Figure 1. The nitrogen fixing process, as mediated by cyanobacteria (utilizing oxygenic photosynthesis as an energy and carbon source) as well as heterotrophic and chemolithotrophic microorganisms, in eutrophic surface waters.
Potential environmental controls, including phosphorus (P) and iron (Fe) availability, energy sources, and dissolved oxygen inhibition, are shown in red. The background photo is of an O 2-supersaturated (during daytime) cyanobacterial surface bloom in Lake Taihu, China. Photograph by H. Paerl.