| Lake sediment in arid or semi-arid areas is abundant in information of climate and environment changes, which is helpful for us to set up high-resolution environment changes sequence at the scale of decade. Environment of Ejina Oasis located in hungriness zone has been exacerbating in recent times, so we attempted to study the processes of environment changes of this area based on the data of environmental multi-proxy from No. 2 Core in Tianehu Lake one of the tail-lakes of Heihe River which lies in Ejina Oasis. A large number of data have been obtained by systematical measure of mineral magnetism, content of carbonate and (210)~Pb dating to calculate sediment age of Tianehu-2 Core. By statistical analysis of those data and comparing with the content of carbonate of another core from Munengnuoer another tail-lake in the same drainage, the deposit characteristic and its contained information of climate change and human activities have been discovered. And through comparing with historical data, the evolvement processes of Tianehu Lake and processes of water system of Ejina River shrinking with tracing to the sources in recent times have been approximately interpreted. So that we can understand the causes and courses of environment changes in the regions of lower reaches of Heihe River more comprehensively and more embedded, probe into relationship between environmental changes and human activities, and offer some constructive proposal for entironment recovering and sustainable development of Ejina Oasis. The main results can be concluded as follows:1. The content of magnetic grains in Tianehu-2 core is very low, which reflects arid climate in the whole sediment period. The content of ferri-magnetic mineral plays a leading role in the magnetic susceptibility, and pseudo single domain (PSD)-multi domain (MD) in size dominant the magnetic properties of the sample. Curve of magnetic susceptibility shows vertical change from bottom up of magnetism of the core, which reflects deferent factor affected the sediment in deferent period: the lower segments reflect the dry-cold climate, the higher segments reflect wet-warm climate, and some extremes reflect intensive human activities.2. The average content of carbonate of Tianehu-2 core is 10.9%, and its trend and range are similar to the other core from Munengnuoer, which means that both of them formed under the same environmental condition. As far as vertical change of the curve form bottom up, both higher segments reflect small replenishment to the lakeand droughty climate, whereas the lower ones reflect large replenishment and wet climate. Therefore we can take content. of carbonate as more precise geo-chemical parameter to distill paleo-environmental information, which approximately indicates fluctuate of lake water and level of aridity around the lake. Particularly, the law has been found that magnetic susceptibility changes roughly inversely to the content of carbonate, especially this negative pertinence is comparatively obvious in some stratums, which indicates that climate changes played a leading role in lake sediment, contrarily in the other stratums without such obvious negative pertinence reflect that human activities affected more intensively.3. According to the deposit velocity measured by (210)~Pb dating the sediment age of Tianehu-2 core is calculated as 200aBP, and it is divided into 7 phases in accordance with different change characteristic of magnetic susceptibility and content of carbonate. In each phases different factors affected the lake sediment on different level, but all the events including climate changes and human activities were recorded in lake sediment, and just corporate effect of both climate changes and human activities led to evolvement of Tianehu Lake and the environment of Ejina Oasis. The natural climate change played an leading role in the process of evolvement of Tianehu Lake during recent 200 years, and human activities affected the lake environment greatly only in special periods.4. The trend of both magnetic susceptibility declinin...
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