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Environment
The lake floristic and faunistic richness as well as other aspects of the Ladoga Lake biodiversity are related to three major groups of factors:
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. |
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