Cyanobacteria biomass in shallow eutrophic lakes is linked to the presence of iron-binding ligands.

Iron (Fe) is an important regulator of phosphorus and nitrogen use efficiency by phytoplankton. We tested the prediction that pelagic cyanobacteria biomass in surface waters of shallow eutrophic lakes with low ferric ion concentration is linked to the presence, and potential utilization, of low molecular weight Fe-binding ligands. We sampled 30 lakes in Alberta, Canada, in 2012 for nutrients, cyanobacteria biomass, Fe-binding ligands (hydroxamates and catecholates), and toxins. Bioavailable ferric ion concentration (estimated as pFe) was significantly correlated to cyanobacteria biomass (curvilinear relationship, r2 = 0.45, P < 0.05). Nonmetric multidimensional models indicated that high cyanobacteria biomass corresponded to lakes with low ferric ion concentration (pFe ∼ 19), and regression tree analyses identified a threshold in ferric ion concentration (pFe = 22.1) that separated lakes with relatively low versus high cyanobacteria biomass. Where ferric ion concentration was low, hydroxamate-reactive compound concentration was positively correlated to cyanobacteria biomass. As the environment goes from higher to lower ferric ion concentration, the presence of cyanobacteria increases, and with further reduction of Fe, the environmental need for Fe-binding ligands becomes manifest. [ABSTRACT FROM AUTHOR]