Changes in the phytoplankton of Lake Trummen induced by restoration

Lake Trummen, previously an oligotrophic lake, was heavily polluted during 1930-1957. The lake was restored by suction dredging of the top sediment layer. After restoration nutrient concentrations and phytoplankton biomass were drastically reduced. Eutrophic species disappeared and more oligotrophic species returned to the lake. The investigation covers 12 years-monthly-bimonthly countings of algae together with electronmicroscopical studies of taxonomically difficult taxa. The investigation was made at the species level (300 species identified and 80 quantitatively recorded).