Experimental Study On Effect Of Water Surface Accumulation Driven By Freeze-thaw Action Of Two Types Of Wetland Soil In Sanjiang Plain

Frozen soil is spread all over the northeast of China, because of its high latitude and cold weather in winter. Frozen-thaw process is an important geographical process in this area, and it is an wetland concentrated distribution area. There is a close relation between frozen soil and wetland. It is significant to study the relationship between freezing and thawing of wetland soil and water migration.To study the law of moisture migration and to discussion similarities and differences of two kinds of wetland soil in frozen-thaw process, we adopt indoor simulating test to obtain temperature and moisture data. Experimental soil samples are typical wetland soil - peat mire soil and meadows soil, which are taken from Honghe Nature Reserve in Sanjiang Plain. Preliminary conclusions are as follows:(1)There are differences between soil profile configuration and physico-chemical properties in the two types of soil. The differences on profile configuration are soil genetic layers, and the differences on physico-chemical properties are topsoil layer. Contrast of surface layer, meadows soil has greater bulk density and proportion but lower porosity, organic matter content and permeability rate than peat mire soil attributing to its good surface ventilation conditions.(2)Temperature change of two kinds of wetland soil are similar in frozen-thaw process, which could be divided into four stages. Temperature change is active in upper layer and inactive in lower layers. Freezing rate of the upper soil is fast, so as heating rate. Freezing rate of the lower soil is fast, but heating rate is slow. This property of wetland soil has a protective effect on the frost..(3)Compared to peat mire soil, meadows soil has larger frost heaving amount, faster frozen speed, and higher soil freezing temperature. The surface temperature gradient of Meadows swamp soil is larger than those of other layers. In frozen-thaw process of peat mire soil, the temperature gradient of lower soil is larger than meadow marsh soil. In melting process, peat mire soil heating slowly, especially in subsoil.(4)In freezing process, the water content of upper layer increase but reduce in subsoil due to the migration of water driven by temperate gradient. Because the characteristics of blocking water of the two kinds of soil during melting, moisture is stayed at 10 ~ 20cm layer. This properties is good for wetland to keep moisture.(5)In freezing process, more water gathered in surface of peat mire soil. In melting process, more water is blocked in upper layer because peat mire soil permeability is lower than meadow marsh soil. The whole freeze-thaw process, the peak of moisture content of meadow happened after soil freeze, while the peak of peat mire soil happened after thawed.