钉螺运动生物学研究　Ⅳ.影响钉螺动水沉降距离的生物学及水力学因素研究

KINETIC BIOLOGY OF ONCOMELANIA Ⅳ. STUDY ON EFFECT OF BIOLOGICAL AND HYDRAULIC FACTORS ON SUBSIDENCE DISTANCE OF SNAILS IN FLOWING WATER

在配有循环水系统的玻璃水槽中，研究了螺龄、吸附载体、以及干燥对钉螺动水沉降距离的影响。结果表明螺龄对动水沉降距离有显著性影响，在同一流速下随螺龄增大，沉降距离逐渐缩短。在螺龄相同时，流速对钉螺的动水沉降距离亦有十分明显影响，表现为正相关。吸附载体能显著地影响钉螺动水沉降距离，与无载体吸附相比，沉降距离明显增长，同时随载体面积变小，吸附部位由中部向端部移动时，沉降距离变短，否则相反。在一定的时间范围内，干燥对钉螺的动水沉降距离有影响，随干燥时间的延长，沉降距离增长。通过对实验结果的分析报导出在V流速下最大推移距离公式（99％可信限）为：L＝349．65V·H。结果还表明在江河渠系中钉螺吸附载体漂浮和作为悬移质随水流失带悬移是钉螺在动水中扩散的更为重要的两种方式，因而在水利阻／灭螺工程中，有无从载体上分离钉螺的设施，以及该设施分离钉螺能力的强弱是考核水利阻／灭螺工程优劣的重要指标之一。

Effects of snail age,carriers adhered and dryness on subsidence distance and velocity of snail subsidence in flowing water were conducted in a glass flume with recycled water system. The results indicated that snail age had significant effect on subsidence distance in flowing water(SDFW). SDFW was shortened as the age grew in the same flowing condition. With snails of the same age,SDFW was positively related with water flow. Carriers adherd could significantly influence the SDFW,showing SDFW increase notably in comparing with thase without carriers adhered. In the mean time,when areas of carrier become smaller and adhered position moved from the center to the peripheral parts,SDFW would be shorten. Effect of dryness on SDFW varied within a period of time. As the time prolonged SDFW increased.Subsidence distance formula in V flowing water was deduced through the analysis of experimental results as L= 349. 65V· H,which could be used to calculate maxium distance of snail suspensien under Ⅴ flowing water and maxium length of subsidence pool in snail-obstrcuting/killing project. The result demonstrated that floatation of snails adhered on carriers and movement as suspension articles by water flow in rivers and canals were two important ways of snail spreading in flowing water. Therefore,whether there are facilities which can seperate snails from their carrier or not and the seperating ability of these facilities is a key indicator to assess the quality of snail-obstructing/killing projects.