| As a typical desertification area in China,the Horqin Sandy Land is a problem that needs to be solved urgently.This paper studies the correlation between groundwater level changes and temperature changes in the groundwater during the freeze-thaw period,and analyzes the dynamic changes of soil temperature,moisture,and groundwater level in the meadow layer,and establishes nonlinear numerical relationships.Groundwater level influences the freezing and thawing process of meadow soil;Through the analysis of the simulation results of two hydrological models in the freeze-thaw period of meadow land,the dynamic variation law of soil freeze-thaw process is studied,and the differences in simulation results are analyzed.The scope of application is discussed to provide technical support for accurately judging the dynamic changes of soil freeze-thaw process in shallow groundwater areas.The following is the result of this study:(1)Studying the change of groundwater level and air temperature,the results show that the freeze-thaw process is divided into three stages according to the change of groundwater level during the freeze-thaw period of meadowland: initial freezing stage,stable freezing stage,and thawing stage.The change trend of groundwater level and temperature during the freeze-thaw period is consistent,and the change of groundwater level has obvious hysteresis.After statistical analysis,a linear equation is established,indicating that the groundwater level is positively correlated with the temperature change during the freeze-thaw period.(2)Analyze the effect of groundwater on soil heat and water processes in the freezing and thawing stage by layer,and analyze it in the two periods of freezing and melting period,establish a nonlinear equation to fit,and study the process of hydrothermal changes and the law in soil freezing and thawing process.The results show that groundwater level has different effects on soil temperature changes at different horizons at the freezing period,and decreases gradually with increasing soil depth;soil moisture changes are significantly affect,especially deep soil.During the ablation period,the change of groundwater level has the same effect on the hydrothermal process,and the soil layer above 40 cm is positively correlated with groundwater level,and the soil layer below 40 cm is negatively correlated.(3)Correlation analysis was made on the impact factors of groundwater shallow-buried area during the freezing period and the thaw period.The results show thatthere is a strong coupling relationship between water and salt in soil freezing stage,and water is the main carrier of salt transport.The correlation between temperature and soil temperature decreases as soil depth increases.Throughout the freeze-thaw process,the soil temperature has a high correlation with water,and soil temperature change is the driving force of soil moisture movement.The impact factors affect the soil freeze-thaw process to varying degrees.Changes in salinity during the ablation period are different from changes in moisture,demonstrating that the dynamics of salt changes during the freeze-thaw period are more complex.(4)The difference between the SHAW model and the COUPMODEL model is analyzed from the mechanism;the output results of the two models are analyzed,and the results show that the output of the COUPMODEL model is better than the SHAW model,and the water and salt heat change process during the overall freeze-thaw period is further improved.It is well described that the SHAW model has a poor ability to simulate the deep soil temperature;the simulated water model SHAW can describe the water change more accurately.The output of the SHAW model is larger than the actual observation result,and the output of the COUPMODEL is compared with the actual observation.Small;for the salt simulation results,SHAW model output better,COUPMODEL model is limited by the calculation method,underestimate the salt diffusion,dispersion,resulting in slightly poorer model output. |
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