An isotopic study of the microbial activity in a vandose zone: A field and mesocosm laboratory study

Isotope studies on carbon, nitrogen and sulphur can contribute to an increased understanding of biogeochemical and chemical processes occurring above and below the water table controlled by biotic, abiotic and hydraulic factors. Microbial induced respiration of organic material supported by oxidants such a dissolved oxygen, nitrate and sulphate increases pCO2 in relation to the atmosphere. As a result of microbial respiration, a diffusion controlled CO2 flux occurs in the vadose zone. Respiration and the hydraulic conditions in the vadose zone control the CO2 flux to the atmosphere and to the underlying water table. Further, at the interface to the water table (anoxic transition range), redox conditions can influence the oxidation state of the compounds. For that reason, carbon isotopes of soil CO2 gas and of the organic/inorganic carbon in soils were investigated in a mesocosm model and at an associated field site (natural scale) near Saskatoon, Canada. The models are equipped with gas and water sampling devices and with devices for controlling physicochemical parameters. Microbial processes have been investigated there for more than 900 d