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Temperature Controls on Diurnal Carbon Dioxide Flux

Implications for Estimating Soil Carbon Loss

USDA-ARS, National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011

View larger version (50K): [in a new window]   Fig. 1. Hourly measurements of soil water content, rainfall, air temperature, surface soil temperature, 0.05-m soil temperature, and soil CO2 flux from Chamber 1 at the Clarion soil site.

View larger version (48K): [in a new window]   Fig. 2. Average diurnal variations in temperature and CO2 flux (right axis) for each of the four chambers. Error bars indicate standard errors of the means (n = 95).

View larger version (39K): [in a new window]   Fig. 3. Average diurnal patterns of temperature and CO2 flux expressed as percent deviation from the 24-h daily average. Error bars indicate standard deviations of duplicate chambers at each site. In cases where error bars are not apparent, they are obscured by the symbols.

View larger version (29K): [in a new window]   Fig. 4. Relationships between percent deviation of CO2 flux (from the daily average CO2 flux) and percent deviation of air temperature (from the daily average air temperature) in each chamber. Symbols: Closed circles, data collected during the hours of the day when temperature was increasing; Open circles, data collected during the hours of the day when temperature was decreasing. Error bars indicate standard deviations of duplicate chambers at each site.

View larger version (29K): [in a new window]   Fig. 5. Relationships between percent deviation of CO2 flux (from the daily average CO2 flux) and percent deviation of surface soil temperature (from the daily average surface soil temperature) in each chamber. Symbols: Closed circles, data collected during the hours of the day when temperature was increasing; Open circles, data collected during the hours of the day when temperature was decreasing. Error bars indicate standard deviations of duplicate chambers at each site.

View larger version (29K): [in a new window]   Fig. 6. Relationships between percent deviation of CO2 flux (from the daily average CO2 flux) and percent deviation of 0.05-m soil temperature (from the daily average 0.05-m soil temperature) in each chamber. Symbols: Closed circles, data collected during the hours of the day when temperature was increasing; Open circles, data collected during the hours of the day when temperature was decreasing. Error bars indicate standard deviations of duplicate chambers at each site.

View larger version (56K): [in a new window]   Fig. 7. Time series analysis of temperature and CO2 flux. (A) Cross correlation between air temperature and CO2 flux; (B) cross correlation between surface soil temperature and CO2 flux; (C) cross correlation between 5-cm soil temperature and CO2 flux. Symbols: Chamber 1 (open circles), Chamber 2 (open triangles), Chamber 3 (closed circles), Chamber 4 (closed triangles).

View larger version (44K): [in a new window]   Fig. 8. Estimated cumulative CO2–C loss predicted by temperature/CO2 flux relationships as function of time-of-day when measurements are taken. In each panel, the different curves are results obtained by different temperature correction algorithms. All closed symbols are corrections based on the 0.05-m soil temperature: closed circles, variable Q10 relationship; closed diamonds, Q10 = 2.00; closed squares, Q10 = 1.50; closed triangles, Q10 = 1.25. All open symbols are corrections based on air temperature: open triangles, Q10 = 1.25, open squares, Q10 = 1.50; open diamonds, Q10 = 2.00.