Sample Unit Size And Sample Spacing Effects Of Oncomelania Snail On Its Spatial Statistics In The Marshland Schistosomiasis Epidemic Area In Nanchang, China

Oncomelania snail is the unique intermediate host of schistosomiasis. Based on the sample methods of “Push-broom” and “equal interval” on the Chayegang marshland in Poyang Lake. Using geo-statistical methods and exploring the spatial variation regulation in different sample unit size and sample spacing of the experimental sample plots. Geo-statistics is used to calculate the parameters Range, Nugget, Sill and Anisotropy at different sampling scales to obtain the characteristics of their spatial variance. And then we tried to analysis the spatial variation of oncomelania snails in different sample unit size and sample spacing.In November 2013, Combinations of different number of basic sampling units(cells) serve as spatial sample unit sizes. The results show there is obvious sample unit size effects. The Range has no relationship with the spatial unit size, but the Nugget and Sill are associated with the sampling unit size. The Nugget and the ratio of Nugget by Sill is inversely associated with sample unit size and the random fraction over total spatial variance decreases when combination of basic cell changes from 1×1 to 9×9. The nugget effect becomes stronger when combination of basic cells changes from 10×10 to 17×17, tallying with the semi-variogram theory. Otherwise, the Sill and the difference between Sill and the Nugget are the biggest when the spatial unit size is 8×8. The study implies that the possible optimal sample unit size for explaining the spatial autocorrelation may be at combinations of 8×8 to 10×10 cells for the field.In November 2014, An "equal interval" method is used to survey the Oncomelania snail data and coverage and height data of vegetation in an experimental field. Combinations of different number of basic sampling units(cells) and different sample spacing serve as spatial sample unit sizes. The results also show there is obvious sample unit size effects. It need enough sample quantity to access the spatial variation information.In a word, when in the survey sampling should clearly choose the appropriate sample unit size.