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Chang, T.J., M.A. Hoover, and T.A. Bartrand, 1996. Optimization of a Vacuum Device for Zebra Mussel Control, Civil Engineering Department, Ohio University -- Reprinted from "Zebra Mussels and Other Aquatic Nuisance Species." Ed. by Frank D'itri, Ann Arbor Press, 1996. Optimization of a Vacuum Device for Zebra Mussel ControlINTRODUCTION Zebra mussels feed on bacteria, algae, and fine organic detritus using a complex arrangement of cilia (Miller et al., 1992). Food particles are selected through the filtration by cilia in the mantle cavity. Although they have adapted to a freshwater habitat, zebra mussels have retained some primitive features, such as free-swimming veligers, simple mantle fusions, and functional byssus in the adults. Byssal threads are formed in the byssal groove of the foot from secretions of the byssal gland. Zebra mussels detach themselves from hard substrata by discarding the entire mass of old threads. This is followed by the secretion of a new series of byssal threads. The reproduction of zebra mussels generally occurs over extended periods when water temperature reaches 11 or 12oC. Adults become sexually mature in their second year of life (Mackie et al., 1989). A female can produce approximately 150 thousand eggs in her life time of 4 to 5 years. Fertilized eggs require calcium for development but are tolerant of low oxygen levels. The first appearance of free-swimming larvae, veligers, in the plankton form is temperature-dependent, preferably at 14 to 20 oC. In the United States, veligers of zebra mussels can be found from May to October. The post veliger and settling larvae are the most sensitive stages to temperature shock and anoxia. It was shown that thermal shock would occur at a temperature of approximately 30oC for zebra mussels acclimated to 5oC and 15oC, and around 35oC for those acclimated to 25oC (McMahon, 1991). Water temperature was used by Chang and Miller (1992) to develop the ZM Index for potential evaluation of zebra mussel infestation. Thermal processes for the removal of zebra mussels from water intakes have been demonstrated to be a successful control technology (Mackie et al., 1989; Walker et al., 1991), however, the use of high-temperature water may result in ecological impacts on other aquatic life. Dissolved calcium in water is an essential constituent of shells for zebra mussels to grow from larvae to veligers and adults. It was shown that there is a significant relationship between calcium content and zebra mussel density (Mackie et al., 1989). Zebra mussels are not found in water with less than 10 mg/l or 10 ppm dissolved calcium. Hence, the dissolved calcium was used as an indicator by Chang (1995) for the evaluation of zebra mussel movement in water bodies. However, practical uses of dissolved calcium for the purpose of zebra mussel control is relatively limited. Dissolved oxygen is essential for zebra mussels especially at the stage of their settling on hard substrata. Oxygen deprivation was recommended by Chang and Miller (1993) as a control technique for removing zebra mussels from infested piping systems. Zebra mussels are clean water inhabitants and usually thrive where the dissolved oxygen is greater than 90 percent saturation. They are stressed in water with less than 40 to 50 percent saturation. Therefore, the dissolved oxygen level can be a good indicator of the potential for zebra mussel presence. The rapid rate of population growth and mobility of veligers are believed to be partially responsible for the quick spread of zebra mussels in the United States. Furthermore, the heavy traffic of our Inland Waterway System makes the dispersal of zebra mussels throughout adjoining river basins inevitable. Chlorine and other chemicals have been commonly used to prevent planktonic veligers of zebra mussels from settling in the piping systems (Lyons et al., 1991; Payne and Lowther, 1992). Unfortunately chlorine is highly toxic to other native aquatic life. Hence, other mechanical means for preventive measures of zebra mussel settlement would be highly desirable. This study proposed and tested a mechanical device based on the reduction of dissolved oxygen for the control of zebra mussels in the piping system. Entire Paper |