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ABSTRACT

In the past two types of laboratory experiments have been employed to determine the dependence of H2 uptake by soils on temperature and moisture: Head space and flow experiments. The former actually measure the rate constant of the H2 removal from the head space, kH, the latter the uptake rate of H2, UH2, both caused by a given volume of soil. From an analytical solution of the diffusion equation in the soil we derive a mathematical relation between kH and ks, the desired uptake rate constant of H2 in soil. Another equation relates UH2 with ks. Both types of experiments actually determine the product of ks with Θa, the air-filled pore volume fraction. ks·Θa for eolian sand and loess loam show zero uptake at very low and high moisture contents and a well defined maximum in between. Unlike soil moisture which also acts on the soil properties, the soil temperature, T, acts essentially on the enzyme activity only. Thus ks(T) is directly proportional to kH(T) or UH2(T) and the data of all experiments can be superimposed by scaling. The resulting average ks(T) shows a broad maximum around 30°C with zero uptake below −20°C and above 80°C.