THOUSANDS of striped Zebra mussels were left clinging to trees after last year's record floods in the Midwest. It was a warning that the invading bivalve has widened its eight-year, $5-billion attack on power plants, municipal water systems, and other surface water users in the United States.
Since 1986, the Zebra mussels have swarmed throughout the Great Lakes, spreading through the Erie Canal into the Mohawk and Hudson Rivers, and infesting the Illinois River through a canal near Chicago. In 1993, the mussels rode the wave of flood waters as far as New Orleans and north to St. Paul, Minn.
Zebra mussels swarm into pipes and clog valves, strip the water of nutrients needed for game fish, and have resisted any attempt to tame their appetite or to limit their relentless spread. An original estimate of damage from the mussels between 1986 and the end of this decade was $5 billion, according to Robert Davis, a former Michigan congressman and president of the National Zebra Mussel Alliance, a Virginia group lobbying for research funding from Congress. But that estimate was made before the floods spread the infestation. No new estimate has been made.
Officials at Detroit Edison's power plant in Monroe, Mich., the third largest coal-fired facility in North America, were startled when they discovered thick coatings of more than 700,000 mussels per square yard attached to their plant intake pipes a few years back, says Bill Kovalak, a biologist with the utility.
``It was a crisis for us - we pump one and a half million gallons of water a minute,'' he says. The mussels not only covered the limestone, steel, and concrete in the plant's intake canal, but also infested quarter-inch internal pipes and clogged valves.
Power plants, municipal water and fire-fighting systems, golf courses, air conditioning units, irrigation, agriculture processors, and many other users of surface water also have been attacked by the pest. Pipes rapidly become clogged and useless.
About 700 years ago, the Zebra mussels infested the Black and Caspian seas. About 175 years ago, they spread to Holland and then West Germany. Today Zebras infest all of Europe.
The United States and Canada are adopting European methods of design and treatment. These include using chlorine, heat, scraping, drying, and smothering to try and kill off the Zebras. In addition, European plants use short, dual-intake pipes, which can be alternately taken out of service for cleaning. US plants often use very long intakes. European plants keep water moving swiftly to prevent larvae from clinging to pipewalls, and they design water tanks without square corners, where mussels will collect.
The cost of reconfiguring existing facilities to fight the Zebra mussels is expected to soar as the bivalves spread. Within a few years, the mussels will likely spread to every inland river and waterway - from the Rocky Mountains to the Atlantic, and from Southern Canada to Florida, says Charles O'Neill of the New York Zebra Mussel Information Clearinghouse at the State University of New York in Brockport, N.Y.
Each female adult Zebra mussel can release from 40,000 to 1 million microscopic larvae a year. They are spread through river systems and into isolated lakes by currents, fish, and birds. They also proliferate in the bilges of boats, engine water, or the water-filled pockets of boat trailers. ``Some power plants have already spent millions, [and] the largest coal-fired power plants in North America have been infested,'' says Mr. O'Neill, who is a central figure in organizing research on the mussels.
The larvae are too small to be filtered out and chemical killers are too inconvenient to use on the huge quantities of water used in cooling systems. Environmental laws also require that molluscicides, such as chlorine injected into incoming water, be neutralized as the water is returned to the waterway. Scientists are working on high-tech solutions that could be cost-effective, such as acoustics to kill larvae, low-intensity electric fields, and ultraviolet light and microbes.
There is a danger that as Zebra mussels multiply and spread, they will consume so much phytoplankton that they will knock the bottom out of the food chain, harming trout and salmon, O'Neill says.
``They are like vacuum cleaners - they suck all the nutrients out of the water,'' he says. ``The West Basin of Lake Erie used to be green ... and you couldn't see your fingers, but now you can see down 30 feet.''