Study On The Law Of Water And Salt Migration And Dynamic Regulation Of Diving Level In The Vadose Zone In The Salinized Area Of The Aksu River Basin

Aksu region is located in the northwest edge of Tarim Basin,with the Khan Tengri in the north and the vast Taklimakan Desert in the south.It is an important production base of high-quality commodity cotton in China and an important production base of grain,fruit and vegetable in the autonomous region.Due to the economic development in recent years,water consumption,population size increases,the aksu river basin soil and water resources development and the ecological environment problems caused by increasingly serious,the development and utilization of agricultural water,surface water and groundwater proportion not harmonious,salt deposition,seasonal water shortage,groundwater salinity increases,including shallow buried groundwater area salinization of soil desertification environment problems such as area enlarges.Therefore,it is urgent to study the law of water and salt migration in the vadospermic belt,clarify the main control factors of soil salinization,and study the dynamic regulation of the submersible site,so as to provide an important theoretical basis for the joint exploitation of surface water and groundwater and the prevention and control of soil salinization in arid and semi-arid areas.The main results of this paper are as follows:1.On the basis of the existing data in the research area,field sampling was conducted,and the salinization of the research area was divided into 6 areas according to the soil structure,irrigation system and planting crops;2.The results of indoor irrigation experiments of different irrigation methods on soil samples buried in different soil structures and different water levels in the study area show that low-salinity irrigation water is more conducive to carrying away the salt in the soil surface of the vaduct zone,while the higher the salt content of high-salinity irrigation water is,the more likely it is to cause the accumulation of salt in the soil surface and the salinization of diving.Under the same conditions,the greater the water flux is,the more salt in the soil enters the groundwater with the water flow;3.The irrigation infiltration coefficient was 0.394 and 0.438,while the irrigation infiltration coefficient in clay was 0.377 and 0.413;4.Soil water conductivity,groundwater depth and salinity are the main factors affecting soil salinization.Through the correlation analysis of soluble salt results in vadossack zone in the study area by mathematical statistics,the relationship between total soil salt and soil water conductivity is obtained as follows:Y=0.184X+0.082,R~2=0.989and the relationship between total soil salt and groundwater depth and groundwater salinity is:Ss=0.011+0.136D+0.076T;5.Based on indoor irrigation,dispersion test,basic geographic data,meteorological data,land use data,hydrogeological parameters,etc.,the hydrus-1D soil column model of aerated zone in different representative A-F group sections was established to simulate vertical water and salt migration in aerated zone.The irrigation quota of planting cotton in group A was 100m~3/a,and the buried depth of underground water level was controlled below 2.3m,which could make the shallow part of the aeration belt in non-salinized state.Group B is the saline-alkali land without growing plants,and group E is the natural grassland.Group C,group D and group F kept the diving level below 1.7m,2.8m and3.2m respectively,which could make the shallow part of the vadose zone in a non-salinized state;6.The submersible surface was used as the link between vaduct zone and saturated zone,and the water salt exchange amount at the lower boundary calculated by hydrus-1D simulation was taken as the source sink term at the upper boundary of groundwater and brought into the GMS-3d groundwater numerical simulation to obtain the changes of water level and salinity.Taking 2018 as the current year,it is predicted that the water level of each observation hole will vary from 1m to 7m by the end of the next five-year plan in2025.In the upper reaches of the north,the southwest,the east and the middle reaches,the groundwater salinity all showed a downward trend,while the groundwater salinity near the upper reaches of the kumara river in the north and the southeast showed an upward trend.The range of soluble salt in the south of the study area was greater than 3g/kg,and the range of salinization increased year by year;7.By using the multi-objective optimization method and using the linprog function in the Matlab optimization toolbox to simulate and optimize the extraction water amount in 2018?2025,it is predicted that the total depth reduction of monitoring points in each administrative region from 2018?2025 after optimization is 4.04m,2.27m,1.47m,and4.69m,respectively.The area of the non-salinized area gradually increases to2884.096km~2 by 2025.The area of the strong salinization zone decreased year by year,from 11780.4 km~2in 2018 to 1267.948km~2.It is proved that the change of soil salinity can improve soil salinization.It is concluded that the establishment of multi-objective optimization model and the application of the multi-objective optimization method to the soil salinization treatment can alleviate the local soil salinization trend.