Inferred Phosphorus Cycling in Shallow and Deep Basins of Eutrophied Lake Hormajärvi, Southern Finland

Abstract Lake Hormajarvi is a typical small lake in southern Finland suffering from human-induced eutrophication. The lake has a complex basin morphology; the western basin is deeper and does not suffer the consequences of eutrophication of the shallower eastern basin, where poor water quality prevents swimming, fishing and other recreational use of the lake. Two short sediment cores from both basins were taken and studied to understand the eutrophication history of the lake, phosphorus (P) cycling within the respective basins and to evaluate needs for lake management and restoration. Sediments were analyzed for diatoms, P fractions, and physical properties. Spherical carbonaceous particles (SCP) were used for dating. Results indicate that diatom inferred autumnal lake surface water total P (DITP) does not follow the trend in accumulated P in the western basin, whereas there is a clear correlation in the eastern basin. The western basin acts as a permanent sink for P, but in the unstratified eastern basin...