LAUSR

The presence of geogenic CO2 has been recently identified as a soil-forming factor in soil on mofette sites. Topsoil samples (with a maximum CO2 concentration of 52% at 10 cm depth) were studied along a transect on a mofette site in the NW Czech Republic to further understand the processes within soil and the soil properties induced by CO2 in the soil atmosphere. Geogenic CO2 negatively affected the cation exchange capacity, the ratio of exchangeable Ca and Mg, and the total contents of Al, Mg and Mn. No effect was detected on a chemical index of weathering and the mineralogical composition of the clay fractions, which might be explained by the acidic parent material and the progress of soil development. Diffuse reflectance infrared spectroscopy indicated that the composition of particulate soil organic matter was partially affected by CO2 concentrations: the higher the CO2 concentrations, the smaller the extent of oxidative transformation and the smaller the abundance of carboxyl groups. In the clay fractions, stabilisation of transformed soil organic matter (SOM) was promoted by exchangeable Al. This study quantifies, for the first time, the correlation between geogenic CO2 and several inorganic soil properties and the composition of SOM in physical fractions.