The Global Nitrogen Cycle

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. 

As mentioned previously, the fixation-denitrification cycle (Fig. 12-7) is the most heavily perturbed by humans. This is due to both the increasing use of nitrogenous fertilizers and the planting of nitrogen-fixing plants. One of the 

A summary of the major N fluxes is presented in Table 12-2 and Fig. 12-8 shows a summary of the N fluxes for atmospheric NH3, N2O, and NO,. 

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Table 12-2 Fluxes in the global nitrogen cycle (units are Tg N/yr)...

Soderlund, R. and Svensson, B. H. (1976). The global nitrogen cycle. In "Nitrogen, Phosphorus and Sulfur - Global Cycles" (B. H. Svensson and R. Soderlund, eds), Ecol. Bull. No. 22, pp. 23-73, SCOPE. Swedish Natural Science Research Council, Stockholm. 

Vitousek, P. M. et al. (1997b). Human alteration of the global nitrogen cycle Sources and consequences. Ecol. Apps. 7, 737-750. 

Vitousek PM, Aber JD, Howarth RW, Likens GE, Matson PA, Schindler DW, Schlesinger WH, Tilman DG (1997) Human alteration of the global nitrogen cycle sources and consequences. Ecol Appl 7 737-750... 

Table 24.3 Estimates of the Total Annual Contribution of Combined Nitrogen to the Global Nitrogen Cycle by Nitrogen Fixation in Benthic Marine Environments. ...

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. 

Numerical models of the global nitrogen cycle 4.4.2.1 Conceptual schemes of the nitrogen cycle in nature... 

A block diagram of the model of the global nitrogen cycle in the biosphere... 

Galloway, J.N. (1998) The global nitrogen cycle changes and consequences. In Proceedings of the First International Nitrogen Conference, pp. 15-24, Elsevier Science, New York. 

Figure 1.15 Schematic budget of the global nitrogen cycle in preindustrial times (black) and how it changed as a result of human intervention (red). Fluxes are in units of Tg N year and inventories (bold italics) inTg N. The flux estimates are based on Gruber and Galloway (2008).

Gruber, N., and Galloway, J. N. (2008). An earth-system perspective of the global nitrogen cycle. Nature 451, 293-296. 

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