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.