RESEARCH

Modeling and measurement of soil CO₂ fluxes

Poster - A.R. Mitchell, D. Or, M. Caldwell and S.B. Jones.  1999.  Gradient method for in-situ measurement of CO2 Flux.  Agronomy Abstracts, ASA, Madison, WI.

Abstract - As part of the Great Basin Ecosystem project, soil CO₂ flux measurements are compared for different plant communities. Present methods of measuring soil CO₂ flux in situ have several limitations, including:

1) a chamber placed on soil surface that perturbs atmospheric boundary conditions,

2) relatively long measurement time limiting number of measurements obtainable, and

3) temporal variations in CO2 flux not captured by infrequent measurements.

The recent availability of inexpensive infrared sensors has prompted interest in developing an alternate gradient method for continuous measurement of soil CO₂ flux. The method was tested in a silt loam soil column with a fixed CO₂ concentration at the lower boundary and ambient atmospheric at the upper boundary. Sensors placed at two depths measured CO₂ gradients. Using previously measured soil gaseous diffusivity and gradient measurements, soil CO₂ flux was estimated for steady-state conditions. Results were compared with soil efflux measurements using standard chamber placed briefly over the soil column.

Poster - Jones, S.B., B.W. Bingham and D. Or. 2000. Measurement of Soil CO2 Gradient for In-situ Estimation of Carbon Fluxes. Submitted for ASA Fall Meeting.

Abstract - An in-situ gradient method for determining soil CO₂ flux employs a bank of infrared gas sensors measuring CO₂ concentration within the soil profile. Flux estimates from the gradient method were similar to CO₂ flux measurements using a standard closed-chamber surface method. The gradient method overcomes some of the disadvantages of the chamber method by avoiding surface pressurization, CO₂ buildup and provides continuous in-situ measurements of CO₂ concentration in addition to the flux estimation. Soil characterization and respiration estimates are enhanced by complimentary subsurface profile measurements of water content, oxygen concentration and soil temperature. The gradient method was tested in sand and soil-filled columns and under field conditions. Soil gas diffusion coefficients for calculating CO₂ flux for each soil were determined using a gas diffusion chamber in the lab. The gradient method should be advantageous for long-term field studies of carbon fluxes.