Nitrogen cycle denitrification

Christensen J. P., Murray, J. W., Devol, A. H. and Codispoti, L. A. (1987). Denitrification in continental shelf sediments has major impact on oceanic nitrogen cycle. Glob. Biogeochem. Cycles 1,97-116. 

The global nitrogen cycle is often referred to as the nitrogen cycles, since we can view the overall process as the result of the interactions of various biological and abiotic processes. Each of these processes, to a first approximation, can be considered as a self-contained cycle. We have already considered the biological cycle from this perspective (Fig. 12-1), and now we will look at the other processes, the ammonia cycle, the cycle, and the fixation/denitrification cycle. 

Delwiche, C. C. (1981). The nitrogen cycle and nitrous oxide. In "Denitrification, Nitrification, and Atmospheric Nitrous Oxide" (C. C. Delwiche, ed.). Wiley, New York. 

Thus, from the viewpoint of environmental risk assessment (critical loads) the most important exposure pathways are nitrate leaching and denitrification, which are both very sensitive to anthropogenic pollution. These links of biogeochemical nitrogen cycle should be firstly quantitatively parameterized to assessing environmental risk. 

In denitrification, part of the biological nitrogen cycle, nitrate in the soil is converted via four enzymatic reactions stepwise to nitrite, nitric oxide and nitrous oxide to finally yield gaseous nitrogen. 

Given all these uncertainties, it is not currently possible to determine whether the nitrogen and/or phosphorus cycles are in a steady state. Indeed, anthropogenic inputs of both are now so large that the maintenance of a steady state seems unlikely. As noted earlier, natural deviations from a steady state in the nitrogen cycle are also deemed likely given the large spatial separation between the locales where denitrification and BNF take place. 

Nitrite reductases (NiRs)—enzymes found in several strains of denitrifying bacteria— catalyze the one-electron reduction of nitrite anion to nitric oxide (Equation 1). - In addition to the importance of this process in the global nitrogen cycle (Figure 1), further incentive for the study of the denitrification process is provided by its environmental impact, ranging from the production of NO as a pollutant and NjO as a potent greenhouse gas, to lake eutrophication due to farm runoff that contains high concentrations of nitrates and nitrites. 

It is remarkable that the nitrogen cycle employs extreme oxidation-reduction states of nitrogen. Nitrification carries N from 3 to 5, whereas denitrification reduces N from 5+ to 0. A more direct cycle using only redox states of N between... 

Joye, S.B., and Paerl, H.W. (1994) Nitrogen cycling in marine microbial mats rates and patterns of denitrification nitrogen fixation. Mar. Biol. 119, 285-295. 

Koike, I., and Sprensen, J. (1988) Nitrate reduction and denitrification in marine sediments. In Nitrogen Cycling in Coastal Marine Environments. SCOPE 33 (Blackburn, T.H., and Sprensen, J., eds.), pp. 251-274, John Wiley, New York. 

Nitrogen is returned to its atmospheric form by the action of denitrifying bacteria such as Pseudomonas thiobacillus and Micrococcus denitriflcans. The process is referred to as denitrification and represents the major mechanism of nitrogen loss in the overall nitrogen cycle whereby various forms of nitrogen in the soil revert to the N2 form. The reactions and their energetics are given below ... 

Nitrate, 334-336 Denitrification, 340 Nitric acid, 23 Nitrification, 334 Nitrogen cycle, 326... 

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