Challenge from the appearance of vadose water within the surface iayer of megadunes, Badain-jaran dune desert, Inner Mongolia
Challenge from the appearance of vadose water within the surface iayer of megadunes, Badain-jaran dune desert, Inner Mongolia
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发表时间：
2004
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通讯作者：
G. Wei-zu;Cheng Jian-sheng
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作者：
G. Wei-zu;Cheng Jian-sheng
表层包气水深度约为2？在1997-2003年的骆驼考察中，观察到7个百万沙丘和1个流动沙丘。这些巨丘的相对高度范围从300到400？m的高度为1？三百？m-1？488？m左右传统的方法是探测风成存款的包气含水量及其物理性质。每年9月25日至27日在该沙海腹地的不同地点进行观测。结果表明，对于所有观测到的巨沙丘，渗流水含量似乎增加体积与深度的量约3%的深度轮2？米以下的megadune表面。它达到了约65%的最大湿度举行的存款（HB），这是在2000年和2003年的考察降雨事件后测量的基质电位。25 ° ~ 30 °深度的包气水δ~（18）O值为正值，而25 ° ~ 30 °深度的包气水δ~（18）O值为正值。cm到1？兆杜恩表面下300 m的深度揭示了重复的充电蒸发过程。降雨事件后，几厘米的渗透深度也观察到沿着120？在沙丘上，它可以通过能量收支测量的蒸发迅速耗尽。结果表明，该地区年平均降水量约为50？从其西北向80？东南方向1.5mm的降水量，即使有一部分凝结，也不足以满足大月面年蒸发量的输出。如果考虑到巨丘区表层包气水中HB含量较高和18 O的富集过程，那么目前认为巨丘区主要补给来源是当地降水的观点将受到挑战。一个重要的地下水补给源的存在远离这个沙丘沙漠，也许，从山区到它的南部，没有直接确定，但它似乎是暗示。
The vadose water within the surface layer with depth of about 2?m of 7 megadunes and 1 movable dune was observed during camel expeditions of 1997-2003. The relative height of these megadunes ranges from 300 to 400?m with the altitude of 1?300?m-1?488?m a.s.l. Traditional methods are used to probe the vadose water content and the physical features of its eolian deposit. Observations were made during 25-27 September every year at different spots in the hinterland of that sand sea. The results show that for all of the observed megadunes, the vadose water content appears to increase volumetrically with the depth with an amount of about 3% at the depth round 2?m below the megadune surface. It reaches to about 65% of the maximum wetness held by matrix potential of the deposit (HB) which was measured after rainfall events during the expeditions of 2000 and 2003. The positive δ~(18)O values of the vadose water at the depths from 25?cm to 1?m beneath the megadune surface reveal a repeated recharge-evaporation process. The infiltration depth of a few centimeters after rainfall event was also observed along a slope of 120?m on a sand dune, it could be quickly exausted through the evaporation measured by energy budget. It is concluded that the local precipitation with annual mean of about 50?mm from its northwest to 80?mm southeastwards seems not sufficient for the output amount of annual evaporation from megadune surface even if a portion of it being condensed. If take into account the high percentage of HB of the vadose water within the surface layer of megadunes and the enrichment process of ~(18)O, the current concept that the main recharge source of the megadune area is the local precipitation will be challenged. The existence of an important groundwater recharge source far away from this dune desert, perhaps, from the mountainuous area to its south, is not directly identified, but it seems to be implied.