Picoplankton and other size groups of phytoplankton in various shallow lakes

Abstract

This paper presents the results of the studies on picoplankton and other size groups of phytoplankton from twelve lakes (maximum depth from 3.5 to 7.8 m) located in the Polish part of Pomerania. Samples were taken from the pelagial zone in August 1993 and 1994. Phytoplankton composition, abundance and biomass were investigated within the three main size groups, i.e. pico-, nano- and phytoplankton >20 μm. Picoplankton numbers ranged from 3.2 x 102 to 1.16 x 106 cell s ml-1. Its population density, with the exception of one lake, was greater by 1-3 orders of magnitude than nano- and >20 μm populations, while its biomass values in the range from <0.001 to 0.65 mg l-1 did not exceed 11% of the total phytoplankton biomass. Picoplanktonic communities were composed of cyanobacteria and/or eukaryotes. A significant, negative correlation between picoplankton contribution to total biomass and total biomass was observed. Phytoplankton >20 μm was the most important constituent of the biomass in most lakes, and it reached highest values and proportions: 23.3 mg l-1 and 99.9%, respectively. In comparison, the nanoplankton biomass was not so high: up to 1.3 mg l-1 and 65.2% proportions.