Dynamic Changes of Plateau Wetlands in Madou County, the Yellow River Source Zone of China: 1990-2013

Plateau wetland is a special kind of ecosystem highly vulnerable to change and shrinkage owing to natural fluctuations and external disturbance. In the past wetlands have been mapped as a single category, making it difficult to assess the relative importance of natural and anthropogenic variables in the change. In this study, wetlands in Maduo County in the headwater zone of the Yellow River were mapped into six types based on their hydro-geomorphic properties from Landsat satellite images of 1990, 2001 and 2013. The changes between wetlands and non-wetlands in two separate decades were detected from the produced wetland maps in ArcGIS. The obtained results indicate that there were 8542 km(2) of wetlands (about 33 % of the county's territory) in 1990. They shrank to 7,061 km(2) in 2001, but expanded to 7,972 km(2) in 2013. During 1990-2001 all six types of wetland suffered a loss, with alpine wetland shrunk the most, followed by piedmont wetland. In general, the higher the ground at which a wetland was located, the more it lost. This trend of decrease was reversed in almost the same order during 2001-2013. Namely, the higher the ground of the wetland, the more it gained. Analysis of climate data suggests that temperature is not critical to the observed change in wetland area. Instead, it is the warm season rainfall that has exerted the most influence over the observed change. Population bears no clear relationship with wetland change. The reduced sheep population by 54.5 % during 2001-2013 helped to improve the eco-environment of the study area and to reverse the shrinking trend of wetlands.