Dynamics of autotrophic picoplankton communities in the epilimnion of a eutrophic lake (Strzeszyńskie Lake, Poland)

The results of 32 seasonal sampling sessions in 2000 were used to assess the dynamics of autotrophic picoplankton (APP), with special reference to the cyanobacterial component in Strzeszynskie Lake, a eutrophic lake in mid-western Poland. The abundance of picocyanobacteria (Pcy) fluctuated from 1.2x104 to 8.1x105cells mL-1 and the average abundance and biomass were 2.0x105cells mL-1 and 0.094 mg L-1, respectively. Pcy development was characterised by maxima in spring and summer. The summer maximum was twice the spring Pcy numbers. Eukaryotic APP (E-APP) were also present but in low numbers and their annual average contribution to the total APP community was only about 0.3% in abundance and about 3% in biomass. The spring Pcy community was dominated by single-celled cyanobacteria (S-Pcy) and in summer by colonial forms (C-Pcy). Throughout the sampling period, C-Pcy constituted on average 55% of the total Pcy and up to 90% in summer. C-Pcy abundance was significantly and positively correlated with water temperature (r=0.40, p=0.023, n=32). S-Pcy exhibited a distinct seasonal variation in FDC, ranging from 10% to 35%. Most FDC values above 30% were recorded from late May to mid July