The estimated total area of wetlands in China is 11 million ha. Using the genesis classification system, combined with a knowledge of China's wetlands, one can divide the wetlands in China into three main categories: eutrophic, mesotrophic and oligotrophic. The distribution of China's wetlands basically coincides with the distribution of wetlands in the world. Wetlands are concentrated in the frigid temperate zone and the humid area of the temperate zone. They are also widely distributed in mountains and plateaus. Generally, wetlands occupy flat or gently sloped areas with plenty of water. They have high biological productivity and resource potentiality, so they can be used for agriculture, forestry, animalhusbandry, and fisheries. Wetlands have also been reclaimed into rice paddies, pastures, forest land and reed production bases. In order to develop wetlands comprehensively, "dike-pond" systems and "field-pond" systems have been established in China. Complex paddy-reed-fish systems have brought about ecological and economic benefits. Ecologically, wetlands can not only play a role in flood control, water storage and climate regulation, but they can also purify water, improve soil, and increase the species and number of wild animals. On the one hand, wetlands can be developed and utilized; on the other hand, some wetlands should be conserved in a natural state.
THE DISTRIBUTION OF WETLANDS IN CHINA
In China, the total wetland area is estimated to be approximately 11 million ha. Wetlands discussed in this article include marshes, swamps and bogs. On a global scale, wetlands of the northern hemisphere are concentrated in the forest and forest tundra of the frigid zone and the forest steppe of the temperate zone (Fig. 1). The distribution of China's wetlands basically coincides with the distribution of wetlands in the world. Wetlands are concentrated in the frigid temperate zone and humid area of the