Bartlett,R., Mortimer,R.J.G. and Morris,K.(2008): Anoxic nitrification: Evidence from Humber Estuary sediments (UK). Chemical Geology, 250, 29-39.

『無酸素(ないし貧酸素)硝化:ハンバー河口(英国)堆積物からの証拠』


Abstract
 Conventional understanding of the nitrogen cycle in marine sediments has changed in recent years with the discovery of an alternative pathway for ammonia oxidation via the reduction of manganese oxides (during anoxic nitrification). In anoxic sediments, the potential for manganese oxides to serve as oxidant for nitrification may be considerable yet previous work on manganese-rich sediments has suggested anoxic nitrification may not be significant. In this study, the potential for anoxic nitrification in a range of sediment types was investigated. Laboratory incubation of sediment from three sites on the Humber Estuary, a microbially diverse environment, showed anoxic accumulation of nitrate, nitrite and dinitrogen gas, with and without the addition of synthetic manganese oxides. Incubation experiments confirmed anoxic nitrification as microbially mediated, with heat-killed controls yielding negative results. The anoxic nitrification reaction significantly depleted ammonia concentrations, and occurred simultaneously with manganese-, iron- and sulphate reduction, and methanogenesis. Taken in conjunction with other studies, results suggest anoxic nitrification may not only be dependent on total manganese concentrations but on manganese dynamics. Anoxic nitrification may be explained as a non-steady state reaction, dependent on the recent stability of a sediment system. Physical perturbation of sediments may cause the redistribution and/or introduction of manganese oxides and promote anoxic nitrification. The significance and persistence of anoxic nitrification is likely to depend on the frequency and magnitude of sediment perturbation, which explains why the reaction varies so widely across studied sites, and why it may not occur in some manganese-rich sediment.

Keywords: Manganese oxides; Nitrogen cycle; Ammonia; Diagenesis; Humber Estuary, UK』

1. Introduction
2. Methodology
 2.1. Sediment sampling
 2.2. Incubation experiments
 2.3. Synthetic MnO2
 2.4. Pore-water analysis
 2.5. Gas analysis
3. Results and discussion
 3.1. Spurn Head sediment
  3.1.1. Biogeochemical cycles
  3.1.2. Anoxic nitrification
 3.2. Skeffling sediment
  3.2.1. Biogeochemical cycles
  3.2.2. Anoxic Nitrification
 3.3. Welwick sediment
  3.3.1. Biogeochemical cycles
  3.3.2. Anoxic nitrification
4. Conclusions
 4.1. The anoxic nitrification reaction
 4.2. Implications
Acknowledgement
References


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