Studies On Ecological Environment And Protection Strategies Of The Dongting Lake Wetland

Abstract: The Dongting Lake is located in the middle reaches of the Yangtze River, with a total surface area of 2 684km2, a maximum volume of 17.4 billion m3(at the water level of 32.00m in Chenglingji), a mean depth of 6.7m, a maximum depth of 30.8m, and an average runoff of 312.6 billion m3. It is a flood-path lake, holding the water from 4 rivers, namely the Xiang River, the Zi River, the Yuan River and the Li River, and connected to the Yangtze River in Chenglingji. From 1956-1998, the average yearly sand amount entering the Dongting Lake was 167.2 million tones, among which 129.0 million tones came from the Yangtze River, accounting for 79.3% of the total, and 29.8 tone from the above-mentioned 4 rivers, amounting to 18.3% of the total. The average yearly sand amount flowing out of the lake from Chenglingji was 42.0 million tones, amounting to 25.8% of the total inflow sand amount. The annual sand deposit in the lake was 120.7 million tones, amounting to 74.2% of the total flowing-in sand total. From 1952-1995, the lake bed increased 1.06m, with an increasing rate of 2.41cm/a. The drawdown area of the lakes fluctuated significantly. It was 1 600-2 200km2 in the low water years, amounting to 67%-85% of the total lake surface area; 1100-1500 km2 in common water years, amounting to 44%-57% of the total; and less than 500km2 in high water years, amounting to less than 20% of the total. When the water level reaches over 32m in Chenglingji, all the drawdown area will be submerged. The wetland is particular in geographical environment and structure, and composed of open water zone, seasonal submerged zone and lowland zone, with an area of 0.877 million hm2. a lot of combined reasons, such as effects of human activities on the land and the lake, sand deposit increase, over-enclosure of the lake, and non-rational agricultural arrangement and culture system, have resulted in the decrease of the wetland area and flood control capacity, increase of flood level and disaster opportunities, and combination of over-exploitation and under-exploitation. In order to rationally develop the wetland resources, it is necessary to strengthen the whole management of the wetland, control the scale of development, return the enclosed parts to the lake, adjust the agricultural arrangement and culture system, and build a highly efficient combination wetland ecosystem. Sustainable development and conservation of the wetland should be completely considered.