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A National Research Council report recommended establishing “benchmark discharge standards” that would clearly reduce coastal organisms below current levels from ballast water exchange to control invasive species.
The report, Assessing the Relationship Between Propagule Pressure and Invasion Risk in Ballast Water, released June 2 by the council's Committee on Assessing Numeric Limits for Living Organisms in Ballast Water, cited challenges in current scientific approaches but emphasized the value of controlling invasive species.
Controlling ballast water that transports invasive species via ships is critical to protecting and preserving existing fish, shellfish, and other wildlife in U.S. waters, according to the report, which was undertaken at the request of the Environmental Protection Agency and U.S. Coast Guard.
Approaches to setting ballast discharge standards have relied primarily on expert opinion, in the absence of data to support a science-based quantitative approach, the report said, adding that currently evaluated data “are extraordinarily coarse-level.”
“Currently, none of the available testing models has been validated, due mainly to a lack of key data,” the report said. Using multiple models for testing could be helpful as more data become available, it said.
In the future, large amounts of ballast water will be treated, and this water will be the primary target of ballast discharge standards, it said.
According to the report, ships' uptake and release of ballast water and associated sediment is one of the most prevalent ways that new aquatic invasive species are introduced.
Coast Guard and EPA ballast management programs are undergoing revisions that focus on setting specific post-treatment discharge standards for ballast water.
Upcoming regulatory deadlines prompted EPA and the Coast Guard to ask the council's Water Science and Technology Board to conduct a study providing technical advice on determining numeric limits for living organisms in ballast water for the next EPA vessel general permit and Coast Guard programs.
They asked the National Research Council to evaluate the science on approaches for assessing the risk of nonnative aquatic species, given certain concentrations of living organisms in ballast water discharges
EPA and the Coast Guard did not ask the committee to propose numeric discharge standards or evaluate treatment systems that might be used to achieve such standards. “The available methods for determining a numeric discharge standard for ballast water are limited by a profound lack of data and information to develop and validate models of the risk-release relationship,” the report said.
Citing freshwater systems in the Laurentian Great Lakes as among the best studied, it said more than 180 invaders have been detected and described—about 55 percent of these from ballast water.
For coastal marine ecosystems, it said, California and western Northern America have received the most in-depth analyses of aquatic invasions, with more than 250 nonnative species of invertebrates, algae, and microorganisms the waters of California alone. Of these, more than 50 percent include ballast water as a possible source.
By Linda Roeder
More information on the National Research Council report, Assessing the Relationship Between Propagule Pressure and Invasion Risk in Ballast Water, is available at http://www.nap.edu/catalog.php?record_id=13184 .
A prepublication copy of the report's summary is available at http://op.bna.com/env.nsf/r?Open=smiy-8hgurh .
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