Fig. 8. (a) Measured and predicted daily average values for soil CO₂ concentration in the O-, A-, B-, and C-horizons over 19 mo at the reference site from May 1998 to November 1999 excluding the winter months from December 1998 to April 1999. Measured values for soil CO₂ concentration are an average of air samples taken from five permanently installed gas samplers in each horizon. The coefficient of variation of the samples ranged, on average, from 0.37 in the humus layer to 0.51 in the B-horizon. (b), (c), (d), and (e) measured and predicted daily average CO₂ concentrations plotted on xy–plot for O-, A-, B-, and C-horizons, respectively.