Simplified denitrification models: Overview and properties

This paper reviews simplified process models for denitrification. More than fifty models were considered. The majority of these (simple) models are based on potential denitrification—either measured as a soilʹs property or computed from organic C dynamics—or consider denitrification as a first-order decay process. As it is generally accepted that environmental soil conditions affect the denitrification process, reduction functions are used. Although denitrification is truly driven by the non-availability of oxygen, most authors argue that oxygen dynamics in soil is hard to simulate (or to measure). Therefore, water content is used as a complementary for oxygen diffusion. The higher the water content, the less oxygen will be present. Other factors that influence denitrification are nitrate–nitrogen content, soil temperature and soil acidity (pH). The availability of easily decomposable organic carbon determines the value of potential denitrification or the first-order decay rate constant. Although there seems to be consensus about the mathematical formulation of the simple process model, the shapes of the reduction functions differ largely between the models, especially for the water content reduction function. From a sensitivity analysis it follows that the model is most sensitive to the parameters of the water content reduction function, indicating that these parameters and the water content must be determined with great accuracy.