[Impact of environmental changes on Oncomelania snail distribution in Dongting Lake beach]

To study the impact of environmental changes on the distribution and the growth and decline of Oncomelania snails in Dongting Lake beaches after the implementation of Three Gorges Project.

T-embankment of Junshan District where there was a greater human factor related to the snail spread and a lake beach named Dongkou of Junshan District where there was a less human factor related to the snail spread were selected as study areas. The various ground elevations were measured and the high points were marked with GPS. The height of vegetation was surveyed regularly, soil moisture content and micro-environment temperature and humidity at different elevations in the lake beaches were detected, and the snail distribution was investigated. Both the longitudinal and retrospective studies were conducted.

In 1993, the soil was taken from the lake beach at the elevation of 25 m to build an isolated canal, and this made snail density decline year by year, and no snails have been found since 1998. The elevation of the vegetation in the T-embankment was significantly lower than that in Dongkou, and there was no high rod plant growth. The snails were found in the elevation from 23.5 to 26.5 m where the vegetation was mainly Cyperus spp. The growth of the vegetation was 16.0 to 54.0 cm 30 days after flood withdrew, and the vegetation reached the highest density 60 days after flood withdrew. The snail density was highest at the elevation from 24.5 to 25.5 m, and the elevation of snails and their eggs was lower than that in 1980s. In the dry season, the water content of the soil in Dongkou was from 46.80% to 52.20%, which was more than that in T-embankment, while at the elevation over 26.0 m, the water content was from 21.36% to 29.77%, which was equal to that in T-embankment.

Three Gorges Project plays an important role in the control of water level of Dongting Lake, but there is no impact on the snail reproduction and density.