Functioning of the Lake Rusałka ecosystem in Poznań (western Poland)

Lake Rusałka is a shallow, artificial, strongly eutrophic reservoir. Thermal stratification is weak and comprises only about 8% of the bottom surface. In summer, the epilimnion is oversaturated with oxygen due to intensive phytoplankton growth (chlorophyll a up to 80.2 μg l^-1), while conditions in the hypolimnion are anaerobic. The high concentration of ammonium nitrogen and low N:P ratio stimulated intense growth of cyanobacteria in the period from June to November. The domination of rotifers in the metazooplankton and low diversity and biomass of benthic macroinvertebrates was the cause of low top-down pressure of these organisms on the phytoplankton. The most advantageous restoration measures were identified to improve water quality and make the recreational use of the lake possible.