The relationship between ETS (electron transport system) activity and oxygen consumption in lake plankton: a cross-system calibration

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Abstract
The ETS (electron transport system) assay to measure respiration of aquatic organisms has been widely applied in studies of marine metabolism, but its use in freshwaters has been much more limited. This method calculates oxygen consumption from the measured ETS activity using an empirical conversion factor. This factor has been calculated for various marine organisms, and for natural plankton communities, but calibrations for freshwater organisms are lacking. The aim of this paper was to determine the relationship between lake plankton respiration and ETS activity, based on measured epilimnetic plankton oxygen uptake and ELS activity in 20 southern Quebéc lakes. The relationship between plankton oxygen consumption and ETS varies significantly both within lakes over the growing season, and among lakes. The magnitude of the error associated with calculating respiration from ETS is, however, similar to the error in other standard limnological procedures used in plankton carbon flow studies. Oxygen consumption is not a linear function of ETS across the range of lakes, but is rather a power function. The respiration:ETS ratio for lake plankton therefore not constant: it is high in oligotrophic and colored lakes, and declines with trophy. These results are consistent with the changes expected in the structure of the plankton along trophic gradients.

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