Consultant's Report - Minnesota State Legislature
Consultant's Report - Minnesota State Legislature
Consultant's Report - Minnesota State Legislature
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Cavitation<br />
MINNESOTA DEPARTMENT OF NATURAL RESOURCES<br />
Feasibility Study to Limit the Spread of Zebra Mussels from Ossawinnamakee Lake<br />
Cavitation is a form of acoustic energy that initiates the formation and collapse ofmicrobubbles.<br />
The bubble formation occurs in the region of decreased density and pressure in an intense<br />
ultrasonic wave or high velocity turbulent water flow (Donskoy and Ludyanskiy 1995). At<br />
frequencies between 10 and 380 kHz, this type ofenergy has demonstrated mortalities ofveliger,<br />
juvenile, and adult zebra mussels (Nalepa and Schloesser 1993). Exposure times are ranges of<br />
seconds for veligers, minutes for juveniles, and hours for adults.<br />
Sound Treatment<br />
Low frequency sound energy has demonstrated prevention of settlement by translocating zebra<br />
mussels and could be a valid option to reduce the spread of zebra mussels. Sound treatment<br />
utilizes water-borne acoustic energy in the fonn of sound waves (20 Hz to 20 kHz) or ultrasound<br />
waves (above 20 kHz) to disrupt the settlement of zebra mussels (Donskoy and Ludyanskiy<br />
1995). This type of acoustic energy is effective against veligers at frequencies below 200 Hz by<br />
causing them to become stressed and immobilized, resulting in detachment and subsequent<br />
sinking in the water column. At frequencies between 39 and 41 kHz, ultrasound acoustic energy<br />
can fragment veligers within a few seconds and can also kill adults within 19 to 24 hours. Two<br />
reports prepared for the Empire <strong>State</strong> Electric Energy Research Corporation (ESEERCO)<br />
document that frequency of 20 kHz or 42 kHz fragment or dissolve veligers in under 30 seconds<br />
(Sonalysts and Aquatic Sciences 1991, Sonalysts 1993).<br />
Vibration<br />
Vibration refers to the use of solid-borne acoustic energy in mechanical structures. This type of<br />
treatment requires that the zebra mussels be settled on a structure that can be subjected to<br />
vibration, such as pipes or water intakes. Vibrational energy is effective in killing zebra mussel<br />
veligers and juveniles at just below 200 Hz and between approximately 10 and 100 kHz (Nalepa<br />
and Schloesser 1993). Long-term effects of vibration may include structural deterioration of<br />
infrastructure (e.g., bridges, water intakes, etc.).<br />
Chemical Treatments<br />
Zebra mussel control technologies are sometimes categorized as chemical or non-chemical in the<br />
literature. They are commonly categorized in this fashion due to the environmental or toxic<br />
impacts that are a factor with chemical additions, but not with other technologies. For this<br />
reason, chemical treatments are very feasible for public facilities that can control the amount of<br />
chemical discharge, but they remain less practical for open water systems. If there is a concern<br />
of environmental impacts or harm to aquatic life, non-chemical treatments are sometimes<br />
targeted. Although many researchers have developed non-chemical strategies for control of<br />
zebra mussels, chemical alternatives remain the most common treatment due to their proven<br />
effectiveness.<br />
There are two main categories of chemical treatments: oxidants and nonoxidants. Oxidizing<br />
agents are very effective in: controlling zebra mussel populations; however, many of them also<br />
V-4<br />
Review ofPotential Control Methods