Postglacial changes in the groundwater table at the Gardemoen, Norway interpreted from diatom ananlysis
The postglacial environmental history of two kettle hole !akes, Bonntjern and Svenskestutjern, with very different water chemistry, has been investigated on the basis of the 6 000 year record of their diatom assemblage. The two !akes are situated only 300 m apart, one is acid and nutrient poor, and the other is neutral to alkaline and nutrient rich. Planktonic diatoms ( Cyclotella spp.) dominated in both !akes up to about 4 000 BP. In Svenskestutjern the Cyclotella flora was followed by a benthic/epiphytic flora up to about 2 500 BP, thereafter very few diatoms were recorded in the lake sediments. In Bonntjern the Cyclotella flora was followed by alternations of planktonic (mainly Cyclotella spp.) and benthic/epiphytic flora. The floral change at about 4 000 BP is interpreted to reflect a lowering of the groundwater tab le. The floral development in the !akes seems to be closely related to regional climatic changes causing changes in the groundwater table.