Ecology, Environment and Conservation Paper

WATER VAPOR CONDUCTANCE OF DRY SOIL – ANALYZING TRANSPORT PROCESSES BY ANALOGY WITH OHM’S LAW

Mohammad Nazari-Sharabian, Moses Karakouzian and Parastoo Pashmchi

Abstract

Soil water vapor conductance is an important part of the total water flux in the unsaturated zone, which has several significant agricultural and engineering implications. In environmental biophysics, transport processes are similar to an electrical circuit. Ohm’s Law states that the electric current in a conductor is directly proportional to the applied voltage and inversely proportional to the electrical resistance of the conductor. Therefore, transport processes can be analyzed by analogy with Ohm’s Law, in an integrated or macroscopic form. In this regard, water vapor concentrations are specified at the surface and in the surroundings, and the transport resistance, or conductance, is defined as the concentration difference divided by the flux density. In this study, considering that the conductance to water loss is a series of combinations of boundary layers and surface conductance, an experiment was set up in an isolated lab with constant air temperature and air pressure, in order to measure the diffusive conductance for water vapor in three dry soil types: sand, sandy loam, and silt loam. A water proof breathable membrane with high water vapor permeability was installed between the soil samples and the water’s surface, to allow water vapor move through soil samples and escape into the atmosphere. The results showed that sand, sandy loam, and loam had water vapor conductance of 0.026 mol/m2 .s’ 0.027 mol/m2 .s’ and 0.031 mol/m2 .s’ respectively.