Periphyton investigations in HUMEX Lake Skjervatjern in 1992: Fid-Bau Portal

Periphyton investigations in HUMEX Lake Skjervatjern in 1992

Lindstrøm, E.-A.

AbstractDuring the first year of artificial acidification of the dystrophic Lake Skjervatjern with a combination of sulphuric acid and ammonium nitrate, extensive growth of filamentous green algae occurred in the acidified half. Therefore, investigations studying the effect of acidified humic water on periphyton started early 1992. Quantitative measurements in the two lake-halves (acidified-A, control-B) were carried out, using small clay flower pots as growth substrates. The pots were placed in the two lake halves at 0.5 and 2 m depth. During the first three months, accumulated periphyton, measured as dry weight and chlorophyll a, was 50–600% higher in the acidified basin A than in B. Chlorophyll a per unit dry weight was higher in A than B, indicating higher photosynthetic activity in the acidified half. C/N-ratios in freeze-dried material from basin A were 10–11, indicating little or no N-deficiency during the first three months of the experiment at both 0.5 and 2 m depth in the acidified half. In the control basin B, C/N-ratios between 15 and 19 indicated N-deficiency during the first three months of the experiment at 0.5 m depth. At 2 m, there was no growth in basin B for the first 56 d of the experiment. After three months, periphyton accrual at 2 m had approximately the same chlorophyll a per unit dry weight and C/N-ratios as in basin A. This indicated that conditions in basin B at 2 m depth changes from strong growth limitations early in the summer to high photosynthetic activity and little or no N-limitation later in the year. The bluegreen alga Hapalosiphon fontinalis (Ag.)Born. is known to fix elemental nitrogen. It proliferated in the control basin, but was scarce in the acidified half. This supported the assumption of nitrogen limitation in the control basin.