| Hydrogen and oxygen stable isotopes in water have important application value in the study of climatology,hydrology and so on.They can sensitively record climatic,environmental and hydrological information,and are considered as tracers of the water cycle.Atmospheric precipitation is one of the main links in the water cycle.Studying the characteristics of the changes and influencing factors of the hydrogen and oxygen stable isotopes in precipitation helps to grasp the regional water cycle laws and atmospheric circulation,and provides important evidence for the scientific utilization of water resources and the protection of hydrological ecosystems.In addition,the study on the hydrogen and oxygen isotopes in precipitation is an important basic work in the process of retrieving paleoclimate.The parallel observation data of hydrogen and oxygen isotopes in modern precipitation and meteorological factors can provide data support for the interpretation of ancient climate inversion indicators.Dajiuhu of Shennongjia is not only a national nature reserve,but also has the advantage conditions for studying the ancient climatic environment.The study of the hydrogen and oxygen stable isotopes in modern precipitation in Dajiuhu will help reveal the climate characteristics of Dajiuhu and provide guidance on water resources and hydrological and ecological environment in this area.It can also provides more information on paleoclimate studies in the area.In this paper,we collected the precipitation and marsh water samples from Dajiuhu,studied stable hydrogen and oxygen isotopes in precipitation and swamp water at the seasonal scale,and pointed out the main factor affecting the stable isotopes of hydrogen and oxygen in precipitation in Dajiuhu,combined with the HYSPLIT backward trajectory model tracks the moisture sources of this area and analyzes the stable isotope characteristics in precipitation in this area.We use two simulation methods to calculate the altitude effect of Shennongjia,and compares it with the altitude effect calculated from the measured values of Yichang and Dajiuhu.We study the relationship between the ?18O in precipitation and altitude in Shennongjia.In addition,Comparing the altitude effect indicated by the oxygen isotope in precipitation and stalagmite in Shennongjia.The main conclusions are as follows:(1)The ?18O and ?D in precipitation with d-excess(d)in the Dajiuhu show significant seasonal variations.The results in rainy season are low while in dry season are high.This feature reflects the important influence of different moisture sources on stable isotopes in precipitation.The slopes and intercepts of the Dajiuhu meteoric water line are all higher than the global average,indicating that the Dajiuhu is significantly affected by the monsoon,and the climate is humid and rainy.It is less affected by secondary evaporation.(2)Correlation analysis of ?18O and ?D in precipitation in Dajiuhu with temperature,precipitation,and relative humidity all show an inverse correlation,but the correlation is different,the correlation with temperature is higher,the precipitation and the correlation of relative humidity is weak,and there is a significant counter-temperature effect at Dajiuhu on the annual and seasonal scales.The correlation between precipitation effect and humidity effect is not significant.This conclusion is different from the significant precipitation effect existing in other regions of the monsoon region.It has a unique stable isotopic signature of atmospheric precipitation,is a feature of China's monsoon region.(3)There is a good correlation between the ?18O and ?D of Dajiuhu swamp water,and the correlation analysis results with meteorological elements are consistent with the results of precipitation.There is a significant anti-temperature effect,which is related to the effect of precipitation and humidity is not significant.(4)The characteristics of various environmental effects in the Dajiuhu indicate that the area is a special point in the monsoon region.The temperature and precipitation referred to by the anti-temperature effect and precipitation effect do not affect the stable isotopes in precipitation in Dajiuhu,different moisture sources and their corresponding properties are the dominant factors that affect the stable precipitation of hydrogen and oxygen in precipitation in Dajiuhu.(5)Using the HYSPLIT-4 model to trace the moisture sources of Dajiuhu,it was found that there were mainly four moisture transport paths during the rainy season:?The water vapor route from the Bay of Bengal,which cross the Indochina Peninsula and eventually reached Dajiuhu;?It originated from the South China Sea region;?Moisture from the Western Pacific;?Evaporation from the east to the west.In the dry season,the moisture transport path is relatively simple.There are two main paths.Firstly,the prevailing westerlies affect moisture from cold and dry Eurasia to the Dajiuhu.Secondly,local evaporation of moisture,local evaporation moisture in the dry season,moisture in Dajiuhu.The supplementary effect is stronger than during the rainy season.Different moisture sources in the rainy season and dry season affected the changes of ?18O and ?D in precipitation of Dajiuhu.(6)Explore the elevation effect of stable isotopes in precipitation in the Shennongjia.Using Yichang as the foot of Shennongjia,combined with the measured value of Dajiuhu,the stable isotope elevation effect of atmospheric precipitation in the Shennongjia was calculated;and the altitude effect of the Shennongjia was simulated by two methods of moisture transport disciplines and ?18O spatial distribution model of precipitation in China.Comparing the three results,it is found that the moisture sources transport disciplines and the altitude effect calculated by Yichang are close,and the precipitation ?18O spatial distribution model results are relatively negative.Comparing the altitude effect of ?18O in modern precipitation and the altitude effect of ?18O in stalagmite in Shennongjia,the altitude effect of ?18O in Shennongjia's atmospheric precipitation obtained in this paper to some extent confirms the results of the altitude effect of ?18O in stalagmite. |
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