Study Of Variable Characteristics Of Stable Water Isotope Composition In Water Cycle And Its Influnce Mechanism In The Dongting Lake Basin

Currently, stable water isotopes have been successfully applied to the water cycle mechanism research, such as moisture sources, rainfall-runoff relationship, evaluation of water resources in the arid and semi-arid regions, the interaction of surface water and groundwater, groundwater origin and age, lake evaporation and water change cycle, the source of water pollutants, geothermal resources and climate change and human activities on the water cycle. Application of hydroxide stable isotope tracer technique to study the water cycle mechanism, there are two essential premises:Firstly, we need to understand variations of stable water isotope composition in different water bodies that involved in the water cycle. Secondly, we need to reveal the mechanisms that affect the isotopic variation. We choose the Dongting Lake Basin as the study area. During the period of2010to2012, we have collected event precipitation, surface runoff (river water), and underground runoff (well water, spring water) samples. After that, we measured all the samples’ hydrogen and oxygen isotope with liquid water isotope analyzer. In addition, water vapor HDO that retrieved from Aura satellite and simulated stable isotopes by GCMs have been used in this study. Variations of stable water isotopes in different water as well as the impact mechanism were studied. We found that:1) Atmospheric water vapor δD in the Asia monsoon region during summer monsoon is significantly higher than during the winter monsoon, and this to be more obvious over the land than the ocean.2) Precipitation stable isotopes, deuterium excess have obviously seasonal variation, showing high values in winter and spring, and low in summer and autumn.3) On daily scale, correlations of precipitation stable isotopes with precipitation amount, relative humidity, precipitable water and temperature were statisticed:precipitation isotope showed precipitation amount effect, humidity effect and anti-temperature effect in the entire year. In addition, we found that the correlation of precipitation stable isotopes with the above meteorological elements in monthly scale drop significantly than that in daily scale.4) On daily scale, the fluctuation of both water vapor and precipitation8D in winter and spring to be more significant than in summer and fall. We thought that it is mainly affected by significant temperature variation and complex moisture sources in winter and spring, when compared with summer and fall.5) The differnce of MWLs generated from snow samples and rainfall samples should not be entirely attributed to the secondary evaporation that under cloud, we believed that the ratio of fractionation effect for sublimation greater than condensation should be taken in mind.6)Considering water vapor flux in summer with precipitation stable isotope during the same period in2010,2011and2012, when the moisture, transported by southwest monsoon, which from the Indian Ocean, named as the far source moisture, is strong, precipitation isotopes shows low values in the Dongting Lake Basin, when the moisture, transported by southeast monsoon, from the Pacific Ocean, named as the near source moisture, precipitation isotopes shows high values in the Basin. Once again, we verified the credibility of the isotope circulation effect.7) Comparing monthly precipitation isotopes observed by GNIP with them simulated by ECHAM4, GissE and MUGCM, we found that the ability of simulating δ18O, deuterium excess and MWL are different, MUGCM is the best for δ18O, ECHAM4is the best for MWL and ECHAM4is best for deuterium excess.8) Considering the variation extent of isotopes in different water bodies, precipitation is the largest. River water isotopes in the Basin show low values in summer and fall, higth in winter and spring, which is consistent with the characteristics of the seasonal variation of precipitation isotopes, this confirmed that surface runoff is mainly recharged by precipitation in the Basin. Isotopes in well water that buried deep are with very small variations in time and significantly enriched, which shows that they have experienced a significant evaporation history and have a stable water supply.