Wetlands dynamics in Yinchuan Plain, China from 1989 to 2009

Wetlands, as a basic source to maintain agriculture and oasis ecosystem, is important to Yinchuan Plain, which locates in arid and semi-arid areas of northwest of China. To protect, manage and rationally develop wetland resources, three scenes of Landsat TM and ETM+ images, acquired in 1989, 1999 and 2009, were used to classify wetlands in Yinchuan Plain by hierarchical and object-oriented classification methods. With the classification results, the dynamic changes of wetland from 1989 to 2009 were analyzed, including the spatial distribution characteristics and the temporal evolution of wetland landscape pattern, the changes between wetland and non-wetland, and the changes between natural and artificial wetlands. The results show that, from 1989 to 2009, the wetland ecological system of Yinchuan Plain had great changes. In recent 20 years, the wetland area was halved from 656.45 km2 to 332.56 km2. The natural wetland area had a sharp reduction, especially the area of Yellow River, decreasing from 342.42 km2 to 98.13 km2, whose average annual decreasing rate was 6.59% in 1989-1999. The area of natural wetlands dominated in 1989, accounting for 75%, but the percentage was less than 60% in 2009. The area of artificial aquaculture was doubled from 30.51 km2 to 70.3 km2 in recent 20 years, especially developed in 1999-2009, in which the average annual increasing rate was 6.24%. Most of the decreases of natural wetlands were reclaimed to agricultural land, aquaculture land and other land use. The wetlands landscape change pattern is the interactional
result of climate warming, the inflow decrease of yellow river, population increase and economic development.