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 about 10-degrees-C. Concentrations and fluxes of N2O in the soil were also determined. Observed delta-C-13 values were in the expected range, and delta-O-18 of soil CO2 was found to be in isotopic equilibrium with the soil water. Delta-O-18 of the CO2 released to the atmoshpere is expected to be lower by roughly 8 parts-per-thousand due to diffusive isotope fractionation; the precise value depends on the competition between CO2 production, equilibrium with soil water and diffusion.