Oxidation of Ammonium to Nitrite Under Iron-Reducing Conditions in Wetland Soils

Laboratory, Field Demonstrations, and Push-Pull Rate Determination

Abstract

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 ¹⁵NH₄⁺ 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.