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

Department of Water Protection, Adam Mickiewicz University, Drzymaty 24, 60-613 Poznan, Poland.

Corresponding author: rgold@amu.edu.pl

Abstract

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.