The Dynamic Change Of Soil Water And Heat And Numerical Simulation Study In Freeze-thaw Period For In Horqin Sandy With Sand-Meadow Land Features

Freezing and thawing of soil moisture is accompanied with a series of complex physical processes in seasonal freezing-thawing areas, such as heat exchange and moisture transfer. This paper relies on the National Natural Science Foundation Project " Coupled transport mechanism and simulation methods in Freeze-thaw Period for soil water-heat-Salt in Horqin Sandy Land with Sand-Meadow Land Features(51169012)" and "Field experiment and simulation coupling transportation of water, heat, salt, energy during freezing and thawing period in cold and dry regine(50769003)", analyzed the dynamic changes of the dunes-meadow soil water and heat of the seasonal freezing and thawing and the main factors influencing their freezing and thawing process, applied the SHAW model and multiple linear regression model to simulate the dynamic changes of soil water and heat. The main research results are as follows:First, seasonal freezing-thawing process of soil in the areas of dune alternate with meadow in Horqin sand was divided into the unstable freezing stage、the stable freezing stage、the ablation thawing stage.The characteristic of the seasonly freezing and thawing soil manifested that when it went with one direction, it would be frozen while with the both directions, it could be melt. During the text years, the freezing time of meadow is longer than the dune, but the largest freezing depths was shallow.Second, in the soil layers with temperature daily variation, the daily range affected by the outside temperature increases and decreased with depth, the temperature difference between day and night temperatures,the daily range was greater, the soil temperature daily range of the meadow was smaller than the dunes in the same depth; Soil vertical profile temperature of different depths change have lag during freeze-thaw period, and the lag time increases with the increasing depth, the ability to stabilize the temperature changes and regulate soil temperature of the meadow is stronger than the dune. Meadow soil profile temperature alleviated with air temperature changes than the dune.Third, the soil moisture changes magnitude in meadow was larger than the dune. The upper soil was first freezed and gathered moisture in the freezing period; the moisture migrated to the freezing front in the thawing period,the moisture content was greater near the frozen layer. The significant soil contents of freezing and thawing soils with the increasing depth from the surface to the maximum depth was increasingly significant. By comparing the melting of the layers of soil water storage change analysis before and after the freeze-thaw period found that it has a certain level of increase and was conducive to reviving spring vegetation.Fourth,the soil surface temperature lifting trends was consistent with the temperature during the freezing and thawing process,generally decreased and then increased,the surface temperature fluctuations of meadow land was smaller than the dune land;the freeze-thaw depths of the soil was related to the cumulative negative temperature of the surface evidently.Fifth,the multiple linear regression model could be better used in simulation soil water and heat of the transport process. It was a convenient tool for the simulation of soil water and heat in freeze-thaw period.SHAW model has more advantages to simulate Horqin sandy dune soil freezing and thawing process,and it can more successfully simulate freezing and thawing of soil water heat coupling dune migration process under natural conditions.