沙漠绿洲过渡带柽柳灌丛沙堆—丘间地系统土壤粒度分异规律

Spatial heterogeneity of soil grain size on Tamarix ramosissima nebkhas and interdune in desert-oasis ecotone

以塔克拉玛干沙漠南缘策勒绿洲西部过渡带为研究区,从风沙地貌的角度详细研究了柽柳灌丛沙堆—丘间地系统土壤粒度空间异质性变化规律。结果表明,研究区以极细沙为主,其次为粉沙和细沙,属于风力有效搬运的粒径范围。随着植被总盖度从30%→15%~20%→10%→〈5%降低,0~10 cm土层平均粒径从74.41→77.28→86.29→92.71μm变化,并伴随着黏粒消失和粗沙出现。相同植被条件下,以灌丛下土壤平均粒径最小、沙堆边缘和风影区次之、丘间地最大,分选性则以丘间地最好而灌丛下最差。过渡带植被可截获相当部分远程输送的悬移质,使表土物质组成细化;灌丛沙堆明显的细粒富集效应及丘间地土粒相对粗化与风力分选和沙物质原地再分配密切相关;随着植被总盖度降低到5%以下,灌丛沙堆及丘间地普遍发生风蚀,表土粒度组成粗化,＂资源岛＂效应消失。至少要维持大于10%的植被覆盖是过渡带灌丛沙堆科学保育的前提。

Based on the understanding of regular pattern of ground surface erosion and deposition, we investigated the spatial variation of soil grain size on Tamarix ramosissima nebkhas and interdune in Qira desert-oasis ecotone at the southern rim of the Taklimakan Desert,Xinjiang of northwestern China. Our investigation showed that the study area was dominated by very fine sand and silt,which belong to the particle size range that could be transported effectively by wind force. With the vegetation cover decreasing from 30% to 15%- 20% to 10% and to 5%,the average particle size in 0- 10 cm soil layer increased gradually from 74. 41 to 77. 28 to 86. 29 and to 92. 71 μm. Clay disappeared and coarse sand appeared in the surface with plant coverage less than 5%. Under the same vegetation condition,the minimum soil particle size was distributed mainly under shrubs,and the maximum value mainly in the interdune. For different positions of nebkhas,the sorting coefficient of interdune soil was the best,while under shrub it was the worst. In conclusion,the vegetation in desert-oasis ecotone can intercept a considerable part of suspended sediment transported from places far away by wind and result in finer surface material of the study area. The area under shrub had much finer grains and the interdune had coarser sand apparently,which was closely related to wind-driven sorting and redistribution of sand grain in situ. When the vegetation cover was less than 5%,widespread soil erosion existed both on nebkhasand interdune surface and therefore the resource islands effects disappeared. From the perspective of nebkhas stability,the total vegetation coverage should be maintained at least 10% in the desert-oasis ecotone.