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Abstract

The SCENTO-System was used to study the carbon dynamics between phytoplankton primary production and heterotrophic bacterial secondary production. Most of the methods used nowadays in situ for limnological synecology studies were applied. Primary production measurement showed an increasing tendency with increasing content of chlorophylla. It provided a true photosynthetic rate lying within the range of eutrophic lakes. Net EOC released from the algae ranged from 8.5 to 27.5 μg C l−1(6h)−1. Accompanying the algal products the number of bacteria increased from 1.475 ×109 to 8.074×109 cells l−1. The bacterial mean cell volume was small, between 0.0315 and 0.0548μm3. Bacterial carbon production from direct growth estimates was compared with independent calculations of bacterial growth from EOC uptake and3H-thymidine incorporation. Direct estimates were 2.97–10.0 μg Cl−1 (24h)−1 with the exception of a zero-growth on the third day. EOC uptake was 123.5–191.0 μg Cl−1 (6h)−1. That calculated from3H-thymidine incorporation was 0.2–0.5 μg Cl−1 (6h)−1.14C-glucose dark uptake ran parallel to the increasing bacterial biomass. The respiration of glucose was 6.5% (avg.) of the gross uptake. Since the system operated without grazing pressure, a real carbon flow from primary production to bacterial secondary production could be observed.