Response of pelagic cyanobacteria to iron additions--enclosure experiments from Lake Erken

In this study, low epilimnetic iron availability during the summer stagnation period was concluded to be a limiting factor for cyanobacterial development in Lake Erken. In three enclosure experiments, different combinations of phosphate, nitrate and ammonium additions were tested both with and without additions of dissolved iron. The addition of iron increased the growth of diazotrophic cyanobacteria significantly compared with enclosures not receiving iron. This was especially evident for the colony-forming cyanobacterium Gloeotrichia echinulata. In one experiment, colonies of G.echinulata disappeared in enclosures not receiving iron, while the abundance of this species increased in those enclosures to which iron was added.