A new mathematical approach for calculating the contribution of anammox, denitrification and atmosphere to an N₂ mixture based on a ¹⁵N tracer technique

Abstract

Denitrification and anaerobic ammonium oxidation (anammox) have been identified as biotic key processes of N₂ formation during global nitrogen cycling. Based on the principle of a ¹⁵N tracer technique, new analytical expressions have been derived for a calculation of the fractions of N₂ simultaneously released by anammox and denitrification. An omnipresent contamination with atmospheric N₂ is also taken into account and is furthermore calculable in terms of a fraction. Two different mathematical approaches are presented which permit a precise calculation of the contribution of anammox, denitrification, and atmosphere to a combined N₂ mixture. The calculation is based on a single isotopic analysis of a sampled N₂ mixture and the determination of the ¹⁵N abundance of nitrite and nitrate (simplified approach) or of ammonium, nitrite, and nitrate (comprehensive approach). Calculations are even processable under conditions where all basal educts of anammox and denitrification (ammonium, nitrite, and nitrate) are differently enriched in ¹⁵N. An additional determination of concentrations of dissolved N compounds is unnecessary. Finally, the presented approach is transferable to studies focused on terrestrial environments where N₂ is formed by denitrification and simultaneously by codenitrification or chemodenitrification. Copyright © 2007 John Wiley & Sons, Ltd.