Control of Zebra Mussels in Pipes

What are Zebra Mussels?

·      Zebra mussels, a freshwater bivalve mollusk, have been invading America’s lakes and streams ever since it was detected in Lake St. Clair in 1988.

o   Located just west of Detroit, Lake St. Clair is a relatively large lake located in between Lake Huron and Lake Michigan, both of which are connected to St. Clair by a waterway.

·      Zebra mussels originate in streams located in the Balkans, Poland, and the former Soviet Union.

·      It is believed that zebra mussels were picked up in a freshwater European port in the ballast water of a ship and were later discharged into the Canadian side of Lake St. Clair.

·      Zebra mussels live 4 to 5 years and inhabit freshwater at a depth of 6 to 24 feet.

o   Zebra mussels begin to reproduce at two years of age and females can lay over 1 million eggs in a spawning season.

·      Zebra mussels use byssal threads to attach themselves to hard surfaces and are difficult to remove, which is unusual of freshwater mussels due to the lack of wave action.

·      Zebra mussels can withstand being out of water for several days as long as conditions are moist and humid.

·      Zebra mussel larvae (called veligers) are microscopic in size and are undetectable by the human eye. They can be unknowingly transported in boat live wells and bait buckets or anything that carries small amounts of water, even on SCUBA equipment.

·      Zebra mussels spread rapidly throughout the Great Lakes region and in the large navigable rivers of the eastern Mississippi drainage including the Mississippi, Tennessee, Cumberland, Ohio, Arkansas, and Illinois rivers. They can also be found in the Hudson River on the Atlantic Slope.

o   Barge traffic in these large rivers helped to disperse zebra mussels their first few years here. Since then, dispersal has been mostly into small lakes within the Great Lakes region.

o   Currently, there are more than two hundred and thirty lakes that have zebra mussels. Much of this recent dispersal can probably be attributed to recreational activities such as boating and fishing.

·      They are primarily algae feeders. They feed by filtering the water through a siphon, up to a liter per day.

o   This is why they like the insides of pipes so well, there is a constant supply of water and food flowing by them.

o   One adult zebra mussel can filter almost a quart of water per day, and whole colonies can filter all the water in a lake in one day. The massive loss of algae in the water causes a great increase of water clarity in infested lakes.

·      Native species do not feed heavily enough on zebra mussels to keep the population under control.

Why are they a Problem?

·      Zebra mussels will attach to almost any hard surface, either natural or manmade.

o   On boats, they may attach to the hull, motor, or any item immersed in the water. Both large and small boats can be severely impacted by increased drag caused by thousands of mussels. Small zebra mussels may get into the engine cooling systems, causing overheating and other damage.

·      Zebra mussels pose a threat to navigational buoys, piers, docks, and other structures in the water.

o   Navigational buoys have been sunk under the weight of attached zebra mussels. Wood, steel, and concrete are all damaged by prolonged attachment of the mussels.

·      Many power plants and water users have had to spend millions of dollars cleaning out zebra mussels from their facilities. In addition, more money has been spent on retrofitting facilities with devices to keep zebra mussels out and to monitor for them. These costs get passed along to consumers.

o   Mussels have blocked pipes, screens, condenser units, and many other small openings through which water passes. They do this by forming druses (clumps of mussels) or simply attaching to available hard substances with byssal threads.

·      There is evidence that zebra mussel byssal threads may accelerate corrosion around joints and rivets of metal structures of power plants. Bacteria are present in the area between the substrate and the pad of the byssal thread. Through anaerobic respiration, these bacteria produce an acidic compound that increases the corrosion and pitting of iron and steel surfaces.

·      Even if mussels are killed by a control technique, the shells and any decaying animal material may remain behind, causing additional problems. Thus, killing the mussels may be only part of the solution to opening a blockage. A complete solution may require removal of mussel shells.

Possible Removal Solutions

·      Acoustics

o   Advantages:

§  Less likely to kill non-targeted organisms

§  Has no obvious residue effects

§  Equipment can be installed relatively easily

o   Disadvantages

§  Investigations of the effectiveness of acoustics have been inconsistent and more research is needed to adequately develop this strategy

o   Three approaches to solution:

§  Cavitation – the formation and collapse of microbubbles.

§  Sound treatment – the use of water-borne acoustic energy (acoustic waves) having intensity below the cavitation threshold. These include sounds (20-Hz to 20-kHz) and ultrasound (above 20-kHz) waves.

§  Vibration – the use of solid-borne acoustic energy (vibration) in mechanical structures (pipes, walls, etc.).

·      UV radiation

o   Advantages:

§  Zebra mussel veligers and adults are sensitive to UV-B radiation, provided that the radiation is applied constantly.

§  UV lights easily installed at intake bays of pipes

o   Disadvantages:

§  Non-target species may also be killed

§  Most applicable to medium to small sized raw water systems