Researches On The Meteorological Factors Effecting The Southern Border Of The Tengger Desert And The Topsoil Trace Elements

Located in the north of China,the southern border of the Tengger Desert is highly unstable in spatial and temporal scales,and the region could be easily influenced by the global climate changes,resulting in the migration of the southern desert border which could heavily threaten the daily life and production of surrounding inhabitants.Therefore,strengthen the research about the migration of the southern border of the Tengger Desert in the northern China is of great importance.There are many important factors that can affect the migration of the desert border,including geomorphologic factors,climate and even human elements and so on.The modern southern border of the Tengger Desert protrudes southward at the east and west ends and recedes northward in the central part.However,by analyzing the geomorphologic factors arounding the desert,we found that no satisfactory explanation can be given for the shape of this border according to geomorphologic elements.To discuss the relationship between modern meteorological elements and the southern border of the Tengger Desert,we collected the recent60-year data set of the annual average values of wind speed, temperature, precipitation and humidity at13meteorological stations near the desert and converted them into contour maps. From these maps, we found that from the west to east of the south of the Tengger Desert, there is a gradual change in precipitation, humidity, temperature and mean wind speed, differing from the abrupt modeled change in the desert’s southern border distribution. The indication is that these meteorological elements are not the main factors controlling the migration of the southern border. The extreme wind speed and maximum wind speed in the Tengger Desert are not only stronger than the threshold velocity for sand transportation in intensity, but they also have a dominant northwest direction. The extreme and maximum wind speeds at the east and west ends of the Tengger Desert are stronger than those of the central part. Consequently, the sand dunes at both ends move faster than those of the central part, causing the southern border of the Tengger Desert to protrude southward at each end and recede northward in the central part. Consequently, wind occurring in winter and spring, especially the strong northwest wind in spring, is the main controlling factor for the migration of the southern border of the Tengger Desert.Located in the desert-loess transitional zone,the natural environment of the south area of the Tengger Desert is quite vulnerable and could be easily affected by various contaminants, especially heavy metal pollutants generated by human activity. The increasing population and the "Go West" campaign initiated by the Chinese government over the course of the last decade have led to the rapid rise of towns in the desert-loess transitional zone, which has brought considerable economic benefits to the area. However, various contaminants, including heavy metals, have also entered the environment as a result of the economic activity, and the contamination has had unprecedented negative impacts on the vulnerable local ecology. When the soil was polluted by the heavy metals,it will degraded and occured the desertification,making the desert move southward and then threaten the survival of surrounding inhabitants.Therefore,strengthen researches on soil heavy metal pollution in vulnerable ecological regions of the south-central arid area of northwest China is important for regulating and guiding local industrial and municipal activities and for protecting the environment. Thus,48surface soil samples were collected in the desert-loess transitional zone in the south of the Tengger Desert. The distributions of heavy metals and the differences between urban and natural soils were analyzed. We found that As, Pb, Cu, Zn and S were obviously enriched in the Baiyin area, and Ni and Cr were mainly enriched in the Zhongwei area. V, Mn, Ti, Bi, Co and W were enriched in southeast margin of the Tengger Desert, where there is relatively little human activity. In the whole study area, Ce, La and Nd were widely distributed across areas with high and low human activity. Based on the distributions of elements, we suggest that in the desert-loess transitional zone in the south of the Tengger Desert, there are strong anthropogenic sources of As, Pb, Cu, Zn, S, Ni and Cr, but natural sources for the elements V, Mn, Ti, Bi, Co, W, Ce, La and Nd.Therefore,in order to protect our environment and health,the necessary preventive and treating measures must be conducted to manage the heavy metal pollution in the Baiyin and Zhongwei areas.