Poyang Lake Morphological Characteristics And Its Response To Runoff And Sediment Of Poyang Lake Basin

Poyang Lake is one of the important lakes in the mainstream of Yangtze River. It plays a large part in flood storage, biodiversity protection of Yangtze River basin and so on. Poyang Lake wetland is one of the 7 wetlands of international importance in China, and one of the global important ecotopes demarcated by World Wildlife Fund as well. Poyang Lake is an essential part of global ecosystem. Therefore, study on Poyang Lake is significant to guarantee the regional, national and even international ecological security.Dongting and Poyang Lake are the only two lakes still linked with the Yangtze River in the middle and lower reaches, and are playing a very important part in the regional flood storage. The area of Dongting Lake has decreased rapidly since 1950s. Compared with Dongting Lake, Poyang Lake is shrinking slowly but still getting small obviously. Therefore, this paper simulates the runoff, sediment load and the response of lake area and volume to them, based on the morphological characteristics change of Poyang Lake, the trend and persistence/antipersistence of land use, precipitation and vaporation of Poyang Lake basin in recent 50 years. Then the lake area and volume in the future are predicted quantificationally, when land use and climate condition changes. All these works could provide scientific references for improving the decrease of lake area and volume, maintaining its flood storage capacity, coordinating and handling the relationship among the five rivers, Yangtze River and Poyang Lake. They also could make up the deficiency of the research on morphological characteristics of Poyang Lake.The area and volume are decreasing gradually in recent 50 years, especially the area above 14m and volume above 16m reduce obviously. The shoreline has become shorter and simpler. After 1990s, the change of area and volume gets stable, while the shoreline changes more significantly. The impact factors on lake morphology of Poyang Lake region mainly include soil erosion and inning. The other part of Poyang Lake basin changes the lake form through the direct influence of natural conditions and human activities on runoff and sediment load getting into the lake. Precipitation and vaporation are the primary factors affecting the runoff, and rainfall, runoff and land use dominate the sediment load changes.On the basis of vaporation, precipitation and land use in Poyang Lake basin, runoff output-and-affluence theory-based C++ program, wavelet v-support vector machines and adaptive and normal mutation particle swarm optimization are used to simulate the runoff, sediment load getting into the 6 hydrological stations and the response of lake form to their change. It shows that the daily flow simulated is consistent with the observed values. The annual runoff simulation is high in precision and the error principally comes from the original data itself and the ignorance of complicated natural conditions. The relative error ranges of sediment load and form response simulation are±1%. Model composed of wavelet v-support vector machines and adaptive and normal mutation particle swarm optimization fits much better than BP neural network and multiple linear regression.Land use transition matrix of Poyang Lake basin shows that cover areas of different land use types convert frequently from 1990 to 2000. The most obvious transition occurs among grassland, paddy, forest, irrigated field and built-up land. The area change amplitude of water is smallest and that of built-up land is greatest. Unused land mainly coverts to forest, irrigated field and built-up land and the area converted to built-up land is largest. The transition of unused land to all the three types will result in decrease of lake area and volume either in dry year or normal year. When it converts into forest, the area and volume change slightly; when it converts into irrigated field and built-up land, especially the latter, the lake area and volume decrease significantly.Mann-Kendall test and R/S method are used to analyze the change trends and persistence/antipersistence of annual vaporation, annual and flood season precipitation in Poyang Lake basin. As a result, in recent 50 years, the annual precipitations of all the stations have increased and most of the stations show persistence on 3 different time scales of 3,5 and 10 years; the flood season precipitation of the stations change differently and all of them show persistence on 3 time scales; the vaporation has decreased obviously and all the stations show persistence on 3 time scales. The persistence levels of vaporation are similar on 3 time scales. The daily variations of different persistence/antipersistence classes are determined based on the extreme change of precipitation and vaporation in recent 50 years, and then the new data are input into the 3 models. It indicates that the lake area and volume may increase either in the next 3 or 10 years. In the land use conditions of 2009, Poyang Lake area at Hukou station's water level of 21m will vary between 3441.69 and 4330.22km2, and the volume will vary between 253.37 and 280.69X 108 m3 in the next 3 years; in the next 10 years, the variance of area will range from 3974.37 to 4450.07 km2, and that of volume will range from 262.17 to 290.71 X 108m3.The conclusions of this paper indicate that land use type changes the lake form mainly in terms of the sediment load, while the impact of precipitation and vaporation on Poyang Lake morphology primarily comes from the direct influence of runoff. Besides, the variation of natural condition in the future will not lead to the decrease of lake area and volume. It is the change of land use types that may make the lake get smaller.