Observation of Soil Temperature Regime in Cryic-Wetland at the Depth of 40～80 cm at Haibei, Qilian Mountains
LI Ying-nian, BAO Xin-kui, CAO Guang-min (Northwest Plateau Institute of Biology, the Chinese Academy of Sciences, Xining Qinghai810001, China)
Cryic-wetland is characterized by great soil heat capacity, low heat conductivity and slow heat transference because of its potential water supply from underground, its bad water drainage, its surface water accumulation, and its water over-saturation. Its daily and annual temperature variation is less than that of other types of wetland. The general seasonal variation of temperature in the cryic-wetland at the depth of 40 ～80 cm is that it begins to drop from the end of September and reaches its minimum at the end of January or later at the beginning of March at 80 cm deep; from the end of January to the middle of September, it increases gradually, and reaches its maximum in September. It is also shown that in cold winters and cool summers, soil temperature gradient is great, with rapider temperature change; when cold season changing into warm seasn or warm season changing into cold season, soil temperature gradient is small, with slower temperature change. Seasonally frozen soil is less deep, usually about 1 m, less than that in the area with sub-high mountainous weadow soil. Warm season (June to September) mean and annual mean temperature in cryic-wetland at the depth of 50 cm are relatively low, usually less than 5 ℃. The soil is wet, and there is surface water all year round. So this type of soil, according to the characterizations of China soil systematic classification, belongs to cryic soil, one of the orthic histosols.