Nonlinear dynamic model describing the fractionation of stable nitrogen isotopes in denitrification process with nitrous oxide formation

Soil thawing in permafrost zones can lead to the formation of readily digestible organic matter. This intensifies nitrate denitrification processes, leading to the formation of nitrous oxide, which produces a considerable greenhouse effect, and its release into the atmosphere. Therefore, studying denitrification processes is an important problem at a planetary scale. A mathematical model is proposed, based on a modification of the classical Monod dependence for the rate of the process as a function the concentrations of two substrates—nitrate and organic matter—describing the fractionation dynamics of stable nitrogen isotopes 14N and 15N in the process of denitrification of nitrates (NO3−). The model was calibrated against experimental data. The model gives a description of nonlinear fractionation dynamics at both excess and deficiency of digestible organic matter. The conventional Rayleigh equation, derived from first-order kinetics with respect to the substrate (nitrate) and the nonlinear model yield similar results.