Application Of Hydrogen And Oxygen Stable Isotopes In The Study Of Evaporation Intensity And Water Cycle Model Of Surface Water In Yinchuan Plain

Yinchuan Plain is an arid and semi-arid area in Northwest China.Due to the impact of human activities and the demand of regional development for water resources,it is necessary to have a clear understanding of the water cycle model of the whole region for sustainable water management.Water for residents in Yinchuan Plain is mainly groundwater,while water for agriculture and industry is mainly yellow river water.Therefore,it is very important to understand the relationship between groundwater and surface Yellow River water.Therefore,this paper first makes a quantitative analysis on the supply proportion of three kinds of water bodies in Yinchuan Plain:atmospheric precipitation,Yellow River water and shallow groundwater.After that,the experiment of water evaporation of the Yellow River and the experiment of farmland irrigation water distribution ratio were carried out respectively.The important contents and conclusions are as follows:?1?Before the quantitative calculation of"three water"transformation,the enrichment law of hydrogen and oxygen isotope composition of precipitation in Yinchuan Plain is analyzed.In order to better analyze the law of precipitation hydrogen and oxygen isotope enrichment,this paper compares the atmospheric precipitation isotope characteristics of Hong Kong,a coastal city,with that of Yinchuan plain.The results show that there are different precipitation isotopic enrichment in Hong Kong and Yinchuan Plain in the same season.The hydrogen and oxygen isotopes of precipitation in Yinchuan Plain are less abundant in dry season,but more abundant in wet season.The hydrogen and oxygen isotopes of precipitation in Hong Kong are more abundant in dry season,but less abundant in wet season.This situation is related to the air humidity,geographical factors and the source and path of cloud migration.This shows that the hydrogen and oxygen isotopic composition of precipitation is the result of the interaction of local factors and water vapor sources.?2?The isotopic data of Huanghe River,atmospheric precipitation and shallow groundwater in Yinchuan Plain were analyzed by linear regression analysis,and the average values of hydrogen and oxygen relationship lines and isotopic composition of the three water bodies were obtained.From the data analysis,the slope and average value of the relationship line of the shallow groundwater lie between the water of the Yellow River and the atmospheric precipitation,indicating that the shallow groundwater is supplied by the mixture of the atmospheric precipitation and the water of the Yellow River.The slope and average value of the relation line of the Yellow River water are more close to the shallow groundwater,which indicates that the Yellow River water is the main source of supply for the shallow groundwater.Based on the mixture ratio of hydrogen and oxygen stable isotopes,90.31%and 9.69%of the shallow groundwater are supplied by the Yellow River water and atmospheric precipitation.?3?The indoor evaporation experiment of Yellow River water was carried out in Wuzhong City of Yinchuan plain.Two evaporation line equations were obtained:?D=4.4044?¹⁸O-27.694??D=4.337?¹⁸O-25.565.In this experiment,the experimental evaporation ratio is also compared with the results of three calculation methods of equilibrium fractionation coefficient,dynamic fractionation coefficient and effective fractionation coefficient.The results of two experimental water samples show that the calculation results of effective fractionation coefficient method are closer to the actual evaporation situation.?4?The Yellow River runs through the whole Yinchuan plain and flows from southwest to northeast.This paper divides the Yellow River into six parts:Qingtongxia,Wuzhong,Yongning,Yinchuan,Pingluo and Huinong.The phase evaporation ratio calculated by?¹⁸O is 0.99,0.978,0.973,0.942 and 0.948respectively;the phase evaporation ratio calculated by?D is 1.004,0.99,0.952,0.923and 0.938 respectively.The gradual decrease of evaporation rate along the route indicates that the evaporation degree of the Yellow River water is gradually increased.In addition,the composition of hydrogen and oxygen isotopes of the Yellow River water in Yinchuan Plain is relatively stable,and there is no interference from other supply sources.?5?An experiment was carried out in the rice field of Yinchuan plain to explore the distribution proportion of irrigation water.The water discharge of rice field in Yinchuan plain can be divided into three parts:evaporation,transpiration and infiltration.The distribution ratio of irrigation water in two days was determined by experiment.On the first day,the proportion of evaporation,transpiration and infiltration was 52.56%,1.02%,46.42%;on the second day,the proportion was 47.9%,2.84%,49.26%.It can be seen from the calculation results that the farmland irrigation water is mainly discharged by evaporation and infiltration.At the same time,the calculation results also show that the relationship between the Yellow River water and the shallow groundwater is relatively close.The water supply of the Yellow River will raise the groundwater level,and the strong evaporation may cause the problem of soil salinization.In addition,it was found that there was a positive correlation between the conductivity and temperature of the water samples in the evaporation bucket near the paddy field.