A Survey Of Ecological Environment Evolution In Heihe River Basin During History Period

The Heihe River Basin located in northwest arid inland areas. Its ecological environment is fragile. With the increase of population and the rapid development of social economy, its ecological environment degenerated seriously in recent several decades. In order to effectively control the ecological environment, to study the historical evolution of the ecological environment and to find the rule of ecological environment evolution is necessary. Consequently, the paper studies about the historical evolution process and the evolution rule of Heihe River Basin's ecological environment by consulting a large number of historical documents and archaeological materials, in combination with the hydrological and meteorological data. The study includes four aspects:water evolution, oasis evolution, towns and villages evolution and population evolution. The paper proposes suggestions for the sustainable development of ecological environment, according to the ecological environment evolution rule.(1) As the lifeblood of human survival and development, water is the main force to cause ecological environment evolution. Since the Han Dynasty, the water transferred along the river to the around, transferred from downstream delta to upstream mountains and transferred from natural water system to artificial water system. Water resource is rich during the Han Dynasty, the Northern and Southern Dynasties, the mid-late of Tang Dynasty, the late Yuan Dynasty and the middle of Ming Dynasty. It is scarce during the Wei and Jin Dynasties, the late Northern and Southern Dynasties, the early Tang Dynasty, the Five Dynasties, the early Yuan Dynasty and the early Ming Dynasty. It is close to the average during the Song Dynasty, the Qing Dynasty and the 20th century. (2) As the place of human survival and development, the evolution of oases is an important reaction to the ecological environment evolution. The prosperous period of oasis development is mainly focus on the Han Dynasty, the Wei and Jin Dynasties, the middle of Tang Dynasty, the Xixia Dynasty and since the Ming and Qing Dynasties. Oasis first appeared in the downstream delta, and then traced on the move and stayed in the alluvial fan and plains in the upper reaches of Heihe River since the Han Dynasty, gradually transferred to the upstream areas since the Ming and Qing Dynasties. Since the 20th century emerged new oasis, it expands unceasingly and finally connects into oasis belt. At last, oasis shows an expanding trend around the watershed.(3) Urban settlement is the product of socio-economic development of Heihe River Basin, its emergence, development and decline process is the direct manifestation of ecological environmental evolution. The prosperous period of urban settlements development mainly concentrated in the Han and Tang Dynasties, the decline period mainly concentrated in the late of Han Dynasty and the mid-late of Tang Dynasty. Since the reform and opening up, the internal structure of urban changed gradually. The urban settlements first appeared and developed on the Juyan ancient oasis in the downstream of Heihe River Basin, then developed from the downstream to the upstream, finally stable developed in the upper part of the alluvial fan and formed today's urban distribution pattern.(4) The population is an important indicator to measure the intensity of human activity in Heihe River Basin. Before the Qing Dynasty, the population density has not beyond the "critical index" which can cause desertification in arid desert. The influence of human activities on the ecological environment desertification is weak. Since the mid-Qing Dynasty, the population density has beyond the "critical index", so human activities play a leading role to ecological environment change.(5) Desertification and oasis are two main behave of ecological environment evolution of the Heihe River Basin. Ecological environment evolution is trend to oasis during the Han Dynasty, the early Sui Dynasty and before the "Anshi War". Ecological environment evolution is trend to desertification during the late of Han Dynasty, the Wei and Jin Dynasties, the Northern and Southern Dynasties, the late of the Sui Dynasty and after the "Anshi War", and desertification degree and scope expand gradually. In the space, desertification first appeared on the natural oases in the downstream, then spread to the middle gradually, finally spread to upstream mountainous areas. As a result, it caused desertification in the whole basin.(6) Based on the thorough analysis about the rule of ecological environment evolution of the Heihe River Basin, the paper proposes suggestions for the sustainable development of ecological environment. The Heihe River Basin should protect the ecological environment in the upstream, should improve the utilization efficiency of water resources and protect the artificial oases while expanding the natural oases, should accelerate urbanization by adjusting the industrial structure, should limit the population growth rate, and so on.