification in sediments is presented. The water overlying intact sediment cores was enriched with 15NO3- which mixed with the 14NO3- of the natural sources of NO3-. The formation by denitrification of single-labeled (14N15N) and double-labeled (15N15N) dinitrogen pairs was measured by mass spectrometry after a few hours incubation. Total denitrification including the formation of unlabeled (14N14N) 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.