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| Titel |
Eddy Covariance measurements of stable CO2 and H2O isotopologues |
| VerfasserIn |
Jelka Braden-Behrens, Alexander Knohl |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110944
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| Publikation (Nr.) |
 EGU/EGU2015-15214.pdf |
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| Zusammenfassung |
| The analysis of the stable isotope composition of CO2 and H2O fluxes (such as 13C, 18O and
2H in H2O and CO2) has provided valuable insights into ecosystem gas exchange.
The approach builds on differences in the isotope signature of different ecosystem
components that are primarily caused by the preference for or the discrimination
against respective isotope species by important processes within the ecosystem (e.g.
photosynthesis or leaf water diffusion). With the ongoing development of laser
spectrometric methods, fast and precise measurements of isotopologue mixing ratios
became possible, hence also enabling Eddy Covariance (EC) based approaches to
directly measure the isotopic composition of CO2 and H2Ov net fluxes on ecosystem
scale.
During an eight month long measurement campaign in 2015, we plan to simultaneously
measure CO2 and H2Ov isotopologue fluxes using an EC approach in a managed beech forest
in Thuringia, Germany. For this purpose, we will use two different laser spectrometers for
high frequency measurements of isotopic compositions: For H2Ov measurements,
we will use an off axis cavity output water vapour isotope analyser (WVIA, Los
Gatos Research Inc.) with 5 Hz response; and for CO2 measurements, we will use
a quantum cascade laser-based system (QCLAS, Aerodyne Research Inc.) with
thermoelectrically cooled detectors and up to 10ÂHz measurement capability. The resulting
continuous isotopologue flux measurements will be accompanied by intensive sampling
campaigns on the leaf scale: Water from leaf, twig, soil and precipitation samples will be
analysed in the lab using isotope ratio mass spectrometry. During data analysis we
will put a focus on (i) the influence of carbon and oxygen discrimination on the
isotopic signature of respective net ecosystem exchange, (ii) on the relationship
between evapotranspiration and leaf water enrichment, and (iii) on the 18O exchange
between carbon dioxide and water. At present, we already carried out extensive
instrument performance tests for both laser spectrometers that will be presented here. In
addition, we will present the instrumentation, the measurement periphery as well as
anticipated analysis approaches required for the planned measurement campaign. |
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