Production and stable isotopic composition of CO2 in a soil near Bern, Switzerland

During a period of one year, we measured the concentration and the stable isotopic composition of CO2 in weekly soil air samples from two depths in a grass-covered soil. The CO2 production rate, as estimated from the diffusion equation and the observed concentration gradient, was 15 mmol/m-2/h-1, as an annual mean. During the cold season, the production rate varied with soil temperature, but no correlation existed with temperature above about 10 °C. Concentrations and fluxes of N2O in the soil were also determined. Observed δ13C values were in the expected range, and δ18O of Soil CO2 was found to be in isotopic equilibrium with the soil water. δ18O of the CO2 released to the atmosphere is expected to be lower by roughly 8‰ due to diffusive isotope fractionation; the precise value depends on the competition between CO2 production, equilibrium with soil water and diffusion