A new modeling approach for denitrification taking internal chemical gradients into account

In this paper a new modeling approach for denitrification and similar processes, which depend on the geochemical gradient between the air-filled larger pores in a soil and a water-filled matrix, is presented. The new modeling approach is capable of taking soil structural properties (obtained e.g. from X-ray CT) into account without requiring a high-resolution simulation. The model approach is explained and its application is demonstrated by simulating denitrification experiments conducted with repacked soil samples to assess the challenges and possibilities of the new approach. The main result of the modeling is that the nitrous oxide emission measured in the experiment can not be explained by a limited supply with oxygen alone at a carbon turnover rate derived from carbon dioxide emissions. It is additionally necessary that the microbial activity is concentrated in localized hot spots to create anaerobic conditions. This is confirmed by analytical solutions.