Research On The Spatial Quantitative Relationship Between Distribution Of Snails And Environmental Factors

Schistosomiasis is a zoonotic parasitic diseases. It seriously harms to people's life, health and security. It can also indirectly causes unnecessary economic losses to local people. Oncomelania is the unique intermediate host of Schistosoma. Studying the environmental conditions of the snail breeding and finding out the erlated environmental factors have very important effect and social value for eliminating the snail.After the field survey, we selected a marshland(310m * 350m) for the study area, and fixed the 1085 sampling points in the study area. Systematic sampling survey of the snail count number, plant species coverage & height, soil temperature, humidity, electrical conductivity, elevation was carried out in the Chayegang marshland near Henghu farm of Xinjian Country in the Poyang Lake region. Ten established GIS layers were selected as the snail-breeding inductive environmental factors. GIS spatial analysis, Certainty factor method and Weight of evidence method were used to study the snails' relationship with the ten environmental factors. The results show:1) Research by certainty Factors probability model shows that: the snail tends to distribute in the environments of: A the coverage above 16% and height above 80 cm of miscanthus sacchariflorus; B Carex coverage less than 30%; C soil conductivity below 0.09 mS / cm; soil temperature range of 16 ?-19 ?; Soil humidity range of 0.27-0.34%(m3 / m3); E Elevation beyond of 15 m. Results show the factors of height of miscanthus sacchariflorus, coverage of Carex, soil conductivity, height of Carex, soil temperature, soil moisture, Elevation and coverage of miscanthus sacchariflorus control the spatial distribution of the number of snails. Finally through the inspection it was found that high prone and extremely high prone areas accounted for 23.4% of the total area predicted 94.7% high density area of snails. It shows that the model can well predict the presence of absence of the snails.2) Research by weights of evidence method shows that: The factors of Elevation, soil moisture, Carex,miscanthus sacchariflorus, soil conductivity and soil temperature control the spatial distribution of the number of snails. In a certain range,(1)with the increase of elevation, the snail are much more easy to breed;(2)In high humidity environments, there are less snails of distribution;(3)Too dense or sparse of Carex will go against the distribution of snail;(4)Snails is relatively easy to breed in dense miscanthus sacchariflorus area;(5)In high conductivity area, there are fewer snails;(6)Temperature in 16 to 20 degrees there are more snails of distribution. Through the inspection it was found that high prone and extremely high prone areas accounted for 13.7% of the total area predicted 82% high density area of snails. It shows that the model can also well predict the presence of absence of the snails.3) Two methods of predicting area overlap rate is as high as 80.39%.Their prediction results are highly consistent. Both methods can be well applied to predict of propagation of oncomelania.