APPLICATION OF SPATIAL DISTRIBUTION MODEL TO PREDICT THE IMPACT OF 1998'S FLOOD ON SNAIL DISTRIBUTION IN MARSHLAND OF YANGZHOU

Objectives To understand the impact of 1998's flood on snail distribution in Yangzhou marshland and to evaluate the spatial distribution model for Oncomelania snails. Methods Field surveys in combination with remote sensing analysis on snail distribution model by computer were used in the study. After overlapping georeferenced images in ERDAS imagine 8 3 software, the snail potential habitats were extracted followed by Zhou's model, which were labeled by red clolor and were matched with the field survey results. Results The marshland snail distribution area in Yangzhou increased by 27 20% after the 1998's flood, while increased by 61 48% in the 25 sampling potential habitats. The snail density were 0 945/0 1 m2,1 278/0 1 m2 and 1 289/0 1 m2 before (in 1998) and after (in 1999 and in 2000) the flood, respectively. The total correlation rate of the snail potential habitats predicted by spatial distribution model after flood in two years was 88 00%. The correlation rates of snail habitats of which areas were over 300000 m2, 100000～ 300000 m2 and lower than 100000 m2 were 90 00%, 100% and 75%, respectively. Conclusion The snail dispersed obviously in marshland along the Yangtze River near Yangzhou after the 1998's flood. It is important of applying the snail distribution model to quickly screen the snail potential habitats and to define the high risk habitats of snail.