Effect of CuSO 4 on the Photosynthetic Rate of Phytoplankton in Four Danish Lakes

The photosynthetic rate of phytoplankton in water samples from four lakes was altered by the addition of CUSO4. Among the factors which influenced the toxic action of Cu++, was the taxonomic composition of the phytoplankton, their numbers, humus content of the water, and pH. Whereas addition of 25 jig Cu in three of the lakes decreased photosynthesis considerably, in the fourth lake a brown-water lake an increase occurred. In the brown-water lake, humus bound Cu++ so effectively that it must have been present in very low concentrations in the water.