CO_1tn2 and isotope flux measurements above a spruce forest [Elektronische Ressource] / presented by Johannes Ruppert

Ruppert

Sujets

• Biologie

Informations

• Publié par: universitat_bayreuth
• Publié le: 01 janvier 2009
• Nombre de lectures: 31
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

CO and Isotope Flux Measurements above a Spruce Forest 2



This dissertation is submitted to the
FACULTY OF BIOLOGY, CHEMISTRY AND GEOSCIENCES
OF THE UNIVERSITY OF BAYREUTH, GERMANY
to attain the academic degree of
DR. RER. NAT.


It is presented by
JOHANNES RUPPERT
Diplom Geoökologe
born July, 1975
in Stuttgart, Germany.


Düsseldorf, July 2008




CO and Isotope Flux Measurements above a Spruce Forest 2


This doctoral thesis was prepared at the UNIVERSITY OF BAYREUTH at the CHAIR OF
HYDROLOGY, DEPARTMENT OF MICROMETEOROLOGY under the supervision of
PROF. DR. THOMAS FOKEN
The research project was part of the framework of the Bayreuth Institute for Terrestrial
Ecosystem Research (BITÖK) and funded by the Federal Ministry of Education and Research
of Germany (BMBF) (PT BEO51-0339476 D). Important parts of the research were performed
in collaboration with the Max-Planck Institute for Biogeochemistry (MPI BGC) in Jena,
Germany, and under the supervision of Prof. Dr. Nina Buchmann. The experimental work was
partly embedded in the LITFASS-2003 experiment at the Lindenberg Experiment site of the
German Meteorological Service (DWD).


Die vorliegende Arbeit wurde unter der Betreuung von
Prof. Dr. Thomas Foken in der Zeit vom 1.2.2002 bis 15.7.2008 angefertigt.
Vollständiger Abdruck der von der Fakultät für Biologie, Chemie und Geowissenschaften der
Universität Bayreuth genehmigten Dissertation zur Erlangung des akademischen Grades eines
Doktor der Naturwissenschaften (Dr. rer. nat.).
Einreichung der Dissertation: 16.7.2008
Wissenschaftliches Kolloquium: 6.2.2009
Prüfungsausschuss:
Vorsitzender: Prof. Dr. Michael Hauhs
1. Gutachter: Prof. Dr. Thomas Foken
2. Gutachterin: Prof. Dr. Nina Buchmann
Prof. Dr. Yakov Kuzyakov
Prof. Dr. Cornelius Zetzsch
.
II RUPPERT: CO AND ISOTOPE FLUX MEASUREMENTS ABOVE A SPRUCE FOREST 2

Table of Contents

Summary IV
Zusammenfassung VI
Acknowledgments VIII
List of publications and manuscripts IX
List of additional publications from the research project X

1. Introduction 1
2. Objective of the thesis 3
3. Instrument and software development 4
3.1. Development of high precision isotope sampling systems 4
3.2. Software developments 4
4. Experiments and data evaluation 5
4.1. Laboratory experiments 5
4.2. GRASATEM-2002 5
4.3. GRASATEM-2003 6
4.4. WALDATEM-2003 and continuous EC flux data 6
4.5. Additional experimental data 7
5. Assessment of scalar similarity in the turbulent exchange 7
6. Gap-filling of CO net ecosystem exchange (NEE) data 8 2
7. Whole-air relaxed eddy accumulation (REA) isotope flux measurements 9
8. Flux weighted isotopic signatures and discrimination in the ecosystem gas exchange 10
9. Potential and requirements of the isotopic flux partitioning method 11
10. Conclusion 12
11. References 14

Appendix 1: Ruppert et al.: Scalar similarity for relaxed eddy accumulation methods,
(SS-1 to SS-23), 19

Appendix 2: Ruppert et al.: Innovative gap-filling strategy for annual sums of CO net 2
ecosystem exchange, (GF-1 to GF-34), 42

Appendix 3: Ruppert et al.: Whole-air relaxed eddy accumulation for the measurement
of isotope and trace-gas fluxes, (REA-1 to REA-35), 76

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Appendix 4: Ruppert et al.: Ecosystem CO and CO O isotope discrimination measured 2
by hyperbolic relaxed eddy accumulation, (ED-1 to ED-46), 111

