During the last decades Lake Gjersjøen has developed from an oligotrophic state to a level of high eutrophy. The present state is characterized by an intense primary production in the trophogenic zone and anaerobic conditions in the lower part of the hypolimnion during periods of thermal stratification.
The deterioration of the lake as a resource has resulted in research on main components of the ecosystem. Most of the limnological data about the lake are to be found in Johansen (1955), Skulberg (1968), Norwegian Institute for Water Research (1969, 1972), Holtan (1972) and Lillevold (1975).
The intention of the present investigation was to reveal in which way the rapid eutrophication has been manifested in the hypolimnetic sediments and to search for processes in the sediment that could influence a suggested development towards meromixis. This investigation may provide data for further and more specific research on the sediments in Lake Gjersjøen.