Dissolved organic nitrogen assimilation

Figure 10.5 Major processes involved in the biogeochemical cycling of N in estuaries and the coastal ocean (1) biological N2 fixation (2) ammonia assimilation (3) nitrification (4) assimilatory NC>3 reduction (5) ammonification or N remineralization (6) ammonium oxidation (speculative at this time) (7) denitrification and dissimilatory NO3 reduction to NH4+ and (8) assimilation of dissolved organic nitrogen (DON). (Modified from Libes, 1992.)...

The impact of anthropogenic nutrient emissions in the coastal zone is heightened by its chemical speciation. Pollutant nitrogen and phosphorus are delivered to the coastal waters primarily in inorganic form, whereas most of the natural riverine dissolved nitrogen and phosphorus are components of organic compounds, i.e., DON and DOE Thus, the pollutant nutrients are delivered to the coastal waters in a chemical form that can be directly assimilated by coastal plankton, whereas the organically bound (natural) forms must first be remineralized. 

As shown in Figure 15.7 and 15.8, simple correlations in AN, AP, and AO2 are typically observed in lakes and in the ocean. The stoichiometric formulation of equation 3 reflects in a simple way Liebig s law of the minimum. It follows from Figure 15.7a,b that seawater becomes exhausted simultaneously in dissolved phosphorus and nitrogen as a result of photosynthetic assimilation. We infer that nitrogen and phosphorus together determine the extent of organic... 

Nitrate assimilation The utilisation by aquatic organisms of nitrate (N03 ) as a source of dissolved nitrogen. 

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