Characteristics Of Soil Water And Salt And Its Relationship With Groundwater In Minqin Oasis

In the minqin area,the climate is dry,water resources are scarce,and the ecological is fragile.In the long history of human development,the land use type and spatial structure of the oasis have undergone many changes,which in turn affects the stability of the oasis-desert ecosystem.The soil water and salt characteristics are the result of the combined effects of local natural conditions?climate,topography,hydrogeology,vegetation?and human activities?unreasonable irrigation systems,overgrazing,large reclamation?,and unreasonable distribution of soil water and salt will directly lead to soil salinization and even desertification,which will seriously affect the living environment and living conditions of human beings.Therefore,preventing soil salinization and protecting existing land resources are important tasks for the sustainable development of human society.This paper takes the downstream of Shiyang River Basin-Minqin Oasis as the research area..Through field sampling,field investigation and experimental analysis,the water and salt characteristics of different land use types and the impact of Minqin Oasis groundwater environment on soil salinization are carried out.The study concluded the following:?1?There are significant differences in soil water and salt characteristics of different land use types.The soil moisture content is generally low,ranging from 5.35%to 20.58%.The average salt content is 47.02 g·kg^-1,and the degree of salinization is serious.Soil water and salt are moderately variable,indicating that they are susceptible to climate,topography,hydrogeology and human activities.Among the salt segregants in the soil,the anions are mainly Cl^-and SO₄^2-,and the cations are mainly Na⁺.This indicates that the soil in the study area is mainly chloride-sulfate type soil,and the main salts in the soil are NaCl and Na₂SO₄..?2?The vertical distribution of soil water and salt under different land use types is significantly different.The variation of soil water content in the vertical direction is more complicated,but the salt content mainly appears as“surface accumulation”and“oscillating”in the vertical direction.The variation degree of soil salinity is obviously greater than the variation degree of water content,indicating that the spatial dependence of soil salinity is greater than the soil moisture content;the variation of surface soil water and salt is larger,indicating that the surface soil water and salt are susceptible to external factors?such as climate,terrain and human activities?.However,as the depth of the soil layer increases,the influence of external factors gradually weakens,resulting in a gradual decrease in the variation intensity of soil water and salt in the vertical direction.?3?The trend of salt segregants in soils under different land use types is similar in vertical.The c direction content of ions in soils such as natural woodland,abandoned land,saline-alkali land and desert is high,and the whole decreases with the increase of soil depth;The content of ions in soils such as cultivated land,plantations,grasslands and wetlands is low,and there is no significant change in the vertical direction.This indicates that the cultivated land,plantation,grassland and wetland in the oasis area have been artificially improved,and the soil structure,clay content,organic matter content and nutrient content are high,which is suitable for the growth of vegetation;and the natural forest land and abandoned land growing in the oasis and desert interlaced zone.Land,saline-alkali land and desert land are weak due to lack of water resources,weak soil leaching,sparse surface vegetation,large human disturbance,strong evaporation and other factors leading to salt accumulation,high ion concentration,and obvious trend of land salinization and desertification,so it's not suitable for the growth of vegetation.?4?The spatial distribution of soil water and salt in each soil layer of the study area is distributed in strips.The soil moisture content of Minqin Oasis is generally high in the west and low in the east,high in the south and low in the north,while the soil salinity shows the trend of high in the north,low in the south and high in the east and low in the west.The chemical characteristics of groundwater and soil water have significant similarities in spatial distribution,indicating that they interact with each other.Before the 1970s,the surface water resources of Minqin Oasis were sufficient,and the floodwater irrigation caused the groundwater level in the irrigation area to remain high.Under strong evaporation,the salt accumulated on the surface of the soil,resulting in a large area of native salinized soil.After the 1970s,the surface water resources of Minqin decreased day by day,and it was unable to meet the agricultural activities.Therefore,groundwater was pumped up on a large scale,and the salt was brought to the surface with the extraction of groundwater,and it was transported downward with precipitation and irrigation leakage.Under the dual action of strong evaporation and water infiltration,the salt accumulation process and desalination process of the soil are more complicated,the groundwater is repeatedly polluted,and the degree of mineralization is getting higher and higher.Therefore,since the 1970s,the area of high salinity groundwater has become larger and larger,and the degree of soil salinization has become more and more serious.The area of saline soil has expanded from north to south.