KVÄVEBUDGET FÖR BJÖRKAREN – EN IGENVÄXT SJÖ I NORRTÄLJE KOMMUN /Nitrogen Budget for Lake Björkaren, a Shallow Lake in Southern Sweden
The role of wetlands, ponds and lakes in the retention of nitrogen and thus in the decrease of nitrogen transport to the sea is under discussion in Sweden. In this paper nitrogen budgets for Lake Björkaren during four years are presented. The lake is very shallow and almost covered with higher vegetation and the water retention time is very short, 1 to 9 days with an average of 3 days. Nitrate was efficiently reduced during the summer months (often more than 80 % reduction) but on a yearly basis at most 10 % of the nitrate loading to the lake was assimilated or denitrified. The retention of total nitrogen was also low with a maximum figure of 5 % of the yearly loading.