Canonical denitrification

Canonical denitrification is carried out by heterotrophic bacteria during which nitrate (or nitrite) serves as the terminal electron acceptor for organic matter oxidation and the nitrogen oxides are reduced mainly to nitrogen (some nitrous oxide may be formed). The characteristic feature of canonical denitrification is that the reduction of N-oxides is coupled to electron transport phosphorylation (Knowles, 1982, 1996 Koike and Hattori, 1975). The capacity for respiratory denitrification is widespread among bacteria and is distributed across various taxonomic subclasses, mainly within the Proteobacteria (Zumft, 1997). 

Figure 6.1 Denitrification pathway involved in canonical denitrification. The four enzymes involved in the sequential reduction of nitrate are show.

Canonical denitrifiers are mainly facultative anaerobes that can modify their electron transport system to accommodate N-oxides as the terminal electron acceptor for organic carbon oxidation. However, commitment with the oxidation of proteins to CO2 and H2O is the liberation of the amino group as NH " ". Thus, canonical denitrification should be accompanied by the build up of NH " " concentrations, but... 

Like canonical denitrification anammox favorable conditions are those where oxygen has been depleted, and, like canonical denitrification, anammox has been found both in marine sediments and within the water column. Nitrogen stable isotope incubations are commonly used to distinguish between anammox and canonical denitrification. Typically, additions of + N03, and N03 ... 

N2 production in the oxygen depleted waters over the shelf, canonical denitrification was not detectable. 

Denitrification rates in the other two main ODZs, the ETNP and ETSP appear to be about 25 Tg a each Codispoti et al. (2002). In the ETNP denitrification was estimated by the geostrophic flux of nitrate deficit out of the ODZ area, with nitrate deficit determined from nutrient-density relationships (Codispoti, 1973 Codispoti and Richards, 1976). Volumetric estimates of denitrification rate based on ETS activity are in concert with this rate (Codispoti and Richards, 1973 Devol, 1975). The ETSP the denitrification rate is based on measurements of ETS activity (Codispoti and Packard, 1980). As with the Arabian Sea these estimates are again for canonical denitrification. It is likely that processes identified in the Arabian Sea are also occurring in the ETNP and ETSP. Thus, the rate of 25 Tg a might be raised to 50 Tg ar. Given a denitrification rate between 30 and 50 Tg a for each of the major ODZ s, global water-column denitrification would appear to between 90 and 150 Tg a. ... 

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