JMEE HomeIssue Contents

Chemical and Physical Characterization of Ballast Water Part 2:
Determining the Efficiency of Ballast Exchange
D.J. Oemcke and J(Hans) Van Leeuwen

Ballast water is recognized as a major vector for the translocation of aquatic pests around the world, and several countries and the International Maritime Organization are introducing regulations aimed at controlling the movement of these species. The only technique currently used internationally is ballast exchange, where the ballast water from coastal and inland ports is replaced with oceanic seawater. Verification of this is difficult.

This research examined the potential of ballast water characterization as a tool to check on the efficacy of the exchange process. Ballast water and sludge samples from a number of ships entering North Queensland ports were analysed for a range of physical and chemical characteristics to determine their potential as indicators of the effectiveness of ballast exchange. The characteristics used were salinity, pH, Alkalinity, DOC, TOC, nitrate, nitrite, ammonia, phosphate, chlorophyll a and pheophytin. The results indicate that on 14 to 57% of ships reporting ballast exchange at sea, it was either ineffective or not done. This conclusion was based on a chemical characterization process, which compared the composition of ballast water with what would be expected from oceanic water. Reasons for ineffective exchange include re-contamination of the oceanic water by residual sediments and water that remains in ballast tanks, poor exchange practice or non-exchange. Characterization may have a useful role in monitoring the exchange process, although antecedent conditions in ballast tanks must be taken into account and the chemical conditions in ballast tanks may affect some measurements. Chemical and biological recontamination of exchanged ballast water by residuals is likely, it would appear from these results. The determinants investigated cannot be relied on to provide clear evidence on whether ballast exchange at sea has indeed taken place.

Full Text (IP)