N ₂O isotope approaches for source partitioning of N ₂O production and estimation of N ₂O reduction – validation with the ¹⁵N gas-flux method in laboratory and field studies

The approaches based on natural abundance inline-formulaN₂O stable isotopes are often applied for the estimation of mixing proportions between various inline-formulaN₂O-producing pathways as well as for estimation of the extent of inline-formulaN₂O reduction to inline-formulaN₂. But such applications are associated with numerous uncertainties; hence, their limited accuracy needs to be considered. Here we present the first systematic validation of these methods for laboratory and field studies by applying the inline-formula¹⁵N gas-flux method as the reference approach.

Besides applying dual-isotope plots for interpretation of inline-formulaN₂O isotopic data, for the first time we propose a three dimensional inline-formulaN₂O isotopocule model based on Bayesian statistics to estimate the inline-formulaN₂O mixing proportions and reduction extent based simultaneously on three inline-formulaN₂O isotopic signatures (inline-formulaδ¹⁵N, inline-formulaδ¹⁵Ninline-formula^SP, and inline-formulaδ¹⁸O). Determination of the mixing proportions of individual pathways with inline-formulaN₂O isotopic approaches often appears imprecise, mainly due to imperfect isotopic separation of the particular pathways. Nevertheless, the estimation of inline-formulaN₂O reduction is much more robust, when applying an optimal calculation strategy, typically reaching an accuracy of inline-formulaN₂O residual fraction determination of about 0.15.