Vertical distribution of organic compounds in the bottom sediments of two steppe lakes in Southern Siberia

New data on the distribution of organic compounds at different horizons (0–10, 30–40, and 70–80 cm) of bottom sediments of the fresh Fyrkal Lake (Republic of Khakaßsia) and the salt Lake Mormyshanskoe (Altai Territory) have been collected. The compositions of organic compounds in the sediments in the examined lakes has been found to differ considerably, though some parameters in their composition show changes in the same direction. The concentrations of triterpenoids of the groups of lupane, oleanane, and hopane in the sediments decrease with depth. An increase in the share of saturated compounds in the composition of steroids is accompanied by a decrease in the ratio of their isomers (5β/5α). Terrestrial vegetation dominates among organic matter sources, while, in Lake Fyrkal, the contributions of terrestrial plants and macrophytes are similar. The presence of thermally transformed steroids and triterpenoids throughout the vertical profile of sediments in Lake Mormyshanskoe may be an indication to a slight oil pollution of the water body.