Release of dissolved organic matter by photosynthesizing algae in Lake Kinneret,Israel*

The incorporation of inorganic carbon in particulate and dissolved organic matter by natural populations of photosynthesizing algae has been studied in Lake Kinneret, Israel, from August 1972 to December 1973. The release of dissolved organic material was directly related to the rates of particulate productivity. However, the percentage of extracellular release (PER) of dissolved organic compounds showed an inverse relationship with chlorophyll a concentrations. Mean PER values (for the trophogenic layer) over the experimental period were 3·7%, and were lowest during the exponential growth phase of the annual dinoflagellate bloom (mean PER = 1·9%). Highest PER were measured in deep, light-limited samples (mean = 31·7%; s.d.· 21·9%). In a dense metalimnic layer of photosynthetic sulphur bacteria (Chlorobium phaeobacterioides), PER was not as extremely high as has been reported for a similar layer in Lake Wadolek, Poland. Although the amounts of dissolved organic matter released by phytoplankton in Lake Kinneret were low, they may have significance as growth modulators and as substrates for heterotrophic organism.