Researches On Geological Environment Of The Formation And Development Of Desertification In Northern China

Desertification is a serious environment problem in northern China, not only because of its large area and great changes, but also of varies kinds of geologic disasters and giant loses related to it. In 2004, wind effected desertification in the north occupies more than 97% of 1,839,400km in the whole country. The reasons for that research on geological environment of desertification have not been paid enough attentions and that the human factors been overemphasized could be found in the last 50 years of history. Thus led to the result that the costs of combating desertification are very high and the fruits are little in many places. This research would be of great importance in enriching theory of desertification investigation and study and proposing scientific and suitable measurements for combating desertification and finally realizing human nature harmonics target.On the basis of studying geo-environment and geologic forces that controlling the formation and development of desertification and referring to modern classification system, it has been put forward by the first time the geologic formation classification of land desertification in northern China. For example, wind effected desertification is divided into wind erosion type (i.e. sandy desertification) and accumulation type (i.e. gobi desertification) according to forming process characteristics. Water effected desertification is divided into karstification in limestone area and rocky desertification in other basement rock areas. Desertification related to physical chemical process is divided into salinization and alkalization. It could be divided also into irrigation type, non-irrigation type as well as relic accumulative salty type. The structural and morphologic units could also be use as important basis in the classification. For example, desertification of alluvial plain, plateau and plain depression, river valley and flood land, mountain and plateau residual, loess replat and Yuan types. The geologic classification laid theoretical foundation of studying the formation and development of desertification in the view of geologic aspect.Northern China is divided into seven desertification geo-environment regions and twenty three sub-regions according to geologic tectonics, morphologic, climatic, hydrologic and hydrogeology conditions. The geo-environment regions are as follows, inland arid basin, mid-western plateau, mid-eastern plateau, loess plateau, east plain, northeast Qinghai-Tibet plateau and mountain regions. This classification is both the fundamental of desertification geo-environmental investigation and research and combating district division.Holocene climate variation is the main cause to the formation and development of desertification in northern China. The climate in inland basins and mid-plateau are respectively arid and semi-arid which effected prominently by the East Asian monsoon system. The east plain is dominated by worm and humid climate. The climate pattern of northern China controls the distribution of desertification. But the climatic variations control the expansion and reverse of desertification. Since the last ice age, the 1500a cyclic climate oscillations dominate the desertification in northern China. Desertification at about 1000aBP, 8000aBP, 5500aBP, 4000aBP, 3000aBP and 1500aBP are respectively corresponded to the Holocene events numbered 7, 5, 4, 3, 2, and 1. This suggests that the sandy desertification processes in northern China are identical with main climate events. However, desertification in recent 100 years and in some places from 10th century is affected predominantly by human beings.Cenozoic tectonic uplift controls global climate changes. The uplift of Qinghai—Tibet plateau is the basic force of northern China climate changes. Qinghai—Tibet plateau makes the westerly wind circulation changed, leading to moisture rainfall at the west side of mountains and remarkable reduced that in the east basins on one side. On the other side, Qinghai—Tibet plateau divided westerly jet into two branches, leading to the north branch become to anticyclone all the year round, and enhanced arid climate in Northwest China. Finally, the uplift of Qinghai—Tibet plateau enhanced also Siberian—Mongolian high pressure, led to powerful winter winds and extraordinary dry in Northwest China.Aquatic environment is the decisive factor in controlling desertification. In inland arid basins, it is controlled mainly by the surface and ground water flows formed from rainfall and melting snow in surrounding mountains. In short time scale, the redistribution of water resources in endorheic drainage between manmade oasis in mid-upper reaches where desertification lightened and natural oasis in lower reaches where desertification worsened could be the dominantly factors in controlling the clearly different trends of desertification in these regions. In arid basins, waters required for plants grow are mainly from groundwater. Thus, bury and quality of groundwater dominates desertification development. When the ground is below 6.0 m, vegetation start dying, and sandy desertification develops. The middle plateaus stands in the edges of monsoon system, semi-arid climate causes ecologic environment very fragile, and desertification grades have clear relations to precipitation and groundwater levels become the second factor. In these regions, severe destroy of vegetations by human activities could led to sandy desertification expansion if there is a short dry in winter and spring seasons. The water erosion desertification in loess plateau is mainly related to climate and surface water environment. The concentrated rainfalls and low infiltration velocity in loess area make it possible that strong flows can be formed in a short time, and this is the main water erosion pattern. Ground water level dominates the formation of salinization, especially in the inland arid areas. When bury of groundwater is smaller than 2m, strong evaporation in surface led to rapid accumulation of salt in soil. In general, when bury of groundwater is bigger than 3.5m, salinization would probably do not occur. At present, salinization in many severe water shortage areas is caused by irrigation using high TDS groundwater.Different kinds of sediments lead to different desertification types. In depression belts of residual, talus and diluvium distribution areas may be occupied by sandy desertification, while the higher erosion regions would be occupied by gobi desertification. Sandy accumulation in modern and ancient river terraces is the materials of sandy desertification in alluvial areas. Lacustrine deposit in lake basins of both modern and ancient times are the major materials of desert, desertification and sand storms. Lake basins are also the concentrated areas of salinization. Quaternary aeolian sediments are the main materials of sandy desertification in all and around deserts, such as Taklimakan, Tengger, Badain Jaran, Gurbantunggut deserts and Mu Us, Hunshandake, Horqin, Hulun Buir sandy lands. Loess accumulations are the basic materials of water erosion desertification. In addition, Mesozoic and Cenozoic sandstone areas are characterized by both sandy and water erosion desertification, such as the juncture between Shaanxi Province and Inner Mongolia Autonomous Region.In summary, on the basis of data and important sections analysis, it has been studied systematically geo-environment of desertification in northern China, including the types and characteristics of geologic genesis desertification, climate changes and periodicity, Quaternary sediments, surface and groundwater conditions. It has been put forward for the first time the geologic genetic models of desertification in northwest arid basins, middle plateaus and eastern plains. Finally, five principles of combating desertification and a number of counter desertification measurements are proposed.