洪涝灾害后长江下游洲滩钉螺消长和扩散趋势纵向观察

目的　掌握洪灾后钉螺消长规律 ,进一步评价洪涝灾害对长江下游钉螺消长和扩散的影响。方法　每年采用系统抽样结合环境抽查的方法进行江滩钉螺调查 ;采用打捞法定点观察漂浮物携螺扩散情况。结果　 1998～ 2 0 0 3年钉螺面积平均每年递增 11.80 % ,而 1998～ 2 0 0 3年阳性钉螺面积则平均每年递增 2 9.2 5 %。阳性螺面积随钉螺面积的增加而增加。江苏段洲滩有螺框出现率、阳性螺框出现率、钉螺感染率和阳性螺密度在洪灾后 2年内均呈不同程度下降 ,而从第 3年开始出现快速上升趋势。 2 0 0 2年打捞漂浮物检获钉螺 6 83只 ,2 0 0 3年检获 384 6只。调查表明钉螺吸附于漂浮物扩散高峰为 8月。结论　洪涝灾害短期内可促使钉螺蔓延扩散 ,表现为钉螺面积大幅度增加 ,后期则以钉螺密度增长为特征 ;长江水系钉螺在汛期可吸附于漂浮物扩散。

LONGITUDINAL OBSERVATION ON FLUCTUATION TREND OF DISTRIBUTION AND SPREAD OF ONCOMELANIA SNAILS AFTER FLOODWATER IN MARSHLAND OF LOWER REACHES OF YANGTZE RIVER

Objective To understand the fluctuation pattern of Oncomelania snails after floodwater, and to evaluate the impact of the flood disaster to the distribution and spread of snails in lower reaches of the Yangtze River.Methods The systematic and environmental sampling method was used to survey snails in the Jiangsu marshland along the Yangtze River every year. The salvage method was used to observe snail spread situation with the float. Results The areas with the snail increased by 11.80% every year from 1998 to 2003. At the same time, the areas with the infected snail increased by 29.25% every year. The correlation analysis showed that the areas of the infected snail were increasing with the increase of the snail habitats in the marshland. The four indexes, the rate of the frame of living snails, rate of the frame of infected snails, snail infection rate and density of infected snails, fell in varying degrees in two years after the flood disaster, and then rose quickly in the Jiangsu marshland along the Yangtze River. There were 683 snails in the salvaged floats in 2002, while 3 846 snails were found in the salvaged floats in 2003. The highest of snail spread with the floats were in August. Conclusion The flood disaster could impel snails to spread, and result in expanding the area with snails. The density of snails increases in the later stage of the flood disaster. The floats can carry snails in flood season.