冻融过程对景电灌区草窝滩盆地土壤水盐动态的影响

景电灌区为干寒气候，蒸发强烈，季节冻土发育，土壤地下水位以上非饱和带毛细作用发育．在地表蒸发作用下，通过毛细作用，地下水不断地向地表运动．导致大量盐分到达地表．虽然蒸发作用下的毛细水运动在土壤水分垂直运动中占绝对优势，但自上而下的季节冻结和融化过程对土壤中水盐重分布的影响也起着重要的作用．基于冻融作用对水盐迁移驱动力和土壤结构等参数的影响，分析了冻融作用下水盐重分布的综合特征．

The Influence of Freezing and Thawing on the Moisture-Salt Activity of Soil in Caowotan Basin of Jingdian Irrigated Area

There are two ways for water to transfer in soil, one is flowing of liquid water and another is moving of vaporous water through pore spaces. Under arid and cold weather, evaporation is strong and frozen soil develops seasonally in the Jingdian irrigated area in Gansu Province along the Yellow River. The irrigation began in 1972 and since then the water equilibrium in this area has been broken. The groundwater table goes up and the salt content increases. In such circumstance, capillary action strongly develops in the unsaturated part of soil above the groundwater table. The groundwater moves up to the top soil through the capillary force resulted from the continuous evaporation from soil surface. In this process, salt also moves up to the soil surface contemporarily with moisture transfer. Even though the main part of the vertical water movement to topsoil is caused by the capillary action, another periodical action, freezing and thawing, has also an obvious effect on the movement and redistribution of moisture and salt along the soil profile. The effect has two directions. One is a powerful driving force to make water transfer up from the underlying unfrozen layer to the top frozen layer, because the freezing process makes the soil relatively dry off due to ice formation; Another is a strong impedance to stop the moving way of the water, because the ice formation changes the structure of the soil, in particularly, changes the size of the pores in the soil. These two acting directions decide a complex process of water and salt redistribution in soil in the arid and cold area. This paper analyses this process based on the influence of freezing and thawing on the parameters of water driving force and soil structure.