TROPICAL GEOGRAPHY ›› 2018, Vol. 38 ›› Issue (6): 857-865.doi: 10.13284/j.cnki.rddl.003084

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Hydrogen and Oxygen Stable Isotope Study on the Difference of Evaporation between Salt and Pure Water

LI Tong, QIU Guoyu   

  1. ( a. School of Environment and Energy, Peking University; b. Shenzhen Engineering Laboratory for Water Desalination with Renewable Energy, Shenzhen 518055, China)
  • Online:2018-11-30 Published:2018-11-30

Abstract: Water evaporation is an essential part in the water cycle. However, a large amount of research focuses on freshwater or low salinity-saltwater bodies. It is inaccurate to apply the evaporation characteristics or estimation methods of freshwater to all the water bodies. Studying the difference of evaporation between salt water and pure water is crucial to the study of the mechanism of evaporation process and the promotion of innovation in evaporation models. In this study, evaporation pan was used to observe the process of salt and pure water evaporation, and steady-state hydrogen isotopes and oxygen isotopes were used to compare the kinetic fractionation in salt and pure water evaporation. The results show: evaporation of salt water reduced compared with pure water, but the daily variation pattern was consistent with the temperature daily change and reached the maximum evaporate rate around noon. Heavy isotopes were enriched in the liquid phase as water evaporated and salinity significantly suppressed H/D fractionation. The evaporation line of pure water and salt water both had a good linear relationship. The salt caused stronger non-equilibrium fractionation. The thermal infrared imaging observed that the temperature of the brine surface was always higher than that of pure water by 0.1 ~ 2.2°C with an average temperature difference of 1°C, this was because evaporation of salt water was smaller than that of pure water and less heat was released by latent heat. The isotopes of evaporative water vapor calculated through Craig & Gordon model indicated that the heavy isotopes of evaporation water vapor were continuously enriched, but not that strong compared to the remaining water. There is no significant difference between the equations for the hydrogen and oxygen isotopes of water vapor in pure and salt water, that is contrary to the above conclusions, indicating that the application of this equation at small scale deserves further study.

Key words: stable hydrogen isotopes and oxygen isotopes, salt water, evaporation, kinetic fractionation, Craig & Gordon model