季节冻土区黑土耕层土壤冻融过程及水分变化

利用黑龙江省水利科学研究院水利试验研究中心综合实验观测场2011年11月-2012年4月整个冻结融化期的实测野外黑土耕层土壤温度和水分数据,对中-深季节冻土区黑土耕层土壤冻融过程中冻结和融化特征分阴、阳坡进行了分析,研究了冻融过程中不同深度土壤水分的变化情况,并探讨了降水对不同深度耕层土壤含水量变化的影响.结果表明:黑土耕层土壤冻结融化过程分为5个阶段,历时164 d,约5.5个月.阶段I,秋末冬初黑土耕层土壤开始步入冻结期;阶段II,黑土耕层土壤整日处于冻结状态,阴坡比同样深度的阳坡土壤温度低;阶段III为黑土耕层土壤稳定冻结期;阶段IV,黑土耕层土壤步入昼融夜冻的日循环交替状态,冻融循环的土层逐渐向深部发展,阳坡比阴坡融化得更深、更早,阴坡比阳坡经历冻融循环次数更多;阶段V为稳定融化期,在融化过程不存在冻融交替的现象,直到整个冻层内的土壤全部消融.各深度位置阴坡土壤温度的最高值出现时间比阳坡晚约0.5h.经过整个冻结融化期后,阴、阳坡各层土壤含水量均大于冻结前,阴坡土壤含水量比阳坡整体偏低.在整个冻结融化期,阳坡地下1 cm、5 cm、10 cm及15 cm处含水量最大值出现在地下5 cm;阴坡的含水量整体趋于平稳且在融化期受降水影响明显.

Freezing-thawing process and soil moisture migration within the black soil plow layer in seasonally frozen ground regions

The freezing-thawing process, ground temperature and moisture migration within the black soil plow layer were analyzed with the measured data of soil temperature and moisture within the black soil plow layer at the Water Conservancy Comprehensive Experimental Research Center of Heilongjiang Province on the outskirts of Harbin, Heilongjiang Province of China from November 2011 to April 2012, where a typical middle-deep seasonally frozen soil experimental observation field has been set up. In this paper, the freezing-thawing process of middle-deep seasonally frozen plow layer of black soil on shady slopes and sunny slopes are analyzed, including the characteristics of the freezing and thawing process at different depths of black soil plow layer. At different depths of the black soil plow layer, soil moisture migration and soil moisture change with precipitation at different depths are also discussed. The results show that in middle-deep seasonally frozen ground regions, black soil under the plow layer usually has a freezing-thawing period of 164 days, approximately 5.5 months, which can be divided into five stages. Stage I lasts 18 days, when the plow layer of surface black soil begins daily frozen state by day; at this stage the plow layer of black soil thawing by day and freezing at night, with a freezing-thawing cycle in every day; on the sunny slopes of plow layer of black soil, before 08:00 and after 20:00 the air temperatures is lower than soil temperature, and the air temperature is higher than the soil temperature at 14:00 at the depths of 1 cm and 5 cm; on the shady slopes of the plow layer of black soil, ground temperature at 08:00, 14:00 is lower than air temperature, and at 20:00 the air temperature is the same as ground temperature at the depth of 1 cm basically. Stage II lasts 72 days, black topsoil is in a frozen state by day, with a frozen deep going down; at the same depth of soil temperature on shady slopes is lower than that on sunny slopes. Stage III lasts 22 days, which is a soil stably frozen period, when all the frozen layer of soil presents completely frozen state; at 08:00 and 14:00 air temperature substantially exceeds soil temperature on shady slopes. Stage IV lasts 52 days, when black topsoil thaws by day and freezes at night, in an alternating state between day and night, soil freezing-thawing cycle gradually develops downwards; on sunny slopes soil thawing is deeper and earlier than that on shady slopes; on shady slopes topsoil experiences 47 freeze-thaw cycles, and on sunny slopes it is 39. Stage V is a stably thawing period, when alternate freezing and thawing does not present in the thawing process until the frozen layer entirely thawed. In the seasonally frozen ground regions of black soil plow layer, soil temperature continuous curve functional forms of expression are in line with cyclical fluctuations in ground temperature equations. After the whole period of freezing and thawing, soil moisture content on shady slopes and sunny slopes of black soil plow layer is greater than that before freezing. The black soil plow layer soil moisture on shady slope is significantly lower than that on sunny slope. On the sunny slopes, within the black soil plow layer the maximum depth of soil moisture is at the depth of 5 cm in the whole period of soil freezing and thawing cycles. On the shady slopes, soil moisture change within black soil plow layer is not obvious. But on shady slope, within black soil plow layer topsoil moisture changes less at the depth of 1 cm, 5 cm and 10 cm, which significantly dependents on precipitation in the thawing period. Again, soil temperature change will affect the soil moisture content variation in seasonally frozen ground regions with topsoil black soil freezing and thawing cycles.