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

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, 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.