Special Column:Celebration of the 70th Anniversary of IGSNRR, CAS
LI Xiao-yan, XU He-ye, MA Yu-jun, WANG Jian-hua, SUN Yong-liang
In the recent years, Qinghai Lake has experienced severe declines in water level and its watershed is in an advanced state of ecological degradation, which resulted from both natural (climatic) and anthropogenic factors. However, information concerning human activities (e.g., land use/cover change) is scarce, therefore, it is necessary to know land use change and its effects on ecological degradation in the lake watershed. This would help us to have a better understanding of the effect of human activity on the processes of land degradation in the past and may enable the improvement of future planning strategies.Based on the multi-temporal remotely sensed data in 1977,1987,2000 and 2004, this study analyzed the land use change characteristics in the Qinghai Lake watershed from 1977 to 2004 and investigated the spatial difference of land use structures between different counties, by the using of transition matrix of land use types and land use dynamic degree. Then land use intensity in the Qinghai Lake watershed was calculated and compared with other typical regions in China. The conclusions of the study can be drawn as follows: (1) Land use change was characterized by constant land decrease for ecological function and land increase for production as well as degraded land from 1977 to 2004, for instance, the water body area decreased 292.70 km2 in the last 30 years. (2) The increase of farmland and sand derived respectively from occupying the grassland and transferring from the lake sand due to the decline of water level in the Qinghai Lake, the sand area increased 103.22km2because of the decline of water level from 1977 to 2004. (3) The changing rate of farmland area,residential area,sand area and forest area has been slowed down since 1977 while the water area decreased obviously from 2000 to 2004 (0.71%)and the grassland area changed slowly all the year round. On the whole watershed, the changing rate of all the land use types had the characteristics of interannual variation. (4) The differences of land use structures between four counties were obvious with most of the sand distributed in Haiyan (more than 70%),at the same time, Gangcha and Gonghe had 90% of forest and more than 95% of farmland of the whole watershed, moreover, changes of land use structures were various between these four counties. (5)The variation of land use intensity in the Qinghai Lake watershed was insignificant from 1977 to 2004 while the average value of integrated index is 186.47. The comparison of land use intensity between the Qinghai Lake watershed and other typical regions showed that human activity had little effect on the land use/cover change in this study region, so the related researches on regional environmental and ecological problems should pay more attention to the driving process of natural factors.
