黑河中游绿洲及绿洲-荒漠生态脆弱带 土壤含水量空间分异研究

以黑河中游平川绿洲和六坝绿洲为例,对绿洲及绿洲-荒漠生态过渡带土壤含水量空间分异进行了分析研究。结果表明:在无灌溉条件下绿洲及绿洲-荒漠生态过渡带的土壤含水量水平分异明显,绿洲土壤含水量高于绿洲-荒漠生态过渡带和荒漠地区土壤含水量,并出现从绿洲到绿洲-荒漠过渡带和荒漠依次递减的趋势,主要受土壤性状、土壤水分水平运动和绿洲-荒漠局地大气环流影响;绿洲活动层土壤含水量垂直分异上表现为从表层向下逐渐增加,而过渡带和荒漠区活动层土壤含水量垂直分异则是表层和底层比20~30cm处低,可能与荒漠土壤凝结水的形成与运动有关。受绿洲地下水过度开采和绿洲边缘人类活动影响,在绿洲-荒漠过渡带形成了生态裂谷,对绿洲生态系统的安全构成威胁。

Study on spatial diversification of soil moisture content of oasis and oasis-desert ecotone in the middle reaches of the Heihe River

Taking Pingchuan and Liuba oases in the middle reaches of the Heihe River as examples, the spatial diversification of soil moisture content in oasis and ecotone is analysed using methods of combination of field sampling with laboratory analysis. The results show that the level diversification of soil moisture content along the oasis-desert is distinct in nonirrigated areas, the soil moisture content is higher than that of ecotone and desert. The soil moisture content shows a declining trend from the oasis to ecotone and desert, that is, the soil moisture content decreases from 20% in oasis to 2.9% in the oasis-desert ecotone. Firstly, the differences of soil moisture content are mostly influenced by soil characteristics and soil texture, secondly, influenced by microclimate conditions such as level airflow near ground of oasis-desert belts where soil can transport vapor from oasis area to near desert, and thirdly, the oasis soil moisture content likely moves levelly to desert soil. The active layer soil moisture content at soil profile in the oasis shows an increasing trend from surface layer to understratum. In the range of 0~60cm, the trend of soil moisture content increases in evidence from surface layer to understratum, and the change extent is about 3.12%~21.77%. Whereas in the ecotone and desert soil profiles, the soil moisture contents in surface layer and understratum are lower than that in the middle layer of 20~30cm, this is likely related with the formation and movement of condensation water of desert soil. It is proved that there is dry sand bed in 0~20cm that has distinct restrained effect to evaporation in substrate.It is beneficial to soil moisture content maintenance in that layer. It has important ecological meaning for sandy vegetation. Because of over extracting of groundwater in the oasis and obvious impact of human activities in the ecotone, the ecological gap has been formed, constituting a threat to the ecosystem security. The changes of soil moisture content in the oasis-desert ecological ecotone reflect the extents of water utilization of human being.