N2O isotope approaches for source partitioning of N2O production and estimation of N2O reduction - validation with 15N gas-flux method in laboratory and field studies.

The approaches based on natural abundance N₂O stable isotopes are often applied for the estimation of mixing proportions between various N₂O producing pathways as well as for estimation of the extent of N₂O reduction to N₂. But such applications are associated with numerous uncertainties and hence their limited accuracy needs to be considered. Here we present the first systematic validation of these methods for laboratory and field studies applying the ¹⁵N gas-flux method as the reference approach. Besides applying dual isotope plots for interpretation of N₂O isotopic data, for the first time we propose a three dimensional N₂O isotopocule model based on Bayesian statistics to estimate the N₂O mixing proportions and reduction extent based simultaneously on three N₂O isotopic signatures (δ¹⁵N, δ¹⁵N^SP and δ¹⁸O). Determination of mixing proportions of individual pathways with N₂O isotopic approaches appears often imprecise, mainly due to imperfect isotopic separation of the particular pathways. Nevertheless, the estimation of N₂O reduction is much more robust, when applying optimal calculation strategy, reaching typically accuracy of N₂O residual fraction determination of about 0.1. [ABSTRACT FROM AUTHOR]