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Clay-Water Interaction, the Behavior of ³H and ²H in Adsorbed Water, and the Isotope Effect¹

ABSTRACT

Reference clay minerals and a field kaolinitic soil were allowed to equilibrate with water tagged with tritium and deuterium. Ratios of tritium and deuterium concentrations of tenaciously adsorbed water to respective concentrations of bulk pore water were approximately equal to one for all soils and clay minerals tested. This suggests that no significant isotopic fractionation occurs in adsorbed water. Thermodynamic theory, relating isotopic fractionation to the energetics of adsorbed water, also predicts that isotopic fractionation is not a function of the energy status of adsorbed water. Data from another experiment, where oven dry samples equilibrated with water vapor in a controlled atmosphere, showed that tenaciously adsorbed water on kaolinitic mineral surfaces is not as labile to exchange with the vapor phase as was adsorbed water on montmorillonite and illite surfaces.

¹ Contribution from the Department of Plant and Soil Sciences, Massachusetts Agr. Exp. Sta., University of Massachusetts, Amherst, Mass. 01002.

² Associate Professor of Soil Physics, Univ. of Massachusetts.

Received for publication July 28, 1971. Accepted for publication January 27, 1972.