Zebra Mussels Could Be Factor In Bridge Corrosion

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(Host) Scientists say thick mats of zebra mussels in Lake Champlain can increase corrosion of things in the water near them.

They say it’s possible that the tiny invasive species might have played a role in the structural damage of the Champlain Bridge.

VPR’s John Dillon reports.

(Dillon) The Champlain Bridge was closed last month. And now officials say it’s beyond repair and will have to be demolished.

Underwater video shows deep grooves and cracks in the concrete support piers. What made the concrete fail so dramatically?

A tiny mollusk – native to the Black Sea -is known to aggravate corrosion.

(Watzin) "The bridge is kind of a constellation of wonderful habitats for zebra mussels and therefore bad potentially for the bridge itself."

(Dillon) Mary Watzin heads the Rubenstein School of the Environment at the University of Vermont. She’s part of a 10 year research project that’s looking at how the mussels accelerate the deterioration of underwater shipwrecks in the big lake.

Watzin says the mussel colonies foster the growth of bacteria. The microscopic creatures excrete material that breaks down iron and steel. The biological process also reduces levels of sulfur, which makes the water more acidic and therefore more corrosive.

(Watzin) "Those bacteria do end up lowering the pH. So the low pH and some of the other by-products really enhance the corrosion rate."

(Dillon) Watzin was referring to metal corrosion. The concrete piers of the 80-year-old Champlain Bridge are not reinforced with steel and engineers say the structures have been weakened by the constant freezing and thawing in the lake.

(Watzin) "I mean I wouldn’t say that the zebra mussels are the cause of the deterioration. But they certainly haven’t helped."

(Dillon) A report by the United State Geological Survey notes that the possible impact of zebra mussels. The report says the tiny mollusks – quote – "can cause corrosion of steel and concrete affecting its structural integrity."

But John Zicconi of the Vermont Agency of Transportation discounts the theory. He says the agency’s engineers and environmental scientists are not aware of mussels contributing to concrete damage.

(Zicconi) "There’s nothing that they have in their literature. In conferences that they attend this is not considered an issue anywhere on the local or national level".

(Dillon) Adam Kane is a nautical archaeologist with the Lake Champlain Maritime Museum. He’s worked with UVM on the 10 year research project to assess mussel damage to the lake’s shipwrecks. Kane says that the creatures not only cover the artifacts, but they also accelerate the breakdown of the wood and metal.

(Kane) "Whether or not those results can be extrapolated out the bridge, I’ll leave that for someone else to decide. But for the wrecks of the lake, it’s certainly not a good news story."

(Dillon) Governor Jim Douglas says more needs to be known about whether underwater environment contributed to the bridge failure.

(Douglas) "Zebra mussels are a problem for navigation and for water quality. But perhaps they’re also a problem in terms of the infrastructure of our bridges. We, of course, have other concrete piers. More recent ones are reinforced with steel. But it would be good to know if zebra mussels are playing a role."

(Dillon) The zebra mussels are here to stay. They arrived in the Great Lakes in the mid-1980s, and are now found almost everywhere in Lake Champlain.

For VPR News, I’m John Dillon in Montpelier.

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