| Hydrological cycle is the material basis of the sustainable utilization of water resources. Using the hydrogen and oxygen stable isotopes technique to study the composition characteristics and influential factors of hydrogen and oxygen isotopes in different water bodies involved in the hydrological cycle, we can better understand the law of river basin hydrological cycle and provide important basis for reasonable exploitation and utilization and protection of water resources. We chose the Heihe river in Shaanxi province as the research area and collected the samples of precipitation, river water, spring, plants and soil in a full year form August 2014 to August 2015. The samples'hydrogen and oxygen isotopes were measured using liquid water isotope analyzer. In addition, the water was firstly extracted from plants and soil samples using LI-2000 plant-soil extraction system. In combination with the meteorological data, we analysed the composition characteristics and influential factors of hydrogen and oxygen isotopes in different water bodies in hydrological cycle and researched the conversion correlation and supply ratio between different water bodies. The results show that:(1) Hydrogen and oxygen isotopes in precipitation have high values in spring and winter and low values in summer and fall. Comparing with the global meteoric water line, the meteoric water line of the river basin has slightly lower intercept and slope. The ?18O in atmospheric precipitation of Heihe river basin in Shaanxi province showed negative correlation with the precipitation throughout the year, but the negative correlation was not significant and there was no correlation between ?18O and temperature. The precipitation effect was significant in summer and the temperature effect didn't exist throughout the seasons. In addition, the basin precipitation hydrogen and oxygen isotopes decreased while the altitude increased, which showed exist of elevation effect. D-excess values presented the characteristics that it has high values in autumn and winter and low values in summer. The differences between the meteoric water line of the river basin and global meteoric water line were caused by the effect of secondary evaporation under the cloud. The non-significan temperature effect and precipitation effect were mainly caused by the lacation of Heihe river basin which is near the Qinling mountains of north-south border and the eastern monsoon transition zone. The variation of d-excess values was closely related to the effect of monsoon on precipitation of river basin.(2) The range fluctuation of ?D and ?18O in river and ground water was small, which was relatively stable than it in atmospheric precipitation. In different seasons, the order of ?D and ?18O in river from high to low was:summer> spring> winter> autumn, which was in accordance with ground water. Compared with the meteoric water line of basin precipitation, the intercept and slope of the oxygen and hydrogen isotopes linear equations of river and ground water were low. In addition, the basin river isotopes showed the elevation effect in summer and the vertical lapse rate is 0.15%o/100m. The d-excess values in river were low in summer and autumn and high in winter. The d-excess values in ground water were low in autumn, high in winter and changed slightly in spring and summer. Reasons for the difference between the changees of isotopes in river and ground water were the different meteorological elements and recharge sources in different seasons. The differences between the oxygen and hydrogen isotopes linear equations of river and ground water and meteoric water line of basin precipitation were caused by water evaporation(3) The average values of 8D and ?18O in soil water have a tendency to decrease with the increase of altitude; under the same altitude, hydrogen and oxygen isotopes values of soil water have a tendency to decrease with the increase of soil depth. The range fluctuation of ?D and ?18O in soil water was large. In summer, the ?18O in soil water increased gradually from surface to 20cm of soil and then decreased; in winter, it gradually decreased with the increase of the depth; in spring and autumn, it didn't change significantly. The d-excess values of soil water have a great difference with the d-excess values in atmospheric precipitation, river and ground water, which were whole biased and changed significantly. The large range fluctuation of ?D and ?18O in soil water was mainly due to the surface soil greatly influenced by environmental factors and isotope fractionation effect caused by the soil evaporation.The isotopes in plants water were lowest in fall, highest in summer and in between them in winter and spring which have a small changing scale. The values of hydrogen and oxygen isotopes in plant water didn't change significantly with the increase of altitude. The d-excess values of plants and soil water were relatively similar which were negative on the whole, low in summer and high in autumn and winter.(4) The distribution characteristics of hydrogen and oxygen isotopes in different water bodies showed that different water bodies in river basin have different supply sources. Using binary linear model and ?18O tracer, the supply ratios of river from atmospheric precipitation and ground water were calculated. The results showed that the main supply source of river was the precipitation in summer and autumn in which the supply ratios were 66.00% and 66.67% respectively and the main supply source was ground water in spring and winter in which the supply ratios were 73.97% and 88.95% respectively. The main supply source of river in summer and autumn was the precipitation because the precipitation of Heihe river basin was more concentrated in summer and autumn; the main supply source of river in spring and winter was ground water because the precipitation of Heihe river basin was short in spring and winter. The supply sources of plant water and soil water were investigated. The results showed that the supply ratios of precipitation and soil water to plant water were 43.54% and 56.46% respectively in Chen He station and were 45.91% and 54.09% respectively in Yun Longgou station. The supply ratios of precipitation and soil water to plant water were very close and the main supply source of plant water was soil water. In spring, summer, autumn and winter, the supply ratios of precipitation to soil water were 66.85% ,88.86%, 68.70%,63.86% respectively and the supply ratios of ground water to soil water were 33.15%,11.14%,31.30%,36.14% respectively. The main supply source of soil water was precipitation, because the soil was shallow in the river basin and the supply of precipitation to soil water was more direct. |
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