Hydrological regime change and its ecological responses in East Dongting Lake, China

Abstract

Extent, frequency and duration of lake water level fluctuations (WLF) are dominant forces controlling the functioning of lake ecosystems, especially in the lake's littoral and aquatic-terrestrial interface processes. In East Dongting Lake, Carex life history synchronize the arrival of overwintering birds, Carex meadow provide vital wintering ground for migratory waterbirds, especially for the Lesser White-fronted Geese. However, significant changes had taken place in the hydrological regime of East Dongting Lake and our research showed it caused chiefly by sediment deposition in the lake basin and the replenishment of the Three Gorges Dam. The annual lowest water level of the East Dongting Lake had gradually risen and the annual water level amplitude had decreased obviously over the past 60 years. Since the operation of the Three Gorges Dam, the average water level increased significantly from January to June. The Three Gorges Dam holder the incoming water from late September to late October that the status will change from flood control limited water level to normal water level, meanwhile the water level of East Dongting Lake declined significantly through the same duration, especially in October. The operation of the Three Gorges Dam decreased flooding days in the areas above 22-m elevation, resulting in lowering of the minimum elevation of vegetation-covered area and synchronous downward movement of vegetation distribution pattern. As the timing of water level recession at elevations of 24–27 m were 12, 17, 19 and 16 days earlier than that in 1981–2002, the optimum elevation for Carex growth decreased from 25–26 m to 24–25 m. After the operation of the Three Gorges Dam, the annual reversal times of water level increased significantly, which is not conducive to the formation of stable habitat and the utilization of resources by organisms.