Spatiotemporal Variability Of Stable Hydrogen And Oxygen Isotope Composition In Soil Water And Its Influencing Factors

Soil moisture as an important part in terrestrial ecosystem and plays an important role in regulating natural water circulation and maintaining the ecological environment.Soil moisture monitoring is an important part of studying agricultural and hydrological processes.As an environmental tracer,water stable isotope is widely used in many fields of soil moisture research,but due to the influence of different environmental factors,soil moisture has spatiotemporal variability,and these factors and soil moisture migration process also lead the spatiotemporal variability of soil water hydrogen and oxygen isotopes,but the current research on the spatiotemporal variability of hydrogen and oxygen isotopes is still relatively little.Therefore,in this study,Luancheng agro-ecosystem experimental station was taken as the research object.Samples were taken in December 2018,April 2019,June and July 2019.The spatio-temporal variability of stable hydrogen and oxygen isotope composition of soil water and its influencing factors were analyzed on the field scale and the spatial multi-scale obtained by using multivariate empirical mode decomposition.The study found that:（1）On the section scale,theδ¹⁸O andδD in soil water have the largest variation range in the surface layer,and the variation range decreases slowly as the soil depth increases.Comparing the variation range ofδ¹⁸O andδD in different seasons,it can be found thatδ¹⁸O andδD are slowly biased from winter to spring to summer.（2）On the section scale,the soil water content has a good correlation withδ¹⁸O andδD in April and June at the depth of 10cm.As the depth increases,the correlation gradually decreases.There were not well correlated between soil matrix potential,soil texture,soil organic matter andδ¹⁸O andδD.The MRD trend ofδ¹⁸O andδD in each layer is inconsistent with the MRD trend of soil water content,and its position near zero is not the same.It is indicated that although the change of soil moisture consistent with the change of hydrogen and oxygen isotope,but the represent point are different.（3）At mutil-scale,soil water content and soil matrix potential have certain effects on the spatio-temporal variability ofδ¹⁸O andδD,but they are affected by sampling depths,sampling time and decomposition scales.The soil texture has a strong effect on the spatial variation ofδ¹⁸O andδD.Although the factors that affectδ¹⁸O andδD on a particular scale will not vary with the season,the positive and negative correlation betweenδ¹⁸O andδD will vary with the seasons,depths and scales.（4）At the same scale,the trends of MRDs ofδ¹⁸O andδD are different at the different depths.At the same time,the variation trends ofδ¹⁸O andδD is also different at different scales and same soil depths,which mean that the represent points ofδ¹⁸O andδD are different at the vertical distance and the horizontal distance.Meanwhile,the trend of MRD of soil water content and soil matrix potential is also different from that ofδ¹⁸O andδD at different scales and soil depths.It is shown that the spatio-temporal variability of soil water content and soil matrix potential is consistent with that ofδ¹⁸O andδD in soil water,but its representative position is not consistent.In this study,it was found that soil texture had a great influence on the spatial variability of soil water hydrogen and oxygen isotopes,and the spatio-temporal variability of soil water content and soil matrix potential was consistent with the spatio-temporal variability of soil water hydrogen and oxygen isotopes,but the representative points were not consistent.The results provide a certain theoretical basis and research basis for making a more complete sampling plan and more accurate use of isotope tracer technology to explore the process of soil water transport.