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Waters and sedimentsLake Ladoga drains an enormous territory in the European north-west of Russia. The lake accepts runoff from the catchment area of 258,600 km2. The length of the watershed area from north to south is over 1000 km, from west to east - about 600 km (fig. 1.2). The most voluminous tributaries of the lake are the rivers Svir, Vuoksa, Volkhov and Syass. Annually 67 819 106 m3 of water are carried to the lake by rivers (Malinina, 1966). Another contribution to the lake water budget alongside with inflow from rivers is made by atmospheric precipitation and groundwater inflow. Total annual inflow to Lake Ladoga is 78 373 106 m3. Bottom sediments in Lake Ladoga are comprised of varied terrigenous components covering the whole particle size spectrum from blocks and boulders to clayey silts (fig. 3.3.1.1). The wide size range of the bottom sediments is due to the structural heterogeneity of glacial and late-glacial deposits which are the main source of sedimentary material for the lake (Usenkov, 1993). Most common in the southern shallow part of the lake are sands, in the central and northern parts - argillaceous and argillaceous-sandy silts. Gravel-and-pebble sediments mixed with sand at a depth of 12-20 m are the products of glacial sediment reworking by water. They formed when the water level in the lake was lower, i.e. can be classed as relict sediments. The factors responsible for the distribution of the bottom sediment types are bottom topography and hydrodynamic patterns. Data of integrated geo-ecological survey indicate the reduction of anthropogenic pollution of the bottom layer waters in relation to the bottom landscape in general (fig. 3.3.1.1, 3.3.1.2). This tendency reflects the more prolonged period of anthropogenic aureole formation, persistence and destruction in bottom sediments as compared with water currents, as well as an overall attenuation of anthropogenic load on Lake Ladoga (the survey was held after the Priozersky pulp-and-paper mill - formerly one of the largest polluter-enterprises in the area, had been closed). To conclude, the bottom sediments are a accumulate many kinds of anthropogenic pollutants in the lake ecosystem. Contaminants are most actively stored by loose, fine and rich in organic matter sediments of the accumulation zones. However, evaluations of the current contamination of the Lake differ significantly among organizations, that conducted studies (fig. 3.3.1.2., 3.3.1.3., 3.3.1.4.) |
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