The trophic history of Enäjärvi, SW Finland, with special reference to its restoration problems

Despite improved wastewater-treatment technology, eutrophication remains a problem in many lakes in southern Finland. Sediment core, diatom, and chironomid samples were collected in Enajarvi, an eutrophic lake in the region, to evaluate the reactions of biota to eutrophication over time. Sediment-core analysis revealed that no significant changes have occured in diatom taxa during the 9000-yr natural history of the lake. However, since the lake was lowered 1 m in 1928, Aulacoseira ambigua, A. italica, and Cyclotella astraea have increased dramatically. Data on the phosphorus concentrations in the sediment indicated that P has increased in the surface sediment, due mostly to wastewater disposal from the village of Nummela. Restoration efforts must focus on stabilizing the surface sediment and improving its natural P-binding capacity.