Study On The Response Of Water And Salt Differentiation Of Closed Unit To Groundwater Dynamic Change In Jingdian Irrigation Area

In Northwest China,there are sufficient light and heat conditions,but a large area of land suitable for cultivation has long been barren due to lack of water.The country has built a large number of water diversion and irrigation projects to improve the regional agricultural environment and promote economic development.Since large-scale artificial irrigation has been carried out for a long time,the rules of regional hydrological cycle and the process of soil water-salt differentiation have been constantly changed,and the spatio-temporal variation and distribution characteristics of water and salt in the region have also changed accordingly.The climate conditions of high evaporation and low rainfall in arid areas,coupled with a large amount of water diversion irrigation,lead to the continuous rise of the groundwater level,which causes the water in the lower layer of the soil to carry salt to the upper layer.Water enters the atmosphere due to evaporation,and salt precipitates and gathers on the surface of the soil,resulting in soil deterioration and eventually the emergence of a large area of salinized soil,which greatly destroys the local land resources and ecological environment.In this study,the closed unit in Jingdian irrigation area is selected as the study area,and the spatial and temporal changes of water and salt characteristic values in the area are obtained through spatial interpolation.Use point-to-point comparison and correlation analysis to determine the leading factors of the change in the regional soil salinity.clarifies the mathematical relationship between the process of soil salinization and groundwater changes,a regional groundwater model be established to predict changes in groundwater depth,and combine the two to obtain the distribution of soil salinization in the irrigation area after many years.Research on the response of water and salt differentiation in closed unit to groundwater dynamic changes is conducive to formulating reasonable irrigation systems,developing scientific irrigation methods and appropriate planting structures,and protecting the ecological environment of irrigation areas.It can provide a reference for realizing the harmonious and efficient development of regional ecology,agriculture,and economy.The main research work and conclusions of this paper are as follows:(1)Clear spatial and temporal distribution characteristics of regional water and salt.Based on the long series monitoring data of the closed units in Jingdian irrigation area,four water and salt elements,including soil total salinity,groundwater depth,groundwater salinity and surface irrigation amount,were selected and spatial-temporal distribution characteristics of the four factors were analyzed by using Surfer software for spatial interpolation.The total soil salinity in the study area increased gradually from the southwest to the northeast,the groundwater salinity increased from the west to the east,and the groundwater depth decreased from the west to the east.The surface irrigation water spread to both sides along each branch canal in strips,and most of the surface irrigation water was concentrated in the southwest and northwest areas.(2)Study on the prediction of soil total salinity.Each point by point comparison,extract on the spatial interpolation of four factors as a result,the correlation analysis of various factors,for each point total salt in soil and groundwater depth of nonlinear regression analysis,total salt in soil and groundwater depth is significantly negative correlation,the leading factor in the regional soil soluble for the buried depth of groundwater,It was found that the growth rate of soil total salt in the irrigated area was negatively correlated with the depth of groundwater.According to the different interval time,it can be divided into three relations,namely 5 years,10 years and 15 years,according to which the total soil salinity can be predicted.(3)Study on numerical modeling of groundwater.The three-dimensional unsteady flow model of groundwater in irrigation area was established by Visual Modflow software.The average annual climate in the irrigated area was taken as the input of climate change,and the distribution of cultivated land and irrigation system were taken as the input of human activities to predict the groundwater depth in the future.The results show that there will be groundwater overflow in the study area.In 2026,some areas in the northwest and a small part in the northeast will overflow to the surface and form marshes.In 2031,the marsh area was increasing,and a small area of marsh also appeared in the southeastern margin.In general,the average buried depth of the whole study area decreased from 2016 to 2031,and groundwater overflowed the surface.The area with buried depth of 0?5m is expanding continuously,and it will account for more than half of the study area by 2031.The area with a buried depth of more than 25 m decreases continuously,and the area with a buried depth of more than 25 m has disappeared by 2031.(4)Prediction of regional salinization.The distribution of soil salinization degree in the closed geological units in 2026 and 2031 can be obtained by combining the groundwater depth with the obtained relationship.On the whole,the area of the non-salinized soil did not change greatly,while the area of the salinized soil decreased significantly,while the area of the medium-salinized soil and the light-salinized soil increased to varying degrees.The area of the medium-salinized soil in the northeast continued to increase outward,and almost occupied the whole northern region by 2031.