Nitrogen analysis nitrification

Nitrogen exists in the ocean at oxidation states from -3 to +5. There are three forms of fixed inorganic N NOs", N02 and NH4+. Nitrate is the final oxidation product and is the dominant form of fixed N in the deep ocean. Nitrite generally occurs at very low concentrations because it is an intermediate in the processes of nitrification (NH4+ —> N02 —> NOs") and denitrification (N03 —> N02 —> NO —> N2O —> N2) and so seldom accumulates to a large degree. Concentrations of NH4+ are highly variable but tend to be near the limit of detection in open ocean surface waters. Each of the inorganic forms has a number of manual and automated methods of analysis. We discuss the most widely used below. 

Arabian Sea. After extracting the gases by equihbration, they utilized cryofocusing of N2O with separation from CO2 on a capillary column before isotopic analysis by CF-IRMS of the N2O. They found the vast bulk of N2O was produced from N02 reduction, with htde contribution from nitrification at any depth within the suboxic waters. Their results also suggested an alternate source of nitrogen for dentrification, such as DON or DNRA via internal couphng to N2 production. 

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