I. Introduction
Wetlands are a unique ecosystem on Earth, as they are located at the interface between aquatic and terrestrial ecosystems. Wetlands are known as the “kidney of the earth” because of their rich biodiversity and productivity [1], [2]. In addition, wetlands do not only provide resources for living and manufacturing such as grain, meat, fish, medicinal materials, energy resources and industrial materials, but also play an important role in water restoration, flood control, pollutant removal, regional climate regulation and biodiversity protection [3], [4]. However, large areas of wetlands have been damaged due to the pressures of economic development and population explosion. As a result of the shrinking of wetlands, these ecosystems are deteriorating each year. In China, 50,360 , approximately 14% of total wetlands were lost between 1990 and 2000. Most of these losses are due to the conversion to agricultural and farm lands [5]. Recently, the value and importance of wetlands conservation have been recognized, and many countries have taken measures to protect wetlands by formulating relevant laws and establishing wetland nature reserves [6].