 |
 |
 |
Waters, sediments and biotaGenesis of the lake flora and fauna requires special consideration with a distinction bet- ween the near-shore and the deep parts due to the considerable heterogeneity of the settings. The role of local factors is much more pronounced in the near-shore zone. The effect produced by the composition of the parent rock and the catchment characteristics is particularly conspicuous in hydrologically isolated areas (bays. skerries). In spite of the close interest exhibited by numerous organizations the lake is poorly studied. A considerable part of the underwater landscapes is still a "white spot" on the lake map. There is a complete lack of data on a number of crucial issues related to the sources, directions and patterns of both natural and technogenic sedimentary material transports. The littoral - an important part of the near-shore zone has a number of features found in this natural phenomenon only. Higher plant cenoses generate the microclimatic conditions in the near-shore zone and influence hydrodynamic processes. The near-shore zone is much affected by the inflowing waters which constitute the bulk of the lake water budget (over 85% of the influx). The distinctions between the water chemical compositi- on in the tributaries and the lake, as well as the hydrological characteristics of the estuarine areas also contribute to the diversity of conditions in the lake. In the lake deep-water part the role of pelagic communities in the function of the lake system is far more important than the role of benthic communities. The pelagial zone is a more uniform habitat which therefore has a lower species diversity than the near-shore zone in general. Still, various parts of the lake differ in what concerns the structure of planktonic communities. Uniquely specific of this biotope is the cold-water (hypometalimnetic) species complex. A significant part in it is played by glacial relict forms which prefer habitats with higher oxygen content. This group of species is essential for the ecosystem while is performs much of the organic matter transformation and transport between different biotopes of the lake. Fore more than 35 years now the lake has been suffering heavy human-induced load. The near-shore zone is exposed to the most powerful impact, serving as a barrier guarding the lake from biogenic substances and various pollutants. The emergence in disturbed areas (e.g., Shchuchij bay) and spread of cosmopolitan and euritopic species not found in Lake Ladoga before and of invading species can hardly be regarded a positive process, though formally speaking this expands the species lists (see Section "Ecology. Aquatic ecosystems. Fauna."). |
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|
|
|
|
|
|
| ||
|
|