近稳定光源照射下干沙层的形成特征及剖面水汽运移阻力研究

Characteristics of dry surface layer formation and the resistance to the transfer of vapor in soil profile under almost stable radiant intensity

干沙层是干旱半干旱地区土-气界面的重要且普遍的现象,影响着土壤蒸发及地表植被的生长。文中以毛乌素沙地风积沙为研究对象,通过室内物理试验测定近稳定光源照射下土壤剖面不同深度的温度、含水率、相对湿度、基质势等物理量,观测不同水位埋深干沙层的极限厚度。通过对观测数据的分析表明,包气带剖面上各物理量的变化曲线均在干沙层底边界突变,且在干沙层底部存在厚约5cm的过渡带,使得主要水分运移方式由液态水运移向汽态水运移过渡。通过探讨土壤表面水汽运移的空气动力阻力ra、干沙层中水汽运移阻力rd二者与干沙层厚度Zd的关系可知,随着干沙层厚度的增加,ra与rd增减趋势相反。Zd≤20mm时,土壤蒸发主要受限于土壤表面的空气动力阻力ra;Zd>20mm时,蒸发主要受控于干沙层中的水汽运移阻力rd;Zd>100mm时,ra对蒸发的影响很小,可忽略。

Dry surface layer is an important and widespread phenomenon on the interface between soil and atmosphere in the arid and semi-arid regions.DSL drives the circulation of surface water and groundwater,and affects evaporation and vegetation growth.In this research,the aeolian sand in Mu Us sandy land was applied as the research object,by the means of the indoor physical experiment,under almost stable radiant intensity,the temperature,water content,relative humidity and matric potential were observed in different depths,and the max depth of DSL in different groundwater levels was measured.The results shows that a sharp change was found in the parameters profiles.And the transition zone of water and vapor transport which was about 5 cm was formed under the bottom boundary of the DSL.The quantificational interrelation of the surface aerodynamic resistance ra,and the resistance to the transfer of vapor in the DSL rdwith the thickness of DSL Zdwere analyzed in order to study the inhibiting effect of soil drying on evaporation.The conclusion is that the radecrease and rdincrease,respectively with the thickness of DSL increasing.（ ⅰ） Zd≤20 mm,the evaporation is mainly limited by ra,（ ⅱ） Zd 20 mm,the evaporation is mainly limited by rd,（ ⅲ） Zd 100 mm,rahas little impact on evaporation,which could be negligible.