Hybrid Treatment to Control Plankton Densities in Ballast Water Tanks

PAOLUCCI, E. M.; HERNANDEZ M. C..; POTAPOV A.; MACISAAC H,

Niagara Falls

Conferencia; 18th International Conference on Aquatic Invasive Species; 2013

Invasive Species Centre (ISC)

In an effort to reduce the considerable magnitude of ballast water as a vector for the introduction of non-indigenous species, and align with increasingly strict shipping legislation, we evaluated the efficiency of mid-ocean Ballast Water Exchange (BWE), Chlorination (Cl), and the interaction effects of their combination (BWE+Cl) on microplankton and bacteria densities in ballast tanks. The four treatments were compared over four experimental trips conducted on the bulk carrier Federal Venture between Canada and Brazil from April-November 2012. A total of ten ballast tanks were used for each run (4) of the experiment. Initially, empty ballast tanks were filled with freshwater in Canadian ports, and initial samples collected before injection of a first dose of chlorine (~20ppm) in 5 port side tanks. Between four and five days after departing, BWE with seawater, or BWE plus a second dosing of chlorine, were carried out on applicable tanks. Final samples and measures of environmental conditions were obtained around two days after the BWE, pumping water from three different levels within each ballast tank. Samples for microplankton and bacteria analysis were collected and processed on board. A block design ANOVA was applied to analyze statistical differences for different plankton groups between treatments. In general, the chlorine and BWE+Cl treatments had the lowest final densities among all treatments for Enterococcus, coliforms and E. coli bacteria, and microplankton. For Enterococcus and E. coli, the BWE+Cl treatment exhibited a significant synergistic effect (p < 0.04 and 0.05, respectively). The control and BWE-only treatments typically had highest plankton abundances, and, in some cases, increasing densities of  bacteria were observed in the BWE treatment. The lowest final values of microplankton density were observed in the BWE+Cl treatment, in which the combination of both treatments resulted in a significant interaction (p = 0.04), though with antagonistic effects. This trend was similar regardless of the wide range of initial concentrations of organisms among the four trips, and the hybrid (BWE+Cl) treatment displayed one of the best performances with final values lower than the proposed IMO D-2 standard