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Ammonium and nitrite oxidation at nanomolar oxygen concentrations in oxygen minimum zone waters

Abstract.

"A major percentage of fixed nitrogen (N) loss in the oceans occurs within nitrite-rich oxygen minimum zones (OMZs) via denitrification and anammox. It remains unclear to what extent ammonium and nitrite oxidation co-occur, either supplying or competing for substrates involved in nitrogen loss in the OMZ core. Assessment of the oxygen (O2) sensitivity of these processes down to the O2 concentrations present in the OMZ core (<10 nmol⋅L−1) is therefore essential for understanding and modeling nitrogen loss in OMZs. We determined rates of ammonium and nitrite oxidation in the seasonal OMZ off Concepcion, Chile at manipulated O2 levels between 5 nmol⋅L−1 and 20 μmol⋅L−1. [...]"

Source: Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Authors: Laura A. Bristow et al.
DOI: 10.1073/pnas.1600359113

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Fixed-Nitrogen Loss Associated with Sinking Zooplankton Carcasses in a Coastal Oxygen Minimum Zone (Golfo Dulce, Costa Rica)

Abstract.

"Oxygen minimum zones (OMZs) in the ocean are of key importance for pelagic fixed-nitrogen loss (N-loss) through microbial denitrification and anaerobic ammonium oxidation (anammox). Recent studies document that zooplankton is surprisingly abundant in and around OMZs and that the microbial community associated with carcasses of a large copepod species mediates denitrification. Here, we investigate the complex N-cycling associated with sinking zooplankton carcasses exposed to the steep O2 gradient in a coastal OMZ (Golfo Dulce, Costa Rica). 15N-stable-isotope enrichment experiments revealed that the carcasses of abundant copepods and ostracods provide anoxic microbial hotspots in the pelagic zone by hosting intense anaerobic N-cycle activities even in the presence of ambient O2. [...]" 

Source: Frontiers in Marine Science
Authors: Peter Stief et al.
DOI: 10.3389/fmars.2017.00152

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Aerobic and anaerobic ammonium oxidizers in the Cariaco Basin: distributions of major taxa and nitrogen species across the redoxcline

Abstract.

"Depth distributions of cells and functional gene copies from anaerobic ammonium-oxidizing (anammox) bacteria, aerobic ammonium-oxidizing bacteria (AOB) and archaea (AOA) in the Cariaco Basin, Venezuela were obtained using FISH and q-PCR assays. These distributions were compared to concentrations of dissolved ammonium (NH4+), nitrite (NO2-), nitrate (NO3-), hydrogen sulfide (H2S) and oxygen (O2) along the redoxcline during 3 cruises. Cell counts of anammox bacteria and copies of their nitrite reductase gene (Scalindua-nirS) were consistently observed in 2 distinct layers: the suboxic zone (≤1.1 × 106 cells l-1) and the upper euxinic zone (≤4.7 × 106 cells l-1). [...]"

Source: Aquatic Microbial Ecology 79
Authors: Sara Cernadas-Martín et al.
DOI: 10.3354/ame01817

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Seasonal and short-term variation in denitrification and anammox at a coastal station on the Gulf of Finland, Baltic Sea

(January 2008)

Abstract. 

"Benthic processes were measured at a coastal deposition area in the northern Baltic Sea, covering all seasons. The N2 production rates, 90–400μmol Nm−2d−1, were highest in autumn-early winter and lowest in spring. Heterotrophic bacterial production peaked unexpectedly late in the year, indicating that in addition to the temperature, the availability of carbon compounds suitable for the heterotrophic bacteria also plays a major role in regulating the denitrification rate. Anaerobic ammonium oxidation (anammox) was measured in spring and autumn and contributed 10% and 15%, respectively, to the total N2 production. [...]"

Source: Hydrobiologia 596
Authors: Susanna Hietanen & Jorma Kuparinen
DOI: 10.1007/s10750-007-9058-5

Full article


N2 production rates limited by nitrite availability in the Bay of Bengal oxygen minimum zone

Abstract.

A third or more of the fixed nitrogen lost from the oceans as N2 is removed by anaerobic microbial processes in open ocean oxygen minimum zones. These zones have expanded over the past decades, and further anthropogenically induced expansion could accelerate nitrogen loss. However, in the Bay of Bengal there has been no indication of nitrogen loss, although oxygen levels are below the detection level of conventional methods (1 to 2 μM). Here we quantify the abundance of microbial genes associated with N2 production, measure nitrogen transformations in incubations of sampled seawater with isotopically labelled nitrogen compounds and analyse geochemical signatures of these processes in the water column. We find that the Bay of Bengal supports denitrifier and anammox microbial populations, mediating low, but significant N loss. Yet, unlike other oxygen minimum zones, our measurements using a highly sensitive oxygen sensor demonstrate that the Bay of Bengal has persistent concentrations of oxygen in the 10 to 200 nM range. We propose that this oxygen supports nitrite oxidation, thereby restricting the nitrite available for anammox or denitrification. If these traces of oxygen were removed, nitrogen loss in the Bay of Bengal oxygen minimum zone waters could accelerate to global significance.

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