Studies On The Relationship Between Vegetation And Oncomelania Snail Distribution In Poyang Lake Region

Oncomelania, the only intermediate host of Schistosomajaponicum, plays a vital role in transmission and prevalence of Schistosomiasis. The habitats and distribution of snails is closely related to its ecological environment, and the vegetation is one of the main factors which form snail habitat areas. Therefore, study on relationship between vegetation and snail distribution has theoretic and practical significance in enriching snail ecology, and snail and Schistosomiasis control.In order to understand the spatial distribution features and patterns of vegetation and snail, and their relationship, the layered systematic sampling method was employed to survey the species, height, coverage, frequency and vitality of vegetation, and the distribution of snail inside and outside embankment in studying sites around Poyang lake which were selected from spring, 2005 to autumn, 2006, including Fuqian village and Changjiang marshland, Xindong village and Zhangonghu marshland in Yugan county, Yufeng village and Shanzi marshland in Nanchang county, and Luojia village and Niu marshland in Jinxian county. At the same time, this study tried to classify the snail-ridden areas of marshland in Poyang lake combined snail and vegetation data with remote sensing data acquired by 3S technology.The results showed that, there is a significant difference between vegetation inside and outside embankment. The species of vegetation inside embankment are varied and its distribution has no regular patterns with snail not being found. The coverage area of vegetation outside embankment is large with assuming the distribution of an unregulated annulus or patch. Vegetation of marshlands can be classified 3 types of zone according to altitude. There are lots of species of vegetation in high altitude zone with low coverage Cynodon dactylon and Hemarthria compressa etc. as the main species. The species of vegetation at middle altitude are concentrated with Carex cinerascen, Miscanthus sacchariflorus and Phalaris arundinacea as the main species. The species of vegetation at low altitude are fewer with Eleocharis tuberose, Polygonum criopolianum or Polygonum hydropiper as the main species. The distribution of snail assumes the characteristics of "two lines and three zones", mainly confined in 15-17m of high and middle altitude zone, and are closely related with vegetation in marshlands. Quadratic curvilinear relation can be observed between coverage of Carex cinerascen, Miscanthus sacchariflorus, Phalaris arundinacea and the density of snail with curvilinear regression equations being respectively: Y_c=-82.933+3.920X_c-0.031X_c~2; Y_m=13.890+1.166X_m-0.012X_m~2; Y_p=-76.677+4.003X_p-0.033X_p~2, The results also indicated that the distribution of vegetation and snail in marshland was closely related, and there was a significant difference in distribution of vegetation and snails between inside and outside embankment. There were some changes in the type, height, coverage, and frequency of vegetation at each altitude in different seasons with the habitats of snails having changes accordingly. In spring, snails were. mainly distributed at middle and high altitudes. In autumn, snails were mainly distributed at middle, high and low altitudes.3S technology was used to classify the habitats of snails and marshlands in heavy endemic regions with Schistosomiasis around Poyang Lake. The environment of the marshlands can be classified 5 types, i.e. water, sand, swamp, low beach of lake, and high beach of lake. The last three types can be identified by TM satellite remote sensing image, and can be used to illuminate the vegetation of the marshlands. The remote sensing analysis also spatially conformed the distribution pattern of snails, i.e. the habitats of snails were mainly distributed in the vegetation areas of low beach of lake. Therefore, the situation of snails habitats can be clearly, precisely, and quickly understood by superposing the features of vegetation and data of snail distribution to remote sensing images.This study provides a new research data for snail ecology. It is expected to be helpful to the improvement of surveillance of ecological environment of snails and vegetation, and to contribute to control and elimination of snails in focal transmission site of Schistosomiasis, and consequently to force the development of Schistosomiasis control in Poyang Lake regions.