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Quantifying unfrozen water in frozen soil by high-field H-2 NMR

Journal article
Authors T. Sparrman
M. Oquist
Leif Klemedtsson
J. Schleucher
M. Nilsson
Published in Environmental Science & Technology
Volume 38
Issue 20
Pages 5420-5425
ISSN 0013-936X
Publication year 2004
Published at Botanical Institute
Pages 5420-5425
Language en
Links <Go to ISI>://000224519500029
Keywords MAGNETIC-RESONANCE, HEAVY-WATER, ICE, EMISSIONS, MINERALIZATION, EQUILIBRIUM, HYDROGEN, LIQUID, CURVE
Subject categories Biological Sciences

Abstract

To understand wintertime controls of biogeochemical processes in high latitude soils it is essential to distinguish between direct temperature effects and the effects of changes in water availability mediated by freezing. Efforts to separate these controls are hampered by a lack of adequate methods to determine the proportion of unfrozen water. In this study we present a high-field (H2O)-H-2 NMR method for quantifying unfrozen water content in frozen soil. The experimental material consisted of the humic layer of a boreal spruce forest soil mixed with varying proportions of quartz sand and humidified with deuterium-enriched water. The relative standard deviation of unfrozen water content (measured as NMR signal integral) was less than 2% for repeated measurements on a given sample and 3.5% among all samples, based on a total of 16 measurements. As compared to H-1 NMR, this H-2 NMR method was found to be superior for several reasons: it is less sensitive to field inhomogeneity and paramagnetic impurities, it gives a bigger line shape difference between the ice and liquid signal, it shows a sharper response to water fusion, and it excludes the possibility of hydrogen in the organic material interfering with the measurement.

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