Unabated Nitrogen Pollution Favors Growth of Toxic Cyanobacteria over Chlorophytes in Most Hypereutrophic Lakes

Matthew J. Bogard*, Richard J. Vogt, Nicole M. Hayes, Peter R. Leavitt

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)
89 Downloads (Pure)


Human release of reactive nitrogen (N) to the environment has increased 10-fold since 1860 and is expected to increase by a further ∼75% by 2050. Much of this N enters phosphorus (P)-rich, eutrophic lakes in agricultural and urbanized watersheds. While N pollution of eutrophic lakes can promote toxic cyanobacterial growth, some cases of extreme N loading have led to the dominance of chlorophytes (green algae). As N loads required to shift communities from cyanobacterial to chlorophyte dominance are unclear, we experimentally tested phytoplankton responses to a gradient of N loading in a P-rich lake. Low-to-moderate doses (1-3 mg N L-1 week-1) promoted toxic cyanobacterial dominance and elevated concentrations of the hepatotoxin microcystin. Conversely, loads characteristic of pure urban or agricultural effluents (up to 18 mg N L-1 week-1) led to the dominance of chlorophytes over cyanobacteria and lower microcystin content. This indicates that N loads needed to sustain chlorophyte dominance are uncommon, likely restricted to select shallow lakes directly exposed to urban or agricultural effluents. As most N pollution regimes in P-rich lakes will favor toxic cyanobacterial dominance, restricting future N pollution will help curb further cyanobacterial dominance in lakes both directly and by constraining the capacity for future P loading and climate warming to drive cyanobacterial growth.

Original languageEnglish
Pages (from-to)3219-3227
Number of pages9
JournalEnvironmental Science and Technology
Issue number6
Early online date20 Feb 2020
Publication statusPublished - 17 Mar 2020

ASJC Scopus subject areas

  • General Chemistry
  • Environmental Chemistry


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