沙坡头人工植被固沙区天然降水的入渗和分配研究

Infiltration Processes of Precipitation in a Revegetated Sand Dune with Caragana korshinskii Shrub

土壤、植被冠层与大气界面间 (SVAT)物质传输过程日益成为水文学研究最感兴趣的领域 ,降水量的迁移与转换是非灌溉区SVAT主要的物质传输过程。干旱半干旱区稀疏灌丛蒸散量占降水量的 90 %以上 ,因此对降水入渗与水分在土壤内植物根际区再分配的研究显得十分重要。试验于 2 0 0 1年 8月 1 7日至 9月 30日在中国科学院沙坡头试验站进行 ,主要观测人工植被荒漠灌木柠条 (Caraganakorshinskii)灌丛固定沙丘降水入渗与再分配过程。结果表明 :在 7次不连续降水过程中 ,土壤入渗深度与降水强度呈简单线性相关关系 ,土壤入渗速率约为降水强度的 1 0倍。当次降水过程中降水强度小于 0 46mm·h- 1 时 ,土壤入渗速率约为 0cm·h- 1 ,此时的降水对沙区土壤基本上没有水分补给作用。受荒漠灌木柠条根系吸水作用的影响 ,其根系密集剖面深度 40～ 1 4 0cm内降水水分入渗积累不明显。降水入渗速率及入渗深度受土壤剖面初始含水率多寡而变化 ,干燥土壤剖面有助于提高瞬时入渗速率。降水以后随着时间的推移 ,人工固沙区微环境内空气温度、湿度等气象条件适宜 ,柠条生长进入相对旺盛阶段 ,其根系密集层 1 4 0cm深度处土壤含水率在总体上下降的过程中 ,表现出昼消夜长的趋势 ,试验期间翌日8:0

The experiment on precipitation infiltration and redistribution was conducted in an artificial shrub sand dune at Shapotou Desert Experimental Research Station, Chinese Academy of Sciences, from August 17 to September 30, 2001. The study site is located at southeast of the Tengger Desert at an elevation of \{1 330\} m (MSL) with latitude of 37°27′N and longitude of 104°57′E. The climate of Shapotou region is semi\|arid. A mean monthly maximum temperature of 24\^3℃ was recorded during July and the lowest value of -6\^9℃ during January. The average monthly relative humidity was the lowest (32\^7%) during April, while the highest value of 54\^1% during August. The sunshine hours during January and October range from 6.9 to 6\^7 hour per day, and 7\^0 to 8\^2 hour per day in the remaining months. Average annual rainfall is 191\^1 mm, of which 83% is received during May through September. During the experimental period, there were seven individual rainfall events, the precipitation varying from 1\^5 mm to 40\^7 mm. The maximum infiltration rate for precipitation of 40\^7 mm was up to 0\^42 mm\5min -1 , under a maximum rainfall intensity of 3\^4 mm h -1 (14:00～15:00, Sep.18), with an average initial volumetric soil moisture of 5\^4%. For the precipitation of 38\^9 mm, the individual rainfall event started at around 16:00, August 17, 2001, lasting for about 26 hours to 18:00, August 18, 2001, it has an average rainfall intensity of 1\^50 mm\5h -1 . The highest rainfall intensity of 5\^3 mm\5h -1 was recorded between 9:00～10:00, Aug 18, the overall precipitation amounts for 38\^9 mm. The result indicated that the infiltration rate differed significantly under each individual rainfall with different initial soil moisture status and rainfall intensity. A drier soil profile favors the infiltration process, and obviously, there is a simple linear relationship between the infiltration rate and the rainfall intensity, whilst that the infiltration rate has a 10 times magnitude of the rainfall intensity. It has no contribution to the soil water supplement if the intensity of an individual rainfall event is less than 0\^46 mm\5h -1 . Due to the soil-water uptake by vegetation root activities, the overall cumulative infiltration depth was less than 60 cm under an individual precipitation of around 40 mm with a intensity of 1\^50 mm\5h -1 . At a certain soil depth of 140 cm, where featured by the concentration of rooting system, the soil moisture was depleted gradually, though it still varied in a fluctuation way of 12 h periodically between daytime and night, mainly due to the vegetation water consumption at daytime and the soil moisture flow concentration at night, the difference from dawn to the end of daytime was around 0\^1%～0\^3%.