The significance of photoautotrophic picoplankton in the eutrophic Lake Belau (Bornhöveder Seenkette, North Germany)

AbstractThe significance of photoautotrophic picoplankton (APP) was investigated for three years in the eutrophic Lake Belau. Using epifluorescence microscopy with green excitation, the abundance of APP was found to vary seasonally with maximum values reaching 1.7* 106 cells ml−1 in June and July. Above a threshold of 12°C, cell numbers of APP in the epilimnion were strongly correlated with the water temperature (r = 0.837 > r(34;0.001) = 0.526). The horizontal distribution varied by a factor of 1.1 to 3.3. All stations in the different parts of the lake, including the littoral zone, exhibited a similar seasonal pattern. Photoautotrophic picoplankton accounted for up to 54% of the total picoplankton carbon content (bacteria and photoautotrophic picoplankton) and averaged 8% over the entire year. It contributed