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

The ETS (electron transport system) assay to measure respirationof aquatic organisms has been widely applied in studies of marinemetabolism, but its use in freshwaters has been much more limited.This method calculates oxygen consumption from the measuredETS activity using an empirical conversion factor. This factorhas been calculated for various marine organisms, and for naturalplankton communities, but calibrations for freshwater organismsare lacking. The aim of this paper was to determine the relationshipbetween lake plankton respiration and ETS activity, based onmeasured epilimnetic plankton oxygen uptake and ELS activityin 20 southern Quebéc lakes. The relationship betweenplankton oxygen consumption and ETS varies significantly bothwithin lakes over the growing season, and among lakes. The magnitudeof the error associated with calculating respiration from ETSis, however, similar to the error in other standard limnologicalprocedures used in plankton carbon flow studies. Oxygen consumptionis not a linear function of ETS across the range of lakes, butis rather a power function. The respiration:ETS ratio for lakeplankton therefore not constant: it is high in oligotrophicand colored lakes, and declines with trophy. These results areconsistent with the changes expected in the structure of theplankton along trophic gradients.