Accurate measurement of the soil water characteristic at low water contents is challenging but presents numerous opportunities for vadose zone research. We present a new, rapid, and automated approach to obtain accurate water vapor sorption isotherms for soils. Selected soil properties derived from measured isotherms, and ideas for further research in various vadose zone areas including water repellency, contaminant volatilization, and hysteresis are proposed. Eminent environmental challenges such as remediation of contaminated sites, the establishment and maintenance of nuclear waste repositories, or the design of surface landfill covers all require accurate quantification of the soil water characteristic (SWC) at low water contents. Furthermore, several essential but difficult-to-measure soil properties, including clay content and specific surface area, are intimately related to water vapor sorption. Until recently, it was a major challenge to measure detailed water vapor sorption isotherms accurately within a reasonable time frame. This priority communication illustrates potential applications of a new, fully automated, and rapid Vapor Sorption Analyzer (VSA) to pertinent issues in vadose zone research. Detailed vapor sorption isotherms for 25 variably textured soils were measured with the VSA within 1 to 3 d. Links between generated isotherms and pesticide volatilization, toxic organic vapor sorption kinetics, and soil water repellency are illustrated. Several methods to quantify hysteresis effects and to derive soil clay content and specific surface area from VSA-measured isotherms are presented. Besides above mentioned applications, potential relationships to percolation threshold for solute diffusion in unsaturated soil and to soil cation exchange capacity are discussed to stimulate new and much-needed vadose zone research.
Vadose Zone Journal, 2014, Vol 13, Issue 1, p. 1-7
Accurate quantifications; Cation exchange capacities; Environmental challenges; Nuclear waste repositories; Percolation thresholds; Soil water characteristics; Soil water repellency; Water vapor sorption