| Jiangsu coastal economic zone is located in the intersection area of the main axis of China's three major productivity layouts(the Yangtze River coast,the eastern coast and along the Longhailan New Line).It has a significant geographical advantage and has become an important economic growth pole in eastern China.However,affected by the soil background,a large area of coastal saline soil is widely distributed in the region,with high soil salinity and fragile ecological environment.Soil salinization has become an important environmental problem restricting the comprehensive development of the region.It is urgent to carry out saline soil improvement work to ensure the coordination and unity of regional ecological environment and social and economic development.Based on this,this paper takes Xuwei New District,Lianyungang City,Jiangsu Province as the research area,and finds out the development law of soil salinization and the migration law of water and salt in saline soil through field comprehensive investigation,in-situ monitoring of soil and groundwater.On this basis,according to the characteristics of soil salinization in the study area,indoor soil column simulation experiment was carried out to optimize the material and structure of saline soil matrix improvement material and composite salt barrier layer.Through field field test,the improvement effect of soil water and salt regulation scheme was tested to provide reference and technical guidance for saline soil improvement and ecological restoration in coastal high saline soil areas.The following conclusions are obtained through this study:(1)Field survey data showed that the main hazards of saline soil in the study area were salinization,soil alkali stress was not significant,and the main harmful ions were Cl~-and Na~+.The spatial distribution of soil salinity at 0?-1,-1?-2,-2?-3 depths showed moderate spatial autocorrelation,showing a horizontal distribution pattern of'high in the east and low in the west'.In terms of vertical distribution,the vertical distribution of soil salinity showed two main types of bottom aggregation and surface aggregation.Coastline change,groundwater depth,TDS content and land use pattern were the main environmental factors affecting the spatial distribution of soil salinity in the study area.(2)Affected by monsoon climate factors,the groundwater depth,electrical conductivity and soil moisture content in the study area showed significant seasonal variation characteristics,and the soil desalination-salt accumulation process occurred alternately during the monitoring period.According to the dynamics of soil salinity,the process of soil desalination and salt accumulation in the monitoring period can be divided into three stages:December 2019 to March 2020,April to September,October to December.The response characteristics of soil salinity to rainfall process can be divided into two stages.In the early stage of rainfall,the upper soil salinity caused by rain leaching is transmitted downward layer by layer,which makes the soil salinity form a temporary high value period.With the continuous rainfall,the soil salt leaching rate is accelerated,the soil salt content is gradually reduced,and the soil enters the desalination period.(3)Compared with homogeneous soil,the mixed application of straw and sawdust can produce physical mixing effect on soil,improve the structure of saline soil,increase soil water permeability,and provide necessary conditions for soil salt leaching.The comparison of the improvement effect of the two materials showed that the improvement effect of straw was better than that of sawdust under the same mixing ratio,and the difference of the improvement effect was related to the density and structure of the material.Comprehensive comparison of two kinds of improved materials and different adding amount of saline soil desalination rate and desalination time,it is suggested that straw is used as the improvement material of saline soil matrix in the study area,and the addition amount of straw is 2%?4%,which can basically meet the requirements of soil improvement.(4)The experimental results of salt resistance of the composite salt-resisting layer showed that the new composite salt-resisting layer structure could effectively block the capillary ascending channel of soil,prevent the upper soil from returning salt due to the migration of salt with capillary water to the surface layer,and protect the upper soil of the salt-resisting layer.(5)The field test results show that the saline soil improvement scheme proposed in this study can improve the physical structure of soil,and the soil salt can be rapidly discharged with the migration of water,which increases the soil desalination rate.At the same time,it effectively prevents the soil salinization caused by the rise of capillary water,and achieves good saline soil improvement effect. |
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