Coastal versus open-ocean denitrification in the Arabian Sea

Abstract. The Arabian Sea contains one of the three major open-ocean denitrification zones in the world. In addition, pelagic denitrification also occurs over the inner and mid-shelf off the west coast of India. The major differences between the two environments are highlighted using the available data. The perennial open-ocean system occupies two orders of magnitude larger volume than the seasonal coastal system, however, the latter offers more extreme conditions (greater nitrate consumption leading to complete anoxia). Unlike the open-ocean system, the coastal system seems to have undergone a change (i.e., it has intensified) over the past few decades presumably due to enhanced nutrient loading from land. The two systems also differ from each other with regard to the modes of nitrous oxide (N2O) production: in the open-ocean suboxic zone, an accumulation of secondary nitrite (NO2−) is invariably accompanied by depletion of N2O whereas in the coastal suboxic zone high NO2− and very high N2O concentrations frequently co-occur, indicating, respectively, net consumption and net production of N2O by denitrifiers. The extents of heavier isotope enrichment in the combined nitrate and nitrite (NO3−+NO2−) pool and in N2O in reducing waters appear to be considerably smaller in the coastal region, reflecting more varied sources/sinks and/or different isotopic fractionation factors.

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Coastal versus open-ocean denitrification in the Arabian Sea

Biogeosciences ◽

10.5194/bg-3-621-2006 ◽

2006 ◽

Vol 3 (4) ◽

pp. 621-633 ◽

Cited By ~ 103

Author(s):

S. W. A. Naqvi ◽

H. Naik ◽

A. Pratihary ◽

W. D'Souza ◽

P. V. Narvekar ◽

...

Keyword(s):

Arabian Sea ◽

Nutrient Loading ◽

Isotopic Fractionation ◽

Coastal Region ◽

Open Ocean ◽

N2o Production ◽

Coastal System ◽

Nitrate Consumption ◽

Suboxic Zone ◽

Nitrate And Nitrite

Abstract. The Arabian Sea contains one of the three major open-ocean denitrification zones in the world. In addition, pelagic denitrification also occurs over the inner and mid-shelf off the west coast of India. The major differences between the two environments are highlighted using the available data. The perennial open-ocean system occupies two orders of magnitude larger volume than the seasonal coastal system, however, the latter offers more extreme conditions (greater nitrate consumption leading to complete anoxia). Unlike the open-ocean system, the coastal system seems to have undergone a change (i.e., it has intensified) over the past few decades presumably due to enhanced nutrient loading from land. The two systems also differ from each other with regard to the modes of nitrous oxide (N2O) production: In the open-ocean suboxic zone, an accumulation of secondary nitrite (NO2−) is invariably accompanied by depletion of N2O whereas in the coastal suboxic zone high NO2− and very high N2O concentrations frequently co-occur, indicating, respectively, net consumption and net production of N2O by denitrifiers. The extents of heavier isotope enrichment in the combined nitrate and nitrite (NO3−+NO2−) pool and in N2O in reducing waters appear to be considerably smaller in the coastal region, reflecting more varied sources/sinks and/or different isotopic fractionation factors.

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Isotopic fractionation associated to nitrate attenuation by ferrous iron containing minerals

E3S Web of Conferences ◽

10.1051/e3sconf/20199812013 ◽

2019 ◽

Vol 98 ◽

pp. 12013

Author(s):

Rosanna Margalef-Marti ◽

Raul Carrey ◽

Albert Soler ◽

Neus Otero

Keyword(s):

Nitrate Reduction ◽

Ferrous Iron ◽

Laboratory Experiments ◽

Isotopic Fractionation ◽

Rapid Decrease ◽

Nitrite Reduction ◽

N2o Production ◽

Preliminary Results ◽

Nitrate And Nitrite ◽

N Compounds

Biotic and abiotic laboratory experiments of nitrate and nitrite reduction by Fe-containing minerals were performed and the isotopic fractionation of the different reactions was calculated in order to determine whether it is possible to distinguish biotic and abiotic reactions involving N compounds. Results of biotic experiments showed nitrate reduction up to 96 % with transient NO2- accumulation and no significant N2O production. No significant nitrate attenuation was observed in abiotic nitrate reduction experiments. Abiotic experiments of nitrite reduction showed a rapid decrease in nitrite concentrations in those experiments with added Fe2+ coupled with a significant N2O production. Preliminary results of the N and O isotopic fractionation of the biotic experiments of nitrate reduction show differences in the ε15NNO3 and ε18ONO3 when different minerals were added. The abiotic experiments of nitrite reduction contrarily, showed similar ε15NNO2 in all the experiments.

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Nitrogen and oxygen availabilities control water column nitrous oxide production during seasonal anoxia in the Chesapeake Bay

10.5194/bg-2018-113 ◽

2018 ◽

Author(s):

Qixing Ji ◽

Claudia Frey ◽

Xin Sun ◽

Melanie Jackson ◽

Yea-Shine Lee ◽

...

