Larisa A. Shirenko (email@example.com)
Institute of Limnology Acad.Sci.Russia, Sevastyanov Str.,9, St. Petersburg, 196 199, Russia.
Karelian Isthmus is a lake district situated between Lake Ladoga and the Baltic Sea (NW Russia). Granitic bedrock and a thin layer of soil predetermine the northern part of the Karelian Isthmus territory to be highly sensitive to acid deposition. Surveys of small lakes in the northern part of the territory have indicated changes in water chemistry of the lake since the 1960's. Increases in sulphate concentrations and in alkalinity were observed. In several lakes with a low buffering capacity, the pH has decreased by 0.5-1 units during the last 30 years. Chemistry of these small lakes in the central and southern parts of the Karelian Isthmus have not changed. There are several small clear-water lakes located on the central part of the Karelian Isthmus which have acidified due to natural processes.
The impacts of acidification on freshwater ecosystems have been characterized, mainly on the bacterial component of aquatic food webs and the balance of primary production and destruction. Density of bacterial populations and bacterial activity (bacterial production and destruction, respiration per cell) decreased in the acid lakes. The ratio of primary production to destruction decreased with decreasing pH.
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