Nitrogen global cycle

Prior to estimating the global N cycle let us consider the nitrogen reservoirs in the biosphere (Table 17). 

Use as of 1996 was approximately 83 x 10 ton N per year. Approximately half of the inorganic nitrogen fertilizer that has ever been used on Earth has been applied during the last 15 years. 

Production of nitrogen fertilizer is the largest process whereby human activity mobilizes nitrogen globally (Box 4). 

The Fate of Nitrogen Fertilizer in North America (After Howarth et al, 2002) When nitrogen fertilizer is applied to a field, it can move through a variety of flow paths to surface and grounds waters (Fignre 24). 

Reservoir Soderlund Svensson, McEItoy. Stedman Shelter, Dobrovolsky Mackenzie,  

---

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. 

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... 

Krapivin V.F. (2000b). Global nitrogen cycle modeling. Problems of Environment and Natural Resources, 10, 2-15 [in Russian]. 

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. 

---