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Isotopic constraints on seasonal N2O dynamics in marine and lacustrine environments

English title Isotopic constraints on seasonal N2O dynamics in marine and lacustrine environments
Applicant Lehmann Moritz
Number 147106
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 01.04.2013 - 31.03.2015
Approved amount 211'003.00
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All Disciplines (3)

Discipline
Oceanography
Geochemistry
Hydrology, Limnology, Glaciology

Keywords (9)

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

Lay Summary (German)

Lead
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.
Lay summary

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 Gesamt-Lachgasproktion können jeweils den Prozessen Ammoniumoxidation, Nitrifikanten-Denitrifizierung und Denitrifizierung in den beiden Studiengebieten  zugeordnet werden? 
  • Welche biogeochemischen Faktoren (e.g., pH, O2) sind primär für die Steuerung von Nitrifikanten-Denitrifizierungsraten verantwortlich, und gibt es sytematische Unterschiede zwischen marinen und lakustrinen Milieus?
  • Gibt es direkte und diagnostisch verwertbare Zusammenhänge zwischen den Konzentrationen und Isotopenzusammensetzungen von N2O, NO2-, NO3-, and NH4+ und den gemessenen N2O Umsatzraten in den Studiengebieten?

In beiden Studiengebieten werden mittels 15N-Tracermethoden N2O-Produktionsraten sowie Schlüsselparameter wie  pH, Chlorophyll a, Sauerstoffkonzentration (O2) und Konzentrationen und Sickstoffisotopenverhältnisse anorganisch-gelöster Stickstoffverbindungen gemessen mit dem Ziel, Lachgasproduktionsmechanismen  und relevante Kontrollfaktoren besser zu beleuchten.

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: 25.03.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
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.
Year-round N2O production by benthic NOx reduction in a monomictic south-alpine lake
Freymond Chantal, Wenk Christine, Frame Caitlin, Lehmann Moritz (2013), Year-round N2O production by benthic NOx reduction in a monomictic south-alpine lake, in Biogeosciences, 10, 8373-8383.

Collaboration

Group / person Country
Types of collaboration
University of Hamburg (Prof. Dr. K. Emeis) Germany (Europe)
- Research Infrastructure
LSA Lugano/FH Lugano (Dr. M. Veronesi and Dr. M. Simona) Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
University of Southern Denmark (Odense) (Prof. B. Thamdrup, Dr. L. Bristow) Denmark (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Fall Meeting of the American Geophysical Union Poster N2O production by nitri er denitri cation in the Benguela Upwelling System 07.12.2014 San Francisco, United States of America Frame Caitlin;
Fall Meeting of the American Geophysical Union Poster Lake acidification and oxygen depletion may synergistically enhance nitrous oxide (N2O) production by nitrifier denitrification in a subalpine lake 08.12.2013 San Francisco, United States of America Frame Caitlin;


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)
159197 Environmental controls on N2O production by ammonium oxidizing bacteria in marine and lacustrine environments - a stable isotopic approach 01.04.2015 Project funding (Div. I-III)
170876 Advanced understanding of autotrophic nitrogen removal and associated N2O emissions in mixed nitritation-anammox systems through combined stable ISOtopic and MOLecular constraints (ISOMOL) 01.09.2017 Sinergia
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

Nitrous oxide (N2O) is now the third largest contributor to radiative forcing of the long-lived greenhouse gases. Human inputs of nitrogen (N), mainly as fertilizers, have stimulated the microbial N cycle transformations that are the dominant source of N2O. The partitioning between the anthropogenic and natural N2O sources is relatively well constrained at 7 and 11 Tg N/yr, respectively. However, large uncertainties remain in the relative contributions of terrestrial versus aquatic environments and with regards to the underlying biogeochemical controls on microbial N2O production. Such uncertainties present challenges for those devising and implementing N2O emissions policies, and make it difficult to interpret prehistoric atmospheric N2O fluctuations and predict the response of N2O production rates to future climate change.Aquatic N2O fluxes are often highly variable through time and space. The variation is likely modulated by fluctuations in the biogeochemical conditions, which may affect microbial N2O production pathways differentially. N2O can be produced by several processes, such as microbial nitrification (ammonia oxidation), denitrification, and nitrifier-denitrification, and multiple groups of microorganisms are involved. Yet, the exact environmental controls on temporal/spatial variations in net N2O production and the balance between the different pathways are still poorly constrained. It is highly probable that changes in the microbial processes that generate N2O are closely linked to seasonal changes in water productivity, organic matter remineralization rates, and in turn water-column redox-conditions.In this study we propose using incubation-based stable N-isotope tracer methods and natural N isotope measurements in dissolved N2O to identify and quantify specific N2O production pathways in two aquatic environments with strong seasonal N cycle dynamics: eutrophic Lake Lugano in southern Switzerland and the highly productive Benguela Upwelling region along the coast of southwestern Africa. Our main goals will be to shed light on the dynamics and controls on N2O production in two comparable environments. Within the frame of one postdoctoral project we propose to address the following research questions:•How much do ammonia oxidation, nitrifier-denitrification, and denitrification, respectively, contribute to N2O formation in Lake Lugano and the Benguela Upwelling?•Which biogeochemical factors control nitrifier-denitrification rates, and are there systematic differences between the marine and freshwater environment?•How do the concentrations and stable isotopic signatures of N2O, NO2-, NO3-, and NH4+ observed in Lake Lugano and the Benguela Upwelling zone relate to the rates of the studied pathways?In both environments, key variables, such as water pH, chlorophyll a, oxygen (O2), and dissolved inorganic N concentrations, will be measured, and some of these parameters will be manipulated in incubations to study their impacts on N2O production rates. Combining natural abundance N2O isotope measurements and N2O turnover measurements, and integrating the results in a 1-D geochemical model (for Lake Lugano) we attempt to gain information on the N and O isotope effects that are associated with N2O cycling processes. Measurements of the isotope effects and isotopic signatures associated with N2O production by natural microbial communities are valuable biogeochemical information because they allow detection of N cycle transformation processes in environments where direct rate measurements cannot be made. Our study is designed to capture the temporal dynamics associated with N2O production in both aquatic environments. The University of Basel has been invited to join two research cruises (R/V Meteor) to the Benguela Upwelling zone that are scheduled for the seasonal maximum in upwelling intensity (September 2013) and the minimum (February 2014). The upcoming cruises will provide a unique opportunity to identify seasonal change in biological N2O production mechanisms and rates, as well as the physical parameters that affect sea-to-air fluxes of N2O.The research proposed here will result in a detailed characterization of seasonal cycles in N2O biogeochemistry. The study in Lugano has been designed to produce clear information for water resource managers describing the aspects of water quality that most influence N2O emissions in nutrient-impacted lakes. The Benguela cruises will provide maximum and minimum N2O flux constraints on this geochemically important upwelling region. Both studies will be used to provide new information about the controls on aquatic N2O that are needed to accurately model the global dynamics of this powerful greenhouse gas.
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