Keyword(s):

Nitrous Oxide ◽

Chesapeake Bay ◽

Water Column ◽

Nitrogen Deficiency ◽

Coastal Region ◽

N2o Emission ◽

N2o Production ◽

Relative Contribution ◽

Environmental Controls ◽

Nitrate And Nitrite

Abstract. Nitrous oxide (N2O) is a greenhouse gas and an ozone depletion agent. One of the major uncertainties in the global N2O budget is the contribution of the coastal region, including estuaries, which can be sites of intense N2O efflux. Incubation experiments with nitrogen stable isotope tracer (15N) enabled the investigation of the environmental controls of N2O production in the water column of Chesapeake Bay, the largest estuary in North America. The highest potential rates of N2O production (7.5 ± 1.2 nmol-N L−1 hr−1) were detected during summer anoxia, during which oxidized nitrogen species (nitrate and nitrite) were absent from the water column. At the top of the anoxic layer, N2O production from denitrification was stimulated by addition of nitrate and nitrite. The relative contribution of nitrate and nitrite to N2O production was positively correlated with the ratio of nitrate to nitrite concentrations. Increased oxygen availability, up to 7 µM oxygen inhibited both N2O production and the reduction of nitrate to nitrite. Therefore, reducing the nitrogen input into the Chesapeake Bay has two potential impacts on the N2O efflux: In the short-term, N2O emission will be mitigated due to nitrogen deficiency. In the long-run, eutrophication will be alleviated and subsequent re-oxygenation of the bay will further inhibit N2O production.

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Paired N and O isotopic analysis of nitrate and nitrite in the Arabian Sea oxygen deficient zone

Deep Sea Research Part I Oceanographic Research Papers ◽

10.1016/j.dsr.2017.01.002 ◽

2017 ◽

Vol 121 ◽

pp. 121-131 ◽

Cited By ~ 10

Author(s):

T.S. Martin ◽

K.L. Casciotti

Keyword(s):

Arabian Sea ◽

Isotopic Analysis ◽

Nitrate And Nitrite

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Nitrogen and oxygen availabilities control water column nitrous oxide production during seasonal anoxia in the Chesapeake Bay

Biogeosciences ◽

10.5194/bg-15-6127-2018 ◽

2018 ◽

Vol 15 (20) ◽

pp. 6127-6138 ◽

Cited By ~ 3

Author(s):

Qixing Ji ◽

Claudia Frey ◽

Xin Sun ◽

Melanie Jackson ◽

Yea-Shine Lee ◽

...

Keyword(s):

Nitrous Oxide ◽

Chesapeake Bay ◽

Water Column ◽

N2o Emissions ◽

N2o Production ◽

Isotope Tracer ◽

Relative Contribution ◽

Environmental Controls ◽

Long Run ◽

Nitrate And Nitrite

Abstract. Nitrous oxide (N2O) is a greenhouse gas and an ozone depletion agent. Estuaries that are subject to seasonal anoxia are generally regarded as N2O sources. However, insufficient understanding of the environmental controls on N2O production results in large uncertainty about the estuarine contribution to the global N2O budget. Incubation experiments with nitrogen stable isotope tracer were used to investigate the geochemical factors controlling N2O production from denitrification in the Chesapeake Bay, the largest estuary in North America. The highest potential rates of water column N2O production via denitrification (7.5±1.2 nmol-N L−1 h−1) were detected during summer anoxia, during which oxidized nitrogen species (nitrate and nitrite) were absent from the water column. At the top of the anoxic layer, N2O production from denitrification was stimulated by addition of nitrate and nitrite. The relative contribution of nitrate and nitrite to N2O production was positively correlated with the ratio of nitrate to nitrite concentrations. Increased oxygen availability, up to 7 µmol L−1 oxygen, inhibited both N2O production and the reduction of nitrate to nitrite. In spring, high oxygen and low abundance of denitrifying microbes resulted in undetectable N2O production from denitrification. Thus, decreasing the nitrogen input into the Chesapeake Bay has two potential impacts on the N2O production: a lower availability of nitrogen substrates may mitigate short-term N2O emissions during summer anoxia; and, in the long-run (timescale of years), eutrophication will be alleviated and subsequent reoxygenation of the bay will further inhibit N2O production.

