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

In this study, low epilimnetic iron availability during thesummer stagnation period was concluded to be a limiting factorfor cyanobacterial development in Lake Erken. In three enclosureexperiments, different combinations of phosphate, nitrate andammonium additions were tested both with and without additionsof dissolved iron. The addition of iron increased the growthof diazotrophic cyanobacteria significantly compared with enclosuresnot receiving iron. This was especially evident for the colony-formingcyanobacterium Gloeotrichia echinulata. In one experiment, coloniesof G.echinulata disappeared in enclosures not receiving iron,while the abundance of this species increased in those enclosuresto which iron was added.