A PALEOLIMNOLOGICAL STUDY OF EUTROPHIED LAKE ARENDSEE (GERMANY)

To study the algal microfossil assemblages of eutrophic Lake Arendsee (Germany) prior to the beginning of a restoration project, a 47-cm lon g freeze core, dating back to ca. 1800, was taken from the deepest are a of the lake. Based on the CRS modeled Pb-210 and Cs-137 profiles fro m the core, 1948 is around 15 cm and the sedimentation rate has increa sed from similar to 21.2 mg cm(-2) yr(-1) in 1900 to similar to 56.6 m g cm(-2) yr(-1) in 1986. The sediments were dominated by three centric diatoms. Stephanodiscus binatus, a species associated with eutrophic environments, dominated the upper 19 cm of the core. Cyclotella rossii , a species commonly found in less productive freshwater systems, was found to dominate the lower portion of the core and was absent above 1 6 cm. S. agassizensis was found throughout the core. In addition to th e centric diatoms, three penate diatoms were found to be abundant. Fra gilaria crotonensis was found throughout the core, but was most abunda nt from 19 cm to 16 cm. Asterionella formosa was prevalent below 15 cm , while Diatoma elongatum was found to be common from 17 cm to the sur face. The abundances of algal remains of cyanobacteria, chlorophytes, cryptophytes and dinoflagellates decrease dramatically below 25 cm. Zo oplankton remains were most abundant around 20 cm, with copepod sperma tophores, fecal pellets and protozoa remains most common in the lower portion of the core. The major species shifts observed in the core fro m Lake Arendsee occur in a transition zone between 20 cm and 15 cm (19 20-1940), a time when agricultural production was being increased with the use of inorganic fertilizer.