Bottom Sediments

The share of the fine fraction (<0.05 mm) in the bottom sediments ranges from 0 to 100%. Its lowest values are observed in the near-shore zone. The further from the shore, the greater the share of the fine fraction, which is maximum in deep depressions in the northern part of the lake.

Sandy sediments are dominated by quarz (40-85%), feldspars (up to 32%), detritus (up to 30%), biotite (2-28%), muscovite (up to 13%). The main minerals of the coarse fraction are amphiboles (predominantly hornblende), black ore minerals (chiefly ilmenite), garnet group minerals (almandine), epidote, apatite and zircon. The clay-size fraction is dominated by hydromica (illite) and chlorite.

Average redox potential of the lake surface sediments is +200 mV. The lowest values (down to -280 mV) are recorded from the vicinity of Priozersk, Pitkaranta and Sortavala.

Average pH in the bottom sediments of the near-shore zone is 6.7. Some increase in pH (to 7.0) was observed in the sediments from the areas near Volkhov, Svir, Syass river estuaries.

Erosion areas in Lake Ladoga are common in the near-shore zone at the depths of 10-15 m, but occur also within bottom uplift sections. These areas typically contain solid sediments ranging from bedrock to glacial clays.

Sediment transport areas dominate at the depths of 10-15 to 50-55 m. Sediments in the areas are varied, represented by fractions ranging from sands to clayey silts. Wide-spread are mixed sediments. Heavy storms and mass motions of the soils often cause the fine-grain material on the steep slopes of the lake northern part to get suspended and be carried out to deeper areas of the lake.

Accumulation zones appear in the places where particles smaller than 0.05 mm are continuously deposited. These are the final deposition zones - "end stations", for the finest material. They occur in plains and depressions in the deep zone of the lake (deeper than 50-55 m) where silts and clayey silts are common.

webmaster@www.krc.karelia.ru