The Influence Of The River-lake Relation Change On The Dongting Lake Wetland Ecology Evolution And Its Regulation

The middle and lower parts of Yangtze River Basin are rich in water resources and are densely covered with rvers and lakes. The river-lake relations, whose major point is storage and discharge of water and sand, influence processes of water resource and water ecology and water environment and so on. Dongting lake is the important taking in and sending out lake in the middle and lower parts of Yangtze River Basin. The water of Dongting lake comes from four rivers, which are Xiangjiang River, Zishui River, Yuanjiang River and Lishui, and three entrances, which are Songzi, Taiping, Ouchi. The scouring, deposition and storage of the lake are seriously influenced by the river-lake relations. Under the influence of climate change and regional water and soil resource exploitation, especially the operation of the Three-Gorges Project, the river-lake relations have notably changed and have formed new river-lake relation pattern. This new pattern directly influences the water level change of Dongting lake and then influences the scale and structure of the lakeside wetland types. The change of lakeside wetland types will be the major study point as the ecologic sensitive regions.The river-lake relations directly influence the water level change of Dongting lake. This paper analyzed the lake’s water level change inter-annual and within the year and quantified the factors’ influences. For the inter-annual water level change, it can be divided into three parts:the lower water level in1960s to1980s, for the inning’s damaging effect; the higher water level in1980s to2000s, for the reducing rate of the lake area and volume slowing down; the dropped water level after2000, especially after2003, largely for the influence of the Three-Gorges Project. For the change within the year, the amplitude of water level variation has reduced; for the monthly variation:the water level in December to March in dry season has increased notably, and the water level in October to November has reduced. The water level in dry season is most influenced by the four rivers, while the water level in flood season especially in August to October is most influenced by the three entrances. The influence of precipitation is relatively not notable and the precipitation’s influence in May to August is above normal.The river-lake relations cause the water level change of Dongting lake, which then influence the scale and structure of lakeside wetland. The paper analyzed the lakeside wetland area change from1960to2008with the data of water level and lakebed elevation and analyzed the scale and structure change of lakeside wetland types before and after the operation of the Three-Gorges Project (2000and2005). For the scale change of lakeside wetland, the water-level-fluctuating zone area from1960to2008was analyzed, which is calculated by the submerging area between the largest and lowest water level. Studying the lakeside wetland types of lake, river, bottomland, marsh, paddy field and reservoir-swag locating in and out of water-level-fluctuating zone, shows that the overall area of lakeside wetlands has little change while the area within the fluctuating zone has reduced, in which the bottomland and marsh transferred over the fluctuating zone. The elevation location change of bottomland, marsh and paddy field, was studied, which showed that the paddy field area reduced in each elevation section, while bottomland and marsh area in the main section hasd not increased.The wetland ecology protect objection should consider the natural evolvement rule and the society economy demand. For natural evolvement rule, the paper set the level of1980s to2000s as the protect objection, in which the water level is23.3m and the water-level-fluctuating zone area is2538km2. For the ecology sensitive region such as natural preservation areas, the wetland type and elevation distribution should be considered. The bottomland and marsh area protect object is574km2and362km2within the water-level-fluctuating zone, which is the data in2000. For the society economy demand, the water level change and the influence of the Three-Gorges Project on the lake’s water level were analyzed to adjust the discharge of the project.