Stable Isotope Tracing For Analysis Of The Supply Sources Of The Runoff From Mountain Areas In Heihe Reive Basin

The ecological environment is fragile in the Heihe River Basin.Water resources are the link between the ecosystem and the social economy.However,the shortage of water resources has become the important limiting factor for the sustainable development of the socio-economic environment of the region.In the past 30 years,various water resources problems have become increasingly severe with the global climate chan ge and the development of social and economic.Therefore,this study takes the source area of Heihe River Basin as the study area and analyzes the runoff changes and influencing factors and carries out hydrological process research by using stable isotope tracing technology.based on field observations and statistical analysis of historical hydrological data from 196 8 to 2016.The main conclusions are as follows:?1?Annual runoff shows an increasing trend,and precipitation is the most important factors affecting runoff.From 1968 to 2016,the annual mean value of runoff in the source region of the Heihe River showed a significant increasing trend.At the same time,the annual mean value of runoff changed with seasonal changes,and the replenishment effect of precipitation on runoff was more obvious.The change in annual runoff from the source area to the exit is increasing.The annual change trend rate of annual runoff in the Yanniugou Basin,Babao River Basin and the source area is 0.36%/10a,0.26%/10a and 0.6%/10a,respectively.There is a significant positive correlation between annual runoff and precipitation in the source region of the Heihe River.At the same time,the trend of runoff change is consistent with precipitation on the time scale,there is no hysteresis,and there is a certain hysteresis with temperature changes.?2?The stable isotope characteristics of each water body indicate that the river water is recharged by multiple sources.The stable isotope value of precipitation in the study area changes seasonally and decreases with the elevation.The temperature effect of precipitation isotope is significant?0.64‰/°C?and there is only weak precipitation effect in summer.Under-cloud evaporation has a significant effect on the stable iso tope concentration of precipitation.In May-August,the average raindrop evaporation rate of precipitation?^{1 8}O was 23%,11%,12%,and 16%,and the evaporative enrichment rate under the cloud was 46%,27%,38%,and 32%,respectively.The stable isotope of river water in the east branch of Heihe River has no obvious seasonal variation and elevation effect.Soil moisture is affected by the replenishment of precipitation infiltration and evapotranspiration,so that the stable isotope value of soil water change s continuously with the change of profile depth.The stable isotope values of spring water and well water are between river water and groundwater in the active layer of frozen soil,and the stable isotope value of well water has a small change range,which is consistent with the change trend of river water.The stable isotopic concentrations of river water and groundwater in the source area of the Xizhilai River are similar,reflecting that groundwater is mainly recharged by river water,and also confirming the frequent conversion of river water and groundwater.The relatively positive isotope concentration of ice and snow melts reflects the effect of soil evaporation.Both the river and groundwater at Jiayuguan Station showed no obvious seasonal changes,while the Tole Station was the opposite,reflecting that the water bodies in the mountain area of the source area were first converted to groundwater,and the sufficient mixing effect caused the seasonal change effect of stable isotope concentration to be gradually smoothed.?3?The main source of runoff from the mountain is precipitation.The contributions of atmospheric precipitation,groundwater in the active layer of frozen soil,and ice and snow melt to the runoff of the east branch source area were 65%,28%,and 7%,respectively,and the contribution rates to the runoff of the west branch source area were 51%,38%,and 11%,while in the West Expenditure Pass,the corresponding contribution rates are 79%,15%,and 6%,respectively.Compared with the Heyuan District,the contribution of precipitation to runoff at the exit is significantly increased,reflecting the impact of precipitation on runoff in cold regions.The influence gradually increases with the distance from the river source area.