A SIMPLE MODEL FOR THE EUTROPHICATION OF LAKE RINGSJÖN
The present eutrophic status of Lake Eastern Ringsjön in Southern Sweden can be predicted using a simple mass balance model based on 2 trophic levels. The system was modelled using growth and mortality kinetics for fish and plankton, and sediment-fish-water interactions. The model predicts the transition to eutrophic lake from a stable oligotrophic state in 1960-1965. The model calculations confirm the importance played by fish in maintaining a large internal flux of phosphorus between the sediment and the watercolumn. The critical external phosphorus load for Lake Eastern Ringsjön is calculated to approximately 3.8 ton P/yr. The model calculations indicate that the lake will not reverse to its natural oligotrophic status, unless the total phosphorus input load from both external and internal sources are reduced below the critical load of the system.