Cycling of nitrogen

Environmental Fate. Ammonia combines with sulfate ions in the atmosphere and is washed out by rairtfall, resulting in rapid return of ammonia to the soil and surface waters. Ammonia is a central compound in the environmental cycling of nitrogen. Ammonia in lakes, rivers, and streams is converted to nitrate. 

The biogeochemical cycling of nitrogen is very much controlled by redox reactions. This perspective is presented in Figure 24.3 for the redox reactions that take place in the water column and sediments. The major pathways of reduction are nitrogen fixation, assimilatory nitrogen reduction, and denitrification. The major oxidation processes are nitrification and anaerobic ammonium oxidation (anammox). Each of these is described next in further detail. 

FIGURE 2 Cycling of nitrogen in the biosphere. Gaseous nitrogen (N2) makes up 80% of the earth s atmosphere. 

Fig. 4. Compartmental model describing the cycling of nitrogen in a planktonic community in the mixed layer of a water column. Flow pathways are represented by arrows and numbers which correspond to mathematical expressions described in Table 2. The nitrogen pool represents all abiotic nitrogen (nitrate, ammonia and urea), and other compartments represent bacteria, zooflagellates, larger protozoa, and micro-mesozooplankton, giving off waste products (F+U). Arrows (13) and (14) depict sedimentation of zooplankton faeces and phytoplankton cells, respectively (After Moloney et al., 1985).

Table 4.6. Estimates of some parameters of the global biogeochemical cycle of nitrogen in the biosphere.

Savchuk, O.P., and Wulff, F. (2001) A model of the biogeochemical cycles of nitrogen and phosphorus in the Baltic. In Ecological Studies, A System Analysis of the Baltic Sea (Wulff, F., ed.), pp. 374-415, Springer-Verlag, Berlin. 

Figure 10 Chemical forms and cycle of nitrogen (From O NeiU. )...

Figure 11 Schematic representation of the biogeochemical cycle of nitrogen, indicating the approximate magnitude of fluxes and reservoirs (After O Neill. )...

Both populations benefit from the relationship, but the relationship is not an obligatory one, as both populations are capable of surviving in their natural environment on their own. For example, there are synergistic relationships among bacterial populations involved in the cycling of nitrogen. 

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