Study On The Isotopes And Moisture Source In Precipitation In The Shule River Basin

Atmospheric precipitation isotopes are particularly sensitive to the change of climate and environment,and can be the foundation for studying the evolution of water cycle,the inversion of ancient climate,and the cycle and replenishment of groundwater.The chemical property of atmospheric precipitation is an effective solution for evaluating the transform and transportation of atmospheric composition and its effect on the environment.Further,the reorganization and quantization of the source for water vapor in the rainfall is an effective method to analyze the atmospheric circulation pattern and involved meteorological information.All the above mentioned is the key in the research of water cycle.This thesis mainly study the spatial and temporal distribution characters of water chemistry and stable isotope in the atmospheric precipitation of Shule River Basin based on the obtained 323 precipitation samples from four stations during June 2013 to July 2016.Next,with the assistance of method of meteorology,we investigate the vapor source and the isotopes in the rainfall,and quantize the input,output and net balance of the water vapor,the evolution of isotopes in a continuous precipitation and the isotope property and vapor source in a heavy precipitation.The study can provide a base for the allocation and sustainable utilization of the water source in Shule River Basin,and further for the theory in hydrology,meteorology and palaeoclimatology.The main conclusions are as follows:The main anion and cation of the rainfall is SO42– and Ca2+ in Shule River Basin,the concentrations are 728.81μeq/L and 1486.83μeq/L,respectively.The ionic concentration at plain terrain is higher than that in mountainous area,which can be attributed to the frequently sand and dust weather in the desert of plain terrain.The ionic concentration can be clearly different in different seasons,and the ionic concentration can be enhanced due to the leaching effect in summer.By analyzing the enrichment factor,ionic source and the rate of contribution,we find that Cl– mainly comes from the marine origin;SO42– and NO3– comes from anthropogenic contribution almost;the input rate of K+from the marine origin is the same with the soil origin;Ca2+ and Mg2+ is mainly from the soil;Na+ is mainly contributed by the marine origin,but the input rate from the soil origin can increased to 58.35% in winter,which is caused by the introduction of salt minerals.For the whole basin,the δ18O value ranged from –28.27‰ to 8.14‰ with a mean of –6.78‰ and δ2H ranged from –225.58‰ to 39.72‰ with a mean of –50.07‰.The stable isotope of the atmospheric precipitation in Shule River Basin is getting depletion from high altitude to low altitude,as well as from north to south.The interannual variation of δ2H and δ18O depends on seasons,and the stable isotope is enriched in warm months and diluted in cold months.The LMWL in Shule River Basin is δ2H=7.51δ18O+0.81.The intercept and slope are smaller than the GMWL,which is caused by the strong secondary evaporation.The intercept and slope at mountainous areas are larger than that at plain areas,in the cold seasons are larger than that in hot seasons.The amount of precipitation in Shule River Basin is not obvious due to the influence of temperature effect on the isotopes of atmospheric precipitation.The vertical lapse rate between δ18O and altitudes is 0.08‰/100 m,which is much lower than the global average value 0.28‰/100 m.The deuterium excess d(inverse proportional to the temperature)at warm months is much smaller than that at cold months,which is caused by the stronger secondary evaporation at higher temperature.In cold months,there still exists weak secondary evaporation.Temperature,amount of precipitation,and relative humidity of atmosphere are the main factors that influence the secondary evaporation.However,amount of precipitation can be less important to the secondary evaporation when the amount of precipitation is more than 10 mm.The rate of secondary evaporation of Shule River Basin in warm months is between 10%~13.5% and the average value is 11.6%,while the rate in cold months is 0%~3.9% and the average value is 2.1%.The Shule River Basin is mainly affected by water vapor of westerlies and local recirculation water vapor.Besides,the water vapor of southwest monsoon and the northern polar can also make contributions.The water vapor of westerlies is resulted from the continental air mass in the central Asia and high-latitude area of Continent of Europe.The water vapor of westerlies with fewer isotopes comes from the oceanic water vapor of North Atlantic Ocean and the Black Sea.The local recirculation type is from the evaporation of nearby areas such as Xinjiang,Qinghai and Xizang.The northern polar vapor comes from continental vapor(from the south mainland of the Arctic ocean,Russia mainland and Greenland)and has fewer stable isotopes than westerlies type due to the temperature.The southwest monsoon in warm seasons is mainly contributed by oceanic water vapor from the Indian Ocean,while in cold seasons it is difficult to arrive Shule River Basin.The evaporated vapor along the southwest monsoon comes from Qinghai-Tibet Plateau and provides vapor to Shule River Basin.The quantity of vapor transfer of the selected area along the weft direction is much more than that long the warp direction,and most water vapor is contributed by westerlies.The net vapor import is negative in 2013 and 2014,while it’s positive in 2015 and 2016,which further lead to the increase of rainfall in last two years.The vapor is mainly imported in warm seasons while exported in cold seasons.Based on the isotopes and meteorological features during the sustained rainfall of the Dangchengwan station from June 15 to June 19 in 2013,we find that the stable isotopes decrease,the relative humidity of atmosphere increases and the temperature decreases.The rainfall experiences 4 steps: local recirculation water precipitation,mixed precipitation of local recirculation and southwest monsoon,southwest monsoon precipitation,and mixed precipitation of southwest monsoon and westerlies.The isotopes in southwest monsoon precipitation agree with the Rayleigh fractional model.The results show that there has precipitable water of 9.87 mm,and 79% of which becomes rainfall.According to the equation describing the amount of precipitable water and surface vapor pressure,the precipitable water during the precipitation process can be 10.53 mm,which is in accordance with the results from isotopes.By analyzing the isotopes and meteorological features of 14 precipitation processes in Shule River Basin,we conclude that the properties are large relative humidity of atmosphere,low stable isotope,high Deuterium surplus,and weak second evaporation.Also,we find that westerlies provide a lot of water vapor,and the heavy precipitation is resulted from the combination of westerlies and other directions.The southwest water vapor makes contribution to most of the heavy precipitation,and the north vapor gives less contribution,while the mixed vapor and local vapor provide the least.