Temperature gradient effects on stable isotope and chloride profiles in dry soils
1989
Barnes, C.J. | Allison, G.B. | Hughes, M.W.
Experimental profiles of oxygen-18 and deuterium observed after evaporation from soil are compared with theoretical ones. The theoretical profiles are based on a simplified version of previously presented theory for nonisothermal movement of the stable isotopes of water. Under the experimental conditions described here, the analytical model yields an excellent fit to the data, and allows predictions of the effects of a temperature gradient to be made. The theory is used to show that errors of 100% or more in estimates of evaporation rate may result if the temperature distribution in the soil is ignored. A second set of experimental profiles obtained from sealed, nonisothermal tubes is also discussed. Results from these experiments give insights into the relative importance of liquid and vapour transport, and differences that might be expected between isotopes and nonvolatile solutes (e.g. Cl) used as tracers for determining water movement. It is found that although the water content and stable isotope profiles rapidly attained steady state, chloride profiles were far from equilibrium after nearly a year. This implies that field profiles involving nonvolatile solutes evolve at vastly different rates to those involving the naturally occurring isotopes of water.
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