Field Test And Simulation In Freeze-thaw Period For Transfer Of Soil Water And Heat In Dune Alternated With Meadow Area In Horqin Sand

Frozen and thawed of soil water is accompanied with physical processes during the freezing and thawing period, such as heat exchange and moisture transfer.This thesis is based on the National Natural Science Foundation Project"Simulation for the course of atmospheric, hydrological, ecological coupling in the areas of lowland alternate with dune in Horqin sand (50669002)"and"Field experiment and simulation coupling transportation of water, heat, salt, energy during freezing and thawing period in cold and dry regine(50769003)", selected the research area in the dune alternate with meadow in Horqin sand, ultilized the measured data of field test from November in 2008 to May in 2009, analyzed and discussed the dynamic change process of soil hydrothermal during the freezing and thawing period under two kinds of conditions, which were meadow and sand land,then simulated the process by constructing the multiple regression of mathematical model.The main conclusions are as follows.(1)Seasonal freezing-thawing process of soil in the areas of dune alternate with meadow in Horqin sand was divided into five stages:①initial freezing and thawing stage,②continuous freezing stage,③freezing maintained stage,④continuous melting stage,⑤freezing of surface layer stage.The freezing-thawing period duration of meadow land is longer than that of sand land for one month.(2)Analyzed the observational data of soil temperature in the freezing and thawing period, which included A3,C3,A1,D1,E1 and F1 six experimental sites with different geomorphological types, and found the ability for stabilizing soil tempreture change of meadow land was better than ability of sand land. The soil tempreture was mainly affected by atmospheric temperature, with the soil depth decreased, correlation coefficient of atmospheric temperature and soil tempreture reduced increasingly,that was because heat transfer of soil lagged behind tempreture exchange, the hysteretic nature of meadow land was more obvious than that of sand land. (3)Utilized the Neutron Probe and TDR to continuous observe soil water content of site A3 and site C3 during the freezing and thawing period,and analyzed the observational results,then knew the variable law of holard and unfrozen water content,and found the variation of soil ice packing fraction indirectly.(4)Correlation analysis was processed among environmental factors which affected the soil tempreture and soil moisture,and got to know that atmospheric temperature, gross radiation quantity, sunshine duration, environmental humidity and groundwater level were the main environmental factors that influenced soil tempreture. Soil temperature, gross radiation quantity, and groundwater level were the main factors that influenced soil water content.(5)Simulated the hydrothermal dynamic by using multiple linear regression model in the dune alternate with meadow during the freezing and thawing period, the simulated values fitted well with the observed ones,and the multiple linear regression model had provided a better simulation to the coupled transfer of soil water and heat process.