Experimental Study on the Migration Characteristics of Nitrate in the Vadose Zone during the Freezing Process
In order to explore the migration law of nitrate in the vadose zone during freezing,using KNO3 as a typical pollution compo-nent,key parameters such as temperature,unfrozen water content,and solution concentration are analyzed through indoor simulation ex-periments.The results show that under the experimental conditions,the vertical water migration on the profile is quite obvious.As the freezing front moves downward,the liquid water content at the front decreases,the capillary negative pressure decreases,and the capillary force increases,causing the water in the lower part to move upward.The influence range of the freezing cover is about 10 cm,and the closer to the freezing front,the smaller the unfrozen water content;the unfrozen water content has a significant negative correlation with the solution concentration.During the freezing process,as the solid ice increases,the unfrozen water content decreases,and the solute in the solution migrates to the liquid water.Therefore,while the unfrozen water content decreases,the concentration of the solution contin-ues to increase;the initial concentration of the solution is 0.3 mg/L,and the concentration after solute migration due to the freezing process is0.35～0.5 mg/L.
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