Estimating Surface CO2 Flux Based on Soil Concentration Profile

Abstract

Aims: To estimate the surface CO2 flux derived from CO2 concentration profiles and to validate the results by previous data of surface CO2 flux obtained from the measurements using close-chamber method. Study Design: The measurement of soil CO2 concentration profile, soil properties, and soil temperature was carried out to estimate surface CO2 flux using the derived model of mass balance equation. The results were subsequently compared with measurements of surface CO2 flux using close-chamber method. Place and Duration of Study: INAS field located in Ito Campus of Kyushu University (Japan) from November 2015 to March 2016. Methodology: CO2 gas was sampled in four different depths to analyze its concentration within the soil layer. Soil temperature was monitored throughout the measurement and soil properties such as density, porosity and moisture content were measured as well to estimate the diffusion rate. Derived from mass balance equation, the surface CO2 flux was estimated. It was validated using the previous measurement data of surface CO2 flux using close-chamber method that had been conducted formerly at the same location. Results: A total of seven measurements of soil CO2 concentration profile showed that the CO2 concentration increased with soil depth and it was fitted with logarithmic trend (R2 = 0.981 in average). A range of CO2 concentration values was measured at each depth, i.e., 1300 to 8700 ppm at 0.1 m depth; 2500 to 10800 ppm at 0.2 m depth; 4200 to 13200 ppm at 0.3 m depth; and 5800 to 16500 ppm at 1.0 m depth. High CO2 concentration in 0.1 m soil depth indicated high surface CO2 flux. Conclusions: Soil CO2 concentration in INAS field increased following a logarithmic trend. Based upon this trend, an equation to estimate the surface CO2 flux was proposed using derived model from mass balance equation and gas diffusion model. The estimated surface CO2 flux was compared and showed a good agreement with measured one. The equation presented herein is potentially suitable to estimate the surface CO2 flux.