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

In this study, low epilimnetic iron availability during the summer stagnati on period was concluded to be a limiting factor for cyanobacterial developm ent in Lake Erken. In three enclosure experiments, different combinations o f phosphate, nitrate and ammonium additions were tested both with and witho ut additions of dissolved iron. The addition of iron increased the growth o f diazotrophic cyanobacteria significantly compared with enclosures not rec eiving iron. This was especially evident for the colony-forming cyanobacter ium Gloeotrichia echinulata. Tn one experiment, colonies of G.echinulata di sappeared in enclosures not receiving iron, while the abundance of this spe cies increased in those enclosures to which iron was added.