Comparison of two methods to measure algel release of dissolved organic carbon and the subsequent uptake by bacteria

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Abstract
Two methods were used to compare phytoplankton release and bacterial uptake of extracellular organic carbon (EOC) products. A size fractionation and an antibiotic method were used simultaneously during several diel in Situ studies in Danish lakes and one coastal area. Phytoplankton populations were very sensitive to even small concentrations of antibiotics (1 μg ml −1 ). Generally the bacterial activity was inhibited by ∼50%. In cases where the antibiotics did not affect phytoplankton photosynthesis, the two methods agreed reasonably. Bacterial respiration data obtained with the antibiotic method were in the range of values from the literature. This supports the conclusion that the partial uncoupling of EOC release and uptake with antibiotics can be used to follow the flux of EOC in situ . The effect on the phytoplankton must however, be evaluated in each experiment. The methodological problems of both approaches are discussed.