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Environmental controls on N2O production by ammonium oxidizing bacteria in marine and lacustrine environments - a stable isotopic approach

English title Environmental controls on N2O production by ammonium oxidizing bacteria in marine and lacustrine environments - a stable isotopic approach
Applicant Lehmann Moritz
Number 159197
Funding scheme Project funding (Div. I-III)
Research institution Institut für Umweltgeowissenschaften Universität Basel
Institution of higher education University of Basel - BS
Main discipline Oceanography
Start/End 01.04.2015 - 31.03.2016
Approved amount 104'612.00
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All Disciplines (3)

Discipline
Oceanography
Geochemistry
Hydrology, Limnology, Glaciology

Keywords (9)

Lake Lugano; upwelling zones; ammonia oxidation; nitrogen isotopes; nitrous oxide; nitrification; Benguela; denitrification; nitrifier denitrification

Lay Summary (German)

Lead
Ziel des Projektes ist ein verbessertes Verständnis von mikrobieller Lachgasproduktion in marinen und lakustrinen Umweltsystemen mit saisonal stark variierenden Umweltbedingungen zu erlangen. Mittels Isotopenmethoden soll herausgefunden werden, inwiefern Ammoniumoxidations- oder Nitrifikanten-Denitrifizierungsraten durch spezifische Umweltbedingungen (z.B. pH, O2) moduliert werden.
Lay summary

Lachgas (N2O) ist ein wichtiges und langlebiges Treibhausgas, dessen  anthropogene und natürliche Quellen recht gut bekannt sind (7 bzw. 11 Tg N/yr). Grosse Unsicherheiten bestehen jedoch bezüglich der jeweiligen Anteile terrestrischer gegenüber aquatischer Quellen an den Gesamt-Lachgasemissionen sowie der biogeochemischen Mechanismen welche die N2O Produktion in aquatischen Systemen steuern.

Unser übergeordnetes Ziel ist, zu einem verbesserten Verständnis von Lachgasproduktion durch verschiedene Mikroorganismen in marinen und lakustrinen Umweltsystemen mit saisonal stark variierenden Umweltbedingungen beizutragen. Unsere Studiengebiete sind: der Luganersee (Schweiz) sowie das hoch-produktive Auftriebsgebiet vor der Küste Namibias. Im Detail sollen folgende Fragen beantwortet werden:
• Welche Anteile der Lachgasproktion können jeweils den Prozessen Ammoniumoxidation oder Nitrifikanten-Denitrifizierung in den beiden Studiengebieten  zugeordnet werden? 
• Welche biogeochemischen Faktoren (z.B., pH, O2) sind primär für die Steuerung von Nitrifikanten-Denitrifizierungsraten verantwortlich, und gibt es sytematische Unterschiede zwischen marinen und lakustrinen Milieus?

Unsere Arbeit wird neue und wichtige Informationen bezüglich der Rolle von Auftriebsgebieten und produktiven Seen in globalen N2O Budgets liefern. Auch wird sie neue Erkenntnisse über einen bisher von wissenschaftlichen Studien eher wenig berücksichtigten aber im globalen Stickstoffkreislauf vermutlich überaus wichtigen Prozess, der Nitrifikanten-Denitrifizierung, erlauben.

Direct link to Lay Summary Last update: 30.03.2015

Responsible applicant and co-applicants

Employees

Publications

Publication
Acidification Enhances Hybrid N2O Production Associated with Aquatic Ammonia-Oxidizing Microorganisms
Frame Caitlin H., Lau Evan, Nolan E. Joseph, Goepfert Tyler J., Lehmann Moritz F. (2017), Acidification Enhances Hybrid N2O Production Associated with Aquatic Ammonia-Oxidizing Microorganisms, in Frontiers in Microbiology, 7, 10.3389/fm.
Differential N 2 O dynamics in two oxygen-deficient lake basins revealed by stable isotope and isotopomer distributions Differential N 2 O Dynamics in Two Lake Basins
Wenk Christine B., Frame Caitlin H., Koba Keisuke, Casciotti Karen L., Veronesi Mauro, Niemann Helge, Schubert Carsten J., Yoshida Naohiro, Toyoda Sakae, Makabe Akiko, Zopfi Jakob, Lehmann Moritz F. (2016), Differential N 2 O dynamics in two oxygen-deficient lake basins revealed by stable isotope and isotopomer distributions Differential N 2 O Dynamics in Two Lake Basins, in Limnology and Oceanography, 61(5), 1735-1749.

