季节性冻土区土体冻融过程及其对水热因子的响应

利用内蒙古赛罕乌拉森林生态系统国家野外观测研究站试验地的森林小气候观测塔,根据2015—2016年冻融期野外观测的气温、降水量、土壤温度和水分数据,对该区季节性冻土的冻融过程和特点进行分析,研究土壤冻结和解冻过程中各土壤层的垂直温度和水分的变化,以及对气温和降水量的响应。结果表明:①季节性冻土的土壤温度随着土层深度增加,土壤冻结和融化滞后天数也会增加,同时与气温的相关性也逐渐减小;②季节性冻土解冻的速度要快于冻结的速度;③在进入解冻期前,3月中旬到5月中旬,各层土壤温度始终保持在-1～1℃之间,不随气温波动;④降水量并不大的解冻期,土壤未冻水含量会迅速增加,说明冻融过程确实能够保存土壤水分,这将有利于植被应对春季干旱。

Freezing-thawing Process of Seasonal Frozen Soil and Its Response to Moisture and Temperature

Thedata of air temperature, precipitation and soil temperature and moisture contentduring the soil freezing-thawing period from 2015 to 2016 were obtained fromthe forest microclimate observation tower of Saihanwula National ForestEcosystem Research Station in Inner Mongolia. The freezing-thawing process andcharacteristics of seasonal frozen soil in this area were analyzed. Thevertical changes of soil temperature and moisture content and their responsesto temperature and precipitation were studied. The results showed: ①The temperature of the seasonal frozen soil at different stages changed,the shallow soil began to freeze or thaw at first, and the lag time of freezing-thawingprocess increased gradually with the increase of soil depth. Moreover, thecorrelation between the air temperature and soil temperature decreasedgradually; ②The thawing speed of frozen soil was higher than that of freezing: ③Before thawing (roughlyfrom mid-March to mid-May), soil temperature at different depths maintained ina range of -1-1℃ and did notfluctuate with air temperature;④The unfrozen watercontent in soil increased rapidly during the thawing period when theprecipitation was not high, which indicated that the freezing and thawingprocesses could hold soil moisture and benefit the vegetation growth againstspring drought.