PROGRESS IN GEOGRAPHY ›› 2015, Vol. 34 ›› Issue (8): 1031-1038.doi: 10.18306/dlkxjz.2015.08.010

• Orginal Article • Previous Articles     Next Articles

Influence of below-cloud secondary evaporation on stable isotope composition in precipitation in the Haihe River Basin, China

ZHAO Shikun1(), PANG Shuoguang1, WEN Rong2, LIU Zhongfang3,*()   

  1. 1. Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China
    2. Key Laboratory of Tibetan Environmental Changes and Land Surface Processes, Institute of Tibetan Plateau Research, CAS, Beijing 100085, China
    3. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
  • Online:2015-08-25 Published:2015-08-25
  • Contact: LIU Zhongfang E-mail:zhaosk0815@gmail.com;liuzf406@gmail.com

Abstract:

Measurement of stable water isotopes (δ2H and δ18O) at the watershed scale can provide a diagnostic indication for hydrological processes and water cycling of the watershed. Kinetic isotope fractionation associated with below-cloud secondary evaporation can significantly affect the observed precipitation isotopic composition and local meteoric water line. Stable isotope composition of δ2H and δ18O in precipitation was investigated in the Haihe River Basin, northern China based on observations at seven stations from July 2012 to January 2013. Linear regression between δ2H and δ18O values of rain samples yielded a correlation equation of δ2H=7.19δ18O-0.74, which is significantly different from that based on snow samples (δ2H=8.42δ18O+15.88). Due to the influence of below-cloud secondary evaporation on rain isotopes, the slope and intercept of correlation between δ2H and δ18O for small amount rainfall samples (<5 mm) progressively decreased with decreasing precipitation, varying from 6.73 to 7.61 and 5.28‰ to -11.04‰, respectively. Correlation of isotope values with local temperature, relative humidity, and precipitation amount provides evidence that small amount rainfall samples underwent secondary evaporation accompanied by mass dependent isotope fractionation during their descent from the cloud base to the ground. Compared to sites in the plain areas, rain stable isotopes at sites in the mountainous areas tended to be influenced by below-cloud secondary evaporation due to the dry atmosphere caused by the rain shadow effect. Since about half of the precipitation events in the observation period were rain samples with amount less than 5 mm, below-cloud secondary evaporation had an important influence on isotope composition of precipitation in the Haihe River Basin. Our study suggests that analysis of isotope composition of individual rainfall events can provide some valuable insight into below-cloud secondary evaporation effect, which is masked to a large extent by analysis of monthly precipitation isotope data.

Key words: precipitation, δ2H and δ18O, temperature, relative humidity, below-cloud secondary evaporation, Haihe River Basin