The lake floristic and faunistic richness as well as other aspects of the Ladoga Lake biodiversity are related to three major groups of factors:
Specific geological characteristics of the lake;
Flora and fauna genesis in the post-glacial period.
Limnogenesis (i.e. the lake succession) is closely connected with all listed above but can also be regarded one of the basic independent factors affecting the lake biological diversity.
In its latest history Lake Ladoga has experienced quite a few
changes of the water level accompanied by considerable variations of the lake
basin area and shape. Formation of the modern morphological structure of the
lake basin was completed in the early-mid Pleistocene. The main factor that has
shaped the modern topography of the lake bottom and shore was the last Valdai
glaciation. The climate warming that occurred some 10 millennia ago caused the
ice cover in Fennoscandia to grow thinner. The isostatic land uplift that followed triggered a rapid regression whereupon Lake Ladoga first became an independent reservoir receiving discharge through the northern part of the Karelian isthmus. Another rise of the lake level about 2000 years ago resulted in the formation of the Neva river.
The distinguishing geological characteristics (genesis) of
the lake are both the parent rock composition and heterogeneous morphometry of
the basin. The lake basin formed at the juncture of the Baltic crystalline
shield and the Russian platform, and is confined to the graben - a geological
structure in the form of a large block of the earth crust with subsided along
the faults (Ilyin, 1978). This fact
predetermines both the large size of the lake and the geomorphological
heterogeneity of its parts. This is the reason why its three parts differ in a
whole number of parameters, including the bottom sediments composition and the water chemism.