Autotrophic picoplankton (APP) in four lakes of different trophic status : composition, dynamics and relation to phytoplankton

Abundance and dynamics of autotrophic picoplankton (APP) were studied in four temperate lakes: oligo-, meso- and eutrophic, as well as dystrophic lake. Orange fluorescing cyanobacteria prevailed in APP community in all four lakes, but in spring and autumn eukaryotic contribution increased. The densities of APP ranged between 2 x 10^4 ml^-1 and 9.5 x 10^5 ml^-1. There was a trend of increase of APP numbers along classical trophic gradient, but its share in total phytoplankton biomass was decreasing importance of picoplankton with eutrophication. Two types of APP seasonal patterns were described. One characterised by only one, spring-early summer peak, was found in mesotrophic and eutrophic lake. The second pattern described for humic lake was characterised by two peaks, in spring and Autumn.