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Vertical segregation among pathways mediating nitrogen loss (N<sub>2</sub> and N<sub>2</sub>O production) across the oxygen gradient in a coastal upwelling ecosystem

Biogeosciences ◽

10.5194/bg-14-4795-2017 ◽

2017 ◽

Vol 14 (20) ◽

pp. 4795-4813 ◽

Cited By ~ 4

Author(s):

Alexander Galán ◽

Bo Thamdrup ◽

Gonzalo S. Saldías ◽

Laura Farías

Keyword(s):

Coastal Upwelling ◽

Nitrite Reduction ◽

15N Tracer ◽

Ammonium Oxidation ◽

N Loss ◽

N2o Production ◽

Coastal System ◽

Central Chile ◽

N Removal ◽

Bottom Waters

Abstract. The upwelling system off central Chile (36.5° S) is seasonally subjected to oxygen (O2)-deficient waters, with a strong vertical gradient in O2 (from oxic to anoxic conditions) that spans a few metres (30–50 m interval) over the shelf. This condition inhibits and/or stimulates processes involved in nitrogen (N) removal (e.g. anammox, denitrification, and nitrification). During austral spring (September 2013) and summer (January 2014), the main pathways involved in N loss and its speciation, in the form of N2 and/or N2O, were studied using 15N-tracer incubations, inhibitor assays, and the natural abundance of nitrate isotopes along with hydrographic information. Incubations were developed using water retrieved from the oxycline (25 m depth) and bottom waters (85 m depth) over the continental shelf off Concepción, Chile. Results of 15N-labelled incubations revealed higher N removal activity during the austral summer, with denitrification as the dominant N2-producing pathway, which occurred together with anammox at all times. Interestingly, in both spring and summer maximum potential N removal rates were observed in the oxycline, where a greater availability of oxygen was observed (maximum O2 fluctuation between 270 and 40 µmol L−1) relative to the hypoxic bottom waters ( <  20 µmol O2 L−1). Different pathways were responsible for N2O produced in the oxycline and bottom waters, with ammonium oxidation and dissimilatory nitrite reduction, respectively, as the main source processes. Ammonium produced by dissimilatory nitrite reduction to ammonium (DNiRA) could sustain both anammox and nitrification rates, including the ammonium utilized for N2O production. The temporal and vertical variability of δ15N-NO3− confirms that multiple N-cycling processes are modulating the isotopic nitrate composition over the shelf off central Chile during spring and summer. N removal processes in this coastal system appear to be related to the availability and distribution of oxygen and particles, which are a source of organic matter and the fuel for the production of other electron donors (i.e. ammonium) and acceptors (i.e. nitrate and nitrite) after its remineralization. These results highlight the links between several pathways involved in N loss. They also establish that different mechanisms supported by alternative N substrates are responsible for substantial accumulation of N2O, which are frequently observed as hotspots in the oxycline and bottom waters. Considering the extreme variation in oxygen observed in several coastal upwelling systems, these findings could help to understand the ecological and biogeochemical implications due to global warming where intensification and/or expansion of the oceanic OMZs is projected.

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Influence of nitrate and nitrite concentration on N2O production via dissimilatory nitrate/nitrite reduction to ammonium inBacillus paralicheniformisLMG 6934

MicrobiologyOpen ◽

10.1002/mbo3.592 ◽

2018 ◽

Vol 7 (4) ◽

pp. e00592 ◽

Cited By ~ 3

Author(s):

Yihua Sun ◽

Paul De Vos ◽

Anne Willems

Keyword(s):

Nitrite Reduction ◽

Nitrite Concentration ◽

N2o Production ◽

Nitrate And Nitrite

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Isotopic Fractionation During Reduction of Nitrate and Nitrite by Extracts of Spinach Leaves

Functional Plant Biology ◽

10.1071/pp9850631 ◽

1985 ◽

Vol 12 (6) ◽

pp. 631 ◽

Cited By ~ 38

Author(s):

SF Ledgard ◽

KC Woo ◽

FJ Bergersen

Keyword(s):

Nitrate Reductase ◽

Nitrite Reductase ◽

Spinacia Oleracea ◽

Reductase Activity ◽

Isotopic Fractionation ◽

Cytosolic Extract ◽

Nitrite Reductase Activity ◽

Reconstituted System ◽

No2 Reduction ◽

Nitrate And Nitrite

The isotopic fractionations of nitrogen during the reduction of NO3- and NO2- in a cytosolic fraction and in a chloroplast preparation from spinach (Spinacia oleracea L.) leaves were determined. The reduction of NO3- to NH3 was studied using a reconstituted system containing cytosolic extract and intact chloroplasts, while a chloroplast system was used for NO2- reduction. In the reconstituted systems the ratio of nitrate reductase activity to nitrite reductase activity had a large effect on the relative amounts of NO2- and NH3 formed. Ammonia predominated when the nitrate reductase to nitrite reductase activity ratio was 1 : 5 and this ratio was used in the isotopic fractionation studies. Significant isotopic fractionation of N was observed in the reconstituted system but not in the chloroplast system. This indicates that the observed isotopic fractionation was associated with the reduction of NO3- to NO2- by nitrate reductase. The isotopic fractionation (i.e. δ15Nproduct - δ15Nsubstrate) for this reaction was - 15‰.

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