A model for nitrite accumulation in soils

There have been recent reports of high nitrite concentrations occurring in both terrestrial and aquatic ecosystems. In the present study, modelling procedures were applied to results from soil incubation studies in order to quantify the relative contribution of nitrification and denitrification to nitrite accumulation. In order to quantify the simultaneous rates of nitrite formation from these processes, 15N pool dilution calculations were employed. These rates were employed as rate-determining steps in an empirical model describing the kinetics of the flow of N between ammonium, nitrite and nitrate compartments in order to simulate nitrite accumulation. Employing nitrification as the sole process generating nitrite results showed excellent agreement between observed and predicted nitrite accumulation. The rate of ammonium oxidation was only required to be slightly in excess of nitrite oxidation in order to generate nitrite accumulation. The available evidence suggests this imbalance in rates was due to nitrite oxidizers (Nitrobacter) being inhibited by free ammonia to a greater extent than ammonium oxidizers (Nitrosomonas).