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 rs=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.

Objective To study the reasons of natural death of Oncomelania hupensis snails in marshland by comparing the differences of environmental factors between snail marshland and non-snail marshland in East Dongting Lake schistosomiasis en-demic areas. Methods Two adjoining marshlands were selected,one was a snail marshland and another was a non-snail marsh-land. The measuring points were set by grid of“20m × 20m”. The soil moisture,elevation,soil pH and temperature of the points were measured,and the snails of the points were surveyed. Results The elevation,soil pH and temperature of the snail natural death marshland were all lower than those of the snail marshland(P<0.01). The soil moisture,elevation,soil pH and temperature of different snail densities in the snail marshland were different(P<0.05). The soil moisture of the non-snail group was higher than that of other four groups(P<0.01)and the soil moisture of the group with 0-11 snails per frame was lower than that of other four groups(P<0.01). The elevation of the group with 0-11 snails per frame was lower than that of the group with 24-39 snails per frame and the group with more than 39 snails per frame(P<0.05). The soil pH of the group without snails was higher than that of other four groups(P<0.01)and the soil temperature of the group with 0-11 snails per frame was lower than that of the group with 24-39 snails per frame. The differences of soil moisture and elevation of different death snail densities were not significant, while the differences of soil pH and temperature were significant. The soil pH of the non-snail died group was higher than that of the 2-died,3-died and more than 3-died groups(P<0.05). The soil temperature of the non-snail died group was higher than that of other four groups(P<0.05). Conclusion The elevation,soil pH and soil temperature within the range of the research may be the factors affecting the snail natural death and the soil moisture,elevation,soil pH and soil temperature may be the factors affect-ing the distribution of snails.

Objective To understand the distribution of univalvia molluscs in Eastern Dongting lake area where the Oncome-lania hupensis is extinct,so as to explore the causes of extinction and to provide the evidence for formulating schistosomiasis con-trol strategy. Methods The univalvia molluscs of the Qianliang Lake district,Jianxin District and Junshan Park were investigat-ed in August of 2013. All the collected snails were classified and identified. The data were analyzed by using the method of Shapiro-Wilk normality test and non-parametric test. The ecological biodiversity differences from each district were compared by the biodi-versity indexes. Results The univalvia molluscs collected were from 6 species in 3 families in Gastropoda class,namely Oncome-lania hupensis Gredler in Pomatiopsidae family,Parafossarulus striatulus,Alocinma longicornis,Parafossarulus sinensis,Bithynia fuchsisana in Bithyniidae family,and one genus provisionally named Radix in Lymaneidae family. In Junshan Park ,a total of 4 553 snails were collected,among which 1 264 were Oncomelania snails. In Jianxin District,336 univalvia molluscs were collect-ed,and no Oncomelania snails were found. In Qianliang Lake district,there were only 7 Alocinma longicornis snails,2 Parafossa-rulus sinensis snails and 1 Parafossarulus striatulus snail collected. There were significant differences among the distributions of the samples from the three districts(χ2=166.225,P<0.01).The Simpson’s diversity indexes in Qianliang Lake area,Jianxin Dis- trict and Junshan Park were 0.402 8,0.718 6 and 0.678 8,respectively,and the Shannon-Wiener indexes of the 3 areas were 0.721 5,1.431 3 and 1.199 9,respectively. Conclusions With the extinction of Oncomelania snails,the species and quanti-ties of other snails become rare in Qianliang Lake area. Whether their causes are relevant is worth further studying.