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Summertime horizontal and vertical advective carbon dioxide fluxes measured in a closed-canopy Douglas-fir forest on a slope Leitch, Adrian
Abstract
An observational study was conducted during an eight-week period in the summer of 2009 at a forested site in British Columbia (“DF49”) to determine the incidence and magnitude of advective carbon dioxide (CO₂) fluxes. The site is situated in a tall, closed-canopy (zh = 35 m, 1100 stems ha-¹, LAI of 7 m² m-²) Douglas-fir forest on a 5-10o slope. Katabatic flow occurs within the subcanopy during a significant portion of the day, especially during the evening and night. Wind vector and CO₂ concentration measurements were made at heights of 1, 2.6, 8, 20 and 42 m on the main flux tower, while CO₂ concentration measurements were made 73.5 m upslope from the tower at heights of 1, 2.6, 8 and 20 m, creating a two-dimensional transect. Eight thermostated non-differential infrared gas analyzers (IRGAs) were paired using a solenoid valve switching system, creating four differential analyzers. The switching system, combined with a twice-daily polynomial IRGA calibration, enabled measurement of CO₂ concentration differences at the four subcanopy measurement heights to an accuracy of 0.5 μmol mol-¹ (horizontal) and 1 μmol mol-¹ (vertical). The system also recorded semi-continuous CO₂ traces at all sample points. Horizontal advective fluxes, averaged over the main measurement period (August 2 - 25), reached 5 μmol m-² s-¹ at night and 10 μmol m-² s-¹ in the afternoon (a net source to the atmosphere) and -2 μmol m-² s-¹ during the morning (net sink). Vertical advective fluxes averaged around zero during the night, 5 μmol m-² s-¹ during the morning and -5 μmol m-² s-¹ during the afternoon. A cumulative sum of advective flux-corrected net ecosystem exchange (NEE) over the main measurement period (-57 g C m-²) was close to that of the friction velocity-corrected NEE (-60 g C m-²), both predicting less carbon uptake by the Douglas-fir forest than the storage-corrected NEE (-86 g C m-²). Additional CO₂ difference measurements made after the main sampling period along the 73.5-m transect demonstrated that horizontal CO₂ differences increased monotonically down slope (on average) at the 2.6-m height, despite an opposing gradient in manual chamber-measured soil CO₂ effluxes.
Item Metadata
Title |
Summertime horizontal and vertical advective carbon dioxide fluxes measured in a closed-canopy Douglas-fir forest on a slope
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2010
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Description |
An observational study was conducted during an eight-week period in the summer of 2009 at a forested site in British Columbia (“DF49”) to determine the incidence and magnitude of advective carbon dioxide (CO₂) fluxes. The site is situated in a tall, closed-canopy (zh = 35 m, 1100 stems ha-¹, LAI of 7 m² m-²) Douglas-fir forest on a 5-10o slope. Katabatic flow occurs within the subcanopy during a significant portion of the day, especially during the evening and night.
Wind vector and CO₂ concentration measurements were made at heights of 1, 2.6, 8, 20 and 42 m on the main flux tower, while CO₂ concentration measurements were made 73.5 m upslope from the tower at heights of 1, 2.6, 8 and 20 m, creating a two-dimensional transect. Eight thermostated non-differential infrared gas analyzers (IRGAs) were paired using a solenoid valve switching system, creating four differential analyzers. The switching system, combined with a twice-daily polynomial IRGA calibration, enabled measurement of CO₂ concentration differences at the four subcanopy measurement heights to an accuracy of 0.5 μmol mol-¹ (horizontal) and 1 μmol mol-¹ (vertical). The system also recorded semi-continuous CO₂ traces at all sample points.
Horizontal advective fluxes, averaged over the main measurement period (August 2 - 25), reached 5 μmol m-² s-¹ at night and 10 μmol m-² s-¹ in the afternoon (a net source to the atmosphere) and -2 μmol m-² s-¹ during the morning (net sink). Vertical advective fluxes averaged around zero during the night, 5 μmol m-² s-¹ during the morning and -5 μmol m-² s-¹ during the afternoon. A cumulative sum of advective flux-corrected net ecosystem exchange (NEE) over the main measurement period (-57 g C m-²) was close to that of the friction velocity-corrected NEE (-60 g C m-²), both predicting less carbon uptake by the Douglas-fir forest than the storage-corrected NEE (-86 g C m-²). Additional CO₂ difference measurements made after the main sampling period along the 73.5-m transect demonstrated that horizontal CO₂ differences increased monotonically down slope (on average) at the 2.6-m height, despite an opposing gradient in manual chamber-measured soil CO₂ effluxes.
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Genre | |
Type | |
Language |
eng
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Date Available |
2010-08-31
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution 3.0 Unported
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DOI |
10.14288/1.0052565
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2010-11
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Rights
Attribution 3.0 Unported