浅层包气带地温与含水量昼夜动态的实验研究

西北荒漠化地区,包气带中的水分除来自大气降水外,还来自凝结水。凝结水对维持荒漠地区的植被生态环境起到至关重要的作用,而凝结水的形成机制又反映在包气带地温与含水量的昼夜动态过程中。文中报告了室外沙坑浅层包气带地温与含水量观测的实验结果。土壤含水量变化采用原位测试的方法观测,避免了传统称重法产生的干扰和不确定性。实验中对深度0~30cm范围的土壤温度进行了高密度观测。结果表明,温度梯度对水汽的运移起到主控作用,温度梯度方向向下,土壤含水量增加,反之,含水量减少。通过热传导方程对土壤中的传热过程进行分析,得到傅立叶级数表示的温度波方程,用于预测不同深度土壤响应地表条件而产生的温度变化。实验中还对近地表微气象以及土壤负压等因素进行了观测。

An experimental study of day and night trends of soil temperature and moisture in the shallow unsaturated zone

In desertification areas of northwest China, the water content in the unsaturated zone originates from atmospheric precipitation and from water condensation. Condensation water plays an important role in sustaining the vegetation and coo-environment in the desertification areas. The development of condensation water may be influenced by day and night trends of temperature and moisture in the vadose zone. An experiment was conducted in a sand-filled bunker at a field site. The variable moisture content of the soil was measured in situ, rather than sample measurement using indoor specimen-weighing method, in order to avoid uncertainties and disturbances caused by traditional methods. The temperature profile across a depth of 0 to 30 cm was recorded hourly. The temperature gradient plays an important role in the transport of vapor in the unsaturated zone. The increase or decrease in moisture contents in buried soil depends on increasing or decreasing temperature gradients. Based on the analytical solution of heat conduction equation, an equation of temperature wave of the type of Fourier series was derived to predict the response of temperature at variable depths to ground surface condition. The micro-meteorological factors in the air and matrix suction in the soil were observed and reported.