Nitrogen cycle processes

Ratios between O2 consumption and inorganic carbon and nutrients regeneration, called the remineralization ratios, provide useful insights into biogeochemical cycles in the oceans (e.g., export of material to the deep sea and depth-dependent preferential regeneration, if any, of one constituent over the others). For the Indian Ocean, these ratios have been derived from observed variations in concentrations of O2, nutrients and inorganic carbon. Utilizing linear relationships between NOs and 

In the open-ocean suboxic zone denitrification does not reach completion, but a minimum in NOs profile invariably occurs within the SNM (Figs. 14.3 and 14.8). 

Potential processes that may be called upon to explain the large discrepancy between excess N2 and NOs deficits within the SNM are (1) sedimentary denitrification, (2) anammox, (3) metal (Fe, Mn)-catalyzed denitrification, and (4) non-Redfieldian organic matter mineralization (Codispoti et al., 2001 Devol et al., 2006a,b). The first of these possibilities requires a decoupling between nitrogen and phosphorus cycles (e.g. possible greater burial of phosphorus in continental margin sediments). The less likely additional requirement is that the maximal inputs from the sediments should occur at the same depth as the water column peak of N02. In other words, the exact coincidence of the extrema in NOs , N02,  

Intermediate nepheloid layer and quantitative significance of denitrification in remineralization 

North Pacific and asserted that nitrification in aerobic deep waters is a minor source of oceanic N2O. As will be shown in Section 4.1, isotopic measurements reveal different compositions of N2O at the shallower and deeper maxima, suggesting the involvement of various formative mechanisms. 

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The influence of benthic macrophytes on nitrogen cycle processes... 

Methodologies Used for Measurements of Nitrogen Cycle Process Rates... 

Table 19.4 Impact of Various Physical Parameters and Chemical Species on Rates of Nitrogen Cycle Processes...

Figure 21.1 Microbial nitrogen cycling processes in sedimentary environments on a coral reef (A) nitrogen fixation (B) ammonification (C) nitrification (D) dissimilatory nitrate reduction and denitrification (E) assimilatory nitrite/nitrate reduction (F) ammonium immobilization and assimilation. Adapted from D Elia and Wiebe (1990). Anammox (the anaerobic oxidation of NH4" with NO2 yielding N2 ) is not represented, as it has not yet been shown to occur on coral reefs, but may be found to be important in reef sediments.

Figure 5.4 Schematic showing the key nitrogen cycle processes in intertidal sediments.

Clark, F. E., and T. Rosswall, eds. (1981). Terrestrial nitrogen cycles processes, ecosystem, strategies and management impacts. Ecol. Bull. (Stockholm) 33. 

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