March/April 1995
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March/April 1995 |
While ballast water in ocean-going ships was first recognized as a means of transport of exotic species in 1900, it was not until the 1980s that specific concerns led to political interest in ballast water management.
In Australia, Japanese dinoflagellates (tiny plankton) released from ballast led to toxic phytoplankton blooms and the closing of shellfish beds. In Canada and the United States, a series of aquatic invasions in the Great Lakes placed ballast water on a "top 10" list of environmental problems. The Eurasian zebra mussel was the sole motivational species, however, for U.S. Public Law 101-646, the "Nonindigenous Species Act" of 1990.
Under this law, the U.S. Coast Guard (USCG) issued regulations in May 1993 that required vessels bound for the Great Lakes to exchange their water, if possible, on the high seas (in depths greater than 2,000 meters or 6,600 feet) to achieve a minimum salinity of 30 parts per thousand. This salinity is a "compromise" because vessels can rarely exchange all of their water; ocean water is generally 35 parts per thousand or greater. The USCG established a detachment at Massena, New York on the St. Lawrence River to board vessels to test their ballast water.
Most vessels coming through Massena since 1993 have exchanged their water and have salinities greater than 30 parts per thousand. The fact that some vessels have not done so and do not have the property salinity is typical of all new quarantine regulations. The four vessels that failed to meet the salinity requirements in the 1993 and 1994 seasons were dealt with by adding salt, by chlorination and by heat treatment. More importantly, "the word" went out to the maritime industry that ships could be found in violation of the new ballast laws, and thereby (as these four ships were) be stopped.
No new established invasions due to ballast water have been reported in the lakes since earlier voluntary guidelines came into effect in May 1989. This does not mean that no new invasions have occurred; reports of new invasions lag behind the actual colonization event by two to five or more years. Nor does this mean that no new inoculations have occurred. In spring 1994 a young European flounder was reported from Lake Superior. This fish is catadromous (moving from fresh to saltwater to reproduce) and cannot establish itself in the lakes. We assume this fish came from ballast released in the preceding two or so years.
How did the ballast that carried this flounder get into the lakes? There are "holes" in all quarantine systems. Recall, for example, that one can easily pass through the "green zone" at international airports and be in possession, intentionally or accidentally, of contraband biological materials, such as plants or soil, and not be caught!
One hole in the current ballast quarantine system is the four or five inches of residual water that remains on the bottom after ballast tanks have been emptied. For tanks 60 feet deep, the mariner would consider these tanks to be empty for all practical purposes. Biologically, however, this shallow layer of water may be rich with life. During normal cargo loading and offloading operations, the vessel may add water at one Great Lakes port and inadvertently resuspend the residual organisms in the tank. The water may then be released at another Great Lakes port, again as part of normal cargo operations.
Another difficult problem is that certain species with broad tolerances to salinity changes may survive ballast water exchange on the high seas. Thus a ship coming from a European port with fresh or brackish water could exchange its ballast on the open Atlantic Ocean, but some residual water would likely remain making the exchange incomplete. If young European flounder were in the tank's residual water, they would survive this change in salt concentration.
It is important to emphasize that all quarantine regulations, including ballast management, form a filter that significantly reduces species invasions, but they do not form a wall that stops all invasions. No set of ballast regulations should be expected to cease all future invasions; rather, ballast regulations should be expected to profoundly diminish the number of new invasions into the Great Lakes.
What does the future hold? There are two pathways. The first is to continue to find and plug the holes. For example, it may be possible to determine the volume of residual water remaining aboard a ship and make the mariner aware of how ship operations could inadvertently resuspend and thus release exotic species to the Great Lakes. Treatment of this water before it is mixed with other ballast water is an additional possibility.
The second is to find technological solutions other than ballast exchange. Of the more than 50 solutions that have been proposed to control ballast water, half involve some form of water treatment -- thermal, ultraviolet, chemical, ultrasound, electrification, filtration and so forth.
A ballast water working group of the Marine Environmental Protection Committee of the International Maritime Organization has formed to address the many management issues. Research groups in Canada, the United States, Australia, Japan and Germany are addressing ballast water environmental issues and control options. The U.S. National Research Council's Marine Board has formed a Committee on Ship's Ballast Operations to review options, sort the wheat from the chaff, so to speak, and make recommendations for the way forward.
A combination of actions will insure there are far fewer invasions in the future. These include increased awareness of the need for ballast water management by the maritime industry, diligent attempts to effect ballast exchange operations that are safe for crew and ship, and the addition of new technological systems that will treat ballast water on the ship. If there is a positive side to the zebra mussel invasion, this may be it.
For more information contact Dr. James T. Carlton, Maritime Studies Program, Williams College-Mystic Seaport, Mystic, Connecticut 06355. Email james.t.carlton@williams.edu ; telephone (203)572-5359; fax (203)572-5329.
Sommaire
Il est important de rappeler que les règlements sur la quarantaine, y compris ceux qui touchent la gestion des eaux de ballast, constituent un filtre qui réduit dans une mesure significative les risques d'infestation, mais sans former pour autant une barrière impénétrable. Il serait illusoire de croire que la réglementation sur les eaux de ballast puisse nous préserver de toute infestation ultérieure; cependant, on peut s'attendre à une diminution considérable des nouvelles infestations dans les Grands Lacs.
Avec la mise en oeuvre d'un ensemble de mesures, les infestations deviendront beaucoup moins fréquentes. Il s'agit entre autres de mieux faire comprendre à l'industrie maritime l'importance de la gestion des eaux de ballast, de veiller avec diligence au changement des eaux de ballast de façon que les opérations soient sans danger, tant pour l'équipage que pour le bateau, et d'utiliser de nouvelles techniques pour traiter les eaux de ballast à bord du bateau. Si l'infestation de nos eaux par la moule zébrée a eu un côté positif, c'est peut-être de nous avoir incités à entreprendre une telle démarche.
Revised: April 8, 1997
Maintained by Kevin McGunagle,
mcgunaglek@ijc.wincom.net