居延海的演变与环境变迁

本文根据实地考察,参考历史资料并利用卫片、航片,对居延海的形成、演变及其湖泊生态环境的变化进行了研究;并对终端湖和居延海的排泄,以及影响湖泊演变的因素等问题加以探讨。

EVOLUTION OF THE JUYAN LAKE

The Juyan Lake is a well-known inland lake in China. Many scien-tists at home and abroad have made investigation on it. In this paper,the evolution process of the lake is studied through field investigationand by means of the interpretation of satellite image and aerial photograph,and the analysis of historical data. The following conclusions can beresulted: (1) In the early Quaternary, the Juyan Lake was a fresh water lakeWith a vast area of water surface. This can be verified by the presenceof snail and fish fossil. From the map which was compiled by E. Norrinet al through field survey in 1930-1933, it can be seen that the easternJuyan Lake and the western Juyan Lake had joined into an integralwhole With a water area of 1200 km sq. Because climate had become driersince the middle Pleistocene and the Ruoshui River was formed in theHolocene,the basin possessed a closed feature and its western branch formedthe western Juyan Lake. (2) In historical period, the Juyan Lake evolved with the gradualadecrease in lake surface, and its general process was desiccation--saliniza-tion--desertification. (3) The drying up of the lake directly affected the ecologicalenvironment. Fresh water habitats disappeared and fishes were extingui-shed; vegetation degenerated from hygrophytes to xerophytes,halophytes andpsammophytes; biological productivity decreased and ecological environmentdeteriorated. (4) The water quality was fresher in the eastern Juyan Lake thanin the western Juyan Lake. Because water was both supplied and drained,the eastern Juyan Lake don't has closed feature, but has the feature of ariver course lake. So the terminal must be the western Juyan Lake. (5) The drying up of the Juyan Lake was related to hydrologicalfactors and water system evolution, especially to human activities.