Abstract:

As the largest freshwater lake in China, the largest wetland in Asia and an important ecological zone in the world for migrating birds, the Poyang Lake plays important roles for ecology, human life and produce. The Poyang Lake has important function on sustaining biodiversity, regulating flood, providing water for the midstream and downstream of the Yangtze River, and is strategic significant for regional and nationwide ecological safety. But it experienced significant changes in recent years under the pressure of global climate change and human disturbance, for example, the frequency of flood and drought increased, causing predicament for the habiting of fishes, migrating birds and finless porpoises, also for shipping, human fetching drinking water. The implement of Ecological Economic Zone Program of Poyang Lake, and the plan of Poyang Lake EcoHydraulic Project, brought new challenges and pressures for ecosystem of the Poyang Lake. Since the change of water level in the Poyang Lake had close relationships with birds migrating, ecological scene, and the development of fisheries, it was essential to study the change of water level for the health of the Poyang Lake ecosystem and the sustainable development of Poyang Lake Ecoeconomic Region, while existing researches mainly aimed to the runoff characteristics in Poyang Lake Basin, seldom focused on the water level. This paper investigated the trend and cyclical characteristic of water level in the Poyang Lake and obtained qualitative and quantitative analysis, employing the MannKendall method and maximum entropy spectral method, basing on water level data in the past 51 years (1962-2012) of Tangyin Hydrological Station, which located in an island surrounded by water in the center of the main body of the Poyang Lake. Almost 55% of inflow water of the Poyang Lake pass nearby this island. Both in highwater period and lowwater period, the water level data of Tangyin Hydrological Station had good representation for the Poyang Lake. The results show as follows. 1)The annual average water level and the annual highest water level had no significant changing trend, and the annual lowest water level had significant downward trend. 2) The mutation point of annual mean water level and the annual highest water level was the year of 2005, and the late mutations were transferred to weak downtrend; the mutations point of annual minimum water level was between the year of 2003 and 2005, and the downward trend was more obvious during the late mutation. Moreover, there were significant decreasing trends especially since the year of 2010. 3) The annual average water level was with 25-26 a in the first cycle, 6-7 a in the second main cycle, 11 a, 12 a, 16 a in the third main cycle; there were 19a cycles in the annual highest water level; there were 6a in the first main cycle in the annual minimum water level, and 16a in the second main cycle. 4)The next ten years, the flood will be without a rising trend, and the flood inundated area will not expand; the low water level will be lower, the dry time will come into being in advance, the disappear of dry time will delay, and the problem of water shortage in extended urban area and shipping will be more serious