Collaboration

Group / person Country
Types of collaboration
West Liberty University (Prof. Dr. Evan Lau) United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
University of Hamburg (Prof. Dr. K. Emeis) Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
University of Southern Denmark (Prof. Dr. Bo Thamdrup, Dr. Laura Bristow) Denmark (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Oceanographic Research Center of South Pacific, COPAS, University of Concepcion (Prof. Dr. L. Farias Chile (South America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Associated projects

Number Title Start Funding scheme
129491 Nitrogen elimination pathways and associated isotope effects in Swiss eutrophic Lake Lugano 01.04.2010 Project funding (Div. I-III)
147106 Isotopic constraints on seasonal N2O dynamics in marine and lacustrine environments 01.04.2013 Project funding (Div. I-III)
153055 Seasonal Dynamics of Coupled Nitrogen, Sulfur, and Carbon Cycling in Redox Transition Zones of Lake Lugano 01.11.2014 Project funding (Div. I-III)

Abstract

With this proposal, we seek funding for a 12-month extension of the postdoctoral project "Isotopic constraints on seasonal N2O dynamics in marine and lacustrine environments" (SNF 147106; April 2013 - March 2015). Large uncertainties exist with regards to the biogeochemical controls on microbial N2O production. The main objectives of SNF project 147106 were to better understand the environmental conditions that modulate N2O fluxes in aquatic environments. In this context, we proposed to study specific biogeochemical controls (e.g., pH, O2, ecosystem productivity) on the rates of different microbial N2O production pathways (specifically, nitrification/ammonia oxidation and nitrifier-denitrification) in two contrasting aquatic environments with strong seasonal N cycle dynamics: eutrophic Lake Lugano in southern Switzerland and the highly productive Namibian Upwelling region along the coast of southwestern Africa. Making use of incubation-based stable N isotope tracer methods and natural N isotope measurements in dissolved N2O, we focused on the following questions:•How much do ammonia oxidation and nitrifier-denitrification, respectively, contribute to N2O formation in Lake Lugano and the Namibian Upwelling Zone?•Which biogeochemical factors control nitrifier-denitrification rates, and are there systematic differences between the marine and freshwater environment?During the first 18 months of the project, we generated a comprehensive data set that provides compelling biogeochemical evidence that under insitu conditions, N2O production in Lake Lugano subsurface waters can be largely attributed to the decomposition of hydroxylamine (NH2OH) during ammonium oxidation. At low pH (pH = 6.5) conditions, however, N2O production by nitrifier denitrification is significantly enhanced, and the impact of lowering the pH appears to be amplified when O2 concentrations are also reduced. While we still lack a clear understanding of the mechanisms responsible for these observations, our data clearly demonstrate that relatively mild pH and redox condition changes can have a strong effect on the proportion of N2O produced by nitrifier denitrification versus NH2OH oxidation, and on the overall N2O production. The “biogeochemical switch” in N2O production observed in Lake Lugano, stands in contrast to observations in the Namibian upwelling system. Here, N2O production by either mechanism was not significant at the in situ pH (pH = 7.7) and fully aerobic conditions (20% headspace O2), yet under reduced pH conditions (pH = 7), N2O production by nitrifier denitrification was also enhanced, implying that periods of upwelling of CO2-rich/low-pH deep waters can stimulate N2O production by nitrifier denitrification.Although the preliminary data are highly promising, not all questions could be addressed unambiguously thus far (due to analytical problems during the initial phase of the project). The robustness of our existing results should be confirmed by additional/outstanding measurements of samples that have already been collected, and by additional incubation experiments with samples from another Swiss Lake, Lake Cadagno, where preliminary N2O concentration/isotope data reveal shallow-water N2O production by nitrifier-denitrification. Additional efforts also include the assessment of ammonium oxidation rates based on existing 15N-label incubation data. Our goal is to compare the ammonia oxidation rates under each set of experimental treatments to the production rates of N2O by both NH2OH decomposition and nitrifier denitrification. We plan to combine the natural abundance N2O isotope measurements and N2O production measurements in a 1-D geochemical model (for Lake Lugano), in an effort to describe N2O production as a function of ammonia oxidation rate, nitrifier denitrification rate, and to gain information on the N and O isotope effects that are associated with shallow N2O production processes. Similarly, using the combined N2O and NOx isotope data from the Namibian upwelling region, we will attempt to assess the relative importance of upwelling-stimulated N2O production to the total N2O emissions to the atmosphere (which includes both “pre-formed” deep N2O which is upwelled to the surface, as well as “new” N2O production stimulated by the upwelling itself). Finally, we propose some molecular biological work, applying next generation sequencing techniques to the microbial community in our tracer incubations from Lugano and the Namibian upwelling, in order to understand the phylogenetic context that may explain why there are differences in the relative rates of N2O production by NH2OH decomposition and nitrifier denitrification in Lugano versus the Namibian Upwelling area. The research proposed here will provide new information about the controls on aquatic N2O production, which are needed to accurately model the global dynamics of this powerful greenhouse gas.
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