Monitoring Wetland Changes on the Source of the Three Rivers From 1990 to 2009, Qinghai, China

The source of The Three Rivers is located in Qinghai-Tibet Plateau, has the richest wetland resources in China. Large areas of the wetlands in this region have diminished because of various factors. Based on a total of 72 Landsat Thematic Mapper (TM) and Landsat Enhanced TM Plus (ETM) images covering three periods of 1988-1991, 2003-2005 and 2008-2009, wetland changes were monitored and analyzed. In this paper, wetland information was extracted from the images acquired using object-oriented classification; and visual interpretation with the aid of geological maps, geomorphologic maps, topographic maps, land use maps, and lake-river thematic data. Results indicated that the wetland resource of the Source of The Three Rivers has declined by 14.13%, from 31,773.96 km² in 1990 to 27,284.7 km² in 2009. The overall accuracy for wetland in three years were 88.66%, 92.16%, and 91.53%. Each wetland type has changed considerably in the past twenty years. Further investigation showed that the annual loss of wetlands has decreased over two periods from 252.39 km² yr^-1 (1990-2004) to 140.7 km² yr^-1 (2004-2009). Furthermore, there is an indication that the wetland ecosystem in the source area of The Three Rivers is gradually recovering.