scholarly journals Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru

2020 ◽  
Vol 17 (8) ◽  
pp. 2263-2287 ◽  
Author(s):  
Claudia Frey ◽  
Hermann W. Bange ◽  
Eric P. Achterberg ◽  
Amal Jayakumar ◽  
Carolin R. Löscher ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Organic Matter ◽  
Particulate Organic Matter ◽  
15N Tracer ◽  
Marker Genes ◽  
Ammonium Oxidation ◽  
Low Oxygen ◽  
N2o Formation ◽  
N2o Production ◽  
Nitrification And Denitrification

Abstract. Oxygen-deficient zones (ODZs) are major sites of net natural nitrous oxide (N2O) production and emissions. In order to understand changes in the magnitude of N2O production in response to global change, knowledge on the individual contributions of the major microbial pathways (nitrification and denitrification) to N2O production and their regulation is needed. In the ODZ in the coastal area off Peru, the sensitivity of N2O production to oxygen and organic matter was investigated using 15N tracer experiments in combination with quantitative PCR (qPCR) and microarray analysis of total and active functional genes targeting archaeal amoA and nirS as marker genes for nitrification and denitrification, respectively. Denitrification was responsible for the highest N2O production with a mean of 8.7 nmol L−1 d−1 but up to 118±27.8 nmol L−1 d−1 just below the oxic–anoxic interface. The highest N2O production from ammonium oxidation (AO) of 0.16±0.003 nmol L−1 d−1 occurred in the upper oxycline at O2 concentrations of 10–30 µmol L−1 which coincided with the highest archaeal amoA transcripts/genes. Hybrid N2O formation (i.e., N2O with one N atom from NH4+ and the other from other substrates such as NO2-) was the dominant species, comprising 70 %–85 % of total produced N2O from NH4+, regardless of the ammonium oxidation rate or O2 concentrations. Oxygen responses of N2O production varied with substrate, but production and yields were generally highest below 10 µmol L−1 O2. Particulate organic matter additions increased N2O production by denitrification up to 5-fold, suggesting increased N2O production during times of high particulate organic matter export. High N2O yields of 2.1 % from AO were measured, but the overall contribution by AO to N2O production was still an order of magnitude lower than that of denitrification. Hence, these findings show that denitrification is the most important N2O production process in low-oxygen conditions fueled by organic carbon supply, which implies a positive feedback of the total oceanic N2O sources in response to increasing oceanic deoxygenation.

scholarly journals Regulation of nitrous oxide production in low oxygen waters off the coast of Peru

2019 ◽  
Author(s):  
Claudia Frey ◽  
Hermann W. Bange ◽  
Eric P. Achterberg ◽  
Amal Jayakumar ◽  
Carolin R. Löscher ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Organic Matter ◽  
Particulate Organic Matter ◽  
15N Tracer ◽  
Marker Genes ◽  
Ammonium Oxidation ◽  
Low Oxygen ◽  
N2o Production ◽  
Carbon Supply ◽  
Nitrification And Denitrification

Abstract. Oxygen deficient zones (ODZs) are major sites of net natural nitrous oxide (N2O) production and emissions. In order to understand changes in the magnitude of N2O production in response to global change, knowledge on the individual contributions of the major microbial pathways (nitrification and denitrification) to N2O production and their regulation is needed. In the ODZ in the coastal area off Peru, the sensitivity of N2O production to oxygen and organic matter was investigated using 15N-tracer experiments in combination with qPCR and microarray analysis of total and active functional genes targeting archaeal amoA and nirS as marker genes for nitrification and denitrification, respectively. Denitrification was responsible for the highest N2O production with a mean of 8.7 nmol L−1 d−1 but up to 118 ± 27.8 nmol L−1 d−1 just below the oxic-anoxic interface. Highest N2O production from ammonium oxidation (AO) of 0.16 ± 0.003 nmol L−1 d−1 occurred in the upper oxycline at O2 concentrations of 10–30 µmol L−1 which coincided with highest archaeal amoA transcripts/genes. Oxygen responses of N2O production varied with substrate, but production and yields were generally highest below 10 µmol L−1 O2. Particulate organic matter additions increased N2O production by denitrification up to 5-fold suggesting increased N2O production during times of high particulate organic matter export. High N2O yields of 2.1 % from AO were measured, but the overall contribution by AO to N2O production was still an order of magnitude lower than that of denitrification. Hence, these findings show that denitrification is the most important N2O production process in low oxygen conditions fueled by organic carbon supply, which implies a positive feedback of the total oceanic N2O sources in response to increasing oceanic deoxygenation.

scholarly journals 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

2017 ◽  
Vol 14 (20) ◽  
pp. 4795-4813 ◽  
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.