Erklärung
III RUPPERT: CO AND ISOTOPE FLUX MEASUREMENTS ABOVE A SPRUCE FOREST 2

Summary
The measurement of the turbulent carbon dioxide (CO ) exchange by the eddy covariance 2
(EC) method has become a fundamental tool for the quantitative determination of the
atmospheric CO net ecosystem exchange (NEE) and the investigation of the carbon mass 2
balances of ecosystems. Such measurements require a high degree of quality control in order to
prevent systematic errors. The determination of the annual sum of NEE and filling of data gaps
is complicated by characteristic diurnal and seasonal variation in the governing gross flux
components of assimilation, i.e. photosynthetic uptake of CO , and respiration. 2
In this dissertation, a set of criteria is suggested for the identification of high quality NEE
data. They are applied to data obtained above a spruce forest in the Fichtelgebirge Mountains in
Germany. The application of the quality criteria resulted in less systematic distribution of data
gaps compared to a commonly applied criterion based on the friction velocity u measured
above the canopy. The suggested method is therefore able to reduce the risk of double
accounting of nighttime respiration fluxes and systematic error in the annual sum of NEE.
The isotopic flux partitioning method can be applied to quantify the assimilation and
respiration flux components. Especially above forest ecosystems, it requires isotope flux
measurements with high analytical precision in order to resolve small gradients in the isotopic
signature of the turbulent exchange. A conditional sampling instrument was developed and
tested in laboratory and field experiments. By combining the hyperbolic relaxed eddy
accumulation method (HREA), whole-air sampling and high precision isotope ratio mass
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spectrometry (IRMS), CO and CO O isotopic flux densities (isofluxes) could be measured 2
with an estimated uncertainty of 10-20% during a three day intensive measuring campaign of
the field experiment WALDATEM-2003 (Wavelet Detection and Atmospheric Turbulent
Exchange Measurements 2003).
Thorough quality control was applied at all stages of the experiment, including the data
evaluation. The sampling process and the assumption of similarity in the turbulent exchange
characteristics of different scalars (scalar similarity) were assessed by simulation of HREA
sampling based on high temporal resolution data of the turbulent energy and gas exchange.
Above three different vegetation types, distinct diurnal changes of scalar similarity were
observed and attributed to events on time scales longer than 60 s, which most likely represent
changes in the source/sink strength or convective or advective processes. Poor scalar-scalar
correlations indicate the risk of systematic underestimation of fluxes measured by HREA. There
is some evidence for good scalar similarity and a generally linear relation between bulk CO 2
mixing ratios and its isotopic signatures in the turbulent exchange. However, the slope of that
relation was observed to change temporarily so that especially for the EC/flask method temporal
and spatial scales represented in flask samples must carefully be considered. HREA isoflux
measurements have a footprint similar to the footprint of EC measurements and are therefore
able to integrate small-scale heterogeneity in ecosystems.
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CO mixing ratios and C and O isotopic signatures measured in updraft and downdraft 2
whole-air samples allowed determining ecosystem integrated and truly flux weighted isotopic
signatures of the atmospheric ecosystem gas exchange and ecosystem isotope discrimination e
and on half-hourly timescales. The observed diurnal variability demonstrates the need for E
their repeated high precision measurement at ecosystem scale for the evaluation of isotopic
mass balances. For the isotopic flux partitioning method, additional data on the integrated
canopy isotope discrimination ' from independent measurements or validated models is canopy
IV




RUPPERT: CO AND ISOTOPE FLUX MEASUREMENTS ABOVE A SPRUCE FOREST 2

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indispensable. An observed fast equilibration of isotopic disequilibria D C and D O between
the assimilation and respiration fluxes may indicate that the successful application of the
isotopic flux partitioning method is limited to short periods after significant environmental
changes on the scale of few days.

V RUPPERT: CO AND ISOTOPE FLUX MEASUREMENTS ABOVE A SPRUCE FOREST 2

Zusammenfassung
Die Messung des turbulenten Kohlendioxidaustausches mit der Eddy Kovarianzmethode
(eddy covariance, EC) ist eine wichtige Methode für die quantitative Bestimmung des CO 2
Netto-Ökosystem-Austausches (net ecosystem exchange, NEE) und die Untersuchung von
Kohlenstoffbilanzen von Ökosystemen geworden. Derartige Messungen erfordern intensive
Qualitätskontrollen, um systematische Fehler zu vermeiden. Erschwert wird die Bestimmung
der Jahressumme des NEE und das Füllen von Datenlücken durch die charakteristischen
täglichen und jahreszeitlichen Schwankungen in den ausschlaggebenden Brutto-Fluss-
komponenten der Assimilation, d.h. der Aufnahme von CO durch die Photosynthese, und der 2
Respiration.
In dieser Dissertation werden Kriterien vorgeschlagen nach denen NEE Daten mit hoher
Qualität identifiziert werden können. Diese Kriterien werden auf NEE Daten angewendet, die
über einem Fichtenwald im Fichtelgebirge in Deutschland gesammelt wurden. Die Anwendung
der Qualitätskriterien ergab eine weniger