A Theoretical Model for Aerobic Soil Incubation Considering Henry’s Law using High Resolution CO2 Measurements

claire.treat [ at ] awi.de


Large amounts of soil organic carbon (SOC) accumulated in cold climate regions are currently exposed to higher temperatures. Microbial SOC decomposition rates increase with temperature. Thus, understanding and predicting how CO2 fluxes change under rapid global warming is of great interest. An often applied method to evaluate decomposability of SOC are incubation experiments. In most cases the experimental set up of aerobic incubation experiments involves a sealed jar with an isolated soil sample where CO2 accumulation is measured. The headspace air of the incubation jar is sampled, mostly at a low temporal resolution (eg. two times within 24 hours) and fitted linearly. However, in many studies the fraction of CO2 soluble in water is not considered. In this study, an aerobic experimental incubation set-up with a high temporal resolution of 1 Hz is deployed. In these experiments, the CO2 accumulation in an incubation jar does not necessarily increase linearly over the course of an incubation measurement, but undergoes an equilibrium reaction only after which it increases approximately linearly. This equilibrium reaction is well described by the solubility of CO2 in the aqueous phase of the soil sample. A theoretical kinetic model is developed that includes the transport kinetics of CO2 over the gas-water phase boundary to describe the observed course of CO2 concentration during a single measurement. An easy applicable correction factor is derived from the theoretical model that includes the water soluble CO2 fraction. This model satisfactorily reproduces the most important processes of the present incubation experiment and thus leads to a better understanding of incubation experiments and can thereby improve predictions of microbial SOC decomposition rates.

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Schwarzer, J. (2022): A Theoretical Model for Aerobic Soil Incubation Considering Henry’s Law using High Resolution CO2 Measurements , Master thesis, Freie Universität Berlin.

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