Spatial heterogeneity for grain size distribution of eolian sand soil on longitudinal dunes in the southern Gurbantunggut Desert

The grain size composition, distribution characteristics and spatial variation of eolian sand soil on distinct positions across two longitudinal dunes and interdune areas were studied by means of conventional grain size analysis and geostatistical methods. In the study, 184 samples of eolian sand soil from the 0-30cm layer were systemically collected and measured from two longitudinal dunes and interdunes in the southern Gurbantunggut Desert. The results show that the dominant grain sizes are fine and very fine sands, and the differences of grain size compositions between the distinct geomorphologic positions are significant. The contents of clay and silt are highest on the interdune areas and lowest on the crests, and higher on the leeward slopes than on the windward slopes. The contents of very fine and fine sands are highest on the windward slopes and lowest on the crests. The contents of medium, coarse and very coarse sands are lowest on the interdune lands, and highest on the crests, and are identical on the two slopes. The coarser sizes (phi(1)) and mean sizes (Mz) for eolian sand soil all have a varying tendency from fine to coarse sizes with interdune area -> leeward slope -> windward slope -> crest, and the sorting (sigma) are poorly to well sorted. The results of geostatistical analysis reveal that phi(1), Mz and a values are moderately to strongly spatially autocorrelated. The values of the spatially correlated ranges are phi(1) < sigma < Mz. The spatial variation for these grain size parameters is significant across the longitudinal dune landscape. From the crests towards the bottom of the slope, there is a varying gradient of zonal distribution, and the gradient values on the leeward slopes are larger than sites on the windward slopes.

Effects of spring-summer grazing on longitudinal dune surface in southern Gurbantunggut Desert

Intensive grazing in spring-summer has been responsible for environmental degradation of the Gurbantunggut Desert in recent years. The coverage of plants and biological crusts, sand surface stability and physicochemical characteristics of soil on the dune surface were conducted in 2002 （winter grazing） and 2005 （spring-summer grazing）. The results showed that over 80% of the total area of the dune surface was covered by well-developed biological crusts and plants in 2002, when the interdune and middle to lower part of dune slopes were stabilized and only the crest had 10-40 m wide mobile belt. Affected by spring-summer grazing in 2005, over 80% of the total cover of biological crust was destructed and the plant coverage only reached 1/5 of that in 2002, especially the ephemeral plant cover had a great change. The value of sand transport potential in 2005 only reached 1/3 of that in 2002, but the total surface activity in 2005 was 1.6 times stronger than that in 2002. Meanwhile the mobile area began to expand from the dune top to the whole dune surface following spring-summer grazing. Compared with 2002, medium sand content of the dune surface soil increased by 13.9%, while that of fine and very fine sands decreased by 7.4% and 8.0% respectively in 2005 and the soil organic matter in 2005 was only about 1/2 of that in 2002. It is obvious that the presence of snow cover and frozen soil in winter could avoid the surface structure destruction in winter, while spring-summer grazing made excessive damage to biologic crusts and ephemeral plants. Spring is the main windy season in Gurbantunggut Desert and therefore intensive activity of dune surface occurred following spring-summer grazing, which led to a great loss of fine sand and organic matter. It can be seen that grazing season have a significant influence on the sustainable development of the desert ecosystem in Northwest China.

Grain-size characteristics of linear dunes on the northern margin of Qarhan Salt Lake, northwestern China

In order to clarify the formation mechanism of linear dunes on the northern margin of Qarhan Salt Lake, northwestern China, we analyzed the grain-size and sorting parameters of the dune and interdune sands. The surface sands （0-30 ram） from the dune base to the crest of both flanks and interdune corridors were sampled along transects from upwind to downwind through the dune field. The results indicated that the grain-size distribution differed at different positions between and within the dunes. The frequency curve for dune sands mainly showed a bimodal distribution, while the interdune sediments showed a trimodal distribution. The grain size distribution of the linear dunes showed a finer crest pattern, i.e. the crests were composed of sands that were generally finer, better sorted than those of base sands. In addition, at the dune field scale, the dune crest sands were tending to become much finer but sorting became worse along the downwind transects. However, the grain-size parameters of sediments in the interdune corridors showed no clear pattern. The results demonstrated that the grain size and sorting parameters exhibited a systematic change not only at the individual scale but also at the dune field scale. Our results quantitatively estimate the limited role of cohesive sediments on the formation of linear dune under unidirectional wind regime. More attention should be paid to a long-term wind regime observation, internal sedimentary structures and their formation ages.

A Study of Kumtag Desert:Progresses and Achievements

The Kumtag Desert, the fourth largest sand desert covered mainly by mobile dunes and shifting sands, had remained as the last untouched natural desert to be fully investigated in a scientific way. Therefore,＂Integrated Scientific Expedition of the Kumtag Desert Programme＂was listed as one of nine key research programmes of China National Science and Technology Basic Research Programmes in December, 2006. The expedition team carried out two large-scale and multidisciplinary scientific expeditions from June 2007 to December 2009, to the Kumtag Desert and collected more than 20 sets of field samples and ground observations. Finally, the expedition team completed not only systematic and integrated scientific expedition of the Kumtag Desert and filled in the gap of the last unexplored desert in China, but also gained fruitful research results in many scientific research subjects. These research results included that：（i） A unique aeolian landform unit, sand-gravel-moraine, developed in the Kumtag Desert, was defined and named for the first time, and the morphologic characteristics of feather-like longitudinal sand dune and its formation process are initially proved;（ii） Two sources and mineral element composition of the surface sedimentation of the Kumtag Desert was determined, and the characteristics of the desert sedimentation and stratum chronology of the Later Cenozoic Era was illustrated;（iii） The chronology of the paleo-aeolian sand was essentially determined and the formation courses and evolution process of the desert was illustrated;（iv） The thorough investigations of water system distribution, hydrology,chemical characteristics of water of the Kumtag Desert were made and six Water System Evolution Maps of the Kumtag Desert were compiled from the Later Cenozoic Era to the contemporary age;（v） The types, formation processes and distribution of soil in the Kumtag Desert were fully determined;（vi）An all-direction, all-weather, full-coverage desert meteorology observation was established and the characteristics and trend of climate change of the Kumtag Desert and nearby districts were adequately illustrated;（vii） It is the first time that the distribution areas of six plant species, including Tamarix taklamakanensis, Tamarix albiflonum, Agriophyllum lateriflorum etc., were catalogued in the Desert;（viii） The varieties, population, quantity and distribution of the wild animal such as the Bactrian Camel （Camelus ferus Przewalski）, are now documented;And （ix） it is the first time that the ecological services and economic function subdivision zones of the Kumtag Desert were classified;the Framework of the Great Dunhuang Special Ecological-Economic Zone was proposed to realize the sustainable development strategy in population, resources, environment, ecology and economics in the Kumtag Desert and nearby districts.