Land cover change and its environmental impact in the Upper reaches of the Yellow River, Northeast Qinghai-Tibetan Plateau

摘要

Many studies have focused on desertification processes in northern China in an attempt to understand desertification-related ecological problems. Desertification on the Qinghai-Tibetan Plateau has received little attention, even though desertification resulting from overgrazing is a widespread phenomenon there. This study focuses on the Gonghe Basin in the upper reaches of the Yellow River, located on the northeast Qinghai-Tibetan Plateau, to shed light on desertification processes and associated environmental impacts during a 10-year period from 1987 to 1996. We first used 2 thematic mapper images to classify land cover for 2 summers (1987 and 1996) into 9 land cover types related to desertification. To assess the severity of desertification and to calculate the total soil carbon emission caused by desertification, we first defined severity by comparing land cover differences between 1987 and 1996 and then determined the differences in organic carbon content of the soil in grasslands during different stages of desertification between 1987 and 1996. The results showed that about 240 km(2) of grasslands was lost to agricultural encroachment and about 190 km(2) became sand-covered area between 1987 and 1996. During the same period, desertification affected 569.6 km(2) of grasslands, with desertification assessed as very severe for 41.8%, severe for 15.1%, and Moderate for 43.1% of the area, The results also show that carbon emissions from grassland deterioration caused by desertification amounted to 2.06 x 10(6) tC during the 10-year period, the average annual emission rate being 0.206 x 10(6) tC.