presentation at nserc strategic project meeting – guelph jan 10, 2008 claudia wagner-riddle...
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Presentation at NSERC Strategic Project Presentation at NSERC Strategic Project Meeting – GuelphMeeting – Guelph
Jan 10, 2008Jan 10, 2008Claudia Wagner-RiddleClaudia Wagner-Riddle
• Previous experience with isotopic CO2 measurements of soil respiration
• Proposed research for 2008, 2009
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Previous Project: Temporal Dynamics of Greenhouse Gas Fluxes linked to Soil Biophysical
Processes and Management Practices
• Co-applicants: U. of Guelph, U. of Manitoba, AAFC • Duration: Sep 30, 2004 to Sep 29, 2007• Funds for purchasing tunable diode laser trace gas
analyzer for 13CO2 and 12CO2 concentration measurements
• One of objectives:
– to determine fraction of soil CO2 flux originating from soil organic carbon or crop residue carbon for no-tillage (NT) vs. conventional tillage (CT) over time
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Research Site: Elora (Ontario)
• Four 1.5 ha plots: conventional practices (2 plots); "best management" practices (2 plots) since 2000; since May 2005 treatments these were NT and CT
• Corn/soybean/winter-wheat/corn/soybean over 2000 to 2004; corn in 2005
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2 (NT)2 (NT)
3 (NT)3 (NT)
1 (CT)1 (CT)
4 (CT)4 (CT)
Trailer
Four 1.5-ha Plots (Ontario)Four 1.5-ha Plots (Ontario)
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Field: -air intakes (up/down x 4 plots)
Trailer: -sampling manifold-tanks-dryer-TGA-pumps
Stable Isotope Studies at EloraStable Isotope Studies at Elora
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30 s tank A
30 s tank B
15 s each height for 4 min
Switching cycle for one plot over 30 minSwitching cycle for one plot over 30 min
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Weekly calibration (working vs. transfer or ’golden’ tanks)Weekly calibration (working vs. transfer or ’golden’ tanks)
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Measured by TGA(diff. in conc. between 2 heights)
Flux Ratio Calculation of 13CR (Griffis et al., 2004)
Note: Applicable to soil respiration only when vegetation is not present
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CO2 Fluxes
Fall 2005
CT × NT +
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Flux Ratio calculation of 13CR
Fall NT ~3.5‰ lower than CT plot Fall to Spring Change ~-4‰
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Keeling Plots
Footprint for concentration measurement larger than 1.5-ha plots so that difference between treatments can not be detected
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Findings• The respired soil CO2 signature showed a stronger C4
signature compared to the no-till field where crop residue was left on the soil surface during fall and spring
• This means a larger proportion of measured soil CO2 flux in fall originated from crop residue in CT compared to NT (76.2 vs. 61.5% in fall; 60% vs. 45.1% in spring)
• These results suggest that NT will increase C storage, contradicting previous studies in eastern Canada
• It may be that decomposition under NT increases at some time subsequent to the measurement periods reported here (i.e. summer, when vegetation is present)
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New Research Question
• How to derive 13CR from in-canopy 13CO2 and 12CO2 concentration measurements?
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13CO2 and 12CO2 concentrations measurements
Proposed MeaurementsProposed Meaurements
• Canopy measurements
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Laser and Dewar
PC
Electronics Absorption tubeReference cell and detector
Sample cell and detector
Edwards et al. (2002)
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• TGA100 adapted to measure mole fractions of 12CO2 and 13CO2 by Bowling et al. (2003) – Based on mostly same hardware– Software change to allow for simultaneous scanning of two
absorption lines (one for each isotopomer)– Analyzer optimized for accuracy and precision
• TGA100 tested in 26-day field experiment in Minnesota (after soybean harvest) by Griffis et al. (2004)
• Characteristics:– 10 Hz noise of 13C 0.5‰, calibrated noise <0.15‰ 13CR can be obtained by ratio of fluxes (F13CO2/F 12CO2) instead
of Keeling plot
Stable Isotope Studies using TDLASStable Isotope Studies using TDLAS