Transient Microsite Models of Denitrification: II. Model Results1
- P. K. McConnaughey and
- D. R. Bouldin2
Solutions to four models of denitrification are presented. The models are based on four coupled reaction-diffusion equations, each model describing a different type of reaction term. The equations were solved by standard finite-difference methods and a boundary tracking technique when needed. For a chosen test problem, the zero-order model predicted sequential reduction of nitrogenous species, a N2/N2O ratio of 0.17, and relatively high transient NO-2 levels. The Michaelis-Menten model with threshold and concentration-dependent NO-3 and NO-2 inhibition of N2O reduction predicted N2/N2O ratios of 19.15 and 6.69, respectively. The competitive inhibition model predicted a N2/N2O ratio of 0.23 and N2 evolution followed N2O. A sensitivity analysis of the Michaelis-Menten model with concentration-dependent inhibition showed that the species of gaseous N evolved depended strongly on NO-3 levels in the soil. N2/N2O ratios were also influenced by O2 fluxes, diffusion coefficients, and diffusion distances that affect anaerobic volume and solute transport. The predicted N2/N2O ratios were less sensitive to the Michaelis-Menten kinetic parameters Vimax and KiM where i = nitrate, nitrite, or nitrous oxide. The qualitative behavior of gaseous N evolution as a function of nitrate levels, gaseous oxygen concentration, and depth of saturation predicted by the models agrees with data in the literature.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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