Isotopic kinetic fractionation of evaporation from small water bodies

•Kinetic fractionation is inversely related to water-air temperature difference.•Slope of local evaporation line is sensitive to kinetic factor for oxygen isotopes.•Kinetic factor is not statistically different between small and large water bodies. The primary objective of this study is to investigate the kinetic fractionation of evaporation of small water bodies. The experiments were performed in outdoor conditions using two evaporation pans and a small fishpond. The work is motivated in part by the high sensitivity of lake evaporation derived from isotopic mass balance to the strength of the kinetic effect. Results show that the kinetic factor εk for the oxygen isotopes is inversely related to the water-to-air temperature gradient, indicating the important role of convective turbulence in kinetic fractionation of evaporation. Although the measured εk displays a weak correlation with the slope of the local evaporation line (LEL), by replacing the default εk value of 14.2 ‰ (for 18O) commonly adopted for lake studies, it greatly improves the performance of a theoretical LEL model. The εk data in this study and reported by other authors do not support the hypothesis that εk decreases with increasing lake size. The overall mean εk is 9.7 ‰ for 18O and 8.5 ‰ for 2H, based on nine outdoor experimental results.