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Continuous Soil Carbon Dioxide and Oxygen Measurements and Estimation of Gradient-Based Gaseous Flux

^a Department of Plants, Soils, and Biometeorology, Utah State University, Logan, UT 84322
^b Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269

View larger version (71K): [in a new window]   Fig. 1. Detailed view of sensor arrangement showing the combination of CO2–O2 sensors and the thermocouple inserted into the soil profile.

View larger version (106K): [in a new window]   Fig. 2. Laboratory soil column showing experimental setup for steady-state CO2 flux determinations. Measured surface soil chamber fluxes were compared with calculated fluxes obtained from the gradient method (Table 1).

View larger version (73K): [in a new window]   Fig. 3. Cut-away of the experimental apparatus showing the sealed 25-cm-diameter PVC pipe used to house the sensors and datalogger. The soil chamber collar is placed directly above the gradient-based sensors, and a soil moisture sensor installed obliquely averages water content over the 0- to 15-cm depth.

View larger version (17K): [in a new window]   Fig. 4. Soil CO2 concentration profile measured in the laboratory under steady-state conditions in dry Kidman soil.

View larger version (25K): [in a new window]   Fig. 5. Greenhouse measurements of (a, b) CO2 and (c, d) O2 gas concentrations and (e, f) soil temperatures measured at two or three depths in the soil profile, during the 2001 and 2002 greenhouse experiments. In 2001, between Days 4 and 7, no water was applied.

View larger version (34K): [in a new window]   Fig. 6. Measured (0–15 cm, dashed line) and Hydrus2D simulated (i.e., for 0–2, 6–8, and 18–20 cm depth) (a, b) soil water content and (c, d) estimated soil gas diffusivity for the 2001 and 2002 greenhouse experiments. (e, f) Surface CO2 flux determined using the gradient-based method (lines) and periodic soil chamber measurements (circles) are shown for both years. (g, h) Calculated near-surface O2 flux.

View larger version (19K): [in a new window]   Fig. 7. A 1:1 comparison of the soil surface CO2 flux measurement using the closed-chamber method vs. the proposed gradient-based method.