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Sample Unit Size Effects of Oncomelania hupensis snail on Its Spatial Statistics in the Marshland schistosomiasis Epidemic Area in China
Science Discovery
Volume 4, Issue 3, June 2016, Pages: 165-172
Received: Jul. 1, 2016; Published: Jul. 5, 2016
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Authors
Liu Qing, School of Geography and Environmental Sciences, Jiangxi Normal University, Nanchang City, China
Zhao An, School of Geography and Environmental Sciences, Jiangxi Normal University, Nanchang City, China; Key Laboratory of Poyang Lake Wetland and Watershed Research, Ministry of Education, Jiangxi Normal University, Nanchang City, China
Ma Yukuan, School of Geography and Environmental Sciences, Jiangxi Normal University, Nanchang City, China
Li Cui, School of Geography and Environmental Sciences, Jiangxi Normal University, Nanchang City, China
Zhang Wenxin, School of Geography and Environmental Sciences, Jiangxi Normal University, Nanchang City, China
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Abstract
Analysis of multi-scale spatial variance and anisotropy was the crucial that should be taken into consideration in optimization of spatial sampling. The aim of this study was to analyse the effect of sampling unit size on perception of spatial variance of Oncomelania snail, the unique schistosomiasis intermediate host. A "push-broom" method was used to investigate Oncomelania snail density in an experimental field, south-western Poyang lake, China, obtaining 22,500 sample cells distributed continuously whole-covered on a square of 50m*50m. Combinations of different number of basic sample cells served as spatial sample unit sizes (sample cells from 1*1 to 17*17). Geo-statistics was used to calculate the parameters range, nugget, sill of anisotropy variograms for different sample unit sizes to obtain the characteristics of their spatial variance. The results showed that the spatial variance had obvious sample unit size effects. The range had no relationship with the spatial unit sizes (about 50m), but the nugget and sill were associated with the sampling unit sizes. The nugget and the ratio of nugget by sill were inversely associated with sample unit sizes and the random fraction over total spatial variance decreases when sample unit sizes changed from 1*1 to 9*9. The nugget effect became stronger when sample unit sizes changed from 10*10 to 17*17, tallying with the semi-variogram theory. Otherwise, the sill and the difference between sill and the nugget were the biggest when the spatial unit sizes was 8*8. The study implied that the possible optimal sample unit size for explaining the spatial autocorrelation might be at combinations of 8*8 to 10*10 cells for this study field. In conclusion, when in the survey sampling should clearly choose the appropriate sample unit size.
Keywords
Oncomelania snail, Sample Unit Size Effects, Spatial Variance, Geo-statistics
To cite this article
Liu Qing, Zhao An, Ma Yukuan, Li Cui, Zhang Wenxin, Sample Unit Size Effects of Oncomelania hupensis snail on Its Spatial Statistics in the Marshland schistosomiasis Epidemic Area in China, Science Discovery. Vol. 4, No. 3, 2016, pp. 165-172. doi: 10.11648/j.sd.20160403.12
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