Records of ballast water operations are currently kept aboard the vast majority of vessels (Carlton et al., 1995). Thus, examination of ships' logs and records (containing mandatory information) for monitoring purposes would not impose any additional burden on the shipping industry, and it could be used in conjunction with basic water quality parameter measurements to verify that ballast had been changed prior to arrival at port. The basic parameters indicative of water quality are readily measured using commercially available instruments and test kits; reliable measurement of pH, conductivity, dissolved oxygen, and temperature is available using a single probe for analysis. Both microprocessor-controlled and digital instrumentation packages can be interfaced with a computer or data-logger for continuous analysis, and many commercial units have been field tested that are suitable for marine applications. Turbidity and concentrations of specific chemicals can also be analyzed using colorimetric and amperometric techniques. Instruments designed for use in process streams can provide continuous measurement of water quality parameters necessary for ballast treatment technologies. Most of these systems are priced between $500 and $2,500, excluding installation costs.
Turbidity may currently be the most useful indirect indicator for establishing the presence of port or inshore water as opposed to open-ocean water; low turbidity would indicate the lack of dense biological populations, such as algal blooms. Measurements of turbidity also reflect relative concentrations of undesirable plankton and suspended sediment. Since it is likely that some sediment will be present at the bottom of the ballast tanks, the results of turbidity measurements can be greatly influenced by sampling location.
Ships arriving from ports and harbors known to be active sites of infestation by known nuisance species may, in addition to the Level I monitoring outlined above, be sampled to check for the presence of the species in question. This would require impounding a vessel until its ballast water had been rigorously examined, unless a "sampling and dispatch" approach could be implemented.
The presence of life in ballast water can be determined quickly by several techniques that assess bioactivity in the water. These techniques, many of which can now be automated, include measuring one or more of the following:
Photosynthetic pigment. The amount of chlorophyll present in the water reflects the biomass of living phytoplankton in the water.
ATP. The presence of a biochemical energy system, adenosine triphosphate, indicates that living cells are present.
Nutrients. The amount of a compound such as nitrate or phosphate in the water indicates that level of nutrients available to support phytoplankton.
Another technique is to determine the presence and abundance of one or more particular species (such as a bacterium or dinoflagellate) known as indicator