The dependence of soil H2 uptake on temperature and moisture: a reanalysis of laboratory data

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, U _H2, 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 k _H and k _s, the desired uptake rate constant of H₂ in soil. Another equation relates U _H2 with k _s. Both types of experiments actually determine the product of k _s with Θ_a, the air-filled pore volume fraction. k _s.Θ_a 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 k _s(T) is directly proportional to k _H(T) or U _H2(T) and the data of all experiments can be superimposed by scaling. The resulting average k _s(T) shows a broad maximum around 30◦C with zero uptake below −20◦C and above 80◦C.