Characterization of water dynamics in frozen soils by solid-state deuteron NMR

The presence of unfrozen water in soils at sub-freezing temperatures is important for biogeochemical processes as well as for the genesis of landscapes and survival of life. While several mechanisms can lead to the existence of liquid water at sub-freezing temperatures, this work focuses on the dynamical (entropic) contribution stemming from motions of water molecules at water-soil or water-ice interfaces. We demonstrate the utility of solid-state H-2 NMR methods for characterization of water dynamics in soils on various time scales. Using a sample from McMurdo Dry Valleys, Antarctica, we show the existence of dynamics spanning a milliseconds to picoseconds time scale range. Computational modeling allows for a quantitative description of the dynamics, which involves models such as an exchange between bound and free water, and changes in effective viscosity of water in the soil matrix. (C) 2012 Elsevier Inc. All rights reserved.