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Adding Nitrogen to Ballast Water Can Prevent Corrosion and Alien Invasions

Aquatic organisms often hitch a ride in the ballast tanks of ocean-crossing ships, ending up in ports far from their native habitats. Upon arrival, these alien species can wreak havoc in their new environs, forcing out native species and incurring huge economic costs. Now a new report published in the journal Biological Conservation suggests that a certain anti-corrosion technique could help prevent such invasions while saving the shipping industry hundreds of thousands of dollars a year.

Corrosion of the ballast tanks of cargo vessels represents a significant cost to the shipping industry. Currently, coats of expensive paint are used to prevent oxidation and rust. The new technique, developed by Japanese scientists, bubbles nitrogen gas through the ballast water to reduce oxygen levels, thereby decreasing oxidation and rust. Noting that many aquatic organisms are also sensitive to oxygen levels, Mario Tamburri of the Monterey Bay Aquarium Research Institute (MBARI) and colleagues mimicked the conditions in these deoxygenated ballast tanks in the laboratory. They subjected three invasive species currently found in U.S waters¿an Australian tubeworm, the common European green shore crab and the European zebra mussel¿to the oxygen-deprived aquatic conditions and found that most of the larvae died after two or three days. Considering that major ocean crossings take weeks, the researchers suggest all the larvae would have perished in that time.

Though some species¿such as anaerobic bacteria or organisms with cyst stages¿could survive a transoceanic trip in a nitrogen-treated tank, the new technique still provides an environmentally benign and economically attractive method for reducing the number of potential invaders. "Deoxygenation was seen as too expensive for controlling invasive species in ballast water," Tamburri says, "but our study shows that the anticorrosion benefit of this technique is a strong economic incentive for the shipping industry."

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