The Observer, December 2004
Exchanging ballast water may reduce threat of NIS invasion
By EMMA VERLING, KAREN EASON, AND GREGORY RUIZ
Smithsonian Environmental Research Center
A six-year series of experiments suggests that ballast-water exchange aboard oil tankers may be an effective way of combating the problem of non-indigenous species invading Alaska waters.
During exchanges, ballast water from port is discharged and replaced on the high seas. Photo courtesy of Smithsonian Environmental Research Center.
Oil tankers traveling with empty cargo tanks carry ballast water for stability during the voyage north to Valdez to take on their next load of North Slope crude. This ballast water is taken on in the port where the tanker has unloaded – usually in Puget Sound, San Francisco Bay, or the Los Angeles area – and millions of microscopic marine organisms are taken on with it.
When the ballast tanks are emptied upon arrival, those organisms are flushed into Prince William Sound, raising the potential that a harmful species could establish itself there and damage native species such as the salmon stocks that support Alaska’s commercial fishing industry.
Ballast-water exchange refers to the practice of replacing the ballast water taken on in port with ballast water from the open ocean. In theory, this could reduce the risk of invasion by non-indigenous species in two ways. One, water on the high seas may contain less microscopic life than coastal waters, because there are more nutrients near the coast. And, two, species that survive well in open ocean may not be well-suited to life in the shallows near shore.
In a series of experiments dating back to 1998, Smithsonian scientists have found that ballast-water exchange is capable of removing more than 90 percent of the coastal organisms taken on in West Coast ports.
The scientists tested three methods of ballast-water exchange:
• 100 Percent Flow-Through. A volume of water equal to the volume of the ballast tank is pumped into it, forcing out an equal volume of water.
• 300 Percent Flow-Through. A volume of water three times the volume of the tank is pumped into and through it.
• 100 Percent Empty-Refill. The tank is completely emptied and then refilled with oceanic water.
These experiments have produced the most extensive, quantitative examination of ballast water exchange and have resulted in the best data-set of its kind anywhere in the world.
The 300 percent Flow-Through method and the 100 Percent Empty-Refill method (now required for vessels arriving from overseas at U.S. ports) removed an average of 99 percent of the original coastal water and more than 90 percent of the coastal organisms originally in the ballast water.
These results, presented at the recent 13th International Aquatic Invasive Species Conference in Ireland, contradict the common perception (which has grown in the absence of such measures) that ballast-water exchange is not effective at removing coastal organisms and reducing the risk of invasions.
This initial body of research, now including 12 different voyages on oil tankers en route to Alaska, has served as an important model for understanding ballast-water exchange. It is now being broadened to include several different voyage routes as well as different vessel types (e.g., container vessels, bulk carriers, and military supply vessels).
The most recent of these voyages took place in June of this year, when two Smithsonian scientists boarded Alaska Tanker Company’s Kenai for a five-and-a-half day voyage from Benicia, California, in San Francisco Bay, to Valdez.
The methodology was typical of how the ballast-water exchange experiments have been conducted since 1998. Throughout the voyage, the scientists repeatedly sampled two pairs of ballast tanks that had been filled in Benicia. Each pair consisted of one “experimental” tank and one “control” tank. Water in the control tank was not exchanged, providing a baseline measure against which the effects of exchanging the water in the “experimental” tank could be gauged.
The scientists measured changes in salinity, and in the concentration of a dye introduced into the tank, to estimate the amount of original coastal water removed by exchange. In addition, biological samples were collected to assess the efficacy of ballast-water exchange at removing various microorganisms from the water. These samples are still being analyzed.
The ballast-water exchange work in Alaska was made possible through a cooperative effort and broad-based support among several partners: the citizens’ council, National Sea Grant, the U.S. Fish and Wildlife Service, the American Petroleum Institute, Great Lakes Protection Fund, and the management and staff of the shipping companies SeaRiver Maritime and Alaska Tanker Company.