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Phreatic Water Evaporation And Dynamics Of Soil Moisture And Salt Under Different Groundwater Depths And Water Salinity

Posted on:2020-09-12Degree:MasterType:Thesis
Country:ChinaCandidate:W D ZhuFull Text:PDF
GTID:2370330599461931Subject:Environmental engineering
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Soil salinization is one of the main ecological environment problems in the Songnen Plain,northeast China.This experiment was carried out to analysis the role of groundwater depth and salinity in the process of salinization of soil through simulation of water and salt transport and phreatic evaporation characteristics of the saline-sodic soil under different water table depths and salinities.The findings would provide theoretical basis for the regulations of water and salt in saline-sodic soils.Five phreatic depths(0 cm,20 cm,40 cm,60 cm,80 cm)and five phreatic salinity treatments(SAR:TEC 0:0,0:10,5:40,10:70,20:100,respectively)were simulated in column experiments.The characteristics water movement and salt dynamics in the soil profile under different phreatic depth and salinity treatments were studied and discussed,the results show that:(1)The water distribution of column soil under different water tables is mainly divided by the water table and the soil-atmosphere interface.When the column soil is below the shallow water surface,the soil is basically saturated.When the soil is above the water table,the farther the soil is from the water surface,the lower the soil water content of the soil.Under different phreatic depths,the change of salt content and water content in the surface soil of soil column is the most obvious.The shallower the phreatic depth is,the more obvious the change of salt content in the surface soil in column is.Soil salinity and sodicity did not occur at the same time during the formation of saline-sodic soil.The electrical conductivity(EC)of surface soil reached the maximum at the beginning of the experiment,while the pH of surface soil decreased first and then increased at the same time.(2)The effects of different shallow groundwater salinity on soil water and salt dynamics are significant.According to the experiment,water with SAR:TEC treatment of 5:40 has an advantage over other treatments in the movement of soil water over a longer distance(>20cm)of soil column,and water with SAR:TEC treatment of 0:10 is suitable for the migration and storage in a shorter distance(>20cm).As for the different salinities,the higher the salinity,the greater the total salinity and the value of EC in soil profile.The distribution trend of Na~+content in soil profile was similar to that of soil salinity and EC,which shows that the ion content of the same treatment and soil layer increases with time.In the same treatment,the total salinity,EC and Na~+content decrease with the depth of soil column layer from shallow to deep.In different phreatic salinity treatments,the EC and Na~+content increase with phreatic mineralization at the same time.The salt content,EC and Na~+content of soil column profile in the same soil layer increase gradually in the same period.(3)Analysis of soil moisture evaporation under different water table depthes and salinities showed that the shallower the water table depth,the faster the water evaporation rate The daily average evaporation of the treatment with depth 80 cm is52% of that of the treatment with depth 0 cm.It is found that temperature and groundwater level are the main factors affecting groundwater evaporation in bare land.A groundwater evaporation model E=T~n-b under different groundwater depths is established by using Levenberg-Marquardt and global optimization calculating method.The determination coefficient is above 0.99,which has a good simulation effect.HYDRUS-1D is used to simulate the evaporation of phreatic water at different water table depths.The results show that the software HYDRUS-1D has a good simulation effect on the experiment.According to the results,the accumulation of soil salinity under shallow water table condition mainly occurs in the range of 0-20 cm.How to remove surface soil salinity is the direction of future research and development.
Keywords/Search Tags:Saline-sodic soil, water table depth, mineralization of underground water, soil water and salt transport, Hydrus-1D
PDF Full Text Request
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