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Smith, G., G. Ruiz, M. Frey, L. Takata, S. Altamn, K. Philips, L. McCann, C. Coss, D. Lipski, T. Huber, B. Steves, and S. Chavez, 2001. Effectiveness of Ballast Water Exchange, Smithsonian Environmental Research Center. Proceedings of the Second International Conference on Marine Bioinvasions, New Orleans, La., April 9-11, 2001, p. 132. Effectiveness of Ballast Water ExchangeBallast water exchange has been a primary tool for control of bioinvasions caused by global transport of organisms between source and recipient ports. But is it effective as a management strategy? From the invasions perspective this is a complex question with many aspects. Our specific question was how well does exchange remove/replace the animate and inanimate content of ballast tanks? We tested and compared the effectiveness of the empty-refill and flow-through exchange methods used commonly by the shipping industry. Empty-refill exchange is just what it sounds like. A tank is emptied to the extent possible and the original water replaced with oceanic water. Flow-through exchange occurs when water is pumped into a tank, displacing the original water while the tank remains full. Experiments were performed aboard crude-oil tankers while these vessels were sailing in ballast between various west-coast refineries (California, Oregon, and Washington) and Valdez, AK. The experimental design included a non-exchanged control tank and one or two treatment tanks, which underwent ballast water exchange. The treatment tanks exchanged between one to three complete volumes at sea. Exchange experiments were performed on eight different voyages. Six of the experimental voyages included both empty-refill and flow-through methods (i.e., in discrete tanks aboard the same vessel). The other two experimental voyages performed only flow-through exchange, due to ship design constraints. We measured changes in the concentration of entrained coastal plankton and the concentration of tracers, which we introduced at the voyage initiation. For tracers, Rhodamine dye and 1µ fluorescent microspheres were introduced via tank-top openings during the initial ballasting operation, performed in the sally port prior to sailing. To measure changes in the concentrations of biota and tracers, a variety of sample types (whole-water samples, net-tow samples, and physical measures) were collected before and after exchange events on each voyage. Our results from inert tracer analysis show that empty-refill is more efficient than flow-through; that one empty-refill exchange can remove a very high percentage of the original water; that three successive exchanges of either type can render tracer added to the original water well nigh undetectable (>99% removal). Taken as a whole our results from biological tracer analysis parallel the inert tracer data. Despite the concordance among these data sets, it is also evident that significant variation exists among voyages and taxonomic groups. Contact: George Smith, Smithsonian Environmental Research Center, Box 28,
Edgewater, MD 21037, USA |