Soil Freezing And Thawing Variation Characteristics Under Different Land Use Types In Mudan Ridge

Frozen soil was a major component of Cryosphere system in the earth, whichshowed significant spatial-temporal variation. The occurrence and distribution wereaffected by various factors. On the local scale, frozen soil was influenced by factorsaffecting water and heat balance including land use type, snow, aspect, slope, soil,lithology types, etc. In Northeast China, vast forest and long-term steady seasonalsnow were the highly characteristic underlaying surface, which had a great influenceon the seasonal frozen soil.Our research aims to investigate the effects of land use type and snow cover onthe temperature of seasonal frozen soil. The study was conducted at Mudan Ridge ofthe Changbai Mountains (Nan hill of Jiang Yuan town in Dun Hua city). Plots wereestablished at three typical land use types including Korean pine-oak forest, cultivatedland, and Carex tato swamp. At each plot, one treatment was set up by shelter snowwhich was, in other words, without snow cover treatment. Three automatic weatherstations and six soil temperature and moisture monitors were set up during theobservation period,2011.10.21-2012.5.28. Through the data analysis, we obtainedthree main conclusions below:1) The effects of vegetation height and cover on the temperature. High plantheight and dense canopy of Korean pine-oak forest could absorb and reflect the solarradiation. Then, canopy bottom receive60%of solar radiation. Therefore, temperatureinner the forest was low and the cooling rate was2°C. In the cultivated land, the plantdensity was low with low stature. Then, the received solar radiation between upperand bottom of canopy were almost the same. Therefore, in the period of melting, thesoil temperature of cultivated land was higher than the other two land types. In thewetland, the plant cover was high with low stature. Then, the solar radiation receivedat the bottom canopy was80%of which at the upper canopy. Therefore, the coolingrate was at the medium level between the forest and the cultivated land.2) The freeze-thaw changes of frozen soil under different land use types weredifferent for the different vegetation types and statures. First of all, the soiltemperatures under different land use types were different. Cooling rate at forest sitewas obvious and the temperature amplitude was2°C. At the melting period of frozensoil, the soil temperature was highest at the cultivated land, followed by grass landand forest land. In the forest site, the soil firstly frozen and showed the lowest soil temperature, followed by the grass land and the cultivated land. The frozen depth ofgrassland was the lowest.3) Snow cover had significant insulation effect for the frozen soil. Snow coverpostponed the frozen time and lowest temperature arrived time of the frozen soilunder different land use types. Through our monitor, under the snow cover, the frozentime and lowest temperature arrived time of the frozen soil at the grass land andcultivated land was postponed by7-10days. Furthermore, with snow cover, thelowest soil temperature was higher by1°C than the no snow cover treatment.In summary, the characteristics of frozen soil under different land use types weredifferent, which was related to the vegetation types and plant stature. In addition,snow cover had significant insulation effect for the frozen soil. Our research analyzedthe characteristics of seasonal frozen soil in the Mudan Ridge in the ChangbaiMountains, which supplied scientific reference for the frozen soil study.