Eutrophication of lakes cannot be controlled by reducing nitrogen input: Results of a 37-year whole-ecosystem experiment

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 105; no. 32; pp. 11254 - 11258
• Main Authors: Schindler, David W, Hecky, R.E, Findlay, D.L, Stainton, M.P, Parker, B.R, Paterson, M.J, Beaty, K.G, Lyng, M, Kasian, S.E.M
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 12-08-2008; National Acad Sciences
• Series: From the Cover
• Subjects: Biological Sciences; Biomass; Chlorophylls; Cyanobacteria; Cyanobacteria - growth & development; Cyanophyta; Ecosystems; Estuaries; Eutrophication; Eutrophication - physiology; Experiments; Fertilization; Fresh Water - microbiology; Freshwater; Lakes; Nitrogen; Nitrogen - metabolism; Nitrogen Fixation - physiology; Phosphorus; Phosphorus - metabolism; Phytoplankton; Phytoplankton - growth & development; Phytoplankton - microbiology; Seasons; Time Factors; Canada, Ontario, Experimental Lakes Area; Canada, Ontario, Precambrian Shield
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0805108105

Lake 227, a small lake in the Precambrian Shield at the Experimental Lakes Area (ELA), has been fertilized for 37 years with constant annual inputs of phosphorus and decreasing inputs of nitrogen to test the theory that controlling nitrogen inputs can control eutrophication. For the final 16 years (1990-2005), the lake was fertilized with phosphorus alone. Reducing nitrogen inputs increasingly favored nitrogen-fixing cyanobacteria as a response by the phytoplankton community to extreme seasonal nitrogen limitation. Nitrogen fixation was sufficient to allow biomass to continue to be produced in proportion to phosphorus, and the lake remained highly eutrophic, despite showing indications of extreme nitrogen limitation seasonally. To reduce eutrophication, the focus of management must be on decreasing inputs of phosphorus.