The effect of eutrophication and global change on heterocystous cyanobacteria in freshwater lakes

Eutrophication and global change have been suggested to promote cyanobacterial blooms. <em>Anabaena, Aphanizomenon and Cylindrospermopsis</em> are heterocystous genera of toxin-producing cyanobacteria. It is yet unclear how eutrophication and climate change will impact heterocystous cyanobacteria. This study investigates the effects of total nitrogen (TN), total phosphorus (TP), TN:TP ratio, temperature, pH and trophic state on the relative abundance of three heterocystous cyanobacteria, using data of 999 lakes obtained from the National Lake Assessment 2012 (NLA) of the U.S. Environmental Protection Agency (EPA). It was demonstrated that elevated TN and TP levels, as well as higher pH levels are related to higher abundance of heterocystous cyanobacteria. <em>Cylindrospermopsis</em> is correlated with TN and temperature, <em>Aphanizomenon</em> is related with TP and negatively correlated to TN:TP. All three heterocysts are correlated with pH. Eutrophication has a higher effect on the relative abundance of heterocystous cyanobacteria than the increased temperatures and increased CO₂ concentrations. Decreasing the concentration of nitrogen and especially phosphorus in lakes may limit the relative abundance of heterocystous cyanobacteria in fresh waters.