Nitrification inhibitor method

Comparison of incubation methods The inhibitor methods using have advantages in higher sensitivity, smaller sample volume, easier analysis and therefore greater throughput than the tracer approaches. Therefore, in spite of the potential artifacts mentioned above, the inhibitor approach remains attractive to some investigators. Incubations of 24 h up to 12 days were used to compare the inhibitor, NH4+ oxidation and dilution methods to estimate nitrification... 

Briefly, any chlorine is removed from a water sample to be tested and the sample or a diluted version of it is adjusted to approximately pH 7. The pH buffer and nutrients are added along with a seed and/ or nitrification inhibitor if necessary. Two BOD bottles are filled to an extent such that insertion of the stoppers displaces all the air. The initial DO level (DOi) of the first bottle is determined using the Winkler titration method (a titrimetric determination) or using one of the modifications of this method (most commonly the azide modification). The second bottle is then incubated for 5 days, at which time the DO level (DOf) is determined ... 

Inhibitor approaches similar to those described earher for water samples have been used in sediments (Henricksen et ah, 1981 MUler et ah, 1993). The methyl-fluoride and difluoromethane methods (Cafifey and MUler, 1995 MUler et al., 1993) seem particularly promising because the gases can diffuse thoroughly into the core with minimal disturbance of microzones and gradients. These NH4 oxidation inhibitors are added to cores and the accumulation of NH4+ over time is assumed to represent the net rate of nitrification. Other processes that consume NH4+ would lead to an underestimate of the rate. De Bie et al. (2002) found that both... 

Both NH3 oxidizers and N02 oxidizers, but especially the former, are susceptible to inhibition by a wide range of compounds, and several different modes of action have been documented (Bedard and Knowles, 1989). The two most common modes of inhibition are (1) interference with the active site of the primary enzyme (i.e., NH3 monooxygenase in AOB N02 oxidoreductase in NOB) by compounds that share structural homology with NH3 or N02 and (2) metal binding compounds, which interfere with the action or availability of copper in the NH3-oxidizing enzymes. In both NH3- and N02 -oxidizers, the susceptibility to inhibitors by key enzymes forms the basis of some methods used to measure the rate of nitrification in the environment (see above). 

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