古尔班通古特沙漠风沙土土壤蒸发特征

Soil evaporation of aeolian sandy soil in Gurbantunggut Desert

土壤表面蒸发是降水的无效损失，其大小直接决定着降水转化为有效土壤水的效率，从而间接决定了植物可利用水分的多寡。在降水稀少的沙漠区，定量认识土壤蒸发的大小和其所占降水的比例显得尤为重要。在2004年全生长期（5～9月）应用自制的微型蒸渗仪（Micro-Lysime-ter）测定了风沙土（有结皮覆盖的丘间低地和裸露沙丘顶部）和对照的荒漠盐碱土的土壤蒸发。结果表明：在相似的气象条件下，风沙土区的丘间低地和荒漠盐碱土的日平均蒸发量分别约是裸露沙丘（风沙土区）的2倍和3倍。整个生长期裸露沙丘的累积蒸发量为18．7mm，丘间低地为38．8mm，荒漠盐碱土为52．1mm。根据整个观测期的累积蒸发量和累积降雨量计算得出的蒸发降雨比分别为：裸露沙丘0．20，丘间低地0．42，荒漠盐碱土0．62，表明裸露沙丘由降水转化为土壤水而储存的比率最高。同时，从数据分析中可以看出：在风沙土区0～5cm土层的含水量对土壤蒸发起决定作用，而盐碱土区的土壤蒸发则受到更深层次土壤水分的影响。裸露沙丘低的土壤蒸发、高的降水转化效率，为植被恢复奠定了良好的基础。因此，裸露沙丘的低蒸发量可以视为植被状况对生态水文过程的一种良性反馈。

Soil evaporation is an ineffective loss of rainfall, it directly determines the amount of rainfall that will eventually become soil water, which is available to plants. In the desert area where rainfall is rare and valuable, study of soil evaporation and its proportion of the rainfall is more important than that in other regions. Experiments were carded out in the whole growing season of 2004 to evaluate the evaporation of aeolian sandy soil and heavy tex- ured saline desert soils using micro-lysimeters. The results indicated that the average daily evaporation of the inter-dune lowland and saline soils are 2 times and 3 times, respectively, to the evaporation from the bare sand dune soil under similar climatic and soil water conditions. Accumulated evaporations from bare sand dune, inter-dune lowland and the desert saline soils for the whole growing season were 18.7 mm, 38.8 mm and 52. 1mm, respectively. Based on the accumulated evaporation and precipitation, the evaporation - precipitation ratios for the whole growing season were calculated as 0.20, 0.42 and 0.62 for bare sand dune, inter-dune lowland and desert saline soils, respectively; which indicated that bare sand dune has the highest storage ratio for precipitation. Close correlation between soil evaporation and soil water content at 0-5 cm （R^2〉0.90 for sandy soils, R^2 is 0.81 for heavy textured saline soil） indicated that the soil evaporation was determined by soil water content in top soil layer for sandy soils and the heavy textured saline soil, it was also influenced by soil water content at the layers below. Low evaporation, high storage ratio to rainfall in bare sand dune creates favorable condition for vegetation restoration, which may be considered as a positive feedback of local vegetation conditions towards eco-hydrological processes.