The previous studies on the effects of artificial oases to the climatic environment were mainly based on the comparison of the observed data from very few sites in short periods (for several days or several months) and the analysis on the differences of the climatic factors between oases and deserts as well as the mechanism of energy exchange. In this paper, the representative series reflecting the climatic background change and the climatic series representing the different oases are developed by carefully selecting the observed data from some meteorological stations where the change of the observation environment is slight, the regions are sparsely populated, and the large-scale water and land exploitations are not undertaken yet. The change ratio differences of the interannual change trends of 10 climatic factors, such as the air temperature, precipitation, vapor pressure, evaporation and wind speed, are analyzed, and the compositive effects of oasis development to the long-term climate change are researched. The results show that the climatic environmental effects caused by oasis development are significant in affecting the local long-term climate change trend. In summer, the increase trend of the mean air temperature in the oases is lower than that of the background change trend, and the change trends of air temperature are in a slight decrease status in some oases, such as in the oases in the Turpan-Shanshan-Toksun Basin and the Yarkant River watershed. The oases play an obvious restraining role in the increase trend of the maximum temperature, in which the change trends of the maximum temperature are in a slight decrease status in the oases in the Yarkant River watershed and the middle reaches of Tarim River. The oases play a certain active role in increasing the minimum temperature, and the oasis effects make the diurnal-nocturnal temperature difference become smaller and smaller. In summer, the oases play an obvious role in increasing the air vapor pressure, and make the evaporation potential become lower and lower and the precipitation be increased to a certain extent. The most significant aspect of the oasis effects is the change of wind speed, that is the average wind speed and the occurring days of gales are sharply reduced in the oases.
The exploitation of resources and an increase in civil engineering projects in the Junggar Basin has caused major environmental disturbance to the fragile desert eco-system. It is a serious problem that attracts global attention on how to restore and reconstruct the stable natural eco-system. Understanding soil moisture content and lateral water movement in arid areas, at a shallow depth, is of practical importance. On the one hand, lateral flow can be expected to reduce the groundwater recharge rate. On the other hand, it may result in a strong variability of water resources over short distances, thus affecting the distribution and composition of the vegetal cover. The eolian soil moisture condition is the primary factor that affects desert plant-cover in the hinter land of Junggar Basin, especially in spring (from March to May). With neutron probe, through field calibration, the soil moisture changes in different terrain parts, which are the crest, slope, the foot of the natural and disturbed dunes and the interdune land were measured. The data shows that the spatial distribution of the soil moisture in spring is closely related to the sun radiation, the depth of snow in winter, landscape position, the depth of soil, plant cover condition (cover-degree, plant species), and human impact. The data also provides scientific information and instruction for restoring and reconstructing the eco-system that has been damaged by engineering disturbance.
The Terrestrial Nitrogen-fixing Blue-green Algae, which are possessed of both photosynthesis and nitrogen fixation, are the leading organisms in the adverse circumstances. With their typical cell structures and physiological abilities, they are strongly resistant to drought, infertility etc. The growth of Terrestrial Nitrogen-fixing Blue-green Algae can rich the soils in nitrogen and organic compounds, which are benefit to other microbes and plants. Terrestrial Nitrogen-fixing Blue-green Algae are widely distributed in Gurbantunggut Desert. It was estimated that about 40% of the surface of the desert are covered by the "Black Crust". "Black Crust" is mainly occupied by Terrestrial Nitrogen-fixing Blue-green Algae. It is Terrestrial Nitrogen-fixing Blue-green Algae that construct the mechanical crust with a little other algae and fungi through biological, chemical and physical actions. So Terrestrial Nitrogen-fixing Blue-green Algae play an important part in desert fixation. It was analyzed that there are three species of the blue-greens in the "Black Crust": <i>Microcoleus vaginatus(Vauch)Gom.,Scytonema ocellatum Lynbye and Schizothrix mella Gardner</i>. We had isolated <i>Microcoleus vaginatus(Vauch)Gom.</i> and <i>Scytonema ocellatum Lynbye</i>. Some tests had been made to prove the feasibility of the desert fixation of the Blue-greens. Under experiment conditions, the blue-greens grown on the surface of sand, covered the sand quickly after the inoculation, and formed a mechanical fixed surface layer (7 days for <i>Microcoleus vaginatus</i>, 15-21 days for <i>Scytonema ocellatum</i>).
