A research team led by Professor XIE Yonghong from the Institute of Subtropical Agriculture of the Chinese Academy of Sciences has found that hydrological conditions at the outlet are the key driver of vegetation succession following the Three Gorges Project in Dongting Lake. 

Their new findings were published in Ecological Indicators.

Due to the combined effects of global climate change and human activities, the hydrological regimes of river and lake ecosystems, as well as the vegetation patterns of floodplain wetlands, are undergoing significant changes. These changes have led to reduced lake water resources, weakened river-lake connectivity, and wetland vegetation degradation. River-connected lakes regulate water exchange between rivers and lakes via their inlets and outlets, playing a crucial role in maintaining regional ecological balance.

The Three Gorges Dam (TGD), the world's largest hydraulic project, has significantly altered the hydrological environment of the middle and lower Yangtze River since its impoundment in 2003. This has had a particularly significant impact on the hydrological conditions and vegetation patterns of Dongting Lake, a typical river-connected lake downstream.

To evaluate these effects, the researchers analyzed long-term hydrological monitoring data, remote sensing imagery, and simulations generated using the MIKE 21 hydrodynamic model. The researchers examined spatiotemporal variations in inundation and vegetation patterns in Dongting Lake before and after TGD operation. They also evaluated the contribution of hydrological conditions at the lake's inlets and outlets to vegetation changes.

Their results show that TGD operations have significantly reduced the water discharge from the three channels and the water level at the outlet. This caused a decrease in inundation duration and depth, particularly in east Dongting Lake.

Concurrently, the area of vegetation expanded and shifted toward the center of the lake, with the area of reeds increasing and encroaching on the area of Carex. This change occurred because Carex and reed have optimal inundation durations of 132–240 days and 110–186 days, respectively; furthermore, reed exhibited a greater competitive advantage under the reduced water level.

Furthermore, the reduction in the outlet's water level was determined to be the primary factor affecting vegetation succession in Dongting Lake after the TGD operation.

This study highlights the role of lake inlets and outlets in governing vegetation distribution in river-connected lakes. The findings provide a scientific basis for predicting vegetation dynamics and ecological restoration in river-connected lakes impacted by dams.