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| Titel |
The isotopic signature of ecosystem respiration and Eddy Covariance measurements of stable CO2 isotopologues in a temperate beech forest |
| VerfasserIn |
Jelka Braden-Behrens, Alexander Knohl, Hans-Jürg Jost |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132377
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| Publikation (Nr.) |
 EGU/EGU2016-12882.pdf |
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| Zusammenfassung |
| Analyzing the isotopic composition of CO2 fluxes has provided valuable insights into
ecosystem gas exchange. Stable isotopes in CO2 have been used for example to analyze
different influencing factors of ecosystem respiration and to partition CO2 fluxes into
assimilation and respiration e.g. by directly measuring the isotopic composition of CO2 net
fluxes on ecosystem scale.
During a three month measurement campaign in autumn 2015, we measured the isotopic
composition of CO2 in nine different heights using a new, easy-to-use Isotope Ratio Infrared
Spectrometer (IRIS) Delta Ray (Thermo Scientific, Bremen) developed for high precision
measurements of 13C and 18O in CO2with automatic calibration. Based on a Keeling Plot
approach we calculated the isotopic signal of ecosystem respiration in 13C as well
as in 18O. Additionally, we performed high frequency (4 Hz) measurements of
the isotopic composition of CO2 in 35 m height using a quantum cascade laser
based spectrometer (QCLAS, Aerodyne Research) with thermoelectrically cooled
detectors.
The Delta Ray Analyzer had a cell turnover time of approximately 12s and high temporal
stability of a target measurement under field conditions as well as high precision. The
minimum of its Allan variance was 0.02‰ for 13δC and 0.03‰ for 18δO with averaging
times of app. 290s. The high frequency QCLAS was used to perform 4Hz measurements and
showed maximum precision for averaging periods of app. 90s with an Allan Deviation of
0.04‰ for 13δC and 0.06‰ for 18δO. The measured isotopic signal of respired CO2 showed
large seasonal variability with nighttime values (taken between 22h and 2h) ranging
from -25 to -38‰ for 13δC and from -7.7 to -48.7 ‰ for 18δO. For both δ-values
we find large day-to-day variability that exceeds the error of the underlying linear
regression. We also show to which extent the two different laser spectrometers
which were calibrated completely independently give consistent results and test the
correlation with the measured meteorological quantities such as vapor pressure deficit
(VPD). Additionally, we plan to present first Eddy Covariance isotopologue fluxes. |
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