THE TROPHIC HISTORY OF ENAJARVI, SW FINLAND, WITH SPECIAL REFERENCE TO ITS RESTORATION PROBLEMS

The eutrophicated Enajarvi was studied by paleolimnological analyses a nd sediment mapping. The sedimentary record indicates that the lake nu trient balance had deteriorated due to lowering of the lake water leve l in the year 1928. From that event onwards Chironomus plumosus and Cy clotella astraea characterize the chironomid and diatom communities. T he concentrations of sedimentary total and mobile phosphorus show that since then the internal load of phosphorus has controlled the nutrien t cycle of the lake. The areal distribution of mobile phosphorus can b e explained by dominant wind directions and wind resuspension of the s ediment is the key factor in the nutrient cycle. Restoration of Enajar vi must be based on actions which stabilize the surface sediment and i mprove its natural phosphorus-binding capacity. They include the regul ation of lake water to as high a level as possible and the removal of the majority of roach.