Study On Characteristics Of Stable Isotopes Of Different Bodies In The Mid-and-lower Reaches Of XiangJiang River

China locates the southeast of Eurasia continent, faces the Pacific Ocean. The terrain gradually drops by three ladders-like forms from west to east. It has a significant monsoon climate, featuring by winter monsoon which has the characteristic of dry and cold climate and by summer monsoon coming from the India Ocean and the Pacific Ocean which has the characteristic of wet and warm climate; This also makes the mid-and-lower-reaches of Xiangjiang River possessing a significant monsoon climate, which affects both by the East Asia monsoon and by South Asia monsoon. Studying the vapor sources and the characteristics of precipitation in the mid-and-lower-reaches of Xiangjiang River is in favor of deeply studying the characteristics of water cycle in Dongtinghu Basin and has an important significance of constructing and restoring the ecological environment. It has a superiority of investigating the precipitation and vapor sources in large-scale basin in means of environmental isotope. Different water bodies (precipitation, river water, spring water and well water) are collected from the mid-and-lower-reaches of Xiangjiang River during January to December2010, analyzed the characteristics of hydrogen and oxygen from four different water bodies (precipitation, river water, spring water and well water) and the relationship between the stable isotopes and various factors, hydraulic connections among different water bodies. Combined both backwards trajectory and stable isotopes in precipitation, water vapor sources are studied.(1) The variables characteristic of stable isotopes in precipitation in China are analyzed in China, the distribution of δ18O in precipitation is not absolutely parallel with latitude, but is a saddle-shaped distribution. The value of δ18O is larger in the southeast coast and northwest region in china than in the northeast and Qinghai-Tibet plateau region in China. There is a significant temperature effect in mid-high latitude, but a very distinguished precipitation amount effect in mid-low latitude. Variables stable isotope of precipitation has a latitude effect in east region in China and a strongly altitude effect from east, northwest to Qinghai-Tibet plateau region in China.(2) The variables characteristic of hydrogen and oxygen in daily precipitation are analyzed in the mid-and-lower-reaches of Xiangjiang River. The results indicate that the stable isotopes have evidently a precipitation amount effect, moisture effect and ant-temperature effect. The composition of stable isotopes in precipitation has a very significant seasonal change, which is negative in summer half year (May-September), but is positive in winter half year (October-April).(3)The distribution and factors of d-excess in precipitation are analyzed in the mid-and-lower-reaches of Xiangjiang River. And the vapor sources of precipitation are studied by combining the backwards trajectory. The d-excess of precipitation is lower in summer half year, which is related to low-latitude marine air masses with high humidity and other properties coming from summer monsoon; however, the d-excess is higher, relating to continental air masses. In winter monsoon period, vapor mainly comes from the Westerlies carried the water vapor and local water vapor circulation, while vapor mainly comes from Bay of Bengal, South China Sea and the Western Pacific Ocean in summer monsoon period. Especially in the monsoon precipitation period, Typhoon has a vital influence on water vapor movement, rotating by the "S" type.(4)The meteoric water line is established in the mid-and-lower-reaches of Xiangjiang River, which is δD=8.41δO+16.9and the Correlation coefficient is0.98.The slope of the meteoric water line is lager than the slope of the global meteoric water line which is8, which indicates that this region has climatic characteristics of humid and rainy, however, the river water line is δD=8.02δ18O+10.9, the spring water line is δD=8.05δ18O+16.3, and the well water line is δD=7.74δ18O+12.5, all of which, to some extent, have deviate from the meteoric water line.This shows that the groundwater and river mainly come from precipitation, and precipitation has partially experienced evaporative fractionation effect before it supplies the groundwater and river, which causes the isotope change.