| Abstrakt: |
Western Jilin Province is a typical seasonally frozen-ground region with a large distribution area of salty soil. The salinization degree of the soil in this area is aggravated by the migration of water and salt caused by freeze-thaw action. To effectively control the increasing trend of soil salinization in this region, this paper studied the water and salt migration characteristics of carbonated soil in western Jilin Province. With carbonate-saline soil obtained from different sampling points and depths in Da'an and Sanzhigou areas of Jilin Province as the research object, characteristics of soil moisture and salinity migration in room temperature, single and repeatedly freezethaw cycles are studied through capillary water rising and freeze-thaw water transfer simulation experiment. The results show that soil samples from different regions and depths have different clay content and different salt content, so their water and salt migration characteristics are also different; The capillary rise of soil samples with high salt content was not obvious, but that of soil samples with low salt content was obvious, the reasons as follows: (1) The proportion of micropore with pore diameter <0.002mm content in soil is relatively large, which hinders the soil capillarity; (2) The clay content of the soil samples is relatively high, and the specific surface area is large, it is easy to form a thick bound water film around the particles, and the overlapping of the thick bound water film can easily block the pores or cause the pores to be too small, which is not conducive to the rise of capillary water; (3) The salinity content of the soil samples at a depth of30cm from the surface of Da'an and Sanzhigou is relatively high, with a lot of exchangeable sodium, a thick diffusion layer can be formed when exposed to water, the bound water film on the surface of adjacent particles overlaps with each other, forming a public hydration film that fills the tiny pore between the particles and hinders the rise path of capillary water. In the simulation experiment of water and salt migration by freeze-thaw method, the phenomenon of water migration about 10cm range of temperature boundary is caused by the action of temperature gradient between different test boxes, rather than the capillary water rising; Salt migration in soil sample freezing process is the result of temperature gradient and concentration gradient. This is mainly because of the effect of temperature gradient, the original soil-water potential balance at different heights of soil column is broken, so that the water migrates from the high-temperature area to the low-temperature area along the water film, thus causing the redistribution of water in the soil, at the same time, the degree of soluble salt crystallization in soil varies with the temperature at different depths, and solute potential gradient will be generated at different heights of soil column. Therefore, the solute potential gradient and temperature gradient between soil layers at different depths make the salt migrate upward with the membrane water. Year after year, through many long freeze-thaw cycles, salt migrate with the film water causes a large amount of salt to accumulate in the frozen layer, and then strong evaporation from the surface during the melting process causes a large accumulation of salt to the surface. Therefore, freeze-thaw cycle aggravates the salinization of land in western Jilin Province. [ABSTRACT FROM AUTHOR] |
