Isotopic kinetic fractionation of evaporation from small 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 epsilon(k) 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 epsilon(k) displays a weak correlation with the slope of the local evaporation line (LEL), by replacing the default epsilon(k) value of 14.2 Too (for 180) commonly adopted for lake studies, it greatly improves the performance of a theoretical LEL model. The epsilon(k) data in this study and reported by other authors do not support the hypothesis that epsilon(k) decreases with increasing lake size. The overall mean epsilon(k) is 9.7 parts per thousand for 180 and 8.5 parts per thousand for 2H, based on nine outdoor experimental results.