Lake Trummen restoration project II. Bacteria, phytoplankton and phytoplankton productivity

Summary

The number of aerobic heterotrophic bacteria in the water did not change after the restoration of Lake Trummen. A marked decrease of protein, starch and glucose decomposing bacteria was observed. In the sediment all the examined physiological groups of bacteria were concentrated to the uppermost 5 cm, where most of them occurred in the same number as before.

In connection with the restoration the mean biomass of phytoplankton from June until September decreased from 75 to 10 mg/1 due to the lower abundance of blue- green algae. The productivity structure of the phytoplankton communities was changed. In spite of the decrease of the mean annual productivity from 375 to 225 g C · m⁻², the yearly productivity of algae with a mean diameter less than 45 μm did not change. More than 60% of the annual phytoplankton production was photosynthesized by algae less than 10 μm. The diversity of phytoplankton increased when the fertility of Lake Trummen decreased.