A research team led by Professor Xie Yonghong from the Institute of Subtropical Agriculture, Chinese Academy of Sciences has found that the Hydrological condition at the outlet is the key driver of vegetation succession after the Three Gorges Project in Dongting Lake. 

Their new findings were recently published in Ecological Indicators.

Under the combined influence of global climate change and human activities, the hydrological regimes of river and lake ecosystems and the vegetation patterns of floodplain wetlands are undergoing profound changes. This has led to issues such as reduced lake water resources, weakened river-lake connectivity, and degradation of wetland vegetation. River-connected lakes regulate the water exchange between rivers and lakes through their inlets and outlets, playing a crucial role in maintaining regional ecological balance. 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, particularly impacting the hydrological conditions and vegetation patterns of Dongting Lake, a typical river-connected lake in the downstream.

Long-term hydrological monitoring data, remote sensing imagery, and MIKE 21 hydrodynamic model were utilized to analyze the spatiotemporal variations in inundation and vegetation patterns in Dongting Lake before and after the TGD operation. At the time, the contribution of hydrological conditions at the lake inlets and outlets to vegetation changes were evaluated.

The results indicated that the TGD operation 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 vegetation area expanded and shifted toward the lake center, with Reed area increasing and encroaching on Carex. The change occurred because Carex and Reed have optimal inundation durations of 132–240 d and 110–186 d, respectively, and Reed exhibited greater competitive advantage under reduced water level.

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

The findings pay attention to the role of lake inlets and outlets in governing vegetation distribution in river-connected lakes. "These findings provide a scientific basis for predicting vegetation dynamics and ecological restoration in river-connected lakes impacted by dams." Professor Xie Yonghong, the corresponding authors of the study said.

Contacted: Xie Yonghong

EMail: yonghongxie@163.com