scholarly journals Interannual variation in summer N<sub>2</sub>O concentration in the hypoxic region of the northern Gulf of Mexico, 1985–2007

2013 ◽  
Vol 10 (11) ◽  
pp. 6783-6792 ◽  
Author(s):  
I.-N. Kim ◽  
K. Lee ◽  
H. W. Bange ◽  
A. M. Macdonald
Keyword(s):  
Nitrous Oxide ◽  
Gulf Of Mexico ◽  
Interannual Variation ◽  
Bottom Water ◽  
Areal Extent ◽  
Low Oxygen ◽  
N2o Production ◽  
Northern Gulf Of Mexico ◽  
The Mean ◽  
Stressed Region

Abstract. Microbial nitrous oxide (N2O) production in the ocean is enhanced under low-oxygen (O2) conditions. This is especially important in the context of increasing hypoxia (i.e., oceanic zones with extremely reduced O2 concentrations). Here, we present a study on the interannual variation in summertime nitrous oxide (N2O) concentrations in the bottom waters of the northern Gulf of Mexico (nGOM), which is well-known as the site of the second largest seasonally occurring hypoxic zone worldwide. To this end we developed a simple model that computes bottom-water N2O concentrations with a tri-linear ΔN2O/O2 relationship based on water-column O2 concentrations, derived from summer (July) Texas–Louisiana shelf-wide hydrographic data between 1985 and 2007. ΔN2O (i.e., excess N2O) was computed including nitrification and denitrification as the major microbial production and consumption pathways of N2O. The mean modeled bottom-water N2O concentration for July in the nGOM was 14.5 ± 2.3 nmol L−1 (min: 11.0 ± 4.5 nmol L−1 in 2000 and max: 20.6 ± 11.3 nmol L−1 in 2002). The mean bottom-water N2O concentrations were significantly correlated with the areal extent of hypoxia in the nGOM. Our modeling analysis indicates that the nGOM is a persistent summer source of N2O, and nitrification is dominating N2O production in this region. Based on the ongoing increase in the areal extent of hypoxia in the nGOM, we conclude that N2O production (and its subsequent emissions) from this environmentally stressed region will probably continue to increase into the future.

Nitrous oxide emission during nitrification and denitrification in a full-scale night soil treatment plant

1996 ◽  
Vol 34 (1-2) ◽  
pp. 277-284 ◽  
Author(s):  
Hiroki Itokawa ◽  
Keisuke Hanaki ◽  
Tomonori Matsuo
Keyword(s):  
Nitrous Oxide ◽  
Treatment Plant ◽  
Full Scale ◽  
Soil Treatment ◽  
Aeration Tank ◽  
N2o Emissions ◽  
N2o Production ◽  
Mixed Liquor ◽  
Significant Difference ◽  
Nitrification And Denitrification

Nitrous oxide (N2O) emissions from nitrification-denitrification processes in a full-scale night soil treatment plant were measured, and patterns and control of the N2O production were investigated. Estimated N2O emissions ranged from 4.4 to 1,190 gN/(m3 of influent), corresponding to a conversion ratio of influent nitrogen to N2O-N of 0.24-55%. N2O was produced in the intermittent aeration tank (IAT) where nitrification and denitrification were carried out alternately. The produced N2O was either stripped out to the off-gas or remained in the effluent in dissolved form. The former accounted for more than 99.5% of the total emissions. The latter flowed into the following anoxic tank, where 60-98% of N2O was reduced. A significant difference in the extent of N2O supersaturation in mixed liquor of IAT was observed between the cases of high and low N2O emissions. In IAT, N2O tended to be produced discretely either in aerobic or in anoxic phases. It seemed that the completeness of nitrification and denitrification in IAT, indicated from a mass balance between NH4-N and NO3-N and from NO2-N accumulation in mixed liquor of IAT, was one of the important factors affecting the N2O production. This completeness was decided by the time ratio of aerobic and anoxic phases. External addition of methanol to IAT seemed to reduce N2O emissions.

scholarly journals Nitrous oxide dynamics in low oxygen regions of the Pacific: insights from the MEMENTO database

2012 ◽  
Vol 9 (12) ◽  
pp. 5007-5022 ◽  
Author(s):  
L. M. Zamora ◽  
A. Oschlies ◽  
H. W. Bange ◽  
K. B. Huebert ◽  
J. D. Craig ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
N2o Emissions ◽  
Low Oxygen ◽  
N2o Production ◽  
Oxygen Minimum Zones ◽  
A Value ◽  
The Pacific ◽  
Production And Consumption ◽  
The Relationship ◽  
Oxygen Minimum

