Big Headache In A Little Shell

Zebra Mussel A Threat To City, Suburb Water Supply

July 15, 1990|By Stevenson Swanson, Environment writer.

They clogged the 30-inch intake pipe of the municipal waterworks in Monroe, Mich., last year, forcing some residents to go without water for two days and causing $500,000 in damage.

Workers at a Detroit Edison power plant carted away 12 tons of them earlier this year. As many as 700,000 of them clung to a square yard of one of the plant`s underwater surfaces.

They`re zebra mussels, and they have now pioneered the waters of southern Lake Michigan. A dozen of the fast-breeding European mollusks were discovered last week at a Gary chemical plant, and in late June, a fisherman found some in the lake near Kenosha.

It`s hardly a full-scale infestation yet, but municipal and private users of lake water in the Chicago metropolitan area are bracing for the worst, and state officials are asking boaters to take special care to prevent a further spread of the invaders.

``It seems quite likely they`ve arrived here,`` said Rich Hess, Lake Michigan program manager for the Illinois Department of Conservation. ``The conditions here are such that we can expect the zebra mussel to do quite well. And there`s no cure, there`s no panacea, there`s no sure way of protecting water intakes.``

In other words, they are the kudzu of the Great Lakes.

Zebra mussels are thought to have been flushed into Lake St. Clair, between Lake Huron and Lake Erie, in 1986 when a European freighter emptied its ballast water. Some specialists have theorized that the mussels came from a Soviet cargo ship because the species is native to the Caspian Sea.

Adult mussels were first discovered in 1988, and the invaders have since followed the movement of water through the Great Lakes into Lake Erie and western Lake Ontario. A thriving colony has also been found in the St. Lawrence Seaway between Massena, N.Y., and Cornwall, Ontario.

Their spread into the upstream Great Lakes-Huron, Superior, and Michigan- is more ``opportunistic,`` said Hess, since they cannot swim against the flow of water. Instead, they have spread to Duluth, Minn.; Green Bay, Wis.;

and now the Chicago area by clinging to the hulls of ships or boats.

Typically, the discovery of a few zebra mussels in one year precedes the revelation of astonishingly large colonies the next year. A female can produce up to 40,000 offspring a year, and because of their resistance to cold, their numbers are hardly affected by a cold winter.

``It`s early yet in their invasion here,`` said Hess. ``I don`t have any evidence that we`ll have a (widespread) problem by this fall, but I don`t know if that will be true by next spring.``

What makes the southern tip of the lake attractive to the thumbnail-size mollusks is its relative shallowness, which keeps the water somewhat warmer than elsewhere, and the large number of available surfaces to which the creatures can cling.

As long as something is flat and wet, it`s a potential homestead for zebra mussels. That means the area`s piers, steel-sheet pilings, stone rip-rap, buoys, and pleasure boats could be colonized later this year or early next year.

Among the potential problems that zebra mussels might cause is increased corrosion of underwater metal surfaces, slower speeds for infested boats, and a shift in the amount of plankton available to the native aquatic life, which could lead to lower fish populations. Hess said the mussels could also interfere with fish-spawning if they encrust spawning grounds.

But for humans, the most feared result of a mussel invasion is clogged water intakes, which can lead to reduced flows at water-treatment plants and shutdowns at power plants and factories.

Zebra mussels establish the dangerous colonies when the current created by a lakewater intake draws them into pipes and holding tanks. They settle to the bottom and fasten onto the surface with their strong byssal fibers, which protrude from their distinctively striped shell.

As they reproduce, the young spread out and eventually begin to cling to one another. Generation settles atop generation and, like cholesterol accumulating in an artery, gradually chokes off the flow of water.

Repairing the damage they cause can run into the millions. Jon Stanley, an official of the U.S. Fish and Wildlife Service, has estimated that if a large municipal water system like Chicago`s were infested, it would have to spend $30 million to re-engineer its treatment system and spend $10 million a year on maintenance to prevent a recurrence. Repairs at a smaller municipal system or a nuclear-power plant would run $5 million, he estimates.

The Chicago Water Department has been on mussel-alert for nine months, according to Joseph Szawica, deputy commissioner for water operations, who keeps a jar of them on his desk so he will be able to identify any that his workers find during inspections of the city`s offshore water cribs.