HR: 1340h
AN: B13B-1199    [Abstracts]
TI: Grasland Stable Isotope Flux Measurements: Three Isotopomers of Carbon Dioxide Measured by QCL Spectroscopy
AU: * Zeeman, M J
EM: matthias.zeeman@ipw.agrl.ethz.ch
AF: Institute of Plant Sciences, ETH Zurich, Universitaetsstrasse 2, Zurich, 8092, Switzerland
AU: Tuzson, B
EM: bela.tuzson@empa.ch
AF: Laboratory for Air Pollution and Environmental Technology, EMPA, Ueberlandstrasse 129, Dubendorf, 8600, Switzerland
AU: Eugster, W
EM: werner.eugster@ipw.agrl.ethz.ch
AF: Institute of Plant Sciences, ETH Zurich, Universitaetsstrasse 2, Zurich, 8092, Switzerland
AU: Werner, R A
EM: roland.werner@ipw.agrl.ethz.ch
AF: Institute of Plant Sciences, ETH Zurich, Universitaetsstrasse 2, Zurich, 8092, Switzerland
AU: Buchmann, N
EM: nina.buchmann@ipw.agrl.ethz.ch
AF: Institute of Plant Sciences, ETH Zurich, Universitaetsstrasse 2, Zurich, 8092, Switzerland
AU: Emmenegger, L
EM: lukas.emmenegger@empa.ch
AF: Laboratory for Air Pollution and Environmental Technology, EMPA, Ueberlandstrasse 129, Dubendorf, 8600, Switzerland
AB: To improve our understanding of greenhouse gas dynamics of managed ecosystems such as grasslands, we not only need to investigate the effects of management (e.g., grass cuts) and weather events (e.g., rainy days) on carbon dioxide fluxes, but also need to increase the time resolution of our measurements. Thus, for the first time, we assessed respiration and assimilation fluxes with high time resolution (5Hz) stable isotope measurements at an intensively managed farmland in Switzerland (Chamau, 400m ASL). Two different methods were used to quantify fluxes of carbon dioxide and associated fluxes of stable carbon isotopes: (1) the flux gradient method, and (2) the eddy covariance method. During a week long intensive measurement campaign, we (1) measured mixing ratios of carbon dioxide isotopomers (¹²C¹⁶O₂, ¹²C¹⁶O¹⁸O, ¹³C¹⁶O₂) with a Quantum Cascade Laser (QCL, Aerodyne Inc.) spectroscope and (2) collected air samples for isotope analyses (¹³C/¹²C) and (¹⁸O/¹⁶O) of carbon dioxide by Isotope Ratio Mass Spectrometry (IRMS, Finnigan) every two hours, concurrently along a height profile (z = 0.05; 0.10; 0.31; 2.15m). In the following week, the QCL setup was used for closed-path eddy covariance flux measurement of the carbon dioxide isotopomers, with the air inlet located next to an open-path Infra Red Gas Analyzers (IRGA, LiCor 7500) used simultaneously for carbon dioxide measurements. During this second week, an area of grass inside the footprint was cut and harvested after several days. The first results of in-field continuous QCL measurements of carbon dioxide mixing ratios and their stable isotopic ratios show good agreement with IRGA measurements and isotope analysis of flask samples by IRMS. Thus, QCL spectroscopy is a very promising tool for stable isotope flux investigations.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting