Human impact on Lake Ladoga as indicated by long-term changes of sedimentary diatom assemblages

Lake Ladoga is the largest lake in Europe. Eutrophication of the lake, caused by various human activities, has been noticed since the early 1960s. Besides nutrients, Lake Ladoga is also affected by industrial pollution. In order to assess patterns and trends in the aquatic environment quality, we have applied Detrended Correspondence Analysis (DCA) to surface sediment diatom assemblages, collected from different parts of the lake in 1959–60, 1978–79 and 1991–94, and from the main inflowing rivers in 1983–85. The eutrophication process is evident as a general change of the diatom assemblages between the three sampling periods, e.g. appearance of Diatoma tenuis first in the Volkhov Bay area in 1978–79 and subsequently throughout the lake. The eutrophication appears most pronounced near the discharge sites of industrial and municipal effluents and main river inflows. The river sediment assemblages reflect patterns in the riverine inflow quality related to catchment geology and effluent loading.