Nitrogen cycle fluxes

Feedbacks may be affected directly by atmospheric CO2, as in the case of possible CO2 fertilization of terrestrial production, or indirectly through the effects of atmospheric CO2 on climate. Furthermore, feedbacks between the carbon cycle and other anthropogenically altered biogeochemical cycles (e.g., nitrogen, phosphorus, and sulfur) may affect atmospheric CO2. If the creation or alteration of feedbacks have strong effects on the magnitudes of carbon cycle fluxes, then projections, made without consideration of these feedbacks and their potential for changing carbon cycle processes, will produce incorrect estimates of future concentrations of atmospheric CO2. 

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

The nitrogen cycle is closely connected with the fluxes of hydrogen, sulfur, and other chemicals (Smith et al., 1998 Dimitroulopoulou and Marsh, 1997 Chapin et al., 2002 Rhee et al., 2005 Stevenson and Cole, 1999). Nitrogen and hydrogen react under great pressure and temperature in the presence of a catalyst to make ammonia. The study of correlations between the cycles of these elements is necessary to improve... 

The atmospheric part of the nitrogen cycle is a good example of the complicated mechanism of transformation of gas substances that are characterized by an intricate set of fluxes at the borders between the basic reservoirs of nitrogen. Nevertheless, the... 

The fixation of nitrogen by plants directly from the soil via the root systems (flux He) occupies a principle place in the nitrogen cycle, especially in areas that are cultivated. For instance, an increase in the yield of legumes in agriculture can raise He up to 35tkm 2yr 1. Therefore, consideration of this flux in the model is... 

Bronk, D.A., Glibert, P.M., Malone, T.C., Banahan, S., and Sahlsten, E. (1998) Inorganic and organic nitrogen cycling in Chesapeake Bay autotrophic versus heterotrophic processes and relationships to carbon flux. Aquat. Microb. Ecol. 15, 177-189. 

Kristensen, E. (1988) Benthic fauna and biogeochemical processes in marine sediments microbial activities fluxes. In Nitrogen Cycling in Coastal Marine Environments. SCOPE (Blackburn, T.H., and Sprensen, J., eds.), pp. 275-299, Scope, Chichester, UK. 

Figure 11 shows an idealised nitrogen cycle. The numbers in boxes represent quantities of nitrogen in the various reservoirs, while the arrows show fluxes. It is interesting to note that substances involving relatively small fluxes and burdens can have a major impact upon people. Thus nitrogen oxides, NO, NO2, and N2O are very minor constituents relative to N2 but play major roles in photochemical air pollution (NO2), acid rain (HNO3 from NO2), and stratospheric ozone depletion (N2O). 

Fig. 5.4. Proposed model structure for integrating mycorrhizal fungi into an ecosystem framework of carbon and nitrogen cycling. Unless otherwise noted, both carbon and nitrogen fluxes are implied. Dashed lines indicate fluxes of lesser or uncertain importance. SOM = soil organic matter.

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).

Anderson, T. R., and Pondaven, P. (2003). Non-redfield carbon and nitrogen cycling in the Sargasso Sea Pelagic imbalances and export flux. Deep Sea Res. 150, 573—591. 

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