In Finland there are 56 000 lakes larger than 1 ha that cover 32 300 km~2 (Raatikainen Kuusisto 1990). Most of them originate from the early Holocene period and were initiated during two millennia following deglaciation. Since then, the lakes have been subject to accumulation of material transported from the drainage basin or produced within the lake ecosystem. Lake sediments include a varying amount of organic matter and, because of their longevity, can be considered a permanent carbon sink. From 1998-2003, the Geological Survey of Finland studied 140 lakes to quantify the role of lake sediments as a carbon sink. Prior to this research, the size of the lake carbon sink was uncertain, with estimates varying over a wide range (Forsius et al. 1996).
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