[Analysis of relationship between natural death of Oncomelania hupensis snails and water level in Eastern Dongting Lake district].

Objective: To study the reasons of natural death of Oncomelania hupensis snails by comparing the differences of the indicator days covered with water (DCW) in snail marshland and non-snail marshland around the build of Three Gorges Dam in Eastern Dongting Lake areas.

Methods: Two marshlands were selected, one was a non-snail marshland (Qianliang Lake) and another was a snail marshland (Junshan Park). The measuring points were set through the mechanical sampling. The snails and elevation of the points were surveyed, and the data of the water levels from the hydrological station were collected, and then DCWs were calculated.

Results: From 1995 to 2013, DCWs of the marshland of natural death of snails were all more than that of the snail marshland (P < 0.01). In Qianliang Lake marshland, the difference between DCW before natural death and DCW from natural death until the dam was not significant (P = 0.23), while DCWs of the two stages both were more than that after the dam (P1 = 0.045, P2 = 0.002). Before the build of the dam, DCW of the Qianliang Lake marshland of natural death of snails was more than that after the build of the dam (P = 0.013), and there was the same situation in Junshan Park marshland (P = 0.005). The relationship between snail density and DCW was not significant in Junshan Park marshland (r(s) = 0.008, P = 0.914), and the reference range of DCW of all the measuring points was 76-251 days.

Conclusion: In the eastern Dongting Lake district, the build of Three Gorges Dam and DCW may be not the direct factors affecting the natural death of snails and the latter may change the distribution of snails.