Analysis On Experiments And Simulation Of Evaporation Water Stable Isotope Fractionation In Changsha

Evaporation is a significant progress in the water cycle on earth and it impacts the exchange of stable isotopes between evaporation water and vapor in atmosphere. Meanwhile the variation of stable isotopes in evaporation water is closely related to the meteorological factors and evaporation extent. Winter is cold and summer is hot in Changsha. The variation of temperature in a whole year could be nearly 40 ℃. Affected by monsoon, the disparity of humidity also could be spectacular. Conduct water evaporation experiments in this context is helpful to understand the fractionation law of water stable isotope in different weather and the contribution of stable isotopes from water to vapor. Besides, the experiments are the best way to verify the stable isotope fractionation theory.Based on six groups’observation of water evaporation experiments, Paper analyzed the characteristics of stable isotope variation in evaporation water and the relationship of water stable isotope variation and air humidity. Using equilibrium fractionation model and kinetic fractionation model simulate the variation of evaporation water stable isotope and compare it with measured value. During October 2014, the variation of evaporation water stable isotopes and the variation of vapor stable isotopes were observed simultaneously. The main results are as follows:1) The ratio of stable isotope in evaporation residual water is increased along with the decrease of evaporation residual water mass. But during precipitation the ratio of stable isotope in evaporation residual water will decline. The ratio of stable isotope in evaporation residual water and air humidity demonstrated a negative correlation.2) The simulation results of equilibrium model well fitted with measured value. However, it deviated from the measured value in the second half of evaporation. The simulation results of equilibrium model cannot reflect the decline of water stable isotope ratio. But simulation results of kinetic model not only well fitted with the measured value but also reflected the water stable isotope fluctuation in the rainy time.3) The slope of measured water evaporation line in summer and autumn is higher than the slope of kinetic simulation in winter and spring and lower in summer and autumn. It indicated that evaporation in summer and autumn is more intense than the evaporation in winter and spring which limited by temperature.4) The d-excess in six groups of experiments water decline along with the decrease of J. But it will increase during the precipitation time. The decline speed of d-excess in summer is highest and autumn following behind. The d-excess in winter and spring has a lower decline speed.5) S2H in vapor and evaporation residual water decline simultaneously during precipitation time. It proves that during precipitation time, the stable isotope in residual water will affected by meteoric vapor.