疏勒河流域大气降水同位素特征及水汽来源研究
中文摘要
大气降水同位素对气候及环境的变化极其敏感，是研究水循环、古气候记录和地下水补给及循环基础指标；大气降水水汽来源的识别及量化对解读大气环流模式具有重要的意义。以疏勒河流域为研究对象，自2013年6月至2016年7月在流域采集332个降水样品，综合应用同位素、水化学技术和气象学方法，对疏勒河流域大气降水的水化学和稳定同位素的时空分布，水汽来源，水汽输入、输出及净收支，持续降水事件下同位素的变化规律以及强降水事件下降水同位素特征和水汽来源等方面进行了研究。主要结论如下：
疏勒河流域大气降水阳离子以Ca2+和Na+为主，浓度分别为1486.83和889.10μeq/L，阴离子以SO42–为主，离子浓度为728.81μeq/L。平原区大气降水离子浓度要高于山区。离子浓度的季节性变化明显。各主要离子的来源不尽相同，Cl–和Na+以海源输入为主；SO42–和NO3–以人为活动输入为主；K+、Mg2+和Ca2+主要以陆源输入为主；但是在冬季有58.35％的Na+来源于陆地，含盐矿物的输入为Na+提供充足的来源。
疏勒河流域稳定同位素整体变化区间δ18O从-28.27‰～8.14‰，平均值为-6.78‰；δ2H从-225.58‰～39.72‰，平均值为-50.07‰。从低海拔到高海拔、从北向南疏勒河流域大气降水稳定同位素越来越贫化，
δ2H和δ18O的年际变化表现出季节性，夏季稳定同位素富集，冬季稳定同位素贫化。流域大气降水线较小的截距和斜率表明研究区存在着强烈的二次蒸发效应。降水同位素的温度效应明显。氘盈余（d）值夏季较小，二次蒸发效应十分强烈；温度、降水量和大气相对湿度是影响二次蒸发效应的关键指标。疏勒河流域夏季二次蒸发效应强烈，冬季较弱。
在研究时段内，疏勒河流域全年降水以西风水汽为主，局地再循环水汽占据较大比重，西南季风水汽和北部极地水汽也有部分贡献。2013年到2016年期间，平均每年有有18286亿吨和4735亿吨水汽分别从西边界和北边界输入，有20266亿吨和2772亿吨水汽分别从东边界和南边界输出，年均水汽净收支为-17亿吨。疏勒河流域纬向水汽输送量远大于经向水汽输送量，大部分降水水汽来源于西风；夏季为主要的水汽输入期，冬季为水汽输出期。
党城湾站2013年6月15日到2013年6月19日的持续降雨过程的同位素及气象特征研究发现，随着降水事件的持续进行，稳定同位素呈减小趋势，大气相
对湿度越来越高，温度却越来越低；降水过程符合瑞利分馏模型。通过对研究区14次强降水事件的气象和同位素特征研究，发现它们的平均温度较低，大气相对湿度较高，稳定同位素值较贫化，氘盈余值较高，二次蒸发作用较弱；西风为强降水事件提供大量的水汽，其他方向的水汽与西风水汽辐合才会形成强降水，西南水汽引起的强降水事件最多，其次是北部水汽，最少的是混合水汽和局地水汽。关键词：疏勒河流域，降水化学，稳定同位素，氘盈余，水汽来源，水汽收支
Study on the Isotopes and Moisture Source in Precipitation
in the Shule River Basin
Abstract
Atmospheric precipitation isotopes are particularly nsitive 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 rearch 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 bad on the obtained323 precipitation samples from four stations during June2013to July2016.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 evolu
tion of isotopes in a continuous precipitation and the isotope property and vapor source in a heavy precipitation.The study can provide a ba 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 are728.81μeq/L and1486.83μeq/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 dert of plain terrain.The ionic concentration can be clearly different in different asons,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 incread to58.35％in winter,which is caud by the introduction of salt minerals.
For the whole basin,theδ18O value ranged from–28.27‰to8.14‰with a mean of–6.78‰andδ2H ranged from–225.58‰to39.72‰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 ofδ2H andδ18O depends on asons,and the stable isotope is enriched in warm months and diluted in cold months.The LMWL in Shule River Basin isδ2H=7.51δ18O+0.81.The intercept and slope are smaller than the GMWL, which is caud by the strong condary evaporation.The intercept and slope at mountainous areas are larger than that at plain areas,in the cold asons are larger than that in hot asons.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 lap rate betweenδ18O and altitudes is0.08‰/100m, which is much lower than the global average value0.28‰/100m.The deuterium excess d(inver proportional to the temperature)at warm months is much smaller than that at cold months,which is caud by the stronger condary evaporation at higher temperature.In cold months,there still exists weak condary evaporation. Temperature,amount of precipitation,and relative humidity of atmosphere are the main factors that influence the condary evaporation.However,amount of precipitation can be less important to the condary evaporation when the amount of precipitation is more than10mm.The rate of condary evaporation of Shule River Basin in warm months is between10%~
13.5%and the average value is11.6%,while the rate in cold months is0%~3.9%and the average value is2.1%.
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 asons is
mainly contributed by oceanic water vapor from the Indian Ocean,while in cold asons 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 lected 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 in2013and2014,while it’s positive
in2015and2016,which further lead to the increa of rainfall in last two years.The vapor is mainly imported in warm asons while exported in cold asons.
Bad on the isotopes and meteorological features during the sustained rainfall of the Dangchengwan station from June15to June19in2013,we find that the stable isotopes decrea,the relative humidity of atmosphere increas and the temperature decreas.The rainfall experiences4steps: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 of9.87mm,and79%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 be10.53mm,which is in accordance with the results from isotopes.By analyzing the isotopes and meteorological features of14precipitation process in Shule River Basin,we conclude that the properties are large relative humidity of atmosphere,low stable isotope,high Deuterium surplus,and weak cond 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.
Key words:Shule River Basin;Precipitation chemistry;Stable isotopes; Deuterium excess;Moisture sources;Moisture budgets
