Stronger measures needed to protect lakes from ballast invaders
Current rules aimed at minimizing the number of nonnative species that hitchhike into the Great Lakes on oceangoing ships are inadequate and often impractical, a University researcher and colleagues from five other U.S. and Canadian institutions have concluded.
The authors of a three-year study recommend that "saltwater flushing," the practice of rinsing a ship's ballast tanks with deep-ocean water before it enters the St. Lawrence Seaway, be added to a set of requirements called the Code of Best Practices for Ballast Water Management. In 2002 the St. Lawrence Seaway corporations in the United States and Canada adopted rules making compliance with the code mandatory for entry into the seaway.
The study, released July 10, focuses on so-called NOBOB (no ballast on board) ships, those that carry no pumpable water in their ballast tanks. More than 90 percent of the cargo ships entering the Great Lakes through the St. Lawrence Seaway are NOBOBs, and nonnative organisms can lurk in the residual water and sediment left in the mostly empty ballast tanks.
Various approaches for sanitizing ballast waterusing chemicals, heat, ozone or ultraviolet radiation, for exampleare being explored but have not yet been adopted. In the interim, saltwater flushing provides an inexpensive alternative that likely would kill most of the lingering freshwater organisms in NOBOB ballast tanks, says U-M nutrient chemist Thomas Johengen, one of the study's co-leaders.
"We think that saltwater exposure is an effective way to protect freshwater systems. If we could apply it in every NOBOB, we think that we can close a loophole," says Johengen, an assistant research scientist at the School of Natural Resources and Environment.
Johengen and project co-leader David Reid of the Ann Arbor-based Great Lakes Environmental Research Laboratory (GLERL) worked with scientists from the University of Windsor, Old Dominion University, the Smithsonian Environmental Research Lab, and Jenkins & Associates Ltd. GLERL is part of the U.S. National Oceanic and Atmospheric Administration.
The report, "Identifying, Verifying and Establishing Options for Best Management Practices for NOBOB Vessels," was funded by the Great Lakes Protection Fund, with additional support provided by the U.S. Coast Guard and NOAA. Known informally as NOBOB-B, the study is a follow-up to one (NOBOB-A) the same research team released two years ago.
NOBOB ships are loaded to capacity with cargo and carry no declarable ballast water on board. But once they unload their cargo, they take on tons of Great Lakes water for stability. If they then load cargo at another Great Lakes port, they must discharge the ballast water, which now is a mix of Great Lakes water, residual foreign water and sedimentas well as stowaway organisms that can range from pathogenic microbes to mollusks and fish.
At least 185 nonnative aquatic species have been identified in the Great Lakes, and ballast water is blamed for the introduction of about 60 percent of them, Johengen says.
The invaders include the notorious zebra mussel, a small but aggressive Eurasian fish called the river ruffe and two types of goby. Viral hemorrhagic septicemia, which caused a huge Great Lakes fish kill last year, may have arrived in transoceanic ships as well.
The latest NOBOB study included more than 70 salinity-tolerance experiments designed to mimic saltwater flushing of ballast tanks and its effects on various invertebratesincluding larval stages of the zebra and quagga mussels. The tests were conducted in Lake Erie, Lake Michigan, Chesapeake Bay, San Francisco Bay and several European ports.
The experiments showed that many organisms originating in low-salinity ports quickly can be eradicated from ballast water through exposure to full-strength seawater.
"One of the key findings here has been to confirm that saltwater can be quite effective at reducing the risk of invasions from ballast water," Reid says. "It's not 100 percent effective against all types of organisms, but it's far better than what's been going on, which has been basically no regulation at all for NOBOBs."
The study also evaluated the effectiveness of the current Code of Best Practices for Ballast Water Management.
The code requires vessels entering the Great Lakes to apply a precautionary approach that includes minimizing ballast water uptakes at ports where toxic algal blooms, known populations of harmful aquatic organisms and pathogens, sewage outfalls, or dredging activities are present.
The team concluded that the real-world constraints of cargo loading and unloading often make it impractical for crews to carry out the environmental precautions.
In 2005 the U.S. Coast Guard issued a policy statement encouraging mid-ocean ballast tank flushing. Last year Canada adopted management regulations requiring that ballast waterincluding residual water in NOBOBSbe treated with saltwater or salt before the water is discharged in the Great Lakes.
Nearly 2,000 oceangoing vessels conducted Great Lakes trade via the St. Lawrence Seaway between 1999 and 2006, according to the St. Lawrence Seaway Development Corp.