A review article led by Keir Soderberg on methods for soil water vapor isotopic characterization and analysis has just been accepted for publication in Vadose Zone Journal
Keir’s review of soil water isotopic methods has been accepted for publication in Vadose Zone Journal. The article, “Stable isotopes of water vapor in the vadose zone: A review of measurement and modeling techniques” examines use of soil water vapor isotopes as a tracer of hydrologic processes occurring in the vadose zone. The measurement of soil water vapor isotopic composition is challenging due to difficulties inherent in sampling vadose zone airspace in situ. Historically, the soil water vapor isotope signature (δ18O, δ2H) has therefore been modeled as opposed to directly measured, and typically is treated of as being in equilibrium with liquid soil water isotope values. We present a review of the measurement and modeling of soil water vapor isotopes, with implications for studies of the soil-plant-atmosphere continuum at various scales. A contribution of this work is to introduce the use and effects of soil water potential on kinetic fractionation during soil evaporation within the Craig-Gordon modeling framework. Additionally, we assert that the recent development of laser-based isotope analytical systems may allow for the regular in situ measurement of the vadose zone isotopic composition of water in the vapor phase. Some sampling difficulties remain, but indications are that with low flow rates, authentic water vapor samples can be obtained without inducing evaporation in the liquid soil water.