Distribution Characteristics And Cause Of Stable Isotopes In Soil Water In China Based On GCMs

The distribution of stable isotopes in soil water over a large scale is the result of the combined effect of the elements of the natural environment and it played important part of water isotope simulation process.It is important for human society to monitor the soil water isotopes.From the existing research,monitoring field sample of soil water isotopes make the understanding of changes of soil water isotope composition usually limited to smaller sampling site.However,the component characteristics of soil water isotopes in large-scale spatial range were difficult to obtain through limited sampling.The introduction of General Circulation Models(GCMs)helps to understand the spatial pattern of changes of soil water isotope composition.Therefore,this paper divides China into four major natural regions.Based on the measured data of 26 sampling stations and the simulation data of several GCMs including MIROC(free),LMDZ(nudged),LMDZ(free)and HadAM(free),the spatial and temporal characteristics of δ18O in soil water of 26 sampling sites between two different kinds of data were analyzed.The distribution characteristics and causes of stable isotopes in soil water in China were analyzed by using four kinds of GCMs data.The main conclusions were as follows:(1)By using the latitude and longitude information of 26 sampling sites,the corresponding GCMs simulation data were obtained by inverse distance weighted interpolation.By comparing the spatial and temporal distribution characteristics of the two kinds of data,it was founded that the four GCMs simulation results are in good agreement with the temporal and spatial changes of stable isotopes in soil water at the sampling sites.The results can simulate the temporal-spatial variation of δ18O in soil water.The seasonal characteristics of 26 monitoring stations showed that the value ofδ18O in soil water in the Tibetan Plateau and in northwestern China were higher in summer and autumn than in spring,while the value of δ18O in Eastern monsoon region in summer and autumn were lower than in spring.The spatial characteristics of the 26 sampling sites showed that the value of δ18O in soil water in the Tibetan Plateau was lower than in the southern China,and the value of δ18O in northern China was lower than in southern China,The differences of slope about the soil water line between the GCMs and samping sites were quite different.Only in many sites in the southern China,the GCM simulated values were in good agreement with the measured values.However,the other areas were quite different.(2)From the time scale,the value of δ18O in Tibetan Plateau and northwestern China in summer and autumn was higher than that in winter and spring.While the value of δ18O in Eastern monsoon region in summer and autumn were lower than in spring and autumn.The changes in the northern China were more complicated,and the seasonal changes of the four kinds of simulation results were inconsistent.In spatial variation,the value of δ18O in soil water tended to increase from northwest to east.From the space scale,the value of δ18O in soil water tended to increase from northwest to southerneast,while the value of δ18O in soil water in southeastern China were enriched and relatively depleted in northeastern,northwestern China and Tibetan Plateau.The diffferent model resulted the diffferent slope of the soil water line and became more obvious in the space,and the slope of 4 kinds of models is concentrated between 7-10.(3)The value of δ18O in soil water was closely related to temperature and shows a significant positive correlation in mid-high latitudes region with significant temperature effect.The temperature effect was showed in the mid-high latitudes region,the higher latitude,the greater the correlation between them.The relationship between δ18O and temperature was negatively in low latitudes region.The closer to the ocean,the correlation coefficient was lower.(4)The value of δ18O in soil water was correlated with precipitation insouthern China,and the precipitation effect was very weak in northwest China.The correlation coefficients of MIROC(free)and HadAM(free)are negative in the low latitudes of the coastal area,showing obvious precipitation effect.(5)The spatial distribution of δ18O in soil water and precipitation was similar,and the fluctuation range of 5180 in soil water was smaller than the fluctuation range of δ18O in precipitation.The value of δ18O in soil water was more concentrated.The value of δ18O in soil water and precipitation was gradually increasing from northwest to northeast The oxygen isotope in soil water were enriched in southeastern China,and relatively depleted in northeastern,northwestern China and Tibetan Plateau.Soil water δ18O is closely related to precipitation δ18O.In the four models,the correlation coefficients of soil water δ18O and precipitation δ18O was gradually increasing from north to south in the region of northeast.It shows that the δ18O in soil water from north to south was getting stronger and stronger by the effect of δ18O in precipitation,and the supply of soil water by precipitation was more and more.The stable isotopes of soil water in south China are greatly influenced by the stable isotopes of precipitation,which is larger than the northern part of the north.The stable isotopes of water oxygen in soil water were closely related to the oxygen stable isotopes of precipitation,indicating that precipitation is one of the sources of recharge of soil water.