| The Tibetan Plateau is one of the the two regions where lakes concentrated densely in China. With its highest elevation, it is also the origins of many rivers in China and the East Asian region. These lakes located in remote region, and are less affected by human activity. atrophy or dilatation lakes can truly reflect the changes in regional climate and environment, and it’s a sensitive indicator of global climate change. The meteorological and hydrological stations on the Tibetan Plateau are still very sparse for its vast and complex land surface and extreme climate. which leads to enormous in well understanding the watershed hydrological processes using the traditional method of long and systematic hydrological observation. Alternatively, analysis of water isotope tracers is a practical alternative to assess the hydrological processes in such a remote environment. With detailed understanding of the stable isotopic fractionation mechanism in the condensation and evaporation processes and advancements in instrumentation, the stable isotopes oxygen-18and deuterium are ideal tracers for investigation of hydrologic parameters since they are part of water and can be applied naturally to the regional and global hydrologic system.Influenced by the climate change and human activities, the Tibetan Plateau lakes are constantly changing, and that can directly affect the water cycle and water resources. In recent years, due to the precipitation and the glacial meltwater change caused by climate chang, most inland lakes on the Tibetan Plateau are on the state of water level rising. However, in the Yamzhog Yumco Lake, located near Lhasa, the lake water level dropped significantly and the lake area significantly reduced in recent years. Large area of previous lake bed appeared out of water, forming the shore shoal, old shoal into the grass. Because the Yanghu hydro plant, the Yamzhog Yumco Lake water level changes have been concerned.In order to understand the characteristics of the Yamzhog Yumco Lake water, we made a work on the Yamzhog Yumco Lake conventional hydrological studies. This paper discussed the relationship between Lake evaporation and Lake water level, the spatial distribution character of the lake water hydrogen and oxygen stable isotopes, the spatial distribution of the surrounding water hydrogen and oxygen stable isotopes, aiming to reveal the Yamzhog Yumco Lake water present hydrological cycle. The main founding of the work includes:(1) Through Pengman formula to estimate the Yamzhog Yumco Lake water evaporation from1991to2010, the average value of21years is1980mm, the maximum is2067mm, a minimum of1791mm. And with Langkazi hydrological stations (1964-2010), White hydrological stations (1996-2011) evaporation surface measured values are compared. As a result of their value is very similar. We estimate the Yamzhog Yumco Lake surface evaporation is close to the actual value.(2) During1974-2010, the water level of the Yamzhog Yumco Lake experienced down-up-down-up-down process. Using the Langkazi meteorological data analysis the change of water level. Study shows that the Yamzhog Yumco Lake water level decrease in the past a few years can not only influenced by climatic facters such as precipitation,evaporation. Probably, human activity account for the large lake water decrease.(3) Isotope values of the Yamzho Yumco lake water are-6.1‰～-2.3‰for δ18O. Due to the strong lake evaporation fractionation effect, isotope values of lake are all higher than those in precipitation of the corresponding period. Presented the relationship of δD-δ18O in Yamzho Yumco Lake:δD=4.18×δ18O-45.53and local evaporation line:δD=3.67×δ18O-50.1.(4) The surface water isotope of the Yamzho Yumco lake varied with small amplitude. Isotope values of lake water are-5.4‰～-3.8‰for δ18O and-25.1‰～-32.0‰for d-excess during the period of observation, respectively. The δ18O and d-excess value of lake water varied consistent spatially. This spatial difference proved that the smoothly flow of lake water from the river entrance to middle part of the lake, which evaporated in middle of the lake ultimately. Our observation also elucidate the vertical difference of lake water δ18O value was limited which suggest the well-mixed character of different depth lake water of the Yamzho Yumco lake.(5) Presented the relationship of δD-δ18O in Pumo Yumco Lake during2010-2012:δD=4.2δ18O-47.03(R2=0.94, n=89, p<0.0001). Isotope values of Pumo Yumco lake water are-5‰～-8‰for δ18O and-18‰～-28‰for d-excess, respectively.(6) Presented the relationship plot of δD-δ18O for precipitation (LMWL) in the Yamzhog Yumco Lake basin of the central Tibetan Plateau. The regression equations were as follow: Baidi:8D=8.03δ18O+2.15(R2=0.99, n=177, p<0.0001) Wengguo:δD=8.04δ18O+6.72(R2=0.99, n=134, p<0.0001) Dui:δD=8.11δ18O+10.3(R2=0.99, n=167, p<0.0001)(7) Presented the relationship plot of δD-δ18O for Karuxung river:δD=6.6δ18O-17.3, R2= 0.96. The river water isotope characteristics:isotope values δ18O and8D with smaller fluctuation amplitude than in precipitation. The range of δ18O is-13‰～-20‰during the period of observation. Mean isotope value of river water is-17.7‰for δ18O lower than in precipitation is-16.5%o. This is because the Karuxung river water supply from the glacial meltwater on thesurrounding mountains. Isotope composition of river display an obviously seasonal trend, the highest value generally appear from June to July. |
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