Hulth et al.(2005)

Hulth,S., Aller,R.C., Canfield,D.E., Dalsgaard,T., Engstrom（oの頭に¨）,P., Gilbert,F., Sundback（aの頭に¨）,K. and Thamdrup,NB.(2005): Nitrogen removal in marine environments: recent findings and future research challenges. Marine Chemistry, 94, 125-145.

『海洋環境における窒素除去：最近の発見と将来の研究課題』

『Abstract
　Respiratory reduction of nitrate (denitrification) is recognized as the most important process converting biologically available (fixed) nitrogen to N2. In current N cycle models, a major proportion of global marine denitrification (50-70％) is assumed to take place on the sea floor, particularly in organic rich continental margin sediments. Recent observations indicate that present conceptual views of denitrification and pathways of nitrate reduction and N2 formation are incomplete. Alternative N cycle pathways, particularly in sediments, include anaerobic ammonium oxidation to nitrite, nitrate and N2 by Mn-oxides, and anaerobic ammonium oxidation coupled to nitrite reduction and subsequent N2 mobilization. The discovery of new links and feedback mechanisms between the redox cycles of, e.g., C, N, S, Mn and Fe casts doubt on the present general understanding of the global N cycle. Recent models of the oceanic N budget indicate that total inputs are significantly smaller than estimated fixed N removal. The occurrence of alternative N reaction pathways further exacerbates the apparent imbalance as they introduce additional routes of N removal. In this contribution, we give a brief historical background on the conceptual understanding of N cycling in marine ecosystems, emphasizing pathways of aerobic and anaerobic N mineralization in marine sediments, and the implications of recently recognized metabolic pathways for N removal in marine environments

Keywords: Nitrogen; Removal; Marine』

1. Introduction
2. On the evolution of nitrogen species
3. Classical view of nitrogen removal during mineralization
4. Alternative pathways during nitrogen removal
　4.1. Links between nitrogen removal and the Mn and Fe redox cycles
　4.2. N removal by concomitant ammonium oxidation and nitrite reduction
　4.3. Anaerobic ammonium oxidation by nitrite in marine environments
5. Implications of alternative pathways for N removal in marine environments
6. Outlook for future research
Acknowledgements
References

Table 1 Nitrogen-containing compounds can be found in a multiplicity of forms at a wide range of oxidation states in marine environments
Compound 　 Oxidation state

Nitrate NO3^- +V

Nitrogendioxide NO2 +IV

Nitrite NO2^- +III

Nitric oxide NO +II

Nitrous oxide N2O +I

Di nitrogen N2 0

Hydroxylamine NH2OH -I

Hydrazine N2H4 -II

Ammonium NH4⁺ -III

Amino acids R-NH2 -III

Urea NH2CONH2 -III

**Table 1 Nitrogen-containing compounds can be found in a multiplicity of forms at a wide range of oxidation states in marine environments**
Compound		Oxidation state
Nitrate	NO3^-	+V
Nitrogendioxide	NO2	+IV
Nitrite	NO2^-	+III
Nitric oxide	NO	+II
Nitrous oxide	N2O	+I
Di nitrogen	N2	0
Hydroxylamine	NH2OH	-I
Hydrazine	N2H4	-II
Ammonium	NH4⁺	-III
Amino acids	R-NH2	-III
Urea	NH2CONH2	-III

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