Oxidation of ammonium to nitrite under iron-reducing conditions in wetland soils: Laboratory, field demonstrations, and push-pull rate determination

Nitrite (NO2) in soils has been observed under a variety of field conditions. The formation of NO2 in soils is possible during nitrification or denitrification depending on the soil conditions. This study presents a series of experiments performed at different scales that demonstrate the production of NO2 under iron-reducing conditions, in the absence of an initial nitrate pool. These experiments were performed either in a riparian wetland in New Jersey or in laboratory experiments using soils from the same location. The rates of use of NO2 and ammonium (NH4) determined in situ by performing push-pull experiments were of the same magnitude, supporting the observation of a steady-state NO2 pool under such anaerobic conditions. An isotope experiment performed with NH4 conclusively showed an existence of a pathway linking NH4 to dinitrogen gas under anaerobic iron-reducing conditions, in the absence of initial nitrate or NO2. Such observations indicate a possibility for the complete removal of NH4 from wetland soils under anaerobic conditions that develop when soils are water saturated.