Poyang Lake, Yangtze River Basin, China

Abstract

Poyang Lake is the largest freshwater lake in China. Five main tributaries drain into the lake from the south, while the lake empties through a short outlet channel into the Yangtze River. Poyang is one of the two lakes in the mid Yangtze Basin that has retained its free connection to the river. In addition, Poyang has a seasonal, reverse-flow system that occurs in most years where waters from the Yangtze River flow into Poyang Lake during part of the summer. This reverse-flow system greatly contributes to the complexity of Poyang’s yearly hydrological variation. In summer, the lake’s surface area exceeds 4,000 km². Falling water levels during autumn expose extensive mudflats and leave behind isolated sublakes. Dramatic hydrological variations – water levels can fall as much as 11 m between summer floods and winter lows – drive ecological processes within the system and create a wide range of habitats supporting rich biodiversity. The seasonal changes in water levels create two separate ecological phases of Poyang Lake, supporting different sets of species and leading to near year-round productivity and rich diversity of life. Poyang is world famous for its concentrations of wintering waterbirds, including over 98% of the world population of the Siberian crane Leucogeranus leucogeranus. Poyang Lake has major value for flood control, with maximum storage of some 11.75 billion m³, and provides valuable fish harvests. Changes in hydrology pose the greatest threat, while demand for water is growing for irrigation and industry. The Three Gorges Dam has reduced river flows during late summer and autumn. This change, combined with intensive sand dredging near the lake’s outlet, has resulted in faster outflow from the lake into the Yangtze River from July to March, and reduced water storage in Poyang Lake. In addition, a dam has been proposed across Poyang Lake’s outlet to stabilize water levels, which could transform the ecological character of the wetland and flood habitats used by Siberian cranes and many other waterbirds.