The Lake Onegо Ecosystem: Aquatic Communities Response to Anthropogenic Factors and Climate Change

Original and take from the references data on the Lake Onegо anthropogenic load dynamics, plankton and benthos conditions over the period of the previous 55 years have been analyzed in order to assess the ecosystem response to long-term and new impact factors such as climate change, chemical and biological contamination. It has been demonstrated that the lake pollution is of a local character while more than 90% of its water area maintains the initial oligotrophic status. Biogenic matter transported to the lake with the pulp-and-paper mills and domestic waste water caused euthrophication of two North-Western bays. The load caused by point pollution sources decreased over the past decades; this was proved by the reoligotrophication processes that occurred in the euthrophic bays bottom communities. However, diffuse pollution sources appeared. Trout-breeding farms in the North-Western bays are a potential threat of the lake euthrophication. A chronic oil pollution of the lake Petrozavodsk Guba has been revealed, for the time being the lake ecosystem manages to cope with it. Biological contamination associated with immigration of Gmelinoides fasciatus Stebbing Baikal amphipoda has led to the increase of the intertidal zone certain parts’ productivity increase and improving of the perch young nutritive base. Climate change causes reversible deviations in the plankton communities’ structure and season recurrence. In order to maintain economic value of the water body it is recommended to adopt some legislative measures for protection of the Lake Onegо as a strategic source of fresh water and to develop the scientifically-based ecological monitoring criteria with taking into account its heterogeneity.