冻融和非冻融条件下包气带土壤墒情垂向变化的试验与分析

Analysis of the frozen soil moisture profile changes in aeration zone under the conditions of freezing-thawing and non-freezing-thawing

冻结层的存在使得寒区有着与非寒区差别明显的水文循环过程,土壤冻融规律、水热盐运移、融雪水入渗等已成为众多学者的研究对象.寒区低温条件下冻融土壤持水性质与非冻融土壤不同,其包气带冻结层往往具有弱透水性、蓄水保墒和隔热减渗的作用,使得寒区春季冻结层土壤的墒情较高.以冻融土壤和非冻融土壤墒情对比监测为基础,选取地表以下100 cm的土壤为研究对象,在黑龙江大学呼兰校区设置冻融和非冻融对比监测试验场,同时段、同频率、同埋深（间隔20 cm土层）进行土壤结构、水热及环境参数监测.通过对比分析了不同埋深不同冻融阶段的墒情参数,量化了低温冻融条件下土壤墒情较非冻融土壤的高出部分,最后对冻土保墒的机理进行探讨与分析.结果表明：冻结条件下土壤水分重新分布,在土水势的作用下由非冻结区向冻结区迁移.初冻期地表土壤墒情达到最大,冻结期土壤最大墒情值随冻结锋面迁移分别在20、40、60 cm处达到最大,稳定冻结期和融化初期在80 cm处达到最大;土壤最大墒情值一般在冻结锋面前沿的10-20 cm处,较好地保持了土壤水分.无论是从空间（不同埋深）还是时间（不同冻融阶段）角度分析,冻融土壤含水率均大于非冻融土壤,二者含水率的差值随埋深和冻融阶段的推移而加大,在稳定冻结期80 cm处达到最大,差值量可达6.4%-7.8%.

Frozen soil layer makes the hydrological process in cold regions different from non-cold regions. The freezing and thawing cycles, water/heat/salt migration, and snowmelt water infiltration have become the research target to many scholars. Low permeability, high water conservation, high thermal insulation and low infiltration in frozen layers result in higher soil moisture in spring. There is less quantitative experimental study of the influences of frozen soil on soil moisture conservation at present. Soil at the depth of 100 cm was select- ed to be the research object. A freezing test field and a non-freezing test field were set up in Hulan Campus of Heilongjiang University to monitor the soil structural characteristics, soil moisture content, temperature and environmental parameters at the same time, same frequency and same depths （per 20 cm）. Through the comparative analysis of water-thermal parameters at different depths and different stages of freezing-thawing, the vertical variation of frozen soil moisture is studied and analyzed under the conditions of freezing-thawing and non-freezing-thawing. It is found that soil water will redistribute under freezing conditions, and due to the role of potential soil water, it will migrate from non-freezing area to freezing area. In the initial freezing period, the maximum moisture content takes place at the surface, in the freezing period it takes place at 20, 40 and 60 cm depths and in the stable freezing period it takes place at the 80 cm depth. The maximum moisture content gener- ally takes place at 10 -20 cm above the freezing front, in favor of maintaining soil moisture. Both spatial and temporal analyses show that soil moisture content of freezing-thawing soil is greater than that of non-freezing- thawing soil; soil moisture content difference between freezing-thawing soil and non-freezing-thawing soil increa- ses with depths and freezing-thawing duration; in the stable freezing period it will reach the maximum at 80 cm depth, when the difference will be up to 6.4% -7.8%.