[Effects of water vapor source and local environmental factors on the hydrogen and oxygen isotopic compositions of precipitation in Huitong, Hunan Province, China].

Deuterium (D) and oxygen-18 (18O) are common environmental tracers in water. Understanding the isotopic compositions of precipitation is necessary for further studies on local and global water cycling processes. To reveal the mechanism of isotopic compositions of precipitation in subtropical monsoon region in response to environmental changes, we collected 49 precipitation samples and recorded related environmental factors from May 2017 to August 2019 in Huitong field station of Chinese Academy of Sciences in Hunan Province. We analyzed the temporal variations in D and 18O values in precipitation and analyzed the influence of water vapor source and local environmental factor on stable isotopic compositions of precipitation. The local meteoric water line was established as δD=(7.45±0.17)δ18O+(10.10±1.25) (R2=0.93, P<0.01), the slope of which was slightly lower than China's meteoric water line and the global meteoric line. The D and 18O values of precipitation samples were closely coupled with local meteorological conditions and dominant moisture sources. The 18O and D contents were depleted during summer monsoon season but enriched during winter monsoon season. During the summer monsoon and post-monsoon seasons, precipitation in this area came mainly from the Bay of Bengal, the South China Sea, and the West Pacific at three different types of air pressure, which lead to the similarity of the D-excess value of the precipitation to global average. The lower intercept of meteoric water line and the higher D-excess value for precipitation during the winter monsoon season resulted from moisture from remote westerly air masses, degenerated tropical marine air masses from the Bay of Bengal, and inland moisture in the pre-monsoon period, which were also affected by local environmental factors.

[Characteristics of hydrogen and oxygen isotopes in precipitation and moisture sources in Gaoyou, Jiangsu Province, China]. / æ±Ÿè‹é«˜é‚®å¤§æ°”é™æ°´æ°¢æ°§åŒä½ç´ ç‰¹å¾åŠæ°´æ±½æ¥æº.

It is necessary to examine the characteristics of hydrological cycle in Gaoyou area of Jiang-su Province in response to climate change and flood disasters. In this study, 121 atmospheric rain samples were collected and environmental factors were recorded from July 2015 to October 2017. We analyzed the hydrogen and oxygen stable isotopic composition of rain and identify moisture sources in this area. Results showed that the hydrogen and oxygen isotopic composition of rain had an seasonal variation, which was positive in the winter but negative in the summer. D-excess value was higher in winter than that in summer. On the annual scale, significantly negative relationships between δD (δ18O) and temperature and between δD (δ18O) and precipitation indicated the "anti-temperature effect" and "precipitation amount effect", respectively. On the seasonal scale, there was no obvious "temperature effect" but "precipitation amount effect" in autumn and winter. Results from the HYSPLIT model showed that the precipitation in this area came mainly from ocean evaporation that was influenced by the Chinese South Sea, Indian Ocean and Pacific Ocean. Precipi-tation in other seasons mainly came from the water vapor mixture from the Eurasian continent, Atlantic Ocean, Arctic Ocean, as well as local evaporation. The seasonal pattern of δD and δ18O values in precipitation was mainly influenced by monsoon activity and El Niño-Southern Oscillation (ENSO). In addition, the precipitation isotopes clearly indicated the shift in climates from El Niño to La Niña.