Research On Farmland Water Transformation Process In Irrigation Area On The South Bank Of Yellow River In Hangjin Banner Based On Stable Isotope

South bank irrigation area of the Yellow River in Hangjin Banner is one of the representative national large-scale irrigation areas in arid and semi-arid areas.It is in urgent need to maintain the ecological security,ensure the food production and improve the utilization efficiency of agricultural water resources in the irrigation area.In this study,maize,a typical crop in the irrigation area on the south bank of the Yellow River in Hangjin banner,was taken as the research object.Stable isotope tracer technology,multivariate linear mixing model and Bayesian mixing model were used to quantitatively evaluate the utilization ratio of soil water in different depths during different growth stages;based on the stable isotope data of atmospheric precipitation and meteorological data in the study area,the precipitation characteristics in the study area are analyzed,and HYSPLIT model was used to find out the source of water vapor in the study area;through the mutual verification between the stable isotope data of drainage and SWAT model in the study area,the traceability treatment of farmland drainage was carried out,so as to quantitatively evaluate the farmland water transformation process from multiple angles.The main research contents and conclusion are as follows:（1）The equation of local meteoric water line（LMWL）in the study area wasδD=7.13δ¹⁸O-1.67,and the slope and intercept were smaller than the global LMWL and the national LMWL,indicating that there was the strong evaporation effect in the study area.From June to September,2020,the precipitationδD andδ¹⁸O ranged from-129.56‰to-5.15‰and-15.69‰to 0.95‰respectively,which were negatively correlated with precipitation,and precipitation was the main controlling factor of precipitation isotope value change.Deuterium surplus and HYSPLIT air mass trajectory model quantitatively determined that precipitation in the study area mainly came from local evaporative water vapor and water vapor from westerly belt and polar air mass in northwest direction.From the deuterium surplus and HYSPLIT air mass trajectory model,it is quantitatively determined that the precipitation in the study area mainly comes from the local evaporation water vapor and the water vapor in the northwest westerly zone and polar air mass.（2）The fitting result of soil waterline in the study area wasδD=4.4δ¹⁸O-26.The slope and intercept were obviously smaller than LMWL,which shows the distillation effect of soil water isotope decreasing from upstream to downstream at the three sampling points.From the deuterium surplus and HYSPLIT air mass trajectory model,it is quantitatively determined that the precipitation in the study area mainly comes from the local evaporation water vapor and the water vapor in the northwest westerly zone and polar air mass.（3）The results of visual method and 2 models showed that the water use status of crops in the three sampling points was roughly consistent.First of all,corn first uses shallow soil moisture in the whole growth period;as a whole,the soil water use status of maize in the whole growth period is as follows:shallow soil water→deep soil water→shallow soil water（4）The average annual drainage of the irrigation area reached 43.5565 million m3,and the main drainage source of the irrigation area was underground drainage,accounting for about 68%of the total drainage.Interflow was the second largest drainage source,accounting for 31%,while surface drainage accounted for a small proportion,contributing only 1%to drainage.Based on the analysis of stable isotope tracer technique,it was found that irrigation water accounts for 30.08%,groundwater for 34.88%and precipitation for35.04%of farmland drainage in irrigated area.