Author(s): Komulaynen Sergey; Slastina Julia
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Abstract: The ice regime of Karelian rivers is formed in the transition zone between West Europeanmarine and Euras ian continental climates. The ice regime of the rivers is also affected by thenutrition conditions, water content and current velocity of the rivers. The rivers are covered byice in late October-early November. In the river reaches, located near large lake sources, ice is formed much later, and large rapids and falls do not freeze even in severe winters. During the winter season ice is accreted in a non-uniform manner: more intense accretion is observed in November and December, when the rivers begin to freeze. Once the ice cover is formed, accretion intensity decreases. The average duration of freeze-up varies from 78-194 days in North Karelia to 100-158 days in South Karelia. Spring ice run on Karelian rivers is weak, because the ice is not broken up simultaneously. Ice is first broken up in river reaches located downstream from lake sources and rapids and then in quiet waters. Combination of morphological and hydrodynamic conditions on the rivers favours the formation of ice jams and ice dams. The sites, where they are formed, are permanent, and are confined to the break-up of the longitudinal profile and cascade river reaches, causing a considerab le rise in water level. Ice jams and ice dams prevent the formation of stable groups of phytoperiphyton. In the winter, the deve lopment of all algal divisions in the periphyton is minimum, especially in ice-covered reaches. In fact, only scarce diatoms are encountered in the epilithon in unfrozen river reaches; they dominate not only in the number of species but also in abundance and biomass. After a river is frozen up, some algal colonies freeze in the ice and others, primarily dynophytic and diatomaceous algae, persist in a thin intercrystalline water layer. The distribution of algae in the ice is irregular. Maximum numbers of diatoms were observed in the layer adjacent to the lower ice surface.
Year: 2010