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Abstract:
In situ ETS-activity of Schöhsee natural phytoplankton communities and their subsequent size fractionation (<250 - >35; <35 - > 10; and < 10 μm) was studied to determine the relative rate of respiration of different size fractions. In the euphotic zone,
maximum ETS-activity (81.65 mg C m-2 * h-1) and 14-C uptake (88.75 mg C m-2 * h-1)
were observed during the spring period. Minimum ETS-activity (19.84 mg C m-2 * h-1)
and 14-C uptake (17mg C m-2 * h-1) were recorded during the autumn season. Nano-
plankton fraction ( < 35 μm) contributed 45 to 96 % (average 73 %) of the total community respiration. Of the three fractions studied, the < 10μm fraction contributed about
29-75% (average 56 %) of the total respiration. The < 250 - > 35 μm size fractions of
phytoplankton contributed only 3-60% (average 27%) of the total respiration of the
phytoplankton community. From the results of this study it appears that autotrophic
organisms of <10μm range to be accountable for most of the respiration. These size
range organisms also shared most of the carbon assimilation rates as well as biomass
(both as particulate carbon and chlorophyll-a). ln terms of primary productivity, biomass and respiration (ETS-activity) nanoplankton were the most important primary
producers in this mesotrophic Baltic lake (Schöhsee).
