青海湖流域土地沙漠化及表土粒度特征

土地沙漠化是青海湖流域面临的重大生态环境问题之一。本文选取1977、1987、2000、2004年和2010年等5个年份的遥感影像,在地理信息系统技术支持下,得到流域30余年不同时段的土地利用类型及分布状况。空间分析结果表明:20世纪80年代是沙漠化土地增幅最大的时期,之后30年沙漠化土地面积趋于稳定; 1977-2000年是沙漠化土地增长时期,2000年以后沙漠化土地相对稳定并有轻微的逆转趋势。对典型样点的地表沉积物粒度分析结果显示:随着沙漠化程度的加剧,细颗粒物质含量减少,粗颗粒物质含量增加,平均粒径逐渐增大,标准偏差逐渐减少; 植被盖度与地表沉积物粒度特征不完全一致,判断土地沙漠化程度不能完全依赖植被状况,需要综合考虑植被和土壤粒度、养分、水分等其他信息。

Land Desertification and Grain Size Characteristics of Landsurface Deposits in the Qinghai Lake Watershed

Desertification is one of the most serious environmental problems in the Qinghai Lake watershed. Desertification land had been increasing in the last several decades. In this paper, Landsat TM imageries are used to monitor the desertification land in 1977, 1987, 2000, 2004 and 2010, with the spatial analysis tool ArcMap software, we calculate the transfer matrixes and dynamic degree to analyze the temporal and spatial change of desertification types. The desertification land experienced the most significant expansion in 1980s and remained stable in the next 30 years. In particular, desertification land was during a increasing process in 1977-2000, while in 2000-2010, desertification land remained stable and partial reversion. Surface deposits of different desertification types were collected, and then grain size were measured, the results showed that fine particle matter and standard deviation decrease while coarse particle matter and the mean average grain diameter increased with the severity of desertification. The vegetation coverage may not coordinate with the grain size characteristics, so we should take grain size, soil nutrients, soil water conditions and so on into consideration when combating land desertification.