Kinetics of the Nitrite to Nitric Oxide Reaction in Peat

Nitrite consumption and net NO production rates were measured across a pH range of about 3 to 8 and a temperature range of 5 to 40 or 10 to 70°C in nonsterile and sterile peat, respectively. The NO was sparged from stirred peat/water (1:10) slurries by N 2 or Ar carrier gas and analyzed. Addition of small quantities, 1 to 280 µg NO ‐ 2 ‐N g −1 dry peat, resulted in immediate No production. Biological production of NO exceeded chemical (nonbiological) production in nonsterile peat at pH >5. At pH >6, rates were less than 5 × 10 −9 mol min −1 g −1 dry peat with chemical production rates relatively insignificant. Decreasing pH increased rates significantly, particularly the nonenzymatic process, which apparently dominates NO production at pH <4.5. The chemical process was first order with respect to [NO ‐ 2 ]. The dependence of [H + ] was complex, approximating first‐order behavior at [H + ] <4 × 10 −4 mol g −1 dry peat and more strongly dependent at higher concentrations. The activation energy for the chemical reaction at pH 5.09 was 52.3 kJ mol −1 . The average value for nonsterile peat measured at pH 5.45 and 6.26 was 41.4 kJ mol −1 . The stoichiometric coefficient, a , for the overall reaction NO ‐ 2 → a No was 2.14 ± 0.39 in sterile peat and 2.00 ± 0.38 in nonsterile peat. In the latter case, where both enzymatic and nonenzymatic reactions occur, the value may also reflect the nonenzymatic reaction. Other nitrogenous gases, N 2 O, N 2 , NO x and CH 3 ONO were not observed under the flow conditions employed, suggesting that NO is the primary product of NO ‐ 2 reduction.