RELATIONSHIPS BETWEEN THE SURVIVING ONCOMELANIA AND BEACHES ENVIRONMENTAL FACTORS
钉螺分布与滩地环境因子的关系

s On the seasonal beaches,density of the surviving oncomelania( Y ) and the occurring rate of oncomelania ( Y r) are significantly related with the underground water table ( X 1) and the soil water content ( X 2).Y=-1 9686 0 2512X-0 004013X 2 1,Y r= -55 9720 7 5689X 2-0 1180X 2 2; When the underground water table is under 32cm,it has a significant correlation with Y and Y r .When the underground water table is over 32cm,the relationship is negative.If the soil water content is less than 28%,it has a significant positive relation with Y and Y r .If the soil water content is more than 38%,the relationships appear to be significantly negative.Distribution and breeding of oncomelania are highly correlated with beach vegetation types.There are no oncomelania breeding on bare beaches.Once plants invade into the beaches,the oncomelania occurs immediately.The relationships between the density of the surviving oncomelania ( Y ) and plant community types ( X) is as follow; Y=-10 9357 0 8499X-0 0133X 2, and the occurring rate of oncomelalia ( Y r ) are related with the plant community types ( X ) is as follows: Y r=-256 5333 20 1155X-0 3098X 2. The density of oncomelania is the highest at the reed beaches and other grass beaches on the seasonal beaches along the middle and lower reaches of the Yangtze River.The distribution and density of oncomelania at grass beaches are different due to the different cnaracteristics of plant communities.The density of oncomelania is the highest in flatsedge community,and the lowest in Dogtoothgrass community.