Publication

The kinetic fractionation of open-water evaporation against the stable water isotope H-2 O-18 is an important mechanism underlying many hydrologic studies that use O-18 as an isotopic tracer. A recent in-situ measurement of the isotopic water vapor flux over a lake indicates that the kinetic effect is much weaker (kinetic factor 6.2%) than assumed previously (kinetic factor 14.2%) by lake isotopic budget studies. This study investigates the implications of the weak kinetic effect for studies of deuterium excess-humidity relationships, regional moisture recycling, and global evapotranspiration partitioning. The results indicate that the low kinetic factor is consistent with the deuterium excess-humidity relationships observed over open oceans. The moisture recycling rate in the Great Lakes region derived from the isotopic tracer method with the low kinetic factor is a much better agreement with those from atmospheric modeling studies than if the default kinetic factor of 14.2%o is used. The ratio of transpiration to evapotranspiration at global scale decreases from 84 +/- 9% (with the default kinetic factor) to 76 +/- 19% (with the low kinetic factor), the latter of which is in slightly better agreement with other non-isotopic partitioning results.