Gurbantonggut Desert, located at the center of Jungar Basin, has an area of 48,800km<sup>2</sup>, which is the biggest immovable and semi-immovable desert in China. There is profuse oil-gas resource. Along with the oil-gas resource exploiting, more and more engineering has been built in the center of the desert, such as the desert highway and the oil fields and so on. However, aeolian environment in the Gurbantonggut Desert has a great impact on the engineering building and engineering safety. There are more than 20 gale-days per year in the center of the desert, and the main directions of the effective sand-moving winds are NE and NW, and sometimes the strong SE winds occur in the east part of the desert. The effective sand-moving winds appear mainly between April and September, which occupies 80% of whole year. It is obvious that the huge transport potential formed by the strong wind force badly endangers the engineering construction. Primary shapes of sand dunes in the desert are longitudinal and dendritic dunes, which occupy 80% of total area of the immovable and semi-immovable desert. The sand grains of the desert are coarser, and the average grain size is 0.2~0.22mm and 0.15~0.17mm in the southern and the northern part of the desert respectively. The vegetation coverage is 15~50%, and also there is about 85% of the total sand surface to be covered by the microbial crust. In this case, most dunes are fixed or semi-fixed, only on the top of the dunes existing about 30m mobile or semi-mobile sand belts. That indicates that the fixed or semi-fixed sand surfaces are dominant in desert, which prevents blown sand from doing harm to the engineering construction. Meanwhile, with the engineering construction, the fixed or semi-fixed sand surfaces are easy to be destroyed in the desert, which threatens the engineering construction and safety greatly. In general, there are about 1m thick moist sand layers in the desert and the moisture content has great changes in time and space. The moist sand layer in the desert plays an important role on the ecological rehabilitation and the aeolian disaster control in engineering disturbance areas.
The Gurbantunggut Desert of Xinjiang is in temperate climate zone and its eco-environment is very fragile. With the exploitation and development of the oil-gas resources and the implementation of the desert highway and great engineering projects in the Gurbantunggut Desert the impact of human activities on the eco-environment has been increasingly significant. We compared the physical-chemical properties and vegetation community characteristics of Sandic Entisols from two artificial longitudinal dunes with a natural longitudinal dune in an area of engineering construction. Our results show that the depth of rainfall infiltration and soil moisture after rainfall for the artificial longitudinal dune, which lost vegetation (especially microbiological crust), is remarkably higher than the natural longitudinal dune and soil moisture on the artificial dune was subject to greater rates of evaporation. Salt concentration in the soil profile of the artificial dune is relatively uniform and reflects the homogenous environment that has resulted from mixing the soil. In comparison, Sandic Entisols usually show marked variation in salt content with depth, this was observed in the natural longitudinal dune. The nutrient levels of the natural longitudinal dune are higher than that of the artificial longitudinal dune, which is related to the distribution, density and health of the vegetation cover. After installing checkerboards to fix the artificial longitudinal dune, we found that ephemeral plants rapidly colonised the checkerboard environment. However, the re-establishment of shrub and semi-shrub plants required some rehabilitation measures, such as sowing seeds. Although the pioneering vegetation lacks the diversity of the natural vegetation, it creates beneficial conditions to establish additional plant species.
Thus, it can be seen that the desert vegetation and the physical and chemical properties of Sandic Entisols are greatly affected by the disturbance caused by engineering construction. However, our results show that if rehabilitation measures, such as fixing mobile sands and re-sowing seeds, are adopted during or soon after the construction period then the disturbed ecosystem still has some capacity for natural rehabilitation.
Conference Committee Involvement (1)
Ecosystems Dynamics, Ecosystem-Society Interactions, and Remote Sensing Applications for Semi-Arid and Arid Land