Abstract. The eastern tropical Pacific (ETP) is believed to be one of the largest marine sources of the greenhouse gas nitrous oxide (N2O). Future N2O emissions from the ETP are highly uncertain because oxygen minimum zones are expected to expand, affecting both regional production and consumption of N2O. Here we assess three primary uncertainties in how N2O may respond to changing O2 levels: (1) the relationship between N2O production and O2 (is it linear or exponential at low O2 concentrations?), (2) the cutoff point at which net N2O production switches to net N2O consumption (uncertainties in this parameterisation can lead to differences in model ETP N2O concentrations of more than 20%), and (3) the rate of net N2O consumption at low O2. Based on the MEMENTO database, which is the largest N2O dataset currently available, we find that N2O production in the ETP increases linearly rather than exponentially with decreasing O2. Additionally, net N2O consumption switches to net N2O production at ~ 10 μM O2, a value in line with recent studies that suggest consumption occurs on a larger scale than previously thought. N2O consumption is on the order of 0.01–1 mmol N2O m−3 yr−1 in the Peru-Chile Undercurrent. Based on these findings, it appears that recent studies substantially overestimated N2O production in the ETP. In light of expected deoxygenation and the higher than previously expected point at which net N2O production switches to consumption, there is enough uncertainty in future N2O production that even the sign of future changes is still unclear.

Nitrous oxide formation during nitritation and nitrification of high-strength wastewater

2013 ◽  
Vol 67 (11) ◽  
pp. 2494-2502 ◽  
Author(s):  
Yvonne Schneider ◽  
Maike Beier ◽  
Karl-Heinz Rosenwinkel
Keyword(s):  
Nitrous Oxide ◽  
High Strength ◽  
Dominant Factor ◽  
Process Conditions ◽  
Stable Operation ◽  
Ammonium Oxidation ◽  
Formation Factor ◽  
N2o Formation ◽  
Operational Conditions ◽  
Oxidation Rates

The purpose of this study was to investigate the formation of nitrous oxide (N2O) in nitritation and nitrification under stable, comparable and not limiting conditions typical for treatment of high-strength wastewater. A laboratory-scale aerated chemostat was operated with reject water at different sludge retention times, achieving suppression of nitrate formation by wash-out of nitrite-oxidizing bacteria for nitritation. The N2O formation factor during stable nitritation was higher (2.90% N2O-N /NH4−-Nox) than during nitrification (0.74%). The positive correlation of N2O formation rates and ammonium oxidation rates was linear and thus did not contribute to changes of the N2O formation factor. The dominant factor for N2O formation during stable operation was high nitrite concentration, which was positively correlated with N2O formation rates. The highest formation factors were observed during a transition phase from nitrification to nitritation with unstable process conditions (4.81%) and during a short-term experiment with increased pH of 7 (10.28%). The results indicate that even with operational conditions that are regarded favourable for the process of nitritation N2O formation can be limited but not avoided.

scholarly journals Effects of sterilization techniques on chemodenitrification and N<sub>2</sub>O production in tropical peat soil microcosms

2019 ◽  
Author(s):  
Steffen Buessecker ◽  
Kaitlyn Tylor ◽  
Joshua Nye ◽  
Keith E. Holbert ◽  
Jose D. Urquiza-Muñoz ◽  
...  
Keyword(s):  
Organic Matter ◽  
Peat Soil ◽  
Low Ph ◽  
Nitrite Reduction ◽  
Iron Speciation ◽  
Low Oxygen ◽  
Γ Irradiation ◽  
N2o Production ◽  
Tropical Peatland ◽  
Organic Matter Composition

Abstract. Chemodenitrification – the non-enzymatic process of nitrite reduction – may be an important sink for fixed nitrogen in tropical peatlands with low oxygen, low pH, high organic matter, and variable ferrous iron concentrations. Assessing abiotic reaction pathways is difficult because sterilization/inhibition agents can alter the availability of reactants by changing iron speciation and organic matter composition. We compared six commonly used soil sterilization techniques – γ-irradiation, chloroform, autoclaving, and chemical inhibitors (mercury, zinc, and azide) – for their compatibility with chemodenitrification assays for tropical peatland soils (organic-rich low pH soil from the Eastern Amazon). Out of the six techniques, γ-irradiation resulted in soil treatments with lowest cell viability and denitrification activity, and least effect on pH, iron speciation, and organic matter composition. Nitrite depletion rates in γ-irradiated soils were highly similar to untreated/live soils, whereas other sterilization techniques showed deviations. Chemodenitrification was a dominant process in tropical peatland soils assayed in this study. Abiotic N2O production was low to moderate (3–16 % of converted nitrite), and different sterilization techniques lead to significant variations on production rates due to inherent processes or potential artifacts. Our work represents the first methodological basis for testing the abiotic denitrification and N2O production potential in tropical peatland soil.

scholarly journals Year-round N<sub>2</sub>O production by benthic NO<sub>x</sub> reduction in a monomictic south-alpine lake

2013 ◽  
Vol 10 (12) ◽  
pp. 8373-8383 ◽  
Author(s):  
C. V. Freymond ◽  
C. B. Wenk ◽  
C. H. Frame ◽  
M. F. Lehmann
Keyword(s):  
Bottom Water ◽  
Significant Source ◽  
Ammonium Oxidation ◽  
Low Oxygen ◽  
Production Rates ◽  
Overlying Water ◽  
N2o Production ◽  
Water Column Stratification ◽  
Nitrifier Denitrification ◽  
N2o Fluxes

Abstract. Nitrous oxide (N2O) is a potent greenhouse gas, generated through microbial nitrogen (N) turnover processes, such as nitrification, nitrifier denitrification, and denitrification. Previous studies quantifying natural sources have mainly focused on soils and the ocean, but the potential role of terrestrial water bodies in the global N2O budget has been widely neglected. Furthermore, the biogeochemical controls on the production rates and the microbial pathways that produce benthic N2O in lakes are essentially unknown. In this study, benthic N2O fluxes and the contributions of the microbial pathways that produce N2O were assessed using 15N label flow-through sediment incubations in the eutrophic, monomictic south basin of Lake Lugano in Switzerland. The sediments were a significant source of N2O throughout the year, with production rates ranging between 140 and 2605 nmol N2O h−1 m−2, and the highest observed rates coinciding with periods of water column stratification and stably anoxic conditions in the overlying bottom water. Nitrate (NO3−) reduction via denitrification was found to be the major N2O production pathway in the sediments under both oxygen-depleted and oxygen-replete conditions in the overlying water, while ammonium oxidation did not contribute significantly to the benthic N2O flux. A marked portion (up to 15%) of the total NO3− consumed by denitrification was reduced only to N2O, without complete denitrification to N2. These fluxes were highest when the bottom water had stabilized to a low-oxygen state, in contrast with the notion that stable anoxia is particularly conducive to complete denitrification without accumulation of N2O. This study provides evidence that lake sediments are a significant source of N2O to the overlying water and may produce large N2O fluxes to the atmosphere during seasonal mixing events.

scholarly journals Production of oceanic nitrous oxide by ammonia-oxidizing archaea

2012 ◽  
Vol 9 (7) ◽  
pp. 2419-2429 ◽  
Author(s):  
C. R. Löscher ◽  
A. Kock ◽  
M. Könneke ◽  
J. LaRoche ◽  
H. W. Bange ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Ammonia Oxidation ◽  
Selective Inhibition ◽  
Ammonia Oxidizer ◽  
Low Oxygen ◽  
Tropical Ocean ◽  
N2o Production ◽  
Ammonia Oxidizing Archaea ◽  
Tropical North Atlantic ◽  
Oxygen Minimum

Abstract. The recent finding that microbial ammonia oxidation in the ocean is performed by archaea to a greater extent than by bacteria has drastically changed the view on oceanic nitrification. The numerical dominance of archaeal ammonia-oxidizers (AOA) over their bacterial counterparts (AOB) in large parts of the ocean leads to the hypothesis that AOA rather than AOB could be the key organisms for the oceanic production of the strong greenhouse gas nitrous oxide (N2O) that occurs as a by-product of nitrification. Very recently, enrichment cultures of marine ammonia-oxidizing archaea have been reported to produce N2O. Here, we demonstrate that archaeal ammonia monooxygenase genes (amoA) were detectable throughout the water column of the eastern tropical North Atlantic (ETNA) and eastern tropical South Pacific (ETSP) Oceans. Particularly in the ETNA, comparable patterns of abundance and expression of archaeal amoA genes and N2O co-occurred in the oxygen minimum, whereas the abundances of bacterial amoA genes were negligible. Moreover, selective inhibition of archaea in seawater incubations from the ETNA decreased the N2O production significantly. In studies with the only cultivated marine archaeal ammonia-oxidizer Nitrosopumilus maritimus SCM1, we provide the first direct evidence for N2O production in a pure culture of AOA, excluding the involvement of other microorganisms as possibly present in enrichments. N. maritimus showed high N2O production rates under low oxygen concentrations comparable to concentrations existing in the oxycline of the ETNA, whereas the N2O production from two AOB cultures was comparably low under similar conditions. Based on our findings, we hypothesize that the production of N2O in tropical ocean areas results mainly from archaeal nitrification and will be affected by the predicted decrease in dissolved oxygen in the ocean.

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