|其他摘要||Sayram Lake is a mountain lake in the arid area of Xinjiang, its ecological environment is fragile and high sensitivity. Because it is located in the Western Tianshan Mountains of China，we can correctly understand the evolution of the Western Tianshan area environment change by the sediment of this lake. The special geographical position of Sayram Lake gives its important role in the climatic and environmental research. Due to the limited measured data, longer time series of environmental information is not recorded. Lake sediment collects environmental change information of watershed. It is a natural archive of land environment changes and a good carrier to study the environmental changes in the past. So, we reveal the environmental responses of natural and human activities by measured data and lake sediment record in recent two hundred years. The study not only reveals the regularity and mechanism of watershed environmental evolution about Sayram Lake, but also providing reference for the protection of regional ecological environment and decision reference for the protection of ecological security in the watershed. Meanwile the study is conducive to enrich and improve the ecological environment database of mountain lakes in the Tianshan Mountains, providing reference for the environmental management and planning of mountain lakes and watersheds in arid area. The main results are summarized as follows:
Firstly, based on measured data, we studied the change trend of temperature and precipitation in recent 50 years in Sayram Lake basin using Mann-Kendall mutation test method and wavelet analysis. The average temperature takes on a significant rising trend. The abrupt change of annual mean temperature was came up in 1996. The annual mean temperature had three obvious periodic oscillations, in 6, 13 and 28 year. Annual precipitation is a significant fluctuation in the rising trend. The year of 1986 is an precipitation mutation year. The annual mean precipitation also had obvious periodic oscillations, which were 28, 21, 12 and 5 year.
Secondly, after pretreatment, we used supervised classification method to deal with remote sensing image. During 1990-2015, the area of the grassland, woodland and glacier snow had decreased, but in degraded grassland had increased.
Thirdly, the organic carbon and total nitrogen of topsoil samples in Sayram basin were analyzed, the study found that correlation between them is high. As different topsoil organic carbon and total nitrogen content in different vegetation, grassland topsoil organic carbon and total nitrogen content coverage of low vegetation is significantly lower than the high vegetation coverage of grassland and coniferous forest. Finally, we discussed the influence factors of topsoil carbon and nitrogen content.
Fourthly, we used the organic indexes of sediment from Sayram Lake, including total nitrogen, pigment, the total organic carbon and its isotope, in combination with the environmental significance of sediment organic indexes, to reveal environmental information contained in organic matter. The change of the total organic carbon and total nitrogen content in Sayram Lake sediment indicated the lake productivity fluctuation; The change of pigment indicated the preservation conditions of organic matter, indirectly indicated water-heat allocation of lake-watershed; Organic carbon isotope reflected the lake mixture information of internal and external source. Combined with the orderly sample clustering analysis, Sayram lake environment evolution can be divided into four stages.|