Cause Of Harbor Corrosion A Mystery

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By KBJR News 1

Story Published: May 13, 2008 at 9:04 AM CDT

Story Updated: May 14, 2008 at 5:40 AM CDT

The cause of aggressive corrosion in the Duluth-Superior harbor is still a mystery, but studies have identified some suspects.

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One is tannin-rich water, which could be fed from biologically active places like bogs.

Randall Hicks studies aquatic microorganisms at the University of Minnesota, Duluth, and says researchers have been able to isolate an iron-oxidizing bacterium.

But Hicks says that doesn't mean it's the culprit.

Other theories for the rust blame stray electrical current or chemicals like road salt.

In some places in the harbor, the rusting is so bad that it has formed big holes in the metal on shipping docks.

Gene Clark, an engineer with Wisconsin Sea Grant, says replacing all the damaged docks in the Duluth-Superior harbor would cost hundreds of millions of dollars.