Impact of the Three Gorges project on ecological environment changes and snail distribution in Dongting Lake area

Abstract

Background

The Three Gorges Dam (TGD) is a remarkable, far-reaching project in China. This study was conducted to assess the impact of TGD on changes in the ecological environment, snail distribution and schistosomiasis transmission in Dongting Lake area.

Methods

Hydrological data were collected from 12 monitoring sites in Hunan section of Yangtze River before and after TGD was established. Data on snail distribution and human schistosomiasis infection were also collected. Correlation analyses were performed to detect the significance of snail distribution to changes in ecological environmental factors and human schistosomiasis infection.

Findings

A series of ecological environmental factors have changed in Dongting Lake area following the operation of TGD. Volume of annual runoff discharged into Dongting Lake declined by 20.85%. Annual sediment volume discharged into the lake and the mean lake sedimentation rate decreased by 73.9% and 32.2%, respectively. From 2003 to 2015, occurrence rate of frames with living snails and mean density of living snails decreased overall by 82.43% and 94.35%, respectively, with annual decrements being 13.49% and 21.29%. Moreover, human infection rate of schistosomiasis had decreased from 3.38% in 2003 to 0.44% in 2015, with a reduction of 86.98%. Correlation analyses showed that mean density of living snails was significantly associated with water level (r = 0.588, p<0.001), as well as the mean elevation range of the bottomland (r = 0.374, p = 0.025) and infection rate of schistosomiasis (r = 0.865, p<0.001).

Conclusion

Ecological environmental changes caused by the TGD were associated with distribution of snails, and might further affect the transmission and prevalence of schistosomiasis. Risk of schistosomiasis transmission still exists in Dongting Lake area and long-term monitoring is required.

Author summary

Three Gorges Dam (TGD) is a tremendous hydrological project in China, it affects the ecological environment and influences the survival of animals downstream. The Dongting Lake is the first large lake that connects Yangtze River after it flows out of TGD, meanwhile, it accounts for 48% of the total snail habitation in China. Hydrological data from 12 monitoring sites, combined with data on snail distribution and human schistosomiasis infection, were used to assess the impact of TGD on ecological environment changes, snail distribution and schistosomiasis transmission in Dongting Lake area. Based on our analyses, following the establishment of TGD until 2015, the mean density of living snails in Dongting Lake area was under 5 snails/frame, and human infection rate of schistosomiasis declined to below 0.5%. As the impact of TGD on snail distribution and schistosomiasis prevalence in Dongting Lake area is much more complex in the real world, long-term monitoring and in-depth studies are still required.