Lake Flensjøen in S Norway 2013. Status of water quality, zooplankton, benthic invertebrates and fish after liming since 2005

Summary

Lake Flensjøen is an oligotrophic lake with very low ionic strength. pH and acid neutralizing capacity (ANC) were low before liming, which started in the autumn of 2005. However, the water chemistry had improved markedly compared to the situation in the 1970ies and the 1980ies. Comparison of water chemical data from 1992 with data from 2005 also showed a significant effect of decline in acid rain. Liming, which was also performed yearly in 2009-2013, has resulted in further improvement of the water quality. In later years pH has varied in the range 6.8-7.2, and the acid neutralizing capacity (ANC) has varied in the range 107-170 µekv/l. Concentrations of potential toxic Al-forms (LAl) have been very low (4-7 µg Al/l) , even in 2005, before liming.