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Microbial ecologists have employed a variety of methods using radiolabelled organic substrates to measure the activity of heterotrophic bacteria in natural waters. The relationships between natural and added substrate concentrations and between subtrate concentration and uptake rate provide important criteria for evaluating the different methods. The methods presented and discussed are: (1) direct calculation approach, (2) tracer approach, (3) kinetic approaches (including transport kinetics and diffusion kinetics), and (4) an alternative kinetic approach. The first three differ in the data yielded, and are recommended for specific applications where heterotrophic activity is to be measured. The fourth method is not recommended, as it is shown to be based on faulty assumptions. The authors conclude that the available methods are best viewed as tools for investigative research. Moves towards standardization should be made cautiously.
aquatic bacteria, heterotrophic activity, radioisotopes, organic solutes, uptake, turnover time, transport kinetics, diffusion, tracers
Professor of biology, Gordon College, Wenham, Mass.
Section head, Canada Centre for Inland Waters, Burlington, Ontario