Temporal variations in air permeability and soil CO2 flux in volcanic ash soils (island of Vulcano, Italy)

Air permeability is a major physical factor affecting the advective transport of a gas through
the soil, and variations in this parameter can strongly influence the emission of endogenous gases from the
soil to the atmosphere. In this paper, we illustrated a new and simple method for measuring in situ air permeability based on the measurement of air pressure inside a special probe inserted into the soil. The
method was designed and developed primarily to study the relationship between air permeability and the
soil CO2 flux in an active volcanic area. The method was used for continuous monitoring of the air permeability
at two different locations on the island of Vulcano. At the same time, the values of the atmospheric
pressure, temperature, rain, and volumetric water content of the soil were also acquired to investigate their
effect on soil air permeability and soil CO2 flux. The results showed that during the monitoring period, soil
air permeability exhibited minor variations at each site, while larger variations in the soil CO2 flux were
recorded. The effect of soil air permeability on soil CO2 flux was negligible at both sites, whereas a strong
dependence of soil CO2 flux on volumetric water content and on atmospheric pressure was found. Furthermore, the variation in air permeability recorded at both sites was much lower than that predicted using
some well-known predictive models, showing that the relationship among different soil transport parameters
is more complex in real field conditions than would be expected by semiempirical models.