(4b)
The water vapor equilibrium fractionation coefficient ( and ) of lake water during evaporation can be calculated on the basis of the empirical formula of water vapor interface temperature (in Kelvin, K ) (Horita and Wesolowski, 1994). andare the equilibrium enrichment coefficients ofδ 18O and δ D, respectively, reflecting the isotopic enrichment effect of water vapor entering the saturated water vapor layer at the water-gas interface (Craig and Gordon, 1965).andare the kinetic fractionation factor ofδ 18O and δ D, respectively, calculated from empirical formulas based on atmospheric boundary layer conditions and humidity conditions. The above calculation can be seen